//
//  Date+ZIP.swift
//  ZIPFoundation
//
//  Created by Thomas Zoechling on 20.12.22.
//

import Foundation

extension Date {

  // MARK: Lifecycle

  init(dateTime: (UInt16, UInt16)) {
    var msdosDateTime = Int(dateTime.0)
    msdosDateTime <<= 16
    msdosDateTime |= Int(dateTime.1)
    var unixTime = tm()
    unixTime.tm_sec = Int32((msdosDateTime & 31) * 2)
    unixTime.tm_min = Int32((msdosDateTime >> 5) & 63)
    unixTime.tm_hour = Int32((Int(dateTime.1) >> 11) & 31)
    unixTime.tm_mday = Int32((msdosDateTime >> 16) & 31)
    unixTime.tm_mon = Int32((msdosDateTime >> 21) & 15)
    unixTime.tm_mon -= 1 // UNIX time struct month entries are zero based.
    unixTime.tm_year = Int32(1980 + (msdosDateTime >> 25))
    unixTime.tm_year -= 1900 // UNIX time structs count in "years since 1900".
    let time = timegm(&unixTime)
    self = Date(timeIntervalSince1970: TimeInterval(time))
  }

  init(timespec: timespec) {
    let seconds = 1.0e-9 * Double(timespec.tv_nsec)
    let timeIntervalSince1970 = TimeInterval(timespec.tv_sec)
    let absoluteTimeIntervalSince1970 = Constants.absoluteTimeIntervalSince1970
    self.init(timeIntervalSinceReferenceDate: (timeIntervalSince1970 - absoluteTimeIntervalSince1970) + seconds)
  }

  // MARK: Internal

  var fileModificationDateTime: (UInt16, UInt16) {
    (fileModificationDate, fileModificationTime)
  }

  var fileModificationDate: UInt16 {
    var time = time_t(timeIntervalSince1970)
    guard let unixTime = gmtime(&time) else {
      return 0
    }
    var year = unixTime.pointee.tm_year + 1900 // UNIX time structs count in "years since 1900".
    // ZIP uses the MSDOS date format which has a valid range of 1980 - 2099.
    year = year >= 1980 ? year : 1980
    year = year <= 2099 ? year : 2099
    let month = unixTime.pointee.tm_mon + 1 // UNIX time struct month entries are zero based.
    let day = unixTime.pointee.tm_mday
    return UInt16(day + (month * 32) + ((year - 1980) * 512))
  }

  var fileModificationTime: UInt16 {
    var time = time_t(timeIntervalSince1970)
    guard let unixTime = gmtime(&time) else {
      return 0
    }
    let hour = unixTime.pointee.tm_hour
    let minute = unixTime.pointee.tm_min
    let second = unixTime.pointee.tm_sec
    return UInt16((second / 2) + (minute * 32) + (hour * 2048))
  }

}

// MARK: - Date.Constants

extension Date {

  fileprivate enum Constants {
    #if os(macOS) || os(iOS) || os(tvOS) || os(visionOS) || os(watchOS)
    static let absoluteTimeIntervalSince1970 = kCFAbsoluteTimeIntervalSince1970
    #else
    static let absoluteTimeIntervalSince1970 = 978307200.0
    #endif
  }
}

extension stat {

  var lastAccessDate: Date {
    #if os(macOS) || os(iOS) || os(tvOS) || os(visionOS) || os(watchOS)
    return Date(timespec: st_atimespec)
    #else
    return Date(timespec: st_atim)
    #endif
  }
}

extension timeval {

  init(timeIntervalSince1970: TimeInterval) {
    let (integral, fractional) = modf(timeIntervalSince1970)
    self.init(tv_sec: time_t(integral), tv_usec: suseconds_t(1.0e6 * fractional))
  }
}