NSJSONSerialization.swift

// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//

import CoreFoundation

#if os(OSX) || os(iOS)
    import Darwin
#elseif os(Linux) || CYGWIN
    import Glibc
#endif

extension JSONSerialization {
    public struct ReadingOptions : OptionSet {
        public let rawValue : UInt
        public init(rawValue: UInt) { self.rawValue = rawValue }
        
        public static let mutableContainers = ReadingOptions(rawValue: 1 << 0)
        public static let mutableLeaves = ReadingOptions(rawValue: 1 << 1)
        public static let allowFragments = ReadingOptions(rawValue: 1 << 2)
    }

    public struct WritingOptions : OptionSet {
        public let rawValue : UInt
        public init(rawValue: UInt) { self.rawValue = rawValue }
        
        public static let prettyPrinted = WritingOptions(rawValue: 1 << 0)
    }
}


/* A class for converting JSON to Foundation/Swift objects and converting Foundation/Swift objects to JSON.
   
   An object that may be converted to JSON must have the following properties:
    - Top level object is a `Swift.Array` or `Swift.Dictionary`
    - All objects are `Swift.String`, `Foundation.NSNumber`, `Swift.Array`, `Swift.Dictionary`,
      or `Foundation.NSNull`
    - All dictionary keys are `Swift.String`s
    - `NSNumber`s are not NaN or infinity
*/

open class JSONSerialization : NSObject {
    
    /* Determines whether the given object can be converted to JSON.
       Other rules may apply. Calling this method or attempting a conversion are the definitive ways
       to tell if a given object can be converted to JSON data.
       - parameter obj: The object to test.
       - returns: `true` if `obj` can be converted to JSON, otherwise `false`.
     */
    open class func isValidJSONObject(_ obj: Any) -> Bool {
        // TODO: - revisit this once bridging story gets fully figured out
        func isValidJSONObjectInternal(_ obj: Any) -> Bool {
            // object is Swift.String, NSNull, Int, Bool, or UInt
            if obj is String || obj is NSNull || obj is Int || obj is Bool || obj is UInt {
                return true
            }

            // object is a Double and is not NaN or infinity
            if let number = obj as? Double  {
                return number.isFinite
            }
            // object is a Float and is not NaN or infinity
            if let number = obj as? Float  {
                return number.isFinite
            }

            // object is Swift.Array
            if let array = obj as? [Any] {
                for element in array {
                    guard isValidJSONObjectInternal(element) else {
                        return false
                    }
                }
                return true
            }

            // object is Swift.Dictionary
            if let dictionary = obj as? [String: Any] {
                for (_, value) in dictionary {
                    guard isValidJSONObjectInternal(value) else {
                        return false
                    }
                }
                return true
            }

            // object is NSNumber and is not NaN or infinity
            // For better performance, this (most expensive) test should be last.
            if let number = _SwiftValue.store(obj) as? NSNumber {
                let invalid = number.doubleValue.isInfinite || number.doubleValue.isNaN
                return !invalid
            }

            // invalid object
            return false
        }

        // top level object must be an Swift.Array or Swift.Dictionary
        guard obj is [Any] || obj is [String: Any] else {
            return false
        }

        return isValidJSONObjectInternal(obj)
    }
    
    /* Generate JSON data from a Foundation object. If the object will not produce valid JSON then an exception will be thrown. Setting the NSJSONWritingPrettyPrinted option will generate JSON with whitespace designed to make the output more readable. If that option is not set, the most compact possible JSON will be generated. If an error occurs, the error parameter will be set and the return value will be nil. The resulting data is a encoded in UTF-8.
     */
    internal class func _data(withJSONObject value: Any, options opt: WritingOptions, stream: Bool) throws -> Data {
        var jsonStr = String()
        
        var writer = JSONWriter(
            pretty: opt.contains(.prettyPrinted),
            writer: { (str: String?) in
                if let str = str {
                    jsonStr.append(str)
                }
            }
        )
        
        if let container = value as? NSArray {
            try writer.serializeJSON(container._bridgeToSwift())
        } else if let container = value as? NSDictionary {
            try writer.serializeJSON(container._bridgeToSwift())
        } else if let container = value as? Array<Any> {
            try writer.serializeJSON(container)
        } else if let container = value as? Dictionary<AnyHashable, Any> {
            try writer.serializeJSON(container)
        } else {
            if stream {
                throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
                    "NSDebugDescription" : "Top-level object was not NSArray or NSDictionary"
                    ])
            } else {
                fatalError("Top-level object was not NSArray or NSDictionary") // This is a fatal error in objective-c too (it is an NSInvalidArgumentException)
            }
        }
        
        let count = jsonStr.lengthOfBytes(using: .utf8)
        let bufferLength = count+1 // Allow space for null terminator
        var utf8: [CChar] = Array<CChar>(repeating: 0, count: bufferLength)
        if !jsonStr.getCString(&utf8, maxLength: bufferLength, encoding: .utf8) {
            fatalError("Failed to generate a CString from a String")
        }
        let rawBytes = UnsafeRawPointer(UnsafePointer(utf8))
        let result = Data(bytes: rawBytes.bindMemory(to: UInt8.self, capacity: count), count: count)
        return result
    }
    open class func data(withJSONObject value: Any, options opt: WritingOptions = []) throws -> Data {
        return try _data(withJSONObject: value, options: opt, stream: false)
    }
    
    /* Create a Foundation object from JSON data. Set the NSJSONReadingAllowFragments option if the parser should allow top-level objects that are not an NSArray or NSDictionary. Setting the NSJSONReadingMutableContainers option will make the parser generate mutable NSArrays and NSDictionaries. Setting the NSJSONReadingMutableLeaves option will make the parser generate mutable NSString objects. If an error occurs during the parse, then the error parameter will be set and the result will be nil.
       The data must be in one of the 5 supported encodings listed in the JSON specification: UTF-8, UTF-16LE, UTF-16BE, UTF-32LE, UTF-32BE. The data may or may not have a BOM. The most efficient encoding to use for parsing is UTF-8, so if you have a choice in encoding the data passed to this method, use UTF-8.
     */
    open class func jsonObject(with data: Data, options opt: ReadingOptions = []) throws -> Any {
        return try data.withUnsafeBytes { (bytes: UnsafePointer<UInt8>) -> Any in
            let encoding: String.Encoding
            let buffer: UnsafeBufferPointer<UInt8>
            if let detected = parseBOM(bytes, length: data.count) {
                encoding = detected.encoding
                buffer = UnsafeBufferPointer(start: bytes.advanced(by: detected.skipLength), count: data.count - detected.skipLength)
            }
            else {
                encoding = detectEncoding(bytes, data.count)
                buffer = UnsafeBufferPointer(start: bytes, count: data.count)
            }
            
            let source = JSONReader.UnicodeSource(buffer: buffer, encoding: encoding)
            let reader = JSONReader(source: source)
            if let (object, _) = try reader.parseObject(0) {
                return object
            }
            else if let (array, _) = try reader.parseArray(0) {
                return array
            }
            else if opt.contains(.allowFragments), let (value, _) = try reader.parseValue(0) {
                return value
            }
            throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
                "NSDebugDescription" : "JSON text did not start with array or object and option to allow fragments not set."
            ])
        }
        
    }
    
    /* Write JSON data into a stream. The stream should be opened and configured. The return value is the number of bytes written to the stream, or 0 on error. All other behavior of this method is the same as the dataWithJSONObject:options:error: method.
     */
    open class func writeJSONObject(_ obj: Any, toStream stream: OutputStream, options opt: WritingOptions) throws -> Int {
        let jsonData = try _data(withJSONObject: obj, options: opt, stream: true)
        let count = jsonData.count
        return jsonData.withUnsafeBytes { (bytePtr: UnsafePointer<UInt8>) -> Int in
            let res: Int = stream.write(bytePtr, maxLength: count)
            /// TODO: If the result here is negative the error should be obtained from the stream to propigate as a throw
            return res
        }
    }
    
    /* Create a JSON object from JSON data stream. The stream should be opened and configured. All other behavior of this method is the same as the JSONObjectWithData:options:error: method.
     */
    open class func jsonObject(with stream: InputStream, options opt: ReadingOptions = []) throws -> Any {
        var data = Data()
        guard stream.streamStatus == .open || stream.streamStatus == .reading else {
            fatalError("Stream is not available for reading")
        }
        repeat {
            var buffer = [UInt8](repeating: 0, count: 1024)
            var bytesRead: Int = 0
            bytesRead = stream.read(&buffer, maxLength: buffer.count)
            if bytesRead < 0 {
                throw stream.streamError!
            } else {
                data.append(&buffer, count: bytesRead)
            }
        } while stream.hasBytesAvailable
        return try jsonObject(with: data, options: opt)
    }
}

//MARK: - Encoding Detection

internal extension JSONSerialization {
    
    /// Detect the encoding format of the NSData contents
    class func detectEncoding(_ bytes: UnsafePointer<UInt8>, _ length: Int) -> String.Encoding {

        if length >= 4 {
            switch (bytes[0], bytes[1], bytes[2], bytes[3]) {
            case (0, 0, 0, _):
                return .utf32BigEndian
            case (_, 0, 0, 0):
                return .utf32LittleEndian
            case (0, _, 0, _):
                return .utf16BigEndian
            case (_, 0, _, 0):
                return .utf16LittleEndian
            default:
                break
            }
        }
        else if length >= 2 {
            switch (bytes[0], bytes[1]) {
            case (0, _):
                return .utf16BigEndian
            case (_, 0):
                return .utf16LittleEndian
            default:
                break
            }
        }
        return .utf8
    }
    
    static func parseBOM(_ bytes: UnsafePointer<UInt8>, length: Int) -> (encoding: String.Encoding, skipLength: Int)? {
        if length >= 2 {
            switch (bytes[0], bytes[1]) {
            case (0xEF, 0xBB):
                if length >= 3 && bytes[2] == 0xBF {
                    return (.utf8, 3)
                }
            case (0x00, 0x00):
                if length >= 4 && bytes[2] == 0xFE && bytes[3] == 0xFF {
                    return (.utf32BigEndian, 4)
                }
            case (0xFF, 0xFE):
                if length >= 4 && bytes[2] == 0 && bytes[3] == 0 {
                    return (.utf32LittleEndian, 4)
                }
                return (.utf16LittleEndian, 2)
            case (0xFE, 0xFF):
                return (.utf16BigEndian, 2)
            default:
                break
            }
        }
        return nil
    }
}

//MARK: - JSONSerializer
private struct JSONWriter {
    
    private let maxUIntLength = String(describing: UInt.max).characters.count
    private let maxIntLength = String(describing: Int.max).characters.count
    var indent = 0
    let pretty: Bool
    let writer: (String?) -> Void
    
    private lazy var _numberformatter: CFNumberFormatter = {
        let formatter: CFNumberFormatter
        formatter = CFNumberFormatterCreate(nil, CFLocaleCopyCurrent(), kCFNumberFormatterNoStyle)
        CFNumberFormatterSetProperty(formatter, kCFNumberFormatterMaxFractionDigits, NSNumber(value: 15))
        CFNumberFormatterSetFormat(formatter, "0.###############"._cfObject)
        return formatter
    }()

    init(pretty: Bool = false, writer: @escaping (String?) -> Void) {
        self.pretty = pretty
        self.writer = writer
    }
    
    mutating func serializeJSON(_ obj: Any) throws {

        // For better performance, the most expensive conditions to evaluate should be last.
        switch (obj) {
        case let str as String:
            try serializeString(str)
        case let boolValue as Bool:
            serializeBool(boolValue)
        case let num as Int:
            try serializeInt(value: num)
        case let num as UInt:
            try serializeUInt(value: num)
        case let array as Array<Any>:
            try serializeArray(array)
        case let dict as Dictionary<AnyHashable, Any>:
            try serializeDictionary(dict)
        case let null as NSNull:
            try serializeNull(null)
        case _ where _SwiftValue.store(obj) is NSNumber:
            try serializeNumber(_SwiftValue.store(obj) as! NSNumber)
        default:
            throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: ["NSDebugDescription" : "Invalid object cannot be serialized"])
        }
    }

    private func serializeUInt(value: UInt) throws {
        if value == 0 {
            writer("0")
            return
        }
        var array: [UInt] = []
        var stringResult = ""
        //Maximum length of an UInt
        array.reserveCapacity(maxUIntLength)
        stringResult.reserveCapacity(maxUIntLength)
        var number = value
        
        while number != 0 {
            array.append(number % 10)
            number /= 10
        }
        
        /*
         Step backwards through the array and append the values to the string. This way the values are appended in the correct order.
         */
        var counter = array.count
        while counter > 0 {
            counter -= 1
            let digit: UInt = array[counter]
            switch digit {
            case 0: stringResult.append("0")
            case 1: stringResult.append("1")
            case 2: stringResult.append("2")
            case 3: stringResult.append("3")
            case 4: stringResult.append("4")
            case 5: stringResult.append("5")
            case 6: stringResult.append("6")
            case 7: stringResult.append("7")
            case 8: stringResult.append("8")
            case 9: stringResult.append("9")
            default: fatalError()
            }
        }
        
        writer(stringResult)
    }
    
    private func serializeInt(value: Int) throws {
        if value == 0 {
            writer("0")
            return
        }
        var array: [Int] = []
        var stringResult = ""
        array.reserveCapacity(maxIntLength)
        //Account for a negative sign
        stringResult.reserveCapacity(maxIntLength + 1)
        var number = value
        
        while number != 0 {
            array.append(number % 10)
            number /= 10
        }
        //If negative add minus sign before adding any values
        if value < 0 {
            stringResult.append("-")
        }
        /*
         Step backwards through the array and append the values to the string. This way the values are appended in the correct order.
         */
        var counter = array.count
        while counter > 0 {
            counter -= 1
            let digit = array[counter]
            switch digit {
            case 0: stringResult.append("0")
            case 1, -1: stringResult.append("1")
            case 2, -2: stringResult.append("2")
            case 3, -3: stringResult.append("3")
            case 4, -4: stringResult.append("4")
            case 5, -5: stringResult.append("5")
            case 6, -6: stringResult.append("6")
            case 7, -7: stringResult.append("7")
            case 8, -8: stringResult.append("8")
            case 9, -9: stringResult.append("9")
            default: fatalError()
            }
        }
        writer(stringResult)
    }
    
    func serializeString(_ str: String) throws {
        writer("\"")
        for scalar in str.unicodeScalars {
            switch scalar {
                case "\"":
                    writer("\\\"") // U+0022 quotation mark
                case "\\":
                    writer("\\\\") // U+005C reverse solidus
                // U+002F solidus not escaped
                case "\u{8}":
                    writer("\\b") // U+0008 backspace
                case "\u{c}":
                    writer("\\f") // U+000C form feed
                case "\n":
                    writer("\\n") // U+000A line feed
                case "\r":
                    writer("\\r") // U+000D carriage return
                case "\t":
                    writer("\\t") // U+0009 tab
                case "\u{0}"..."\u{f}":
                    writer("\\u000\(String(scalar.value, radix: 16))") // U+0000 to U+000F
                case "\u{10}"..."\u{1f}":
                    writer("\\u00\(String(scalar.value, radix: 16))") // U+0010 to U+001F
                default:
                    writer(String(scalar))
            }
        }
        writer("\"")
    }

    func serializeBool(_ bool: Bool) {
        switch bool {
        case true:
            writer("true")
        case false:
            writer("false")
        }
    }

    mutating func serializeNumber(_ num: NSNumber) throws {
        if num.doubleValue.isInfinite || num.doubleValue.isNaN {
            throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: ["NSDebugDescription" : "Number cannot be infinity or NaN"])
        }
        
        switch num._objCType {
        case .Bool:
            serializeBool(num.boolValue)
        default:
            writer(_serializationString(for: num))
        }
    }

    mutating func serializeArray(_ array: [Any]) throws {
        writer("[")
        if pretty {
            writer("\n")
            incAndWriteIndent()
        }
        
        var first = true
        for elem in array {
            if first {
                first = false
            } else if pretty {
                writer(",\n")
                writeIndent()
            } else {
                writer(",")
            }
            try serializeJSON(elem)
        }
        if pretty {
            writer("\n")
            decAndWriteIndent()
        }
        writer("]")
    }

    mutating func serializeDictionary(_ dict: Dictionary<AnyHashable, Any>) throws {
        writer("{")
        if pretty {
            writer("\n")
            incAndWriteIndent()
        }
        
        var first = true
        
        for (key, value) in dict {
            if first {
                first = false
            } else if pretty {
                writer(",\n")
                writeIndent()
            } else {
                writer(",")
            }
            
            if key is String {
                try serializeString(key as! String)
            } else {
                throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: ["NSDebugDescription" : "NSDictionary key must be NSString"])
            }
            pretty ? writer(": ") : writer(":")
            try serializeJSON(value)
        }
        if pretty {
            writer("\n")
            decAndWriteIndent()
        }
        writer("}")
    }

    func serializeNull(_ null: NSNull) throws {
        writer("null")
    }
    
    let indentAmount = 2
    
    mutating func incAndWriteIndent() {
        indent += indentAmount
        writeIndent()
    }
    
    mutating func decAndWriteIndent() {
        indent -= indentAmount
        writeIndent()
    }
    
    func writeIndent() {
        for _ in 0..<indent {
            writer(" ")
        }
    }
    
    //[SR-2151] https://bugs.swift.org/browse/SR-2151
    private mutating func _serializationString(for number: NSNumber) -> String {
        return CFNumberFormatterCreateStringWithNumber(nil, _numberformatter, number._cfObject)._swiftObject
    }
}

//MARK: - JSONDeserializer
private struct JSONReader {

    static let whitespaceASCII: [UInt8] = [
        0x09, // Horizontal tab
        0x0A, // Line feed or New line
        0x0D, // Carriage return
        0x20, // Space
    ]

    struct Structure {
        static let BeginArray: UInt8     = 0x5B // [
        static let EndArray: UInt8       = 0x5D // ]
        static let BeginObject: UInt8    = 0x7B // {
        static let EndObject: UInt8      = 0x7D // }
        static let NameSeparator: UInt8  = 0x3A // :
        static let ValueSeparator: UInt8 = 0x2C // ,
        static let QuotationMark: UInt8  = 0x22 // "
        static let Escape: UInt8         = 0x5C // \
    }

    typealias Index = Int
    typealias IndexDistance = Int

    struct UnicodeSource {
        let buffer: UnsafeBufferPointer<UInt8>
        let encoding: String.Encoding
        let step: Int

        init(buffer: UnsafeBufferPointer<UInt8>, encoding: String.Encoding) {
            self.buffer = buffer
            self.encoding = encoding

            self.step = {
                switch encoding {
                case String.Encoding.utf8:
                    return 1
                case String.Encoding.utf16BigEndian, String.Encoding.utf16LittleEndian:
                    return 2
                case String.Encoding.utf32BigEndian, String.Encoding.utf32LittleEndian:
                    return 4
                default:
                    return 1
                }
            }()
        }

        func takeASCII(_ input: Index) -> (UInt8, Index)? {
            guard hasNext(input) else {
                return nil
            }

            let index: Int
            switch encoding {
            case String.Encoding.utf8:
                index = input
            case String.Encoding.utf16BigEndian where buffer[input] == 0:
                index = input + 1
            case String.Encoding.utf32BigEndian where buffer[input] == 0 && buffer[input+1] == 0 && buffer[input+2] == 0:
                index = input + 3
            case String.Encoding.utf16LittleEndian where buffer[input+1] == 0:
                index = input
            case String.Encoding.utf32LittleEndian where buffer[input+1] == 0 && buffer[input+2] == 0 && buffer[input+3] == 0:
                index = input
            default:
                return nil
            }
            return (buffer[index] < 0x80) ? (buffer[index], input + step) : nil
        }

        func takeString(_ begin: Index, end: Index) throws -> String {
            let byteLength = begin.distance(to: end)
            
            guard let chunk = String(data: Data(bytes: buffer.baseAddress!.advanced(by: begin), count: byteLength), encoding: encoding) else {
                throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
                    "NSDebugDescription" : "Unable to convert data to a string using the detected encoding. The data may be corrupt."
                    ])
            }
            return chunk
        }

        func hasNext(_ input: Index) -> Bool {
            return input + step <= buffer.endIndex
        }
        
        func distanceFromStart(_ index: Index) -> IndexDistance {
            return buffer.startIndex.distance(to: index) / step
        }
    }

    let source: UnicodeSource

    func consumeWhitespace(_ input: Index) -> Index? {
        var index = input
        while let (char, nextIndex) = source.takeASCII(index), JSONReader.whitespaceASCII.contains(char) {
            index = nextIndex
        }
        return index
    }

    func consumeStructure(_ ascii: UInt8, input: Index) throws -> Index? {
        return try consumeWhitespace(input).flatMap(consumeASCII(ascii)).flatMap(consumeWhitespace)
    }

    func consumeASCII(_ ascii: UInt8) -> (Index) throws -> Index? {
        return { (input: Index) throws -> Index? in
            switch self.source.takeASCII(input) {
            case .none:
                throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
                    "NSDebugDescription" : "Unexpected end of file during JSON parse."
                    ])
            case let (taken, index)? where taken == ascii:
                return index
            default:
                return nil
            }
        }
    }

    func consumeASCIISequence(_ sequence: String, input: Index) throws -> Index? {
        var index = input
        for scalar in sequence.unicodeScalars {
            guard let nextIndex = try consumeASCII(UInt8(scalar.value))(index) else {
                return nil
            }
            index = nextIndex
        }
        return index
    }

    func takeMatching(_ match: @escaping (UInt8) -> Bool) -> ([Character], Index) -> ([Character], Index)? {
        return { input, index in
            guard let (byte, index) = self.source.takeASCII(index), match(byte) else {
                return nil
            }
            return (input + [Character(UnicodeScalar(byte))], index)
        }
    }

    //MARK: - String Parsing

    func parseString(_ input: Index) throws -> (String, Index)? {
        guard let beginIndex = try consumeWhitespace(input).flatMap(consumeASCII(Structure.QuotationMark)) else {
            return nil
        }
        var chunkIndex: Int = beginIndex
        var currentIndex: Int = chunkIndex

        var output: String = ""
        while source.hasNext(currentIndex) {
            guard let (ascii, index) = source.takeASCII(currentIndex) else {
                currentIndex += source.step
                continue
            }
            switch ascii {
            case Structure.QuotationMark:
                output += try source.takeString(chunkIndex, end: currentIndex)
                return (output, index)
            case Structure.Escape:
                output += try source.takeString(chunkIndex, end: currentIndex)
                if let (escaped, nextIndex) = try parseEscapeSequence(index) {
                    output += escaped
                    chunkIndex = nextIndex
                    currentIndex = nextIndex
                    continue
                }
                else {
                    throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
                        "NSDebugDescription" : "Invalid escape sequence at position \(source.distanceFromStart(currentIndex))"
                    ])
                }
            default:
                currentIndex = index
            }
        }
        throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
            "NSDebugDescription" : "Unexpected end of file during string parse."
        ])
    }

    func parseEscapeSequence(_ input: Index) throws -> (String, Index)? {
        guard let (byte, index) = source.takeASCII(input) else {
            throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
                "NSDebugDescription" : "Early end of unicode escape sequence around character"
            ])
        }
        let output: String
        switch byte {
        case 0x22: output = "\""
        case 0x5C: output = "\\"
        case 0x2F: output = "/"
        case 0x62: output = "\u{08}" // \b
        case 0x66: output = "\u{0C}" // \f
        case 0x6E: output = "\u{0A}" // \n
        case 0x72: output = "\u{0D}" // \r
        case 0x74: output = "\u{09}" // \t
        case 0x75: return try parseUnicodeSequence(index)
        default: return nil
        }
        return (output, index)
    }

    func parseUnicodeSequence(_ input: Index) throws -> (String, Index)? {

        guard let (codeUnit, index) = parseCodeUnit(input) else {
            return nil
        }

        if !UTF16.isLeadSurrogate(codeUnit) {
            return (String(UnicodeScalar(codeUnit)!), index)
        }

        guard let (trailCodeUnit, finalIndex) = try consumeASCIISequence("\\u", input: index).flatMap(parseCodeUnit) , UTF16.isTrailSurrogate(trailCodeUnit) else {
            throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
                "NSDebugDescription" : "Unable to convert unicode escape sequence (no low-surrogate code point) to UTF8-encoded character at position \(source.distanceFromStart(input))"
            ])
        }

        let highValue = (UInt32(codeUnit  - 0xD800) << 10)
        let lowValue  =  UInt32(trailCodeUnit - 0xDC00)
        return (String(UnicodeScalar(highValue + lowValue + 0x10000)!), finalIndex)
    }

    func isHexChr(_ byte: UInt8) -> Bool {
        return (byte >= 0x30 && byte <= 0x39)
            || (byte >= 0x41 && byte <= 0x46)
            || (byte >= 0x61 && byte <= 0x66)
    }
    func parseCodeUnit(_ input: Index) -> (UTF16.CodeUnit, Index)? {
        let hexParser = takeMatching(isHexChr)
        guard let (result, index) = hexParser([], input).flatMap(hexParser).flatMap(hexParser).flatMap(hexParser),
            let value = Int(String(result), radix: 16) else {
                return nil
        }
        return (UTF16.CodeUnit(value), index)
    }
    
    //MARK: - Number parsing
    static let numberCodePoints: [UInt8] = [
        0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, // 0...9
        0x2E, 0x2D, 0x2B, 0x45, 0x65, // . - + E e
    ]
    func parseNumber(_ input: Index) throws -> (Any, Index)? {
        func parseTypedNumber(_ address: UnsafePointer<UInt8>, count: Int) -> (Any, IndexDistance)? {
            let temp_buffer_size = 64
            var temp_buffer = [Int8](repeating: 0, count: temp_buffer_size)
            return temp_buffer.withUnsafeMutableBufferPointer { (buffer: inout UnsafeMutableBufferPointer<Int8>) -> (Any, IndexDistance)? in
                memcpy(buffer.baseAddress!, address, min(count, temp_buffer_size - 1)) // ensure null termination
                
                let startPointer = buffer.baseAddress!
                let intEndPointer = UnsafeMutablePointer<UnsafeMutablePointer<Int8>?>.allocate(capacity: 1)
                defer { intEndPointer.deallocate(capacity: 1) }
                let doubleEndPointer = UnsafeMutablePointer<UnsafeMutablePointer<Int8>?>.allocate(capacity: 1)
                defer { doubleEndPointer.deallocate(capacity: 1) }
                let intResult = strtol(startPointer, intEndPointer, 10)
                let intDistance = startPointer.distance(to: intEndPointer[0]!)
                let doubleResult = strtod(startPointer, doubleEndPointer)
                let doubleDistance = startPointer.distance(to: doubleEndPointer[0]!)

                guard intDistance > 0 || doubleDistance > 0 else {
                    return nil
                }

                if intDistance == doubleDistance {
                    return (intResult, intDistance)
                }
                guard doubleDistance > 0 else {
                    return nil
                }

                if doubleResult == doubleResult.rounded() {
                    return (Int(doubleResult), doubleDistance)
                }
                return (doubleResult, doubleDistance)
            }
        }
        
        if source.encoding == String.Encoding.utf8 {
            
            return parseTypedNumber(source.buffer.baseAddress!.advanced(by: input), count: source.buffer.count - input).map { return ($0.0, input + $0.1) }
        }
        else {
            var numberCharacters = [UInt8]()
            var index = input
            while let (ascii, nextIndex) = source.takeASCII(index), JSONReader.numberCodePoints.contains(ascii) {
                numberCharacters.append(ascii)
                index = nextIndex
            }
            
            numberCharacters.append(0)
            
            return numberCharacters.withUnsafeBufferPointer {
                parseTypedNumber($0.baseAddress!, count: $0.count)
            }.map { return ($0.0, index) }
        }
    }

    //MARK: - Value parsing
    func parseValue(_ input: Index) throws -> (Any, Index)? {
        if let (value, parser) = try parseString(input) {
            return (value, parser)
        }
        else if let parser = try consumeASCIISequence("true", input: input) {
            return (true, parser)
        }
        else if let parser = try consumeASCIISequence("false", input: input) {
            return (false, parser)
        }
        else if let parser = try consumeASCIISequence("null", input: input) {
            return (NSNull(), parser)
        }
        else if let (object, parser) = try parseObject(input) {
            return (object, parser)
        }
        else if let (array, parser) = try parseArray(input) {
            return (array, parser)
        }
        else if let (number, parser) = try parseNumber(input) {
            return (number, parser)
        }
        return nil
    }

    //MARK: - Object parsing
    func parseObject(_ input: Index) throws -> ([String: Any], Index)? {
        guard let beginIndex = try consumeStructure(Structure.BeginObject, input: input) else {
            return nil
        }
        var index = beginIndex
        var output: [String: Any] = [:]
        while true {
            if let finalIndex = try consumeStructure(Structure.EndObject, input: index) {
                return (output, finalIndex)
            }
    
            if let (key, value, nextIndex) = try parseObjectMember(index) {
                output[key] = value
    
                if let finalParser = try consumeStructure(Structure.EndObject, input: nextIndex) {
                    return (output, finalParser)
                }
                else if let nextIndex = try consumeStructure(Structure.ValueSeparator, input: nextIndex) {
                    index = nextIndex
                    continue
                }
                else {
                    return nil
                }
            }
            return nil
        }
    }
    
    func parseObjectMember(_ input: Index) throws -> (String, Any, Index)? {
        guard let (name, index) = try parseString(input) else {
            throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
                "NSDebugDescription" : "Missing object key at location \(source.distanceFromStart(input))"
            ])
        }
        guard let separatorIndex = try consumeStructure(Structure.NameSeparator, input: index) else {
            throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
                "NSDebugDescription" : "Invalid separator at location \(source.distanceFromStart(index))"
            ])
        }
        guard let (value, finalIndex) = try parseValue(separatorIndex) else {
            throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
                "NSDebugDescription" : "Invalid value at location \(source.distanceFromStart(separatorIndex))"
            ])
        }
        
        return (name, value, finalIndex)
    }

    //MARK: - Array parsing
    func parseArray(_ input: Index) throws -> ([Any], Index)? {
        guard let beginIndex = try consumeStructure(Structure.BeginArray, input: input) else {
            return nil
        }
        var index = beginIndex
        var output: [Any] = []
        while true {
            if let finalIndex = try consumeStructure(Structure.EndArray, input: index) {
                return (output, finalIndex)
            }
    
            if let (value, nextIndex) = try parseValue(index) {
                output.append(value)
    
                if let finalIndex = try consumeStructure(Structure.EndArray, input: nextIndex) {
                    return (output, finalIndex)
                }
                else if let nextIndex = try consumeStructure(Structure.ValueSeparator, input: nextIndex) {
                    index = nextIndex
                    continue
                }
            }
            throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.propertyListReadCorrupt.rawValue, userInfo: [
                "NSDebugDescription" : "Badly formed array at location \(source.distanceFromStart(index))"
            ])
        }
    }
}