Dmitry Sergeev
94 lines
2.3 KiB
Go
94 lines
2.3 KiB
Go
package playback
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import "errors"
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type PlaylistCommandKind uint8
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const (
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PlaylistSelect PlaylistCommandKind = iota + 1
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PlaylistNext
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PlaylistPrevious
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)
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type PlaylistCommand struct {
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Kind PlaylistCommandKind
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Index int
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}
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type PlaylistState struct {
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CurrentIndex int
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HasSelection bool
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}
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var (
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ErrPlaylistEmpty = errors.New("playlist is empty")
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ErrPlaylistIndexOutOfRange = errors.New("playlist index is out of range")
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ErrUnknownPlaylistCommand = errors.New("unknown playlist command")
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)
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func ApplyPlaylistCommand(
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playlist Playlist,
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current PlaylistState,
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command PlaylistCommand,
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) (PlaylistState, error) {
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if err := playlist.Validate(); err != nil {
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return current, err
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}
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if len(playlist.Entries) == 0 {
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return current, ErrPlaylistEmpty
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}
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lastIndex := len(playlist.Entries) - 1
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switch command.Kind {
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case PlaylistSelect:
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if command.Index < 0 || command.Index > lastIndex {
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return current, ErrPlaylistIndexOutOfRange
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}
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return PlaylistState{CurrentIndex: command.Index, HasSelection: true}, nil
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case PlaylistNext:
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if !current.HasSelection {
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return PlaylistState{CurrentIndex: 0, HasSelection: true}, nil
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}
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if current.CurrentIndex < 0 || current.CurrentIndex > lastIndex {
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return current, ErrPlaylistIndexOutOfRange
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}
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if current.CurrentIndex == lastIndex {
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if playlist.Loop {
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return PlaylistState{CurrentIndex: 0, HasSelection: true}, nil
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}
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return current, nil
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}
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return PlaylistState{CurrentIndex: current.CurrentIndex + 1, HasSelection: true}, nil
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case PlaylistPrevious:
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if !current.HasSelection {
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index := 0
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if playlist.Loop {
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index = lastIndex
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}
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return PlaylistState{CurrentIndex: index, HasSelection: true}, nil
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}
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if current.CurrentIndex < 0 || current.CurrentIndex > lastIndex {
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return current, ErrPlaylistIndexOutOfRange
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}
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if current.CurrentIndex == 0 {
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if playlist.Loop {
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return PlaylistState{CurrentIndex: lastIndex, HasSelection: true}, nil
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}
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return current, nil
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}
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return PlaylistState{CurrentIndex: current.CurrentIndex - 1, HasSelection: true}, nil
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default:
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return current, ErrUnknownPlaylistCommand
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}
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}
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func (s PlaylistState) Entry(playlist Playlist) (PlaylistEntry, bool) {
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if !s.HasSelection || s.CurrentIndex < 0 || s.CurrentIndex >= len(playlist.Entries) {
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return PlaylistEntry{}, false
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}
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return playlist.Entries[s.CurrentIndex], true
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}
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