song.go

package main

import (
	"encoding/json"
	"fmt"
	"strings"
)

type Song struct {
	Filename  string `json:"filename"`
	Path      string `json:"path"`
	Extension string `json:"extension"`
	Title     string `json:"title"`
	Artist    string `json:"artist"`
	Album     string `json:"album"`
	DiscNum   *int   `json:"disc_num"`
	TrackNum  *int   `json:"track_num"` // we use pointer for string, so we can set it to "nil" if there is no track number
	Length    int    `json:"length"`
}

// For sorting songs in a natural way (artist, album, format, track number)
func (song *Song) ToNaturalSortString() string {
	sortables := []string{}

	if song.Artist != "" {
		sortables = append(sortables, song.Artist)
	}
	if song.Album != "" {
		sortables = append(sortables, song.Album)
	}
	if song.Extension != "" {
		sortables = append(sortables, song.Extension)
	}
	if song.DiscNum != nil {
		sortables = append(sortables, fmt.Sprintf("%03d", *song.DiscNum))
	}
	if song.TrackNum == nil {
		sortables = append(sortables, song.Title)
	} else {
		sortables = append(sortables, fmt.Sprintf("%03d", *song.TrackNum))
	}

	if len(sortables) > 0 {
		return strings.Join(sortables, " ")
	}

	return song.Filename
}

// Return a nice title for the song, like "Artist - Title". Fallback to the filename
func (s *Song) NiceTitle() string {
	if s.Title != "" && s.Artist != "" {
		return fmt.Sprintf("%s - %s", s.Artist, s.Title)
	}
	return s.Filename
}

// Convert the raw seconds length to a human-readable string like "04:52" or "01:23:45"
func (s Song) NiceLength() string {
	seconds := s.Length
	minutes := seconds / 60
	hours := minutes / 60

	seconds %= 60
	minutes %= 60

	if hours > 0 {
		return fmt.Sprintf("%d:%02d:%02d", hours, minutes, seconds)
	} else {
		return fmt.Sprintf("%d:%02d", minutes, seconds)
	}
}

// Custom marshaling for adding "nice_title" and "nice_length" to the JSON output
func (s *Song) MarshalJSON() ([]byte, error) {
	type Alias Song
	return json.Marshal(&struct {
		*Alias
		NiceTitle  string `json:"nice_title"`
		NiceLength string `json:"nice_length"`
	}{
		Alias:      (*Alias)(s),
		NiceTitle:  s.NiceTitle(),
		NiceLength: s.NiceLength(),
	})
}