package files

import (
	"fmt"
	"strings"

	id3v2 "github.com/bogem/id3v2/v2"
)

// applyMP3Tags writes only the provided non-empty tags to the MP3 file at
// realPath. It preserves existing frames when not overwritten.
func applyMP3Tags(realPath string, tags map[string]string) error {
	// Open tag for read/write
	tag, err := id3v2.Open(realPath, id3v2.Options{Parse: true})
	if err != nil {
		return fmt.Errorf("open id3v2: %w", err)
	}
	defer tag.Close()

	// Helper to set a text frame (replace existing)
	setFrame := func(frameID, value string) {
		if strings.TrimSpace(value) == "" {
			return
		}
		tag.DeleteAllFrames(frameID)
		tag.AddTextFrame(frameID, tag.DefaultEncoding(), value)
	}

	for k, v := range tags {
		if strings.TrimSpace(v) == "" {
			continue
		}
		switch strings.ToLower(k) {
		case "title":
			setFrame("TIT2", v)
		case "artist":
			setFrame("TPE1", v)
		case "album":
			setFrame("TALB", v)
		case "albumartist", "album artist":
			setFrame("TPE2", v)
		case "composer":
			setFrame("TCOM", v)
		case "year", "date":
			setFrame("TDRC", v)
		case "track":
			setFrame("TRCK", v)
		case "disc":
			setFrame("TPOS", v)
		case "genre":
			setFrame("TCON", v)
		default:
			// write custom text frame under TXXX with description = key
			// Use description to store the original key so we don't collide
			// with standard frames.
			// Note: bogem/id3v2 uses AddTextFrame for TXXX as well.
			tag.AddTextFrame("TXXX", tag.DefaultEncoding(), v)
		}
	}

	if err := tag.Save(); err != nil {
		return fmt.Errorf("save id3v2: %w", err)
	}

	return nil
}