/// What a worker has said about a given day.
///
/// Three states rather than an on/off switch, because "I can work" and "I want
/// work" are different answers and Auto-Match treats them differently: an
/// available day is one it may fill, a preferred day is one it should fill
/// first.
enum DayAvailability { available, prefers, unavailable }

extension DayAvailabilityX on DayAvailability {
  String get label => switch (this) {
    DayAvailability.available => 'Available',
    DayAvailability.prefers => 'Prefers to work',
    DayAvailability.unavailable => 'Unavailable',
  };

  /// The line under the option, in the picker.
  String get blurb => switch (this) {
    DayAvailability.available => 'Can be scheduled any time',
    DayAvailability.prefers => 'Wants shifts — optionally within a time window',
    DayAvailability.unavailable => 'Marked off (vacation, sick, personal)',
  };

  /// The line under the date, once the day is set.
  String get summary => switch (this) {
    DayAvailability.available => 'Can be scheduled any time',
    DayAvailability.prefers => 'Wants shifts',
    DayAvailability.unavailable => 'Not available',
  };
}

/// The hours a worker would rather be given, on a day they want work.
///
/// Both ends are optional and independent: "from 6pm, any end" is a normal
/// thing to want, and forcing a full range would make the worker invent one.
/// Null at both ends means any time, which is also the default.
class PreferredWindow {
  const PreferredWindow({this.from, this.to});

  /// Hour of the day, 0-23. Null is "any time".
  final int? from;
  final int? to;

  static const any = PreferredWindow();

  bool get isAnyTime => from == null && to == null;

  /// How the window reads on its own, as a label.
  String get label {
    if (isAnyTime) return 'Any time';
    if (from != null && to != null) return '${_hhmm(from!)} - ${_hhmm(to!)}';
    if (from != null) return 'From ${_hhmm(from!)}';
    return 'Until ${_hhmm(to!)}';
  }

  /// How the window reads inside a sentence — "look for shifts $sentence
  /// first". The label does not survive being dropped mid-sentence: "look for
  /// From 09:00 first" is not English.
  String get sentence {
    if (isAnyTime) return 'at any time';
    if (from != null && to != null) {
      return 'between ${_hhmm(from!)} and ${_hhmm(to!)}';
    }
    if (from != null) return 'from ${_hhmm(from!)}';
    return 'until ${_hhmm(to!)}';
  }

  PreferredWindow copyWith({
    int? from,
    int? to,
    bool clearFrom = false,
    bool clearTo = false,
  }) => PreferredWindow(
    from: clearFrom ? null : (from ?? this.from),
    to: clearTo ? null : (to ?? this.to),
  );

  static String _hhmm(int hour) => '${hour.toString().padLeft(2, '0')}:00';
}

/// A day's answer: the status, and the window if one was given.
class DayPlan {
  const DayPlan({
    this.status = DayAvailability.unavailable,
    this.window = PreferredWindow.any,
  });

  final DayAvailability status;

  /// Only meaningful while [status] is [DayAvailability.prefers]; kept across
  /// a status change so flipping away and back does not lose the hours.
  final PreferredWindow window;

  bool get isSet => status != DayAvailability.unavailable;

  DayPlan copyWith({DayAvailability? status, PreferredWindow? window}) =>
      DayPlan(status: status ?? this.status, window: window ?? this.window);
}