// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of dart.core;

/// A span of time, such as 27 days, 4 hours, 12 minutes, and 3 seconds.
///
/// A `Duration` represents a difference from one point in time to another. The
/// duration may be "negative" if the difference is from a later time to an
/// earlier.
///
/// Durations are context independent. For example, a duration of 2 days is
/// always 48 hours, even when it is added to a `DateTime` just when the
/// time zone is about to do a daylight-savings switch. (See [DateTime.add]).
///
/// Despite the same name, a `Duration` object does not implement "Durations"
/// as specified by ISO 8601. In particular, a duration object does not keep
/// track of the individually provided members (such as "days" or "hours"), but
/// only uses these arguments to compute the length of the corresponding time
/// interval.
///
/// To create a new Duration object, use this class's single constructor
/// giving the appropriate arguments:
/// ```dart
/// var fastestMarathon = const Duration(hours: 2, minutes: 3, seconds: 2);
/// ```
/// The [Duration] is the sum of all individual parts.
/// This means that individual parts can be larger than the next-bigger unit.
/// For example, [inMinutes] can be greater than 59.
/// ```dart
/// assert(fastestMarathon.inMinutes == 123);
/// ```
/// All individual parts are allowed to be negative.
///
/// Use one of the properties, such as [inDays],
/// to retrieve the integer value of the Duration in the specified time unit.
/// Note that the returned value is rounded down.
/// For example,
/// ```dart
/// var aLongWeekend = const Duration(hours: 88);
/// assert(aLongWeekend.inDays == 3);
/// ```
/// This class provides a collection of arithmetic
/// and comparison operators,
/// plus a set of constants useful for converting time units.
///
/// See [DateTime] to represent a point in time.
/// See [Stopwatch] to measure time-spans.
class Duration implements Comparable<Duration> {
  /// The number of microseconds per millisecond.
  static const int microsecondsPerMillisecond = 1000;

  /// The number of milliseconds per second.
  static const int millisecondsPerSecond = 1000;

  /// The number of seconds per minute.
  ///
  /// Notice that some minutes of official clock time might
  /// differ in length because of leap seconds.
  /// The [Duration] and [DateTime] classes ignore leap seconds
  /// and consider all minutes to have 60 seconds.
  static const int secondsPerMinute = 60;

  /// The number of minutes per hour.
  static const int minutesPerHour = 60;

  /// The number of hours per day.
  ///
  /// Notice that some days may differ in length because
  /// of time zone changes due to daylight saving.
  /// The [Duration] class is time zone agnostic and
  /// considers all days to have 24 hours.
  static const int hoursPerDay = 24;

  /// The number of microseconds per second.
  static const int microsecondsPerSecond =
      microsecondsPerMillisecond * millisecondsPerSecond;

  /// The number of microseconds per minute.
  static const int microsecondsPerMinute =
      microsecondsPerSecond * secondsPerMinute;

  /// The number of microseconds per hour.
  static const int microsecondsPerHour = microsecondsPerMinute * minutesPerHour;

  /// The number of microseconds per day.
  static const int microsecondsPerDay = microsecondsPerHour * hoursPerDay;

  /// The number of milliseconds per minute.
  static const int millisecondsPerMinute =
      millisecondsPerSecond * secondsPerMinute;

  /// The number of milliseconds per hour.
  static const int millisecondsPerHour = millisecondsPerMinute * minutesPerHour;

  /// The number of milliseconds per day.
  static const int millisecondsPerDay = millisecondsPerHour * hoursPerDay;

  /// The number of seconds per hour.
  static const int secondsPerHour = secondsPerMinute * minutesPerHour;

  /// The number of seconds per day.
  static const int secondsPerDay = secondsPerHour * hoursPerDay;

  /// The number of minutes per day.
  static const int minutesPerDay = minutesPerHour * hoursPerDay;

  /// An empty duration, representing zero time.
  static const Duration zero = Duration(seconds: 0);

  /// The total microseconds of this [Duration] object.
  final int _duration;

  /// Creates a new [Duration] object whose value
  /// is the sum of all individual parts.
  ///
  /// Individual parts can be larger than the number of those
  /// parts in the next larger unit.
  /// For example, [hours] can be greater than 23.
  /// If this happens, the value overflows into the next larger
  /// unit, so 26 [hours] is the same as 2 [hours] and
  /// one more [days].
  /// Likewise, values can be negative, in which case they
  /// underflow and subtract from the next larger unit.
  ///
  /// All arguments are 0 by default.
  const Duration(
      {int days = 0,
      int hours = 0,
      int minutes = 0,
      int seconds = 0,
      int milliseconds = 0,
      int microseconds = 0})
      : this._microseconds(microsecondsPerDay * days +
            microsecondsPerHour * hours +
            microsecondsPerMinute * minutes +
            microsecondsPerSecond * seconds +
            microsecondsPerMillisecond * milliseconds +
            microseconds);

  // Fast path internal direct constructor to avoids the optional arguments and
  // [_microseconds] recomputation.
  const Duration._microseconds(this._duration);

  /// Adds this Duration and [other] and
  /// returns the sum as a new Duration object.
  Duration operator +(Duration other) {
    return Duration._microseconds(_duration + other._duration);
  }

  /// Subtracts [other] from this Duration and
  /// returns the difference as a new Duration object.
  Duration operator -(Duration other) {
    return Duration._microseconds(_duration - other._duration);
  }

  /// Multiplies this Duration by the given [factor] and returns the result
  /// as a new Duration object.
  ///
  /// Note that when [factor] is a double, and the duration is greater than
  /// 53 bits, precision is lost because of double-precision arithmetic.
  Duration operator *(num factor) {
    return Duration._microseconds((_duration * factor).round());
  }

  /// Divides this Duration by the given [quotient] and returns the truncated
  /// result as a new Duration object.
  ///
  /// Throws an [IntegerDivisionByZeroException] if [quotient] is `0`.
  Duration operator ~/(int quotient) {
    // By doing the check here instead of relying on "~/" below we get the
    // exception even with dart2js.
    if (quotient == 0) throw IntegerDivisionByZeroException();
    return Duration._microseconds(_duration ~/ quotient);
  }

  /// Whether this [Duration] is shorter than [other].
  bool operator <(Duration other) => this._duration < other._duration;

  /// Whether this [Duration] is longer than [other].
  bool operator >(Duration other) => this._duration > other._duration;

  /// Whether this [Duration] is shorter than or equal to [other].
  bool operator <=(Duration other) => this._duration <= other._duration;

  /// Whether this [Duration] is longer than or equal to [other].
  bool operator >=(Duration other) => this._duration >= other._duration;

  /// The number of entire days spanned by this [Duration].
  int get inDays => _duration ~/ Duration.microsecondsPerDay;

  /// The number of entire hours spanned by this [Duration].
  ///
  /// The returned value can be greater than 23.
  /// For example a duration of four days and three hours
  /// has 99 entire hours.
  int get inHours => _duration ~/ Duration.microsecondsPerHour;

  /// The number of whole minutes spanned by this [Duration].
  ///
  /// The returned value can be greater than 59.
  /// For example a duration of three hours and 12 minutes
  /// has 192 minutes.
  int get inMinutes => _duration ~/ Duration.microsecondsPerMinute;

  /// The number of whole seconds spanned by this [Duration].
  ///
  /// The returned value can be greater than 59.
  /// For example a duration of three minutes and 12 seconds
  /// has 192 seconds.
  int get inSeconds => _duration ~/ Duration.microsecondsPerSecond;

  /// The number of whole milliseconds spanned by this [Duration].
  ///
  /// The returned value can be greater than 999.
  /// For example a duration of three seconds and 125 milliseconds
  /// has 3125 milliseconds.
  int get inMilliseconds => _duration ~/ Duration.microsecondsPerMillisecond;

  /// The number of whole microseconds spanned by this [Duration].
  ///
  /// The returned value can be greater than 999999.
  /// For example a duration of three seconds, 125 milliseconds and
  /// 369 microseconds has 3125369 microseconds.
  int get inMicroseconds => _duration;

  /// Whether this [Duration] has the same length as [other].
  ///
  /// Durations have the same length if they have the same number
  /// of microseconds, as reported by [inMicroseconds].
  bool operator ==(Object other) =>
      other is Duration && _duration == other.inMicroseconds;

  int get hashCode => _duration.hashCode;

  /// Compares this [Duration] to [other], returning zero if the values are equal.
  ///
  /// Returns a negative integer if this [Duration] is shorter than
  /// [other], or a positive integer if it is longer.
  ///
  /// A negative [Duration] is always considered shorter than a positive one.
  ///
  /// It is always the case that `duration1.compareTo(duration2) < 0` iff
  /// `(someDate + duration1).compareTo(someDate + duration2) < 0`.
  int compareTo(Duration other) => _duration.compareTo(other._duration);

  /// Returns a string representation of this [Duration].
  ///
  /// Returns a string with hours, minutes, seconds, and microseconds, in the
  /// following format: `H:MM:SS.mmmmmm`. For example,
  /// ```dart
  /// var d = Duration(days: 1, hours: 1, minutes: 33, microseconds: 500);
  /// d.toString();  // "25:33:00.000500"
  ///
  /// d = Duration(days: 0, hours: 1, minutes: 10, microseconds: 500);
  /// d.toString();  // "1:10:00.000500"
  /// ```
  String toString() {
    String sixDigits(int n) {
      if (n >= 100000) return "$n";
      if (n >= 10000) return "0$n";
      if (n >= 1000) return "00$n";
      if (n >= 100) return "000$n";
      if (n >= 10) return "0000$n";
      return "00000$n";
    }

    String twoDigits(int n) {
      if (n >= 10) return "$n";
      return "0$n";
    }

    if (inMicroseconds < 0) {
      return "-${-this}";
    }
    String twoDigitMinutes =
        twoDigits(inMinutes.remainder(minutesPerHour) as int);
    String twoDigitSeconds =
        twoDigits(inSeconds.remainder(secondsPerMinute) as int);
    String sixDigitUs =
        sixDigits(inMicroseconds.remainder(microsecondsPerSecond) as int);
    return "$inHours:$twoDigitMinutes:$twoDigitSeconds.$sixDigitUs";
  }

  /// Whether this [Duration] is negative.
  ///
  /// A negative [Duration] represents the difference from a later time to an
  /// earlier time.
  bool get isNegative => _duration < 0;

  /// Creates a new [Duration] representing the absolute length of this
  /// [Duration].
  ///
  /// The returned [Duration] has the same length as this one, but is always
  /// positive.
  Duration abs() => Duration._microseconds(_duration.abs());

  /// Creates a new [Duration] with the opposite direction of this [Duration].
  ///
  /// The returned [Duration] has the same length as this one, but will have the
  /// opposite sign (as reported by [isNegative]) as this one.
  // Using subtraction helps dart2js avoid negative zeros.
  Duration operator -() => Duration._microseconds(0 - _duration);
}