import 'dart:collection';

import 'closed_caption_part.dart';

/// Text that gets displayed at specific time during video playback,
/// as part of a [ClosedCaptionTrack]
class ClosedCaption {
  /// Text displayed by this caption.
  final String text;

  /// Time at which this caption starts being displayed.
  final Duration offset;

  /// Duration this caption is displayed.
  final Duration duration;

  /// Time at which this caption ends being displayed.
  Duration get end => offset + duration;

  /// Caption parts (usually individual words).
  /// May be empty because not all captions contain parts.
  final UnmodifiableListView<ClosedCaptionPart> parts;

  /// Initializes an instance of [ClosedCaption]
  ClosedCaption(
      this.text, this.offset, this.duration, Iterable<ClosedCaptionPart> parts)
      : parts = UnmodifiableListView(parts);

  /// Gets the caption part displayed at the specified point in time,
  /// relative to this caption's offset.
  /// Returns null if not found.
  /// Note that some captions may not have any parts at all.
  ClosedCaptionPart getPartByTime(Duration offset) =>
      parts.firstWhere((e) => e.offset >= offset, orElse: () => null);
}