/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

import Foundation

public typealias Timestamp = UInt64
public typealias MicrosecondTimestamp = UInt64

public let ThreeWeeksInSeconds = 3 * 7 * 24 * 60 * 60

public let OneYearInMilliseconds = 12 * OneMonthInMilliseconds
public let OneMonthInMilliseconds = 30 * OneDayInMilliseconds
public let OneWeekInMilliseconds = 7 * OneDayInMilliseconds
public let OneDayInMilliseconds = 24 * OneHourInMilliseconds
public let OneHourInMilliseconds = 60 * OneMinuteInMilliseconds
public let OneMinuteInMilliseconds = 60 * OneSecondInMilliseconds
public let OneSecondInMilliseconds: UInt64 = 1000

fileprivate let rfc822DateFormatter: DateFormatter = {
    let dateFormatter = DateFormatter()
    dateFormatter.timeZone = TimeZone(abbreviation: "GMT")
    dateFormatter.dateFormat = "EEE',' dd MMM yyyy HH':'mm':'ss 'GMT'"
    dateFormatter.locale = Locale(identifier: "en_US")
    return dateFormatter
}()

extension Timestamp {
    public static func uptimeInMilliseconds() -> Timestamp {
        return Timestamp(DispatchTime.now().uptimeNanoseconds) / 1000000
    }
}

extension Date {
    public static func now() -> Timestamp {
        return UInt64(1000 * Date().timeIntervalSince1970)
    }

    public static func nowNumber() -> NSNumber {
        return NSNumber(value: now() as UInt64)
    }

    public static func nowMicroseconds() -> MicrosecondTimestamp {
        return UInt64(1000000 * Date().timeIntervalSince1970)
    }

    public static func fromTimestamp(_ timestamp: Timestamp) -> Date {
        return Date(timeIntervalSince1970: Double(timestamp) / 1000)
    }

    public static func fromMicrosecondTimestamp(_ microsecondTimestamp: MicrosecondTimestamp) -> Date {
        return Date(timeIntervalSince1970: Double(microsecondTimestamp) / 1000000)
    }

    public func toRelativeTimeString() -> String {
        let now = Date()

        let units: NSCalendar.Unit = [NSCalendar.Unit.second, NSCalendar.Unit.minute, NSCalendar.Unit.day, NSCalendar.Unit.weekOfYear, NSCalendar.Unit.month, NSCalendar.Unit.year, NSCalendar.Unit.hour]

        let components = (Calendar.current as NSCalendar).components(units,
            from: self,
            to: now,
            options: [])
        
        if components.year! > 0 {
            return String(format: DateFormatter.localizedString(from: self, dateStyle: DateFormatter.Style.short, timeStyle: DateFormatter.Style.short))
        }

        if components.month == 1 {
            return String(format: NSLocalizedString("more than a month ago", comment: "Relative date for dates older than a month and less than two months."))
        }

        if components.month! > 1 {
            return String(format: DateFormatter.localizedString(from: self, dateStyle: DateFormatter.Style.short, timeStyle: DateFormatter.Style.short))
        }

        if components.weekOfYear! > 0 {
            return String(format: NSLocalizedString("more than a week ago", comment: "Description for a date more than a week ago, but less than a month ago."))
        }

        if components.day == 1 {
            return String(format: NSLocalizedString("yesterday", comment: "Relative date for yesterday."))
        }

        if components.day! > 1 {
            return String(format: NSLocalizedString("this week", comment: "Relative date for date in past week."), String(describing: components.day))
        }

        if components.hour! > 0 || components.minute! > 0 {
            let absoluteTime = DateFormatter.localizedString(from: self, dateStyle: DateFormatter.Style.none, timeStyle: DateFormatter.Style.short)
            let format = NSLocalizedString("today at %@", comment: "Relative date for date older than a minute.")
            return String(format: format, absoluteTime)
        }

        return String(format: NSLocalizedString("just now", comment: "Relative time for a tab that was visited within the last few moments."))
    }

    public func toRFC822String() -> String {
        return rfc822DateFormatter.string(from: self)
    }
}

let MaxTimestampAsDouble: Double = Double(UInt64.max)

/** This is just like decimalSecondsStringToTimestamp, but it looks for values that seem to be
 *  milliseconds and fixes them. That's necessary because Firefox for iOS <= 7.3 uploaded millis
 *  when seconds were expected.
 */
public func someKindOfTimestampStringToTimestamp(_ input: String) -> Timestamp? {
    var double = 0.0
    if Scanner(string: input).scanDouble(&double) {
        // This should never happen. Hah!
        if double.isNaN || double.isInfinite {
            return nil
        }

        // `double` will be either huge or negatively huge on overflow, and 0 on underflow.
        // We clamp to reasonable ranges.
        if double < 0 {
            return nil
        }

        if double >= MaxTimestampAsDouble {
            // Definitely not representable as a timestamp if the seconds are this large!
            return nil
        }

        if double > 1000000000000 {
            // Oh, this was in milliseconds.
            return Timestamp(double)
        }

        let millis = double * 1000
        if millis >= MaxTimestampAsDouble {
            // Not representable as a timestamp.
            return nil
        }

        return Timestamp(millis)
    }
    return nil
}

public func decimalSecondsStringToTimestamp(_ input: String) -> Timestamp? {
    var double = 0.0
    if Scanner(string: input).scanDouble(&double) {
        // This should never happen. Hah!
        if double.isNaN || double.isInfinite {
            return nil
        }

        // `double` will be either huge or negatively huge on overflow, and 0 on underflow.
        // We clamp to reasonable ranges.
        if double < 0 {
            return nil
        }

        let millis = double * 1000
        if millis >= MaxTimestampAsDouble {
            // Not representable as a timestamp.
            return nil
        }

        return Timestamp(millis)
    }
    return nil
}

public func millisecondsToDecimalSeconds(_ input: Timestamp) -> String {
    let val: Double = Double(input) / 1000
    return String(format: "%.2F", val)
}