Date.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

/**
 `Date` represents a single point in time.
 
 A `Date` is independent of a particular calendar or time zone. To represent a `Date` to a user, you must interpret it in the context of a `Calendar`.
 */
public struct Date : ReferenceConvertible, Comparable, Equatable {
    public typealias ReferenceType = NSDate
    
    fileprivate var _time: TimeInterval
    
    /// The number of seconds from 1 January 1970 to the reference date, 1 January 2001.
    public static let timeIntervalBetween1970AndReferenceDate: TimeInterval = 978307200.0
    
    /// The interval between 00:00:00 UTC on 1 January 2001 and the current date and time.
    public static var timeIntervalSinceReferenceDate: TimeInterval {
        return CFAbsoluteTimeGetCurrent()
    }
    
    /// Returns a `Date` initialized to the current date and time.
    public init() {
        _time = CFAbsoluteTimeGetCurrent()
    }
    
    /// Returns a `Date` initialized relative to the current date and time by a given number of seconds.
    public init(timeIntervalSinceNow: TimeInterval) {
        self.init(timeIntervalSinceReferenceDate: timeIntervalSinceNow + CFAbsoluteTimeGetCurrent())
    }
    
    /// Returns a `Date` initialized relative to 00:00:00 UTC on 1 January 1970 by a given number of seconds.
    public init(timeIntervalSince1970: TimeInterval) {
        self.init(timeIntervalSinceReferenceDate: timeIntervalSince1970 - Date.timeIntervalBetween1970AndReferenceDate)
    }
    
    /**
     Returns a `Date` initialized relative to another given date by a given number of seconds.
     
     - Parameter timeInterval: The number of seconds to add to `date`. A negative value means the receiver will be earlier than `date`.
     - Parameter date: The reference date.
     */
    public init(timeInterval: TimeInterval, since date: Date) {
        self.init(timeIntervalSinceReferenceDate: date.timeIntervalSinceReferenceDate + timeInterval)
    }
    
    /// Returns a `Date` initialized relative to 00:00:00 UTC on 1 January 2001 by a given number of seconds.
    public init(timeIntervalSinceReferenceDate ti: TimeInterval) {
        _time = ti
    }
    
    /**
     Returns the interval between the date object and 00:00:00 UTC on 1 January 2001.
     
     This property's value is negative if the date object is earlier than the system's absolute reference date (00:00:00 UTC on 1 January 2001).
     */
    public var timeIntervalSinceReferenceDate: TimeInterval {
        return _time
    }
    
    /**
     Returns the interval between the receiver and another given date.
     
     - Parameter another: The date with which to compare the receiver.
     
     - Returns: The interval between the receiver and the `another` parameter. If the receiver is earlier than `anotherDate`, the return value is negative. If `anotherDate` is `nil`, the results are undefined.
     
     - SeeAlso: `timeIntervalSince1970`
     - SeeAlso: `timeIntervalSinceNow`
     - SeeAlso: `timeIntervalSinceReferenceDate`
     */
    public func timeIntervalSince(_ date: Date) -> TimeInterval {
        return self.timeIntervalSinceReferenceDate - date.timeIntervalSinceReferenceDate
    }
    
    /**
     The time interval between the date and the current date and time.
     
     If the date is earlier than the current date and time, this property's value is negative.
     
     - SeeAlso: `timeIntervalSince(_:)`
     - SeeAlso: `timeIntervalSince1970`
     - SeeAlso: `timeIntervalSinceReferenceDate`
     */
    public var timeIntervalSinceNow: TimeInterval {
        return self.timeIntervalSinceReferenceDate - CFAbsoluteTimeGetCurrent()
    }
    
    /**
     The interval between the date object and 00:00:00 UTC on 1 January 1970.
     
     This property's value is negative if the date object is earlier than 00:00:00 UTC on 1 January 1970.
     
     - SeeAlso: `timeIntervalSince(_:)`
     - SeeAlso: `timeIntervalSinceNow`
     - SeeAlso: `timeIntervalSinceReferenceDate`
     */
    public var timeIntervalSince1970: TimeInterval {
        return self.timeIntervalSinceReferenceDate + Date.timeIntervalBetween1970AndReferenceDate
    }
    
    /// Return a new `Date` by adding a `TimeInterval` to this `Date`.
    ///
    /// - parameter timeInterval: The value to add, in seconds.
    /// - warning: This only adjusts an absolute value. If you wish to add calendrical concepts like hours, days, months then you must use a `Calendar`. That will take into account complexities like daylight saving time, months with different numbers of days, and more.
    public func addingTimeInterval(_ timeInterval: TimeInterval) -> Date {
        return self + timeInterval
    }
    
    /// Add a `TimeInterval` to this `Date`.
    ///
    /// - parameter timeInterval: The value to add, in seconds.
    /// - warning: This only adjusts an absolute value. If you wish to add calendrical concepts like hours, days, months then you must use a `Calendar`. That will take into account complexities like daylight saving time, months with different numbers of days, and more.
    public mutating func addTimeInterval(_ timeInterval: TimeInterval) {
        self += timeInterval
    }
    
    /**
     Creates and returns a Date value representing a date in the distant future.
     
     The distant future is in terms of centuries.
     */
    public static let distantFuture = Date(timeIntervalSinceReferenceDate: 63113904000.0)
    
    /**
     Creates and returns a Date value representing a date in the distant past.
     
     The distant past is in terms of centuries.
     */
    public static let distantPast = Date(timeIntervalSinceReferenceDate: -63114076800.0)

    public func hash(into hasher: inout Hasher) {
        hasher.combine(_time)
    }
    
    /// Compare two `Date` values.
    public func compare(_ other: Date) -> ComparisonResult {
        if _time < other.timeIntervalSinceReferenceDate {
            return .orderedAscending
        } else if _time > other.timeIntervalSinceReferenceDate {
            return .orderedDescending
        } else {
            return .orderedSame
        }
    }
    
    /// Returns true if the two `Date` values represent the same point in time.
    public static func ==(lhs: Date, rhs: Date) -> Bool {
        return lhs.timeIntervalSinceReferenceDate == rhs.timeIntervalSinceReferenceDate
    }
    
    /// Returns true if the left hand `Date` is earlier in time than the right hand `Date`.
    public static func <(lhs: Date, rhs: Date) -> Bool {
        return lhs.timeIntervalSinceReferenceDate < rhs.timeIntervalSinceReferenceDate
    }
    
    /// Returns true if the left hand `Date` is later in time than the right hand `Date`.
    public static func >(lhs: Date, rhs: Date) -> Bool {
        return lhs.timeIntervalSinceReferenceDate > rhs.timeIntervalSinceReferenceDate
    }
    
    /// Returns a `Date` with a specified amount of time added to it.
    public static func +(lhs: Date, rhs: TimeInterval) -> Date {
        return Date(timeIntervalSinceReferenceDate: lhs.timeIntervalSinceReferenceDate + rhs)
    }
    
    /// Returns a `Date` with a specified amount of time subtracted from it.
    public static func -(lhs: Date, rhs: TimeInterval) -> Date {
        return Date(timeIntervalSinceReferenceDate: lhs.timeIntervalSinceReferenceDate - rhs)
    }
    
    /// Add a `TimeInterval` to a `Date`.
    ///
    /// - warning: This only adjusts an absolute value. If you wish to add calendrical concepts like hours, days, months then you must use a `Calendar`. That will take into account complexities like daylight saving time, months with different numbers of days, and more.
    public static func +=(lhs: inout Date, rhs: TimeInterval) {
        lhs = lhs + rhs
    }
    
    /// Subtract a `TimeInterval` from a `Date`.
    ///
    /// - warning: This only adjusts an absolute value. If you wish to add calendrical concepts like hours, days, months then you must use a `Calendar`. That will take into account complexities like daylight saving time, months with different numbers of days, and more.
    public static func -=(lhs: inout Date, rhs: TimeInterval) {
        lhs = lhs - rhs
    }
    
}

extension Date : CustomDebugStringConvertible, CustomStringConvertible, CustomReflectable {
    /**
     A string representation of the date object (read-only).
     
     The representation is useful for debugging only.
     
     There are a number of options to acquire a formatted string for a date including: date formatters (see
     [NSDateFormatter](//apple_ref/occ/cl/NSDateFormatter) and [Data Formatting Guide](//apple_ref/doc/uid/10000029i)), and the `Date` function `description(locale:)`.
     */
    public var description: String {
        // Defer to NSDate for description
        return NSDate(timeIntervalSinceReferenceDate: _time).description
    }
    
    /**
     Returns a string representation of the receiver using the given
     locale.
     
     - Parameter locale: A `Locale`. If you pass `nil`, `Date` formats the date in the same way as the `description` property.
     
     - Returns: A string representation of the `Date`, using the given locale, or if the locale argument is `nil`, in the international format `YYYY-MM-DD HH:MM:SS ±HHMM`, where `±HHMM` represents the time zone offset in hours and minutes from UTC (for example, "`2001-03-24 10:45:32 +0600`").
     */
    public func description(with locale: Locale?) -> String {
        return NSDate(timeIntervalSinceReferenceDate: _time).description(with: locale)
    }
    
    public var debugDescription: String {
        return description
    }
    
    public var customMirror: Mirror {
        var c: [(label: String?, value: Any)] = []
        c.append((label: "timeIntervalSinceReferenceDate", value: timeIntervalSinceReferenceDate))
        return Mirror(self, children: c, displayStyle: .struct)
    }
}

extension Date : _ObjectiveCBridgeable {
    @_semantics("convertToObjectiveC")
    public func _bridgeToObjectiveC() -> NSDate {
        return NSDate(timeIntervalSinceReferenceDate: _time)
    }
    
    public static func _forceBridgeFromObjectiveC(_ x: NSDate, result: inout Date?) {
        if !_conditionallyBridgeFromObjectiveC(x, result: &result) {
            fatalError("Unable to bridge \(NSDate.self) to \(self)")
        }
    }
    
    public static func _conditionallyBridgeFromObjectiveC(_ x: NSDate, result: inout Date?) -> Bool {
        result = Date(timeIntervalSinceReferenceDate: x.timeIntervalSinceReferenceDate)
        return true
    }
    
    public static func _unconditionallyBridgeFromObjectiveC(_ source: NSDate?) -> Date {
        var result: Date? = nil
        _forceBridgeFromObjectiveC(source!, result: &result)
        return result!
    }
}

extension Date : CustomPlaygroundDisplayConvertible {
    public var playgroundDescription: Any {
        let df = DateFormatter()
        df.dateStyle = .medium
        df.timeStyle = .short
        return df.string(from: self)
    }
}

extension Date : Codable {
    public init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let timestamp = try container.decode(Double.self)
        self.init(timeIntervalSinceReferenceDate: timestamp)
    }

    public func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        try container.encode(self.timeIntervalSinceReferenceDate)
    }
}