package radio

import (
	"os"
	"strings"
	"sync"

	"github.com/pkg/errors"
)

// Playlist holds a list of paths to a song files.
type Playlist struct {
	mutex    sync.Mutex
	filePath string
	playlist []string
	cur      int
	repeat   bool
}

// NewPlaylist returns an instance of a Playlist struct with a loaded playlist.
// Returns an error if failed to load a playlist file.
func NewPlaylist(filePath string, repeat bool) (*Playlist, error) {
	p := &Playlist{filePath: filePath, repeat: repeat}
	return p, p.load()
}

// Next returns the next song to play. Returns an empty string if repeat is
// false and the end of a playlist was reached.
func (p *Playlist) Next() (song string) {
	p.mutex.Lock()
	defer p.mutex.Unlock()
	if p.cur == len(p.playlist) {
		// If the end of a playlist was reached and repeat is set to true,
		// then go back to the head of it, thus repeating it. Return an empty
		// string otherwise.
		if p.repeat {
			p.cur = 0
		} else {
			return ""
		}
	}
	song = p.playlist[p.cur]
	p.cur++
	return
}

// Load reads a playlist file.
func (p *Playlist) load() error {
	data, err := os.ReadFile(p.filePath)
	if err != nil {
		return errors.Wrap(err, "cannot open a playlist file")
	}

	if len(data) == 0 {
		return errors.New("a playlist file is empty. Did not update")
	}

	p.mutex.Lock()
	p.playlist = strings.Split(string(data), "\n")
	p.cur = 0
	p.mutex.Unlock()

	return nil
}

func (p *Playlist) Reload() error {
	return p.load()
}