package download

import (
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"strings"

	"github.com/mathismqn/godeez/internal/deezer"
)

// m3uEntry pairs a playlist track with the file it ended up at, so the m3u
// can be written after the fact without re-deriving the path.
type m3uEntry struct {
	track *deezer.Track
	path  string
}

// writeM3U records a playlist's tracks in their original order as an
// extended M3U file next to the downloaded audio.
//
// This exists because the on-disk file names carry no ordering for
// playlists (unlike albums, which get a zero padded track number prefix):
// without an m3u, the sequence the user curated on Deezer is lost the moment
// the tracks land in a directory that any player will list alphabetically.
//
// Skipped tracks are included: they are already on disk from a previous run
// and belong at their playlist position just as much as one downloaded this
// run. Failed tracks are left out since there is nothing on disk to point
// at, and a broken entry would only confuse the player.
//
// Paths are written relative to outputDir so the m3u keeps working if the
// whole playlist folder is moved or copied elsewhere.
func writeM3U(outputDir string, entries []m3uEntry) error {
	if len(entries) == 0 {
		return nil
	}

	m3uPath := filepath.Join(outputDir, filepath.Base(outputDir)+".m3u")

	var b strings.Builder
	b.WriteString("#EXTM3U\n")

	for _, e := range entries {
		duration, err := strconv.Atoi(e.track.Duration)
		if err != nil {
			duration = 0
		}

		rel, err := filepath.Rel(outputDir, e.path)
		if err != nil {
			rel = e.path
		}

		fmt.Fprintf(&b, "#EXTINF:%d,%s - %s\n%s\n", duration, e.track.Artist, e.track.FullTitle(), rel)
	}

	return os.WriteFile(m3uPath, []byte(b.String()), 0644)
}