Fixup naming / documentation

fakelib.go

@@ -40,10 +40,10 @@ func main() {
 		log.Fatalf("failed to load golden file %q: %v", goldenPath, err)
 	}
 	lib.Tracks = *librarySize
-	lib.Tagger = library.AlbumTagger{
-		TracksPerAlbum:  *tracksPerAlbum,
-		AlbumsPerArtist: *albumsPerArtist,
-		MinPathLength:   *minPathLength,
+	lib.Tagger = library.RepeatedLetters{
+		TracksPerAlbum:     *tracksPerAlbum,
+		AlbumsPerArtist:    *albumsPerArtist,
+		MinComponentLength: *minPathLength / 3,
 	}.Tag
 
 	// No need for the file anymore, just close it to drop the handle.

library/library.go

@@ -80,41 +80,36 @@ func (s Song) Read(buf []byte, off int64) {
 	copy(buf, s.data[off:])
 }
 
-// Songs in the library are always generated in the form:
-//    <artist>/<album>/<track>.mp3
-// Where each component is some number of characters from A-Z.
+// RepeatedLetters implements a tagger to generate track metadata using
+// repeated letters. Each component is some number of characters from A-Z.
 // Artists/Albums/Tracks are named in-order, starting at 0. So track 0 is
-//    A/A/A.mp3
+//    Artist: A, Album: A, Title: A
 // Track 1 is:
-//    A/A/B.mp3
+//    Artist: A, Album: A, Title: B
 // etc.
-// Track metadata represents what is shown in the path, except that the track
-// title is the concatenation of <artist>, <album>, <track> with "-" as a
-// separator.
 //
-// When MinPathLength > 3, path components are duplicated to extend the length
-// of the path, while maintaining uniqueness. E.g., when MinPathLength = 4,
-// Track 0 is:
-//    AA/AA/AA.mp3
+// When MinComponentLength is set, track components are duplicated to extend
+// the length of the path, while maintaining uniqueness. E.g., when
+// MinComponentLength = 2, Track 0 is:
+//    Artist: AA, Album: AA, Title: AA
 //
 // When all letters have been exhausted in a category, the name is extended
 // following a "spreadsheet" schema: A, B, ..., Z, AA, AB, ..., ZZ, AAA, ...
-// When MinPathLength > 3, the repeated name is extended. So when
-// MinPathLength = 4, "AB" becomes "ABAB".
-type AlbumTagger struct {
+// When MinComponentLength is set, the repeated name is extended. So when
+// MinComponentLength = 2, "AB" becomes "ABAB".
+type RepeatedLetters struct {
 	TracksPerAlbum  int
 	AlbumsPerArtist int
-	// Number of artists is derived from #of tracks, the track/album, and
-	// album/artist ratios.
+	// Number of artists is derived from the he track/album, and album/artist
+	// ratios.
 
-	// The minimum length of a path. Path elements are repeated to extend this
-	// value. Must be >= 3 or the result is undefined.
-	MinPathLength int
+	// The minimum length of a component. Components are repeated to extend
+	// this value. Defaults to 1 if unset.
+	MinComponentLength int
 }
 
-var letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
-
 func letterName(i int) string {
+	const letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 	var name []byte
 	for {
 		name = append(name, letters[i%len(letters)])
@@ -132,21 +127,17 @@ func letterName(i int) string {
 	return string(name)
 }
 
-func (a AlbumTagger) name(i int) string {
-	minLength := a.MinPathLength
+func (a RepeatedLetters) name(i int) string {
+	minLength := a.MinComponentLength
 	if minLength == 0 {
-		// Special case to make the zero-value useful. Assume 3.
-		minLength = 3
-	}
-	// Divide by 3 because our paths have 3 components.
-	extension := minLength / 3
-	if minLength%3 != 0 {
-		extension++
+		// Special case to make the zero-value useful. Assume 1.
+		minLength = 1
 	}
-	return strings.Repeat(letterName(i), extension)
+	return strings.Repeat(letterName(i), minLength)
 }
 
-func (a AlbumTagger) Tag(idx int) *id3v2.Tag {
+// Tag implements TagFunc to generate an id3v2 tag for a song at each index.
+func (a RepeatedLetters) Tag(idx int) *id3v2.Tag {
 	artist := a.name(idx / (a.TracksPerAlbum * a.AlbumsPerArtist))
 	album := a.name((idx / a.TracksPerAlbum) % a.AlbumsPerArtist)
 	trackIdx := idx % a.TracksPerAlbum
@@ -167,6 +158,16 @@ func (a AlbumTagger) Tag(idx int) *id3v2.Tag {
 	return t
 }
 
+// ArtistAlbumTitle implements PathFunc. The generated path follows a typical
+// <artist>/<album>/<title>.mp3 pattern for the song's title.
+func ArtistAlbumTitle(index int, tag *id3v2.Tag) string {
+	artist := tag.Artist()
+	album := tag.Album()
+	title := tag.Title()
+
+	return path.Join(artist, album, title) + ".mp3"
+}
+
 // TagFunc is a function that generates the tag for the song at the given
 // index in the library.
 type TagFunc func(index int) *id3v2.Tag
@@ -175,14 +176,6 @@ type TagFunc func(index int) *id3v2.Tag
 // the given index and tag.
 type PathFunc func(index int, tag *id3v2.Tag) string
 
-func ArtistAlbumTitlePather(index int, tag *id3v2.Tag) string {
-	artist := tag.Artist()
-	album := tag.Album()
-	title := tag.Title()
-
-	return path.Join(artist, album, title) + ".mp3"
-}
-
 // Library represents a fake library of songs. A single "golden" MP3 is
 // used as the basis for every track in the library, and song metadata is
 // generated on a per-track basis. A new library can be created with `New`.
@@ -192,7 +185,11 @@ type Library struct {
 	// Total number of tracks in the fake library.
 	Tracks int
 
+	// Tagger is invoked to retrieve the tags for the song at each index
+	// position (0-based).
 	Tagger TagFunc
+	// Pather is invoked to generate the path for the song at each index. It
+	// is also passed the tag generated by the Tagger.
 	Pather PathFunc
 
 	// golden is the "golden" track data for this
@@ -225,7 +222,8 @@ func (l *Library) SongAt(idx int) (Song, error) {
 	return Song{tag: buf.Bytes(), data: l.golden}, nil
 }
 
-// New returns a new Library that uses Golden data
+// New returns a new Library that uses Golden data read from the given golden
+// reader.
 func New(golden io.ReadSeeker) (*Library, error) {
 	header, err := id3v2.ParseReader(golden, id3v2.Options{Parse: true})
 	if err != nil {
@@ -244,12 +242,11 @@ func New(golden io.ReadSeeker) (*Library, error) {
 
 	return &Library{
 		Tracks: 1000,
-		Tagger: AlbumTagger{
+		Tagger: RepeatedLetters{
 			TracksPerAlbum:  10,
 			AlbumsPerArtist: 3,
-			MinPathLength:   3,
 		}.Tag,
-		Pather: ArtistAlbumTitlePather,
+		Pather: ArtistAlbumTitle,
 		golden: data,
 	}, nil
 }