package radio

import (
	"strings"
	"sync"

	"github.com/pkg/errors"
)

// Playlist holds a list of paths to a song files.
type Playlist struct {
	sync.Mutex
	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.
func NewPlaylistFromPlaintext(data []byte, repeat bool) (*Playlist, error) {
	p := &Playlist{repeat: repeat}
	return p, p.LoadFromPlaintext(data)
}

// 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) {
	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 accepts a byte array of plaintext data and parses it into an array of strings.
// Also resets a cur index to 0 to start over.
func (p *Playlist) LoadFromPlaintext(data []byte) error {
	if len(data) == 0 {
		return errors.New("an empty playlist array was passed")
	}

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

	return nil
}