JSONEncoder.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

@_implementationOnly import CoreFoundation

/// A marker protocol used to determine whether a value is a `String`-keyed `Dictionary`
/// containing `Encodable` values (in which case it should be exempt from key conversion strategies).
///
fileprivate protocol _JSONStringDictionaryEncodableMarker { }

extension Dictionary : _JSONStringDictionaryEncodableMarker where Key == String, Value: Encodable { }

/// A marker protocol used to determine whether a value is a `String`-keyed `Dictionary`
/// containing `Decodable` values (in which case it should be exempt from key conversion strategies).
///
/// The marker protocol also provides access to the type of the `Decodable` values,
/// which is needed for the implementation of the key conversion strategy exemption.
///
fileprivate protocol _JSONStringDictionaryDecodableMarker {
    static var elementType: Decodable.Type { get }
}

extension Dictionary : _JSONStringDictionaryDecodableMarker where Key == String, Value: Decodable {
    static var elementType: Decodable.Type { return Value.self }
}

//===----------------------------------------------------------------------===//
// JSON Encoder
//===----------------------------------------------------------------------===//

/// `JSONEncoder` facilitates the encoding of `Encodable` values into JSON.
open class JSONEncoder {
    // MARK: Options

    /// The formatting of the output JSON data.
    public struct OutputFormatting : OptionSet {
        /// The format's default value.
        public let rawValue: UInt

        /// Creates an OutputFormatting value with the given raw value.
        public init(rawValue: UInt) {
            self.rawValue = rawValue
        }

        /// Produce human-readable JSON with indented output.
        public static let prettyPrinted = OutputFormatting(rawValue: 1 << 0)

        /// Produce JSON with dictionary keys sorted in lexicographic order.
        @available(macOS 10.13, iOS 11.0, watchOS 4.0, tvOS 11.0, *)
        public static let sortedKeys    = OutputFormatting(rawValue: 1 << 1)

        /// By default slashes get escaped ("/" → "\/", "http://apple.com/" → "http:\/\/apple.com\/")
        /// for security reasons, allowing outputted JSON to be safely embedded within HTML/XML.
        /// In contexts where this escaping is unnecessary, the JSON is known to not be embedded,
        /// or is intended only for display, this option avoids this escaping.
        public static let withoutEscapingSlashes = OutputFormatting(rawValue: 1 << 3)
    }

    /// The strategy to use for encoding `Date` values.
    public enum DateEncodingStrategy {
        /// Defer to `Date` for choosing an encoding. This is the default strategy.
        case deferredToDate

        /// Encode the `Date` as a UNIX timestamp (as a JSON number).
        case secondsSince1970

        /// Encode the `Date` as UNIX millisecond timestamp (as a JSON number).
        case millisecondsSince1970

        /// Encode the `Date` as an ISO-8601-formatted string (in RFC 3339 format).
        @available(macOS 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *)
        case iso8601

        /// Encode the `Date` as a string formatted by the given formatter.
        case formatted(DateFormatter)

        /// Encode the `Date` as a custom value encoded by the given closure.
        ///
        /// If the closure fails to encode a value into the given encoder, the encoder will encode an empty automatic container in its place.
        case custom((Date, Encoder) throws -> Void)
    }

    /// The strategy to use for encoding `Data` values.
    public enum DataEncodingStrategy {
        /// Defer to `Data` for choosing an encoding.
        case deferredToData

        /// Encoded the `Data` as a Base64-encoded string. This is the default strategy.
        case base64

        /// Encode the `Data` as a custom value encoded by the given closure.
        ///
        /// If the closure fails to encode a value into the given encoder, the encoder will encode an empty automatic container in its place.
        case custom((Data, Encoder) throws -> Void)
    }

    /// The strategy to use for non-JSON-conforming floating-point values (IEEE 754 infinity and NaN).
    public enum NonConformingFloatEncodingStrategy {
        /// Throw upon encountering non-conforming values. This is the default strategy.
        case `throw`

        /// Encode the values using the given representation strings.
        case convertToString(positiveInfinity: String, negativeInfinity: String, nan: String)
    }

    /// The strategy to use for automatically changing the value of keys before encoding.
    public enum KeyEncodingStrategy {
        /// Use the keys specified by each type. This is the default strategy.
        case useDefaultKeys

        /// Convert from "camelCaseKeys" to "snake_case_keys" before writing a key to JSON payload.
        ///
        /// Capital characters are determined by testing membership in `CharacterSet.uppercaseLetters` and `CharacterSet.lowercaseLetters` (Unicode General Categories Lu and Lt).
        /// The conversion to lower case uses `Locale.system`, also known as the ICU "root" locale. This means the result is consistent regardless of the current user's locale and language preferences.
        ///
        /// Converting from camel case to snake case:
        /// 1. Splits words at the boundary of lower-case to upper-case
        /// 2. Inserts `_` between words
        /// 3. Lowercases the entire string
        /// 4. Preserves starting and ending `_`.
        ///
        /// For example, `oneTwoThree` becomes `one_two_three`. `_oneTwoThree_` becomes `_one_two_three_`.
        ///
        /// - Note: Using a key encoding strategy has a nominal performance cost, as each string key has to be converted.
        case convertToSnakeCase

        /// Provide a custom conversion to the key in the encoded JSON from the keys specified by the encoded types.
        /// The full path to the current encoding position is provided for context (in case you need to locate this key within the payload). The returned key is used in place of the last component in the coding path before encoding.
        /// If the result of the conversion is a duplicate key, then only one value will be present in the result.
        case custom((_ codingPath: [CodingKey]) -> CodingKey)

        fileprivate static func _convertToSnakeCase(_ stringKey: String) -> String {
            guard !stringKey.isEmpty else { return stringKey }

            var words : [Range<String.Index>] = []
            // The general idea of this algorithm is to split words on transition from lower to upper case, then on transition of >1 upper case characters to lowercase
            //
            // myProperty -> my_property
            // myURLProperty -> my_url_property
            //
            // We assume, per Swift naming conventions, that the first character of the key is lowercase.
            var wordStart = stringKey.startIndex
            var searchRange = stringKey.index(after: wordStart)..<stringKey.endIndex

            // Find next uppercase character
            while let upperCaseRange = stringKey.rangeOfCharacter(from: CharacterSet.uppercaseLetters, options: [], range: searchRange) {
                let untilUpperCase = wordStart..<upperCaseRange.lowerBound
                words.append(untilUpperCase)

                // Find next lowercase character
                searchRange = upperCaseRange.lowerBound..<searchRange.upperBound
                guard let lowerCaseRange = stringKey.rangeOfCharacter(from: CharacterSet.lowercaseLetters, options: [], range: searchRange) else {
                    // There are no more lower case letters. Just end here.
                    wordStart = searchRange.lowerBound
                    break
                }

                // Is the next lowercase letter more than 1 after the uppercase? If so, we encountered a group of uppercase letters that we should treat as its own word
                let nextCharacterAfterCapital = stringKey.index(after: upperCaseRange.lowerBound)
                if lowerCaseRange.lowerBound == nextCharacterAfterCapital {
                    // The next character after capital is a lower case character and therefore not a word boundary.
                    // Continue searching for the next upper case for the boundary.
                    wordStart = upperCaseRange.lowerBound
                } else {
                    // There was a range of >1 capital letters. Turn those into a word, stopping at the capital before the lower case character.
                    let beforeLowerIndex = stringKey.index(before: lowerCaseRange.lowerBound)
                    words.append(upperCaseRange.lowerBound..<beforeLowerIndex)

                    // Next word starts at the capital before the lowercase we just found
                    wordStart = beforeLowerIndex
                }
                searchRange = lowerCaseRange.upperBound..<searchRange.upperBound
            }
            words.append(wordStart..<searchRange.upperBound)
            let result = words.map({ (range) in
                return stringKey[range].lowercased()
            }).joined(separator: "_")
            return result
        }
    }

    /// The output format to produce. Defaults to `[]`.
    open var outputFormatting: OutputFormatting = []

    /// The strategy to use in encoding dates. Defaults to `.deferredToDate`.
    open var dateEncodingStrategy: DateEncodingStrategy = .deferredToDate

    /// The strategy to use in encoding binary data. Defaults to `.base64`.
    open var dataEncodingStrategy: DataEncodingStrategy = .base64

    /// The strategy to use in encoding non-conforming numbers. Defaults to `.throw`.
    open var nonConformingFloatEncodingStrategy: NonConformingFloatEncodingStrategy = .throw
 
    /// The strategy to use for encoding keys. Defaults to `.useDefaultKeys`.
    open var keyEncodingStrategy: KeyEncodingStrategy = .useDefaultKeys
 
    /// Contextual user-provided information for use during encoding.
    open var userInfo: [CodingUserInfoKey : Any] = [:]

    /// Options set on the top-level encoder to pass down the encoding hierarchy.
    fileprivate struct _Options {
        let dateEncodingStrategy: DateEncodingStrategy
        let dataEncodingStrategy: DataEncodingStrategy
        let nonConformingFloatEncodingStrategy: NonConformingFloatEncodingStrategy
        let keyEncodingStrategy: KeyEncodingStrategy
        let userInfo: [CodingUserInfoKey : Any]
    }

    /// The options set on the top-level encoder.
    fileprivate var options: _Options {
        return _Options(dateEncodingStrategy: dateEncodingStrategy,
                        dataEncodingStrategy: dataEncodingStrategy,
                        nonConformingFloatEncodingStrategy: nonConformingFloatEncodingStrategy,
                        keyEncodingStrategy: keyEncodingStrategy,
                        userInfo: userInfo)
    }

    // MARK: - Constructing a JSON Encoder

    /// Initializes `self` with default strategies.
    public init() {}

    // MARK: - Encoding Values

    /// Encodes the given top-level value and returns its JSON representation.
    ///
    /// - parameter value: The value to encode.
    /// - returns: A new `Data` value containing the encoded JSON data.
    /// - throws: `EncodingError.invalidValue` if a non-conforming floating-point value is encountered during encoding, and the encoding strategy is `.throw`.
    /// - throws: An error if any value throws an error during encoding.
    open func encode<T: Encodable>(_ value: T) throws -> Data {
        let value: JSONValue = try encodeAsJSONValue(value)
        let writer = JSONValue.Writer(options: self.outputFormatting)
        let bytes = writer.writeValue(value)
        
        return Data(bytes)
    }

    func encodeAsJSONValue<T: Encodable>(_ value: T) throws -> JSONValue {
        let encoder = JSONEncoderImpl(options: self.options, codingPath: [])
        guard let topLevel = try encoder.wrapEncodable(value, for: nil) else {
            throw EncodingError.invalidValue(value, EncodingError.Context(codingPath: [], debugDescription: "Top-level \(T.self) did not encode any values."))
        }
        
        return topLevel
    }
}

// MARK: - _JSONEncoder

private enum JSONFuture {
    case value(JSONValue)
    case encoder(JSONEncoderImpl)
    case nestedArray(RefArray)
    case nestedObject(RefObject)
    
    class RefArray {
        private(set) var array: [JSONFuture] = []

        init() {
            self.array.reserveCapacity(10)
        }

        @inline(__always) func append(_ element: JSONValue) {
            self.array.append(.value(element))
        }
        
        @inline(__always) func append(_ encoder: JSONEncoderImpl) {
            self.array.append(.encoder(encoder))
        }

        @inline(__always) func appendArray() -> RefArray {
            let array = RefArray()
            self.array.append(.nestedArray(array))
            return array
        }

        @inline(__always) func appendObject() -> RefObject {
            let object = RefObject()
            self.array.append(.nestedObject(object))
            return object
        }

        var values: [JSONValue] {
            self.array.map { (future) -> JSONValue in
                switch future {
                case .value(let value):
                    return value
                case .nestedArray(let array):
                    return .array(array.values)
                case .nestedObject(let object):
                    return .object(object.values)
                case .encoder(let encoder):
                    return encoder.value ?? .object([:])
                }
            }
        }
    }

    class RefObject {
        private(set) var dict: [String: JSONFuture] = [:]

        init() {
            self.dict.reserveCapacity(20)
        }

        @inline(__always) func set(_ value: JSONValue, for key: String) {
            self.dict[key] = .value(value)
        }

        @inline(__always) func setArray(for key: String) -> RefArray {
            switch self.dict[key] {
            case .encoder:
                preconditionFailure("For key \"\(key)\" an encoder has already been created.")
            case .nestedObject:
                preconditionFailure("For key \"\(key)\" a keyed container has already been created.")
            case .nestedArray(let array):
                return array
            case .none, .value:
                let array = RefArray()
                dict[key] = .nestedArray(array)
                return array
            }
        }

        @inline(__always) func setObject(for key: String) -> RefObject {
            switch self.dict[key] {
            case .encoder:
                preconditionFailure("For key \"\(key)\" an encoder has already been created.")
            case .nestedObject(let object):
                return object
            case .nestedArray:
                preconditionFailure("For key \"\(key)\" a unkeyed container has already been created.")
            case .none, .value:
                let object = RefObject()
                dict[key] = .nestedObject(object)
                return object
            }
        }
        
        @inline(__always) func set(_ encoder: JSONEncoderImpl, for key: String) {
            switch self.dict[key] {
            case .encoder:
                preconditionFailure("For key \"\(key)\" an encoder has already been created.")
            case .nestedObject:
                preconditionFailure("For key \"\(key)\" a keyed container has already been created.")
            case .nestedArray:
                preconditionFailure("For key \"\(key)\" a unkeyed container has already been created.")
            case .none, .value:
                dict[key] = .encoder(encoder)
            }
        }

        var values: [String: JSONValue] {
            self.dict.mapValues { (future) -> JSONValue in
                switch future {
                case .value(let value):
                    return value
                case .nestedArray(let array):
                    return .array(array.values)
                case .nestedObject(let object):
                    return .object(object.values)
                case .encoder(let encoder):
                    return encoder.value ?? .object([:])
                }
            }
        }
    }
}

private class JSONEncoderImpl {
    let options: JSONEncoder._Options
    let codingPath: [CodingKey]
    var userInfo: [CodingUserInfoKey : Any] {
        options.userInfo
    }

    var singleValue: JSONValue?
    var array: JSONFuture.RefArray?
    var object: JSONFuture.RefObject?

    var value: JSONValue? {
        if let object = self.object {
            return .object(object.values)
        }
        if let array = self.array {
            return .array(array.values)
        }
        return self.singleValue
    }

    init(options: JSONEncoder._Options, codingPath: [CodingKey]) {
        self.options = options
        self.codingPath = codingPath
    }
}

extension JSONEncoderImpl: Encoder {
    func container<Key>(keyedBy _: Key.Type) -> KeyedEncodingContainer<Key> where Key: CodingKey {
        if let _ = object {
            let container = JSONKeyedEncodingContainer<Key>(impl: self, codingPath: codingPath)
            return KeyedEncodingContainer(container)
        }

        guard self.singleValue == nil, self.array == nil else {
            preconditionFailure()
        }

        self.object = JSONFuture.RefObject()
        let container = JSONKeyedEncodingContainer<Key>(impl: self, codingPath: codingPath)
        return KeyedEncodingContainer(container)
    }

    func unkeyedContainer() -> UnkeyedEncodingContainer {
        if let _ = array {
            return JSONUnkeyedEncodingContainer(impl: self, codingPath: self.codingPath)
        }

        guard self.singleValue == nil, self.object == nil else {
            preconditionFailure()
        }

        self.array = JSONFuture.RefArray()
        return JSONUnkeyedEncodingContainer(impl: self, codingPath: self.codingPath)
    }

    func singleValueContainer() -> SingleValueEncodingContainer {
        guard self.object == nil, self.array == nil else {
            preconditionFailure()
        }

        return JSONSingleValueEncodingContainer(impl: self, codingPath: self.codingPath)
    }
}

// this is a private protocol to implement convenience methods directly on the EncodingContainers

extension JSONEncoderImpl: _SpecialTreatmentEncoder {
    var impl: JSONEncoderImpl {
        return self
    }
    
    // untyped escape hatch. needed for `wrapObject`
    func wrapUntyped(_ encodable: Encodable) throws -> JSONValue {
        switch encodable {
        case let date as Date:
            return try self.wrapDate(date, for: nil)
        case let data as Data:
            return try self.wrapData(data, for: nil)
        case let url as URL:
            return .string(url.absoluteString)
        case let decimal as Decimal:
            return .number(decimal.description)
        case let object as [String: Encodable]: // this emits a warning, but it works perfectly
            return try self.wrapObject(object, for: nil)
        case let date as Date:
            return try self.wrapDate(date, for: nil)
        default:
            try encodable.encode(to: self)
            return self.value ?? .object([:])
        }
    }
}

private protocol _SpecialTreatmentEncoder {
    var codingPath: [CodingKey] { get }
    var options: JSONEncoder._Options { get }
    var impl: JSONEncoderImpl { get }
}

extension _SpecialTreatmentEncoder {
    @inline(__always) fileprivate func wrapFloat<F: FloatingPoint & CustomStringConvertible>(_ float: F, for additionalKey: CodingKey?) throws -> JSONValue {
        guard !float.isNaN, !float.isInfinite else {
            if case .convertToString(let posInfString, let negInfString, let nanString) = self.options.nonConformingFloatEncodingStrategy {
                switch float {
                case F.infinity:
                    return .string(posInfString)
                case -F.infinity:
                    return .string(negInfString)
                default:
                    // must be nan in this case
                    return .string(nanString)
                }
            }
            
            var path = self.codingPath
            if let additionalKey = additionalKey {
                path.append(additionalKey)
            }
            
            throw EncodingError.invalidValue(float, .init(
                codingPath: path,
                debugDescription: "Unable to encode \(F.self).\(float) directly in JSON."
            ))
        }
        
        var string = float.description
        if string.hasSuffix(".0") {
            string.removeLast(2)
        }
        return .number(string)
    }
    
    fileprivate func wrapEncodable<E: Encodable>(_ encodable: E, for additionalKey: CodingKey?) throws -> JSONValue? {
        switch encodable {
        case let date as Date:
            return try self.wrapDate(date, for: additionalKey)
        case let data as Data:
            return try self.wrapData(data, for: additionalKey)
        case let url as URL:
            return .string(url.absoluteString)
        case let decimal as Decimal:
            return .number(decimal.description)
        case let object as [String: Encodable]:
            return try self.wrapObject(object, for: additionalKey)
        default:
            let encoder = self.getEncoder(for: additionalKey)
            try encodable.encode(to: encoder)
            return encoder.value
        }
    }
    
    func wrapDate(_ date: Date, for additionalKey: CodingKey?) throws -> JSONValue {
        switch self.options.dateEncodingStrategy {
        case .deferredToDate:
            let encoder = self.getEncoder(for: additionalKey)
            try date.encode(to: encoder)
            return encoder.value ?? .null

        case .secondsSince1970:
            return .number(date.timeIntervalSince1970.description)

        case .millisecondsSince1970:
            return .number((date.timeIntervalSince1970 * 1000).description)

        case .iso8601:
            if #available(macOS 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *) {
                return .string(_iso8601Formatter.string(from: date))
            } else {
                fatalError("ISO8601DateFormatter is unavailable on this platform.")
            }

        case .formatted(let formatter):
            return .string(formatter.string(from: date))

        case .custom(let closure):
            let encoder = self.getEncoder(for: additionalKey)
            try closure(date, encoder)
            // The closure didn't encode anything. Return the default keyed container.
            return encoder.value ?? .object([:])
        }
    }
    
    func wrapData(_ data: Data, for additionalKey: CodingKey?) throws -> JSONValue {
        switch self.options.dataEncodingStrategy {
        case .deferredToData:
            let encoder = self.getEncoder(for: additionalKey)
            try data.encode(to: encoder)
            return encoder.value ?? .null

        case .base64:
            let base64 = data.base64EncodedString()
            return .string(base64)

        case .custom(let closure):
            let encoder = self.getEncoder(for: additionalKey)
            try closure(data, encoder)
            // The closure didn't encode anything. Return the default keyed container.
            return encoder.value ?? .object([:])
        }
    }
    
    func wrapObject(_ object: [String: Encodable], for additionalKey: CodingKey?) throws -> JSONValue {
        var baseCodingPath = self.codingPath
        if let additionalKey = additionalKey {
            baseCodingPath.append(additionalKey)
        }
        var result = [String: JSONValue]()
        result.reserveCapacity(object.count)
        
        try object.forEach { (key, value) in
            var elemCodingPath = baseCodingPath
            elemCodingPath.append(_JSONKey(stringValue: key, intValue: nil))
            let encoder = JSONEncoderImpl(options: self.options, codingPath: elemCodingPath)

            result[key] = try encoder.wrapUntyped(value)
        }
        
        return .object(result)
    }

    fileprivate func getEncoder(for additionalKey: CodingKey?) -> JSONEncoderImpl {
        if let additionalKey = additionalKey {
            var newCodingPath = self.codingPath
            newCodingPath.append(additionalKey)
            return JSONEncoderImpl(options: self.options, codingPath: newCodingPath)
        }
        
        return self.impl
    }
}

private struct JSONKeyedEncodingContainer<K: CodingKey>: KeyedEncodingContainerProtocol, _SpecialTreatmentEncoder {
    typealias Key = K

    let impl: JSONEncoderImpl
    let object: JSONFuture.RefObject
    let codingPath: [CodingKey]

    private var firstValueWritten: Bool = false
    fileprivate var options: JSONEncoder._Options {
        return self.impl.options
    }

    init(impl: JSONEncoderImpl, codingPath: [CodingKey]) {
        self.impl = impl
        self.object = impl.object!
        self.codingPath = codingPath
    }

    // used for nested containers
    init(impl: JSONEncoderImpl, object: JSONFuture.RefObject, codingPath: [CodingKey]) {
        self.impl = impl
        self.object = object
        self.codingPath = codingPath
    }
    
    private func _converted(_ key: Key) -> CodingKey {
        switch self.options.keyEncodingStrategy {
        case .useDefaultKeys:
            return key
        case .convertToSnakeCase:
            let newKeyString = JSONEncoder.KeyEncodingStrategy._convertToSnakeCase(key.stringValue)
            return _JSONKey(stringValue: newKeyString, intValue: key.intValue)
        case .custom(let converter):
            return converter(codingPath + [key])
        }
    }

    mutating func encodeNil(forKey key: Self.Key) throws {
        self.object.set(.null, for: self._converted(key).stringValue)
    }

    mutating func encode(_ value: Bool, forKey key: Self.Key) throws {
        self.object.set(.bool(value), for: self._converted(key).stringValue)
    }

    mutating func encode(_ value: String, forKey key: Self.Key) throws {
        self.object.set(.string(value), for: self._converted(key).stringValue)
    }

    mutating func encode(_ value: Double, forKey key: Self.Key) throws {
        try encodeFloatingPoint(value, key: self._converted(key))
    }

    mutating func encode(_ value: Float, forKey key: Self.Key) throws {
        try encodeFloatingPoint(value, key: self._converted(key))
    }

    mutating func encode(_ value: Int, forKey key: Self.Key) throws {
        try encodeFixedWidthInteger(value, key: self._converted(key))
    }

    mutating func encode(_ value: Int8, forKey key: Self.Key) throws {
        try encodeFixedWidthInteger(value, key: self._converted(key))
    }

    mutating func encode(_ value: Int16, forKey key: Self.Key) throws {
        try encodeFixedWidthInteger(value, key: self._converted(key))
    }

    mutating func encode(_ value: Int32, forKey key: Self.Key) throws {
        try encodeFixedWidthInteger(value, key: self._converted(key))
    }

    mutating func encode(_ value: Int64, forKey key: Self.Key) throws {
        try encodeFixedWidthInteger(value, key: self._converted(key))
    }

    mutating func encode(_ value: UInt, forKey key: Self.Key) throws {
        try encodeFixedWidthInteger(value, key: self._converted(key))
    }

    mutating func encode(_ value: UInt8, forKey key: Self.Key) throws {
        try encodeFixedWidthInteger(value, key: self._converted(key))
    }

    mutating func encode(_ value: UInt16, forKey key: Self.Key) throws {
        try encodeFixedWidthInteger(value, key: self._converted(key))
    }

    mutating func encode(_ value: UInt32, forKey key: Self.Key) throws {
        try encodeFixedWidthInteger(value, key: self._converted(key))
    }

    mutating func encode(_ value: UInt64, forKey key: Self.Key) throws {
        try encodeFixedWidthInteger(value, key: self._converted(key))
    }

    mutating func encode<T>(_ value: T, forKey key: Self.Key) throws where T: Encodable {
        let convertedKey = self._converted(key)
        let encoded = try self.wrapEncodable(value, for: convertedKey)
        self.object.set(encoded ?? .object([:]), for: convertedKey.stringValue)
    }

    mutating func nestedContainer<NestedKey>(keyedBy _: NestedKey.Type, forKey key: Self.Key) ->
        KeyedEncodingContainer<NestedKey> where NestedKey: CodingKey
    {
        let convertedKey = self._converted(key)
        let newPath = self.codingPath + [convertedKey]
        let object = self.object.setObject(for: convertedKey.stringValue)
        let nestedContainer = JSONKeyedEncodingContainer<NestedKey>(impl: impl, object: object, codingPath: newPath)
        return KeyedEncodingContainer(nestedContainer)
    }

    mutating func nestedUnkeyedContainer(forKey key: Self.Key) -> UnkeyedEncodingContainer {
        let convertedKey = self._converted(key)
        let newPath = self.codingPath + [convertedKey]
        let array = self.object.setArray(for: convertedKey.stringValue)
        let nestedContainer = JSONUnkeyedEncodingContainer(impl: impl, array: array, codingPath: newPath)
        return nestedContainer
    }

    mutating func superEncoder() -> Encoder {
        let newEncoder = self.getEncoder(for: _JSONKey.super)
        self.object.set(newEncoder, for: _JSONKey.super.stringValue)
        return newEncoder
    }

    mutating func superEncoder(forKey key: Self.Key) -> Encoder {
        let convertedKey = self._converted(key)
        let newEncoder = self.getEncoder(for: convertedKey)
        self.object.set(newEncoder, for: convertedKey.stringValue)
        return newEncoder
    }
}

extension JSONKeyedEncodingContainer {
    @inline(__always) private mutating func encodeFloatingPoint<F: FloatingPoint & CustomStringConvertible>(_ float: F, key: CodingKey) throws {
        let value = try self.wrapFloat(float, for: key)
        self.object.set(value, for: key.stringValue)
    }
    
    @inline(__always) private mutating func encodeFixedWidthInteger<N: FixedWidthInteger>(_ value: N, key: CodingKey) throws {
        self.object.set(.number(value.description), for: key.stringValue)
    }
}

private struct JSONUnkeyedEncodingContainer: UnkeyedEncodingContainer, _SpecialTreatmentEncoder {
    let impl: JSONEncoderImpl
    let array: JSONFuture.RefArray
    let codingPath: [CodingKey]

    var count: Int {
        self.array.array.count
    }
    private var firstValueWritten: Bool = false
    fileprivate var options: JSONEncoder._Options {
        return self.impl.options
    }

    init(impl: JSONEncoderImpl, codingPath: [CodingKey]) {
        self.impl = impl
        self.array = impl.array!
        self.codingPath = codingPath
    }

    // used for nested containers
    init(impl: JSONEncoderImpl, array: JSONFuture.RefArray, codingPath: [CodingKey]) {
        self.impl = impl
        self.array = array
        self.codingPath = codingPath
    }

    mutating func encodeNil() throws {
        self.array.append(.null)
    }

    mutating func encode(_ value: Bool) throws {
        self.array.append(.bool(value))
    }

    mutating func encode(_ value: String) throws {
        self.array.append(.string(value))
    }

    mutating func encode(_ value: Double) throws {
        try encodeFloatingPoint(value)
    }

    mutating func encode(_ value: Float) throws {
        try encodeFloatingPoint(value)
    }

    mutating func encode(_ value: Int) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: Int8) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: Int16) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: Int32) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: Int64) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: UInt) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: UInt8) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: UInt16) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: UInt32) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: UInt64) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode<T>(_ value: T) throws where T: Encodable {
        let key = _JSONKey(stringValue: "Index \(self.count)", intValue: self.count)
        let encoded = try self.wrapEncodable(value, for: key)
        self.array.append(encoded ?? .object([:]))
    }

    mutating func nestedContainer<NestedKey>(keyedBy _: NestedKey.Type) ->
        KeyedEncodingContainer<NestedKey> where NestedKey: CodingKey
    {
        let newPath = self.codingPath + [_JSONKey(index: self.count)]
        let object = self.array.appendObject()
        let nestedContainer = JSONKeyedEncodingContainer<NestedKey>(impl: impl, object: object, codingPath: newPath)
        return KeyedEncodingContainer(nestedContainer)
    }

    mutating func nestedUnkeyedContainer() -> UnkeyedEncodingContainer {
        let newPath = self.codingPath + [_JSONKey(index: self.count)]
        let array = self.array.appendArray()
        let nestedContainer = JSONUnkeyedEncodingContainer(impl: impl, array: array, codingPath: newPath)
        return nestedContainer
    }

    mutating func superEncoder() -> Encoder {
        let encoder = self.getEncoder(for: _JSONKey(index: self.count))
        self.array.append(encoder)
        return encoder
    }
}

extension JSONUnkeyedEncodingContainer {
    @inline(__always) private mutating func encodeFixedWidthInteger<N: FixedWidthInteger>(_ value: N) throws {
        self.array.append(.number(value.description))
    }

    @inline(__always) private mutating func encodeFloatingPoint<F: FloatingPoint & CustomStringConvertible>(_ float: F) throws {
        let value = try self.wrapFloat(float, for: _JSONKey(index: self.count))
        self.array.append(value)
    }
}

private struct JSONSingleValueEncodingContainer: SingleValueEncodingContainer, _SpecialTreatmentEncoder {
    let impl: JSONEncoderImpl
    let codingPath: [CodingKey]

    private var firstValueWritten: Bool = false
    fileprivate var options: JSONEncoder._Options {
        return self.impl.options
    }

    init(impl: JSONEncoderImpl, codingPath: [CodingKey]) {
        self.impl = impl
        self.codingPath = codingPath
    }

    mutating func encodeNil() throws {
        self.preconditionCanEncodeNewValue()
        self.impl.singleValue = .null
    }

    mutating func encode(_ value: Bool) throws {
        self.preconditionCanEncodeNewValue()
        self.impl.singleValue = .bool(value)
    }

    mutating func encode(_ value: Int) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: Int8) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: Int16) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: Int32) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: Int64) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: UInt) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: UInt8) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: UInt16) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: UInt32) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: UInt64) throws {
        try encodeFixedWidthInteger(value)
    }

    mutating func encode(_ value: Float) throws {
        try encodeFloatingPoint(value)
    }

    mutating func encode(_ value: Double) throws {
        try encodeFloatingPoint(value)
    }

    mutating func encode(_ value: String) throws {
        self.preconditionCanEncodeNewValue()
        self.impl.singleValue = .string(value)
    }

    mutating func encode<T: Encodable>(_ value: T) throws {
        self.preconditionCanEncodeNewValue()
        self.impl.singleValue = try self.wrapEncodable(value, for: nil)
    }

    func preconditionCanEncodeNewValue() {
        precondition(self.impl.singleValue == nil, "Attempt to encode value through single value container when previously value already encoded.")
    }
}

extension JSONSingleValueEncodingContainer {
    @inline(__always) private mutating func encodeFixedWidthInteger<N: FixedWidthInteger>(_ value: N) throws {
        self.preconditionCanEncodeNewValue()
        self.impl.singleValue = .number(value.description)
    }
    
    @inline(__always) private mutating func encodeFloatingPoint<F: FloatingPoint & CustomStringConvertible>(_ float: F) throws {
        self.preconditionCanEncodeNewValue()
        let value = try self.wrapFloat(float, for: nil)
        self.impl.singleValue = value
    }
}

extension JSONValue {
    
    fileprivate struct Writer {
        let options: JSONEncoder.OutputFormatting
        
        init(options: JSONEncoder.OutputFormatting) {
            self.options = options
        }
        
        func writeValue(_ value: JSONValue) -> [UInt8] {
            var bytes = [UInt8]()
            if self.options.contains(.prettyPrinted) {
                self.writeValuePretty(value, into: &bytes)
            }
            else {
                self.writeValue(value, into: &bytes)
            }
            return bytes
        }
        
        private func writeValue(_ value: JSONValue, into bytes: inout [UInt8]) {
            switch value {
            case .null:
                bytes.append(contentsOf: [UInt8]._null)
            case .bool(true):
                bytes.append(contentsOf: [UInt8]._true)
            case .bool(false):
                bytes.append(contentsOf: [UInt8]._false)
            case .string(let string):
                self.encodeString(string, to: &bytes)
            case .number(let string):
                bytes.append(contentsOf: string.utf8)
            case .array(let array):
                var iterator = array.makeIterator()
                bytes.append(._openbracket)
                // we don't like branching, this is why we have this extra
                if let first = iterator.next() {
                    self.writeValue(first, into: &bytes)
                }
                while let item = iterator.next() {
                    bytes.append(._comma)
                    self.writeValue(item, into:&bytes)
                }
                bytes.append(._closebracket)
            case .object(let dict):
                if #available(OSX 10.13, *), options.contains(.sortedKeys) {
                    let sorted = dict.sorted { $0.key < $1.key }
                    self.writeObject(sorted, into: &bytes)
                } else {
                    self.writeObject(dict, into: &bytes)
                }
            }
        }
        
        private func writeObject<Object: Sequence>(_ object: Object, into bytes: inout [UInt8], depth: Int = 0)
            where Object.Element == (key: String, value: JSONValue)
        {
            var iterator = object.makeIterator()
            bytes.append(._openbrace)
            if let (key, value) = iterator.next() {
                self.encodeString(key, to: &bytes)
                bytes.append(._colon)
                self.writeValue(value, into: &bytes)
            }
            while let (key, value) = iterator.next() {
                bytes.append(._comma)
                // key
                self.encodeString(key, to: &bytes)
                bytes.append(._colon)
                
                self.writeValue(value, into: &bytes)
            }
            bytes.append(._closebrace)
        }

        private func addInset(to bytes: inout [UInt8], depth: Int) {
            bytes.append(contentsOf: [UInt8](repeating: ._space, count: depth * 2))
        }
        
        private func writeValuePretty(_ value: JSONValue, into bytes: inout [UInt8], depth: Int = 0) {
            switch value {
            case .null:
                bytes.append(contentsOf: [UInt8]._null)
            case .bool(true):
                bytes.append(contentsOf: [UInt8]._true)
            case .bool(false):
                bytes.append(contentsOf: [UInt8]._false)
            case .string(let string):
                self.encodeString(string, to: &bytes)
            case .number(let string):
                bytes.append(contentsOf: string.utf8)
            case .array(let array):
                var iterator = array.makeIterator()
                bytes.append(contentsOf: [._openbracket, ._newline])
                if let first = iterator.next() {
                    self.addInset(to: &bytes, depth: depth + 1)
                    self.writeValuePretty(first, into: &bytes, depth: depth + 1)
                }
                while let item = iterator.next() {
                    bytes.append(contentsOf: [._comma, ._newline])
                    self.addInset(to: &bytes, depth: depth + 1)
                    self.writeValuePretty(item, into: &bytes, depth: depth + 1)
                }
                bytes.append(._newline)
                self.addInset(to: &bytes, depth: depth)
                bytes.append(._closebracket)
            case .object(let dict):
                if #available(OSX 10.13, *), options.contains(.sortedKeys) {
                    let sorted = dict.sorted { $0.key < $1.key }
                    self.writePrettyObject(sorted, into: &bytes, depth: depth)
                } else {
                    self.writePrettyObject(dict, into: &bytes, depth: depth)
                }
            }
        }
        
        private func writePrettyObject<Object: Sequence>(_ object: Object, into bytes: inout [UInt8], depth: Int = 0)
            where Object.Element == (key: String, value: JSONValue)
        {
            var iterator = object.makeIterator()
            bytes.append(contentsOf: [._openbrace, ._newline])
            if let (key, value) = iterator.next() {
                self.addInset(to: &bytes, depth: depth + 1)
                self.encodeString(key, to: &bytes)
                bytes.append(contentsOf: [._space, ._colon, ._space])
                self.writeValuePretty(value, into: &bytes, depth: depth + 1)
            }
            while let (key, value) = iterator.next() {
                bytes.append(contentsOf: [._comma, ._newline])
                self.addInset(to: &bytes, depth: depth + 1)
                // key
                self.encodeString(key, to: &bytes)
                bytes.append(contentsOf: [._space, ._colon, ._space])
                // value
                self.writeValuePretty(value, into: &bytes, depth: depth + 1)
            }
            bytes.append(._newline)
            self.addInset(to: &bytes, depth: depth)
            bytes.append(._closebrace)
        }
        
        private func encodeString(_ string: String, to bytes: inout [UInt8]) {
            bytes.append(UInt8(ascii: "\""))
            let stringBytes = string.utf8
            var startCopyIndex = stringBytes.startIndex
            var nextIndex = startCopyIndex

            while nextIndex != stringBytes.endIndex {
                switch stringBytes[nextIndex] {
                case 0 ..< 32, UInt8(ascii: "\""), UInt8(ascii: "\\"):
                    // All Unicode characters may be placed within the
                    // quotation marks, except for the characters that MUST be escaped:
                    // quotation mark, reverse solidus, and the control characters (U+0000
                    // through U+001F).
                    // https://tools.ietf.org/html/rfc8259#section-7

                    // copy the current range over
                    bytes.append(contentsOf: stringBytes[startCopyIndex ..< nextIndex])
                    switch stringBytes[nextIndex] {
                    case UInt8(ascii: "\""): // quotation mark
                        bytes.append(contentsOf: [._backslash, ._quote])
                    case UInt8(ascii: "\\"): // reverse solidus
                        bytes.append(contentsOf: [._backslash, ._backslash])
                    case 0x08: // backspace
                        bytes.append(contentsOf: [._backslash, UInt8(ascii: "b")])
                    case 0x0C: // form feed
                        bytes.append(contentsOf: [._backslash, UInt8(ascii: "f")])
                    case 0x0A: // line feed
                        bytes.append(contentsOf: [._backslash, UInt8(ascii: "n")])
                    case 0x0D: // carriage return
                        bytes.append(contentsOf: [._backslash, UInt8(ascii: "r")])
                    case 0x09: // tab
                        bytes.append(contentsOf: [._backslash, UInt8(ascii: "t")])
                    default:
                        func valueToAscii(_ value: UInt8) -> UInt8 {
                            switch value {
                            case 0 ... 9:
                                return value + UInt8(ascii: "0")
                            case 10 ... 15:
                                return value - 10 + UInt8(ascii: "a")
                            default:
                                preconditionFailure()
                            }
                        }
                        bytes.append(UInt8(ascii: "\\"))
                        bytes.append(UInt8(ascii: "u"))
                        bytes.append(UInt8(ascii: "0"))
                        bytes.append(UInt8(ascii: "0"))
                        let first = stringBytes[nextIndex] / 16
                        let remaining = stringBytes[nextIndex] % 16
                        bytes.append(valueToAscii(first))
                        bytes.append(valueToAscii(remaining))
                    }

                    nextIndex = stringBytes.index(after: nextIndex)
                    startCopyIndex = nextIndex
                case UInt8(ascii: "/") where options.contains(.withoutEscapingSlashes) == false:
                    bytes.append(contentsOf: stringBytes[startCopyIndex ..< nextIndex])
                    bytes.append(contentsOf: [._backslash, UInt8(ascii: "/")])
                    nextIndex = stringBytes.index(after: nextIndex)
                    startCopyIndex = nextIndex
                default:
                    nextIndex = stringBytes.index(after: nextIndex)
                }
            }

            // copy everything, that hasn't been copied yet
            bytes.append(contentsOf: stringBytes[startCopyIndex ..< nextIndex])
            bytes.append(UInt8(ascii: "\""))
        }
    }
}


//===----------------------------------------------------------------------===//
// JSON Decoder
//===----------------------------------------------------------------------===//

/// `JSONDecoder` facilitates the decoding of JSON into semantic `Decodable` types.
open class JSONDecoder {
    // MARK: Options

    /// The strategy to use for decoding `Date` values.
    public enum DateDecodingStrategy {
        /// Defer to `Date` for decoding. This is the default strategy.
        case deferredToDate

        /// Decode the `Date` as a UNIX timestamp from a JSON number.
        case secondsSince1970

        /// Decode the `Date` as UNIX millisecond timestamp from a JSON number.
        case millisecondsSince1970

        /// Decode the `Date` as an ISO-8601-formatted string (in RFC 3339 format).
        @available(macOS 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *)
        case iso8601

        /// Decode the `Date` as a string parsed by the given formatter.
        case formatted(DateFormatter)

        /// Decode the `Date` as a custom value decoded by the given closure.
        case custom((_ decoder: Decoder) throws -> Date)
    }

    /// The strategy to use for decoding `Data` values.
    public enum DataDecodingStrategy {
        /// Defer to `Data` for decoding.
        case deferredToData

        /// Decode the `Data` from a Base64-encoded string. This is the default strategy.
        case base64

        /// Decode the `Data` as a custom value decoded by the given closure.
        case custom((_ decoder: Decoder) throws -> Data)
    }

    /// The strategy to use for non-JSON-conforming floating-point values (IEEE 754 infinity and NaN).
    public enum NonConformingFloatDecodingStrategy {
        /// Throw upon encountering non-conforming values. This is the default strategy.
        case `throw`

        /// Decode the values from the given representation strings.
        case convertFromString(positiveInfinity: String, negativeInfinity: String, nan: String)
    }
    
    /// The strategy to use for automatically changing the value of keys before decoding.
    public enum KeyDecodingStrategy {
        /// Use the keys specified by each type. This is the default strategy.
        case useDefaultKeys
        
        /// Convert from "snake_case_keys" to "camelCaseKeys" before attempting to match a key with the one specified by each type.
        ///
        /// The conversion to upper case uses `Locale.system`, also known as the ICU "root" locale. This means the result is consistent regardless of the current user's locale and language preferences.
        ///
        /// Converting from snake case to camel case:
        /// 1. Capitalizes the word starting after each `_`
        /// 2. Removes all `_`
        /// 3. Preserves starting and ending `_` (as these are often used to indicate private variables or other metadata).
        /// For example, `one_two_three` becomes `oneTwoThree`. `_one_two_three_` becomes `_oneTwoThree_`.
        ///
        /// - Note: Using a key decoding strategy has a nominal performance cost, as each string key has to be inspected for the `_` character.
        case convertFromSnakeCase
        
        /// Provide a custom conversion from the key in the encoded JSON to the keys specified by the decoded types.
        /// The full path to the current decoding position is provided for context (in case you need to locate this key within the payload). The returned key is used in place of the last component in the coding path before decoding.
        /// If the result of the conversion is a duplicate key, then only one value will be present in the container for the type to decode from.
        case custom((_ codingPath: [CodingKey]) -> CodingKey)
        
        fileprivate static func _convertFromSnakeCase(_ stringKey: String) -> String {
            guard !stringKey.isEmpty else { return stringKey }
            
            // Find the first non-underscore character
            guard let firstNonUnderscore = stringKey.firstIndex(where: { $0 != "_" }) else {
                // Reached the end without finding an _
                return stringKey
            }
            
            // Find the last non-underscore character
            var lastNonUnderscore = stringKey.index(before: stringKey.endIndex)
            while lastNonUnderscore > firstNonUnderscore && stringKey[lastNonUnderscore] == "_" {
                stringKey.formIndex(before: &lastNonUnderscore)
            }
            
            let keyRange = firstNonUnderscore...lastNonUnderscore
            let leadingUnderscoreRange = stringKey.startIndex..<firstNonUnderscore
            let trailingUnderscoreRange = stringKey.index(after: lastNonUnderscore)..<stringKey.endIndex
            
            let components = stringKey[keyRange].split(separator: "_")
            let joinedString : String
            if components.count == 1 {
                // No underscores in key, leave the word as is - maybe already camel cased
                joinedString = String(stringKey[keyRange])
            } else {
                joinedString = ([components[0].lowercased()] + components[1...].map { $0.capitalized }).joined()
            }
            
            // Do a cheap isEmpty check before creating and appending potentially empty strings
            let result : String
            if (leadingUnderscoreRange.isEmpty && trailingUnderscoreRange.isEmpty) {
                result = joinedString
            } else if (!leadingUnderscoreRange.isEmpty && !trailingUnderscoreRange.isEmpty) {
                // Both leading and trailing underscores
                result = String(stringKey[leadingUnderscoreRange]) + joinedString + String(stringKey[trailingUnderscoreRange])
            } else if (!leadingUnderscoreRange.isEmpty) {
                // Just leading
                result = String(stringKey[leadingUnderscoreRange]) + joinedString
            } else {
                // Just trailing
                result = joinedString + String(stringKey[trailingUnderscoreRange])
            }
            return result
        }
    }
    
    /// The strategy to use in decoding dates. Defaults to `.deferredToDate`.
    open var dateDecodingStrategy: DateDecodingStrategy = .deferredToDate

    /// The strategy to use in decoding binary data. Defaults to `.base64`.
    open var dataDecodingStrategy: DataDecodingStrategy = .base64

    /// The strategy to use in decoding non-conforming numbers. Defaults to `.throw`.
    open var nonConformingFloatDecodingStrategy: NonConformingFloatDecodingStrategy = .throw

    /// The strategy to use for decoding keys. Defaults to `.useDefaultKeys`.
    open var keyDecodingStrategy: KeyDecodingStrategy = .useDefaultKeys

    /// Contextual user-provided information for use during decoding.
    open var userInfo: [CodingUserInfoKey : Any] = [:]

    /// Options set on the top-level encoder to pass down the decoding hierarchy.
    fileprivate struct _Options {
        let dateDecodingStrategy: DateDecodingStrategy
        let dataDecodingStrategy: DataDecodingStrategy
        let nonConformingFloatDecodingStrategy: NonConformingFloatDecodingStrategy
        let keyDecodingStrategy: KeyDecodingStrategy
        let userInfo: [CodingUserInfoKey : Any]
    }

    /// The options set on the top-level decoder.
    fileprivate var options: _Options {
        return _Options(dateDecodingStrategy: dateDecodingStrategy,
                        dataDecodingStrategy: dataDecodingStrategy,
                        nonConformingFloatDecodingStrategy: nonConformingFloatDecodingStrategy,
                        keyDecodingStrategy: keyDecodingStrategy,
                        userInfo: userInfo)
    }

    // MARK: - Constructing a JSON Decoder

    /// Initializes `self` with default strategies.
    public init() {}

    // MARK: - Decoding Values

    /// Decodes a top-level value of the given type from the given JSON representation.
    ///
    /// - parameter type: The type of the value to decode.
    /// - parameter data: The data to decode from.
    /// - returns: A value of the requested type.
    /// - throws: `DecodingError.dataCorrupted` if values requested from the payload are corrupted, or if the given data is not valid JSON.
    /// - throws: An error if any value throws an error during decoding.
    open func decode<T : Decodable>(_ type: T.Type, from data: Data) throws -> T {
        do {
            var parser = JSONParser(bytes: Array(data))
            let json = try parser.parse()
            return try JSONDecoderImpl(userInfo: self.userInfo, from: json, codingPath: [], options: self.options).unwrap(as: T.self)
        } catch let error as JSONError {
            throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: [], debugDescription: "The given data was not valid JSON.", underlyingError: error))
        } catch {
            throw error
        }
    }
}

// MARK: - _JSONDecoder

fileprivate struct JSONDecoderImpl {
    let codingPath: [CodingKey]
    let userInfo: [CodingUserInfoKey: Any]

    let json: JSONValue
    let options: JSONDecoder._Options

    init(userInfo: [CodingUserInfoKey: Any], from json: JSONValue, codingPath: [CodingKey], options: JSONDecoder._Options) {
        self.userInfo = userInfo
        self.codingPath = codingPath
        self.json = json
        self.options = options
    }
}

extension JSONDecoderImpl: Decoder {
    @usableFromInline func container<Key>(keyedBy _: Key.Type) throws ->
        KeyedDecodingContainer<Key> where Key: CodingKey
    {
        guard case .object(let dictionary) = self.json else {
            throw DecodingError.typeMismatch([String: JSONValue].self, DecodingError.Context(
                codingPath: self.codingPath,
                debugDescription: "Expected to decode \([String: JSONValue].self) but found \(self.json.debugDataTypeDescription) instead."
            ))
        }

        let container = KeyedContainer<Key>(
            impl: self,
            codingPath: codingPath,
            dictionary: dictionary
        )
        return KeyedDecodingContainer(container)
    }

    @usableFromInline func unkeyedContainer() throws -> UnkeyedDecodingContainer {
        guard case .array(let array) = self.json else {
            throw DecodingError.typeMismatch([JSONValue].self, DecodingError.Context(
                codingPath: self.codingPath,
                debugDescription: "Expected to decode \([JSONValue].self) but found \(self.json.debugDataTypeDescription) instead."
            ))
        }

        return UnkeyedContainer(
            impl: self,
            codingPath: self.codingPath,
            array: array
        )
    }

    @usableFromInline func singleValueContainer() throws -> SingleValueDecodingContainer {
        SingleValueContainter(
            impl: self,
            codingPath: self.codingPath,
            json: self.json
        )
    }
    
    // MARK: Special case handling
    
    func unwrap<T: Decodable>(as type: T.Type) throws -> T {
        if type == Date.self {
            return try self.unwrapDate() as! T
        }
        if type == Data.self {
            return try self.unwrapData() as! T
        }
        if type == URL.self {
            return try self.unwrapURL() as! T
        }
        if type == Decimal.self {
            return try self.unwrapDecimal() as! T
        }
        if T.self is _JSONStringDictionaryDecodableMarker.Type {
            return try self.unwrapDictionary(as: T.self)
        }
        
        return try T(from: self)
    }
    
    private func unwrapDate() throws -> Date {
        switch self.options.dateDecodingStrategy {
        case .deferredToDate:
            return try Date(from: self)

        case .secondsSince1970:
            let container = SingleValueContainter(impl: self, codingPath: self.codingPath, json: self.json)
            let double = try container.decode(Double.self)
            return Date(timeIntervalSince1970: double)

        case .millisecondsSince1970:
            let container = SingleValueContainter(impl: self, codingPath: self.codingPath, json: self.json)
            let double = try container.decode(Double.self)
            return Date(timeIntervalSince1970: double / 1000.0)

        case .iso8601:
            if #available(macOS 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *) {
                let container = SingleValueContainter(impl: self, codingPath: self.codingPath, json: self.json)
                let string = try container.decode(String.self)
                guard let date = _iso8601Formatter.date(from: string) else {
                    throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: self.codingPath, debugDescription: "Expected date string to be ISO8601-formatted."))
                }

                return date
            } else {
                fatalError("ISO8601DateFormatter is unavailable on this platform.")
            }

        case .formatted(let formatter):
            let container = SingleValueContainter(impl: self, codingPath: self.codingPath, json: self.json)
            let string = try container.decode(String.self)
            guard let date = formatter.date(from: string) else {
                throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: self.codingPath, debugDescription: "Date string does not match format expected by formatter."))
            }
            return date

        case .custom(let closure):
            return try closure(self)
        }
    }
    
    private func unwrapData() throws -> Data {
        switch self.options.dataDecodingStrategy {
        case .deferredToData:
            return try Data(from: self)

        case .base64:
            let container = SingleValueContainter(impl: self, codingPath: self.codingPath, json: self.json)
            let string = try container.decode(String.self)

            guard let data = Data(base64Encoded: string) else {
                throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: self.codingPath, debugDescription: "Encountered Data is not valid Base64."))
            }

            return data

        case .custom(let closure):
            return try closure(self)
        }
    }
    
    private func unwrapURL() throws -> URL {
        let container = SingleValueContainter(impl: self, codingPath: self.codingPath, json: self.json)
        let string = try container.decode(String.self)

        guard let url = URL(string: string) else {
            throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: self.codingPath,
                                                                    debugDescription: "Invalid URL string."))
        }
        return url
    }
    
    private func unwrapDecimal() throws -> Decimal {
        guard case .number(let numberString) = self.json else {
            throw DecodingError.typeMismatch(Decimal.self, DecodingError.Context(codingPath: self.codingPath, debugDescription: ""))
        }
        
        guard let decimal = Decimal(string: numberString) else {
            throw DecodingError.dataCorrupted(.init(
                codingPath: self.codingPath,
                debugDescription: "Parsed JSON number <\(numberString)> does not fit in \(Decimal.self)."))
        }
        
        return decimal
    }
    
    private func unwrapDictionary<T: Decodable>(as: T.Type) throws -> T {
        guard let dictType = T.self as? (_JSONStringDictionaryDecodableMarker & Decodable).Type else {
            preconditionFailure("Must only be called of T implements _JSONStringDictionaryDecodableMarker")
        }
        
        guard case .object(let object) = self.json else {
            throw DecodingError.typeMismatch([String: JSONValue].self, DecodingError.Context(
                codingPath: self.codingPath,
                debugDescription: "Expected to decode \([String: JSONValue].self) but found \(self.json.debugDataTypeDescription) instead."
            ))
        }
        
        var result = [String: Any]()
        
        for (key, value) in object {
            var newPath = self.codingPath
            newPath.append(_JSONKey(stringValue: key)!)
            let newDecoder = JSONDecoderImpl(userInfo: self.userInfo, from: value, codingPath: newPath, options: self.options)
            
            result[key] = try dictType.elementType.createByDirectlyUnwrapping(from: newDecoder)
        }
        
        return result as! T
    }
    
    private func unwrapFloatingPoint<T: LosslessStringConvertible & BinaryFloatingPoint>(
        from value: JSONValue,
        for additionalKey: CodingKey? = nil,
        as type: T.Type) throws -> T
    {
        if case .number(let number) = value {
            guard let floatingPoint = T(number) else {
                var path = self.codingPath
                if let additionalKey = additionalKey {
                    path.append(additionalKey)
                }
                throw DecodingError.dataCorrupted(.init(
                    codingPath: path,
                    debugDescription: "Parsed JSON number <\(number)> does not fit in \(T.self)."))
            }
            
            return floatingPoint
        }

        if case .string(let string) = value,
           case .convertFromString(let posInfString, let negInfString, let nanString) =
            self.options.nonConformingFloatDecodingStrategy
        {
            if string == posInfString {
                return T.infinity
            } else if string == negInfString {
                return -T.infinity
            } else if string == nanString {
                return T.nan
            }
        }
        
        throw self.createTypeMismatchError(type: T.self, for: additionalKey, value: value)
    }
    
    private func unwrapFixedWidthInteger<T: FixedWidthInteger>(
        from value: JSONValue,
        for additionalKey: CodingKey? = nil,
        as type: T.Type) throws -> T
    {
        guard case .number(let number) = value else {
            throw self.createTypeMismatchError(type: T.self, for: additionalKey, value: value)
        }

        // this is the fast pass. Number directly convertible to Integer
        if let integer = T(number) {
            return integer
        }
        
        // this is the really slow path... If the fast path has failed. For example for "34.0" as
        // an integer, we try to go through NSNumber
        if let nsNumber = NSNumber.fromJSONNumber(number) {
            if type == UInt8.self, NSNumber(value: nsNumber.uint8Value) == nsNumber {
                return nsNumber.uint8Value as! T
            }
            if type == Int8.self, NSNumber(value: nsNumber.int8Value) == nsNumber {
                return nsNumber.uint8Value as! T
            }
            if type == UInt16.self, NSNumber(value: nsNumber.uint16Value) == nsNumber {
                return nsNumber.uint16Value as! T
            }
            if type == Int16.self, NSNumber(value: nsNumber.int16Value) == nsNumber {
                return nsNumber.uint16Value as! T
            }
            if type == UInt32.self, NSNumber(value: nsNumber.uint32Value) == nsNumber {
                return nsNumber.uint32Value as! T
            }
            if type == Int32.self, NSNumber(value: nsNumber.int32Value) == nsNumber {
                return nsNumber.uint32Value as! T
            }
            if type == UInt64.self, NSNumber(value: nsNumber.uint64Value) == nsNumber {
                return nsNumber.uint64Value as! T
            }
            if type == Int64.self, NSNumber(value: nsNumber.int64Value) == nsNumber {
                return nsNumber.uint64Value as! T
            }
            if type == UInt.self, NSNumber(value: nsNumber.uintValue) == nsNumber {
                return nsNumber.uintValue as! T
            }
            if type == Int.self, NSNumber(value: nsNumber.uintValue) == nsNumber {
                return nsNumber.intValue as! T
            }
        }
        
        var path = self.codingPath
        if let additionalKey = additionalKey {
            path.append(additionalKey)
        }
        throw DecodingError.dataCorrupted(.init(
            codingPath: path,
            debugDescription: "Parsed JSON number <\(number)> does not fit in \(T.self)."))
    }
    
    private func createTypeMismatchError(type: Any.Type, for additionalKey: CodingKey? = nil, value: JSONValue) -> DecodingError {
        var path = self.codingPath
        if let additionalKey = additionalKey {
            path.append(additionalKey)
        }
        
        return DecodingError.typeMismatch(type, .init(
            codingPath: path,
            debugDescription: "Expected to decode \(type) but found \(value.debugDataTypeDescription) instead."
        ))
    }
}

extension Decodable {
    fileprivate static func createByDirectlyUnwrapping(from decoder: JSONDecoderImpl) throws -> Self {
        if Self.self == URL.self
            || Self.self == Date.self
            || Self.self == Data.self
            || Self.self == Decimal.self
            || Self.self is _JSONStringDictionaryDecodableMarker.Type
        {
            return try decoder.unwrap(as: Self.self)
        }
 
        return try Self.init(from: decoder)
    }
}

extension JSONDecoderImpl {
    struct SingleValueContainter: SingleValueDecodingContainer {
        let impl: JSONDecoderImpl
        let value: JSONValue
        let codingPath: [CodingKey]

        init(impl: JSONDecoderImpl, codingPath: [CodingKey], json: JSONValue) {
            self.impl = impl
            self.codingPath = codingPath
            self.value = json
        }

        func decodeNil() -> Bool {
            self.value == .null
        }

        func decode(_: Bool.Type) throws -> Bool {
            guard case .bool(let bool) = self.value else {
                throw self.impl.createTypeMismatchError(type: Bool.self, value: self.value)
            }

            return bool
        }

        func decode(_: String.Type) throws -> String {
            guard case .string(let string) = self.value else {
                throw self.impl.createTypeMismatchError(type: String.self, value: self.value)
            }

            return string
        }

        func decode(_: Double.Type) throws -> Double {
            try decodeFloatingPoint()
        }

        func decode(_: Float.Type) throws -> Float {
            try decodeFloatingPoint()
        }

        func decode(_: Int.Type) throws -> Int {
            try decodeFixedWidthInteger()
        }

        func decode(_: Int8.Type) throws -> Int8 {
            try decodeFixedWidthInteger()
        }

        func decode(_: Int16.Type) throws -> Int16 {
            try decodeFixedWidthInteger()
        }

        func decode(_: Int32.Type) throws -> Int32 {
            try decodeFixedWidthInteger()
        }

        func decode(_: Int64.Type) throws -> Int64 {
            try decodeFixedWidthInteger()
        }

        func decode(_: UInt.Type) throws -> UInt {
            try decodeFixedWidthInteger()
        }

        func decode(_: UInt8.Type) throws -> UInt8 {
            try decodeFixedWidthInteger()
        }

        func decode(_: UInt16.Type) throws -> UInt16 {
            try decodeFixedWidthInteger()
        }

        func decode(_: UInt32.Type) throws -> UInt32 {
            try decodeFixedWidthInteger()
        }

        func decode(_: UInt64.Type) throws -> UInt64 {
            try decodeFixedWidthInteger()
        }

        func decode<T>(_: T.Type) throws -> T where T: Decodable {
            try self.impl.unwrap(as: T.self)
        }

        @inline(__always) private func decodeFixedWidthInteger<T: FixedWidthInteger>() throws -> T {
            try self.impl.unwrapFixedWidthInteger(from: self.value, as: T.self)
        }

        @inline(__always) private func decodeFloatingPoint<T: LosslessStringConvertible & BinaryFloatingPoint>() throws -> T {
            try self.impl.unwrapFloatingPoint(from: self.value, as: T.self)
        }
    }
}

extension JSONDecoderImpl {
    struct KeyedContainer<K: CodingKey>: KeyedDecodingContainerProtocol {
        typealias Key = K

        let impl: JSONDecoderImpl
        let codingPath: [CodingKey]
        let dictionary: [String: JSONValue]

        init(impl: JSONDecoderImpl, codingPath: [CodingKey], dictionary: [String: JSONValue]) {
            self.impl = impl
            self.codingPath = codingPath
            
            switch impl.options.keyDecodingStrategy {
            case .useDefaultKeys:
                self.dictionary = dictionary
            case .convertFromSnakeCase:
                // Convert the snake case keys in the container to camel case.
                // If we hit a duplicate key after conversion, then we'll use the first one we saw.
                // Effectively an undefined behavior with JSON dictionaries.
                var converted = [String: JSONValue]()
                converted.reserveCapacity(dictionary.count)
                dictionary.forEach { (key, value) in
                    converted[JSONDecoder.KeyDecodingStrategy._convertFromSnakeCase(key)] = value
                }
                self.dictionary = converted
            case .custom(let converter):
                var converted = [String: JSONValue]()
                converted.reserveCapacity(dictionary.count)
                dictionary.forEach { (key, value) in
                    var pathForKey = codingPath
                    pathForKey.append(_JSONKey(stringValue: key)!)
                    converted[converter(pathForKey).stringValue] = value
                }
                self.dictionary = converted
            }
        }

        var allKeys: [K] {
            self.dictionary.keys.compactMap { K(stringValue: $0) }
        }

        func contains(_ key: K) -> Bool {
            if let _ = dictionary[key.stringValue] {
                return true
            }
            return false
        }

        func decodeNil(forKey key: K) throws -> Bool {
            let value = try getValue(forKey: key)
            return value == .null
        }

        func decode(_ type: Bool.Type, forKey key: K) throws -> Bool {
            let value = try getValue(forKey: key)

            guard case .bool(let bool) = value else {
                throw createTypeMismatchError(type: type, forKey: key, value: value)
            }

            return bool
        }

        func decode(_ type: String.Type, forKey key: K) throws -> String {
            let value = try getValue(forKey: key)

            guard case .string(let string) = value else {
                throw createTypeMismatchError(type: type, forKey: key, value: value)
            }

            return string
        }

        func decode(_: Double.Type, forKey key: K) throws -> Double {
            try decodeFloatingPoint(key: key)
        }

        func decode(_: Float.Type, forKey key: K) throws -> Float {
            try decodeFloatingPoint(key: key)
        }

        func decode(_: Int.Type, forKey key: K) throws -> Int {
            try decodeFixedWidthInteger(key: key)
        }

        func decode(_: Int8.Type, forKey key: K) throws -> Int8 {
            try decodeFixedWidthInteger(key: key)
        }

        func decode(_: Int16.Type, forKey key: K) throws -> Int16 {
            try decodeFixedWidthInteger(key: key)
        }

        func decode(_: Int32.Type, forKey key: K) throws -> Int32 {
            try decodeFixedWidthInteger(key: key)
        }

        func decode(_: Int64.Type, forKey key: K) throws -> Int64 {
            try decodeFixedWidthInteger(key: key)
        }

        func decode(_: UInt.Type, forKey key: K) throws -> UInt {
            try decodeFixedWidthInteger(key: key)
        }

        func decode(_: UInt8.Type, forKey key: K) throws -> UInt8 {
            try decodeFixedWidthInteger(key: key)
        }

        func decode(_: UInt16.Type, forKey key: K) throws -> UInt16 {
            try decodeFixedWidthInteger(key: key)
        }

        func decode(_: UInt32.Type, forKey key: K) throws -> UInt32 {
            try decodeFixedWidthInteger(key: key)
        }

        func decode(_: UInt64.Type, forKey key: K) throws -> UInt64 {
            try decodeFixedWidthInteger(key: key)
        }

        func decode<T>(_: T.Type, forKey key: K) throws -> T where T: Decodable {
            let newDecoder = try decoderForKey(key)
            return try newDecoder.unwrap(as: T.self)
        }

        func nestedContainer<NestedKey>(keyedBy type: NestedKey.Type, forKey key: K) throws
            -> KeyedDecodingContainer<NestedKey> where NestedKey: CodingKey
        {
            try decoderForKey(key).container(keyedBy: type)
        }

        func nestedUnkeyedContainer(forKey key: K) throws -> UnkeyedDecodingContainer {
            try decoderForKey(key).unkeyedContainer()
        }

        func superDecoder() throws -> Decoder {
            try decoderForKey(_JSONKey.super)
        }

        func superDecoder(forKey key: K) throws -> Decoder {
            try decoderForKey(key)
        }

        private func decoderForKey<LocalKey: CodingKey>(_ key: LocalKey) throws -> JSONDecoderImpl {
            let value = try getValue(forKey: key)
            var newPath = self.codingPath
            newPath.append(key)

            return JSONDecoderImpl(
                userInfo: self.impl.userInfo,
                from: value,
                codingPath: newPath,
                options: self.impl.options
            )
        }

        @inline(__always) private func getValue<LocalKey: CodingKey>(forKey key: LocalKey) throws -> JSONValue {
            guard let value = dictionary[key.stringValue] else {
                throw DecodingError.keyNotFound(key, .init(
                    codingPath: self.codingPath,
                    debugDescription: "No value associated with key \(key) (\"\(key.stringValue)\")."
                ))
            }

            return value
        }

        @inline(__always) private func createTypeMismatchError(type: Any.Type, forKey key: K, value: JSONValue) -> DecodingError {
            let codingPath = self.codingPath + [key]
            return DecodingError.typeMismatch(type, .init(
                codingPath: codingPath, debugDescription: "Expected to decode \(type) but found \(value.debugDataTypeDescription) instead."
            ))
        }

        @inline(__always) private func decodeFixedWidthInteger<T: FixedWidthInteger>(key: Self.Key) throws -> T {
            let value = try getValue(forKey: key)
            return try self.impl.unwrapFixedWidthInteger(from: value, for: key, as: T.self)
        }
        
        @inline(__always) private func decodeFloatingPoint<T: LosslessStringConvertible & BinaryFloatingPoint>(key: K) throws -> T {
            let value = try getValue(forKey: key)
            return try self.impl.unwrapFloatingPoint(from: value, for: key, as: T.self)
        }
    }
}

extension JSONDecoderImpl {
    struct UnkeyedContainer: UnkeyedDecodingContainer {
        let impl: JSONDecoderImpl
        let codingPath: [CodingKey]
        let array: [JSONValue]

        var count: Int? { self.array.count }
        var isAtEnd: Bool { self.currentIndex >= (self.count ?? 0) }
        var currentIndex = 0

        init(impl: JSONDecoderImpl, codingPath: [CodingKey], array: [JSONValue]) {
            self.impl = impl
            self.codingPath = codingPath
            self.array = array
        }

        mutating func decodeNil() throws -> Bool {
            if try self.getNextValue(ofType: Never.self) == .null {
                self.currentIndex += 1
                return true
            }

            // The protocol states:
            //   If the value is not null, does not increment currentIndex.
            return false
        }

        mutating func decode(_ type: Bool.Type) throws -> Bool {
            let value = try self.getNextValue(ofType: Bool.self)
            guard case .bool(let bool) = value else {
                throw impl.createTypeMismatchError(type: type, for: _JSONKey(index: currentIndex), value: value)
            }

            self.currentIndex += 1
            return bool
        }

        mutating func decode(_ type: String.Type) throws -> String {
            let value = try self.getNextValue(ofType: String.self)
            guard case .string(let string) = value else {
                throw impl.createTypeMismatchError(type: type, for: _JSONKey(index: currentIndex), value: value)
            }

            self.currentIndex += 1
            return string
        }

        mutating func decode(_: Double.Type) throws -> Double {
            try decodeFloatingPoint()
        }

        mutating func decode(_: Float.Type) throws -> Float {
            try decodeFloatingPoint()
        }

        mutating func decode(_: Int.Type) throws -> Int {
            try decodeFixedWidthInteger()
        }

        mutating func decode(_: Int8.Type) throws -> Int8 {
            try decodeFixedWidthInteger()
        }

        mutating func decode(_: Int16.Type) throws -> Int16 {
            try decodeFixedWidthInteger()
        }

        mutating func decode(_: Int32.Type) throws -> Int32 {
            try decodeFixedWidthInteger()
        }

        mutating func decode(_: Int64.Type) throws -> Int64 {
            try decodeFixedWidthInteger()
        }

        mutating func decode(_: UInt.Type) throws -> UInt {
            try decodeFixedWidthInteger()
        }

        mutating func decode(_: UInt8.Type) throws -> UInt8 {
            try decodeFixedWidthInteger()
        }

        mutating func decode(_: UInt16.Type) throws -> UInt16 {
            try decodeFixedWidthInteger()
        }

        mutating func decode(_: UInt32.Type) throws -> UInt32 {
            try decodeFixedWidthInteger()
        }

        mutating func decode(_: UInt64.Type) throws -> UInt64 {
            try decodeFixedWidthInteger()
        }

        mutating func decode<T>(_: T.Type) throws -> T where T: Decodable {
            let newDecoder = try decoderForNextElement(ofType: T.self)
            let result = try newDecoder.unwrap(as: T.self)

            // Because of the requirement that the index not be incremented unless
            // decoding the desired result type succeeds, it can not be a tail call.
            // Hopefully the compiler still optimizes well enough that the result
            // doesn't get copied around.
            self.currentIndex += 1
            return result
        }

        mutating func nestedContainer<NestedKey>(keyedBy type: NestedKey.Type) throws
            -> KeyedDecodingContainer<NestedKey> where NestedKey: CodingKey
        {
            let decoder = try decoderForNextElement(ofType: KeyedDecodingContainer<NestedKey>.self)
            let container = try decoder.container(keyedBy: type)

            self.currentIndex += 1
            return container
        }

        mutating func nestedUnkeyedContainer() throws -> UnkeyedDecodingContainer {
            let decoder = try decoderForNextElement(ofType: UnkeyedDecodingContainer.self)
            let container = try decoder.unkeyedContainer()

            self.currentIndex += 1
            return container
        }

        mutating func superDecoder() throws -> Decoder {
            let decoder = try decoderForNextElement(ofType: Decoder.self)
            self.currentIndex += 1
            return decoder
        }

        private mutating func decoderForNextElement<T>(ofType: T.Type) throws -> JSONDecoderImpl {
            let value = try self.getNextValue(ofType: T.self)
            let newPath = self.codingPath + [_JSONKey(index: self.currentIndex)]

            return JSONDecoderImpl(
                userInfo: self.impl.userInfo,
                from: value,
                codingPath: newPath,
                options: self.impl.options
            )
        }

        @inline(__always)
        private func getNextValue<T>(ofType: T.Type) throws -> JSONValue {
            guard !self.isAtEnd else {
                var message = "Unkeyed container is at end."
                if T.self == UnkeyedContainer.self {
                    message = "Cannot get nested unkeyed container -- unkeyed container is at end."
                }
                if T.self == Decoder.self {
                    message = "Cannot get superDecoder() -- unkeyed container is at end."
                }
                
                var path = self.codingPath
                path.append(_JSONKey(index: self.currentIndex))
                
                throw DecodingError.valueNotFound(
                    T.self,
                    .init(codingPath: path,
                          debugDescription: message,
                          underlyingError: nil))
            }
            return self.array[self.currentIndex]
        }

        @inline(__always) private mutating func decodeFixedWidthInteger<T: FixedWidthInteger>() throws -> T {
            let value = try self.getNextValue(ofType: T.self)
            let key = _JSONKey(index: self.currentIndex)
            let result = try self.impl.unwrapFixedWidthInteger(from: value, for: key, as: T.self)
            self.currentIndex += 1
            return result
        }
        
        @inline(__always) private mutating func decodeFloatingPoint<T: LosslessStringConvertible & BinaryFloatingPoint>() throws -> T {
            let value = try self.getNextValue(ofType: T.self)
            let key = _JSONKey(index: self.currentIndex)
            let result = try self.impl.unwrapFloatingPoint(from: value, for: key, as: T.self)
            self.currentIndex += 1
            return result
        }
    }
}


//===----------------------------------------------------------------------===//
// Shared Key Types
//===----------------------------------------------------------------------===//

fileprivate struct _JSONKey : CodingKey {
    public var stringValue: String
    public var intValue: Int?

    public init?(stringValue: String) {
        self.stringValue = stringValue
        self.intValue = nil
    }

    public init?(intValue: Int) {
        self.stringValue = "\(intValue)"
        self.intValue = intValue
    }

    public init(stringValue: String, intValue: Int?) {
        self.stringValue = stringValue
        self.intValue = intValue
    }
    fileprivate init(index: Int) {
        self.stringValue = "Index \(index)"
        self.intValue = index
    }

    fileprivate static let `super` = _JSONKey(stringValue: "super")!
}

//===----------------------------------------------------------------------===//
// Shared ISO8601 Date Formatter
//===----------------------------------------------------------------------===//

// NOTE: This value is implicitly lazy and _must_ be lazy. We're compiled against the latest SDK (w/ ISO8601DateFormatter), but linked against whichever Foundation the user has. ISO8601DateFormatter might not exist, so we better not hit this code path on an older OS.
@available(macOS 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *)
fileprivate var _iso8601Formatter: ISO8601DateFormatter = {
    let formatter = ISO8601DateFormatter()
    formatter.formatOptions = .withInternetDateTime
    return formatter
}()

//===----------------------------------------------------------------------===//
// Error Utilities
//===----------------------------------------------------------------------===//

extension EncodingError {
    /// Returns a `.invalidValue` error describing the given invalid floating-point value.
    ///
    ///
    /// - parameter value: The value that was invalid to encode.
    /// - parameter path: The path of `CodingKey`s taken to encode this value.
    /// - returns: An `EncodingError` with the appropriate path and debug description.
    fileprivate static func _invalidFloatingPointValue<T : FloatingPoint>(_ value: T, at codingPath: [CodingKey]) -> EncodingError {
        let valueDescription: String
        if value == T.infinity {
            valueDescription = "\(T.self).infinity"
        } else if value == -T.infinity {
            valueDescription = "-\(T.self).infinity"
        } else {
            valueDescription = "\(T.self).nan"
        }

        let debugDescription = "Unable to encode \(valueDescription) directly in JSON. Use JSONEncoder.NonConformingFloatEncodingStrategy.convertToString to specify how the value should be encoded."
        return .invalidValue(value, EncodingError.Context(codingPath: codingPath, debugDescription: debugDescription))
    }
}