package playback

import "errors"

type PlaylistCommandKind uint8

const (
	PlaylistSelect PlaylistCommandKind = iota + 1
	PlaylistNext
	PlaylistPrevious
)

type PlaylistCommand struct {
	Kind  PlaylistCommandKind
	Index int
}

type PlaylistState struct {
	CurrentIndex int
	HasSelection bool
}

var (
	ErrPlaylistEmpty           = errors.New("playlist is empty")
	ErrPlaylistIndexOutOfRange = errors.New("playlist index is out of range")
	ErrUnknownPlaylistCommand  = errors.New("unknown playlist command")
)

func ApplyPlaylistCommand(
	playlist Playlist,
	current PlaylistState,
	command PlaylistCommand,
) (PlaylistState, error) {
	if err := playlist.Validate(); err != nil {
		return current, err
	}
	if len(playlist.Entries) == 0 {
		return current, ErrPlaylistEmpty
	}

	lastIndex := len(playlist.Entries) - 1
	switch command.Kind {
	case PlaylistSelect:
		if command.Index < 0 || command.Index > lastIndex {
			return current, ErrPlaylistIndexOutOfRange
		}
		return PlaylistState{CurrentIndex: command.Index, HasSelection: true}, nil

	case PlaylistNext:
		if !current.HasSelection {
			return PlaylistState{CurrentIndex: 0, HasSelection: true}, nil
		}
		if current.CurrentIndex < 0 || current.CurrentIndex > lastIndex {
			return current, ErrPlaylistIndexOutOfRange
		}
		if current.CurrentIndex == lastIndex {
			if playlist.Loop {
				return PlaylistState{CurrentIndex: 0, HasSelection: true}, nil
			}
			return current, nil
		}
		return PlaylistState{CurrentIndex: current.CurrentIndex + 1, HasSelection: true}, nil

	case PlaylistPrevious:
		if !current.HasSelection {
			index := 0
			if playlist.Loop {
				index = lastIndex
			}
			return PlaylistState{CurrentIndex: index, HasSelection: true}, nil
		}
		if current.CurrentIndex < 0 || current.CurrentIndex > lastIndex {
			return current, ErrPlaylistIndexOutOfRange
		}
		if current.CurrentIndex == 0 {
			if playlist.Loop {
				return PlaylistState{CurrentIndex: lastIndex, HasSelection: true}, nil
			}
			return current, nil
		}
		return PlaylistState{CurrentIndex: current.CurrentIndex - 1, HasSelection: true}, nil

	default:
		return current, ErrUnknownPlaylistCommand
	}
}

func (s PlaylistState) Entry(playlist Playlist) (PlaylistEntry, bool) {
	if !s.HasSelection || s.CurrentIndex < 0 || s.CurrentIndex >= len(playlist.Entries) {
		return PlaylistEntry{}, false
	}
	return playlist.Entries[s.CurrentIndex], true
}