1 files changed, 158 insertions, 0 deletions
diff --git a/internal/tag/tag_test.go b/internal/tag/tag_test.go
new file mode 100644
index 0000000..f722cb6
--- /dev/null
+++ b/internal/tag/tag_test.go
@@ -0,0 +1,158 @@
+package tag
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// A minimal but genuinely valid MP3: one silent MPEG-1 Layer III frame.
+// id3v2 needs a real file to append a tag to, and a zero-byte file is not one.
+func writeMP3(t *testing.T, dir, name string) string {
+	t.Helper()
+	// 0xFF 0xFB = MPEG-1 Layer III, no CRC; 0x90 = 128kbps 44.1kHz; then padding.
+	frame := []byte{0xFF, 0xFB, 0x90, 0x00}
+	body := append(frame, make([]byte, 413)...)
+	p := filepath.Join(dir, name)
+	if err := os.WriteFile(p, body, 0o644); err != nil {
+		t.Fatalf("writing %s: %v", name, err)
+	}
+	return p
+}
+
+func TestWriteDir_TagsEachFile(t *testing.T) {
+	dir := t.TempDir()
+	writeMP3(t, dir, "01 - The Law of Gravitation.mp3")
+	writeMP3(t, dir, "02 - The Relation of Mathematics to Physics.mp3")
+
+	results, err := WriteDir(dir, Metadata{
+		Album:  "Character of Physical Law",
+		Artist: "Richard Feynman",
+	})
+	if err != nil {
+		t.Fatalf("WriteDir: %v", err)
+	}
+	if len(results) != 2 {
+		t.Fatalf("got %d results, want 2", len(results))
+	}
+	for _, r := range results {
+		if r.Err != nil {
+			t.Errorf("%s: %v", r.File, r.Err)
+		}
+	}
+
+	title, track, ok := Read(filepath.Join(dir, "01 - The Law of Gravitation.mp3"))
+	if !ok {
+		t.Fatal("tags were not readable after writing")
+	}
+	if title != "The Law of Gravitation" {
+		t.Errorf("title = %q", title)
+	}
+	if track != 1 {
+		t.Errorf("track = %d, want 1", track)
+	}
+}
+
+// Read is handed to the feed generator, which relies on ok=false to fall back
+// to the filename. An untagged file is the normal state of a fresh download,
+// not an error.
+func TestRead_UntaggedFileReportsNotOK(t *testing.T) {
+	dir := t.TempDir()
+	p := writeMP3(t, dir, "01 - Untagged.mp3")
+	if _, _, ok := Read(p); ok {
+		t.Error("an untagged file should report ok=false")
+	}
+}
+
+func TestRead_MissingFileReportsNotOK(t *testing.T) {
+	if _, _, ok := Read(filepath.Join(t.TempDir(), "nope.mp3")); ok {
+		t.Error("a missing file should report ok=false, not panic")
+	}
+}
+
+// Track frames are commonly "3/7". Taking the whole string would make the
+// number unparseable and lose the ordering.
+func TestRead_ParsesTrackOfTotal(t *testing.T) {
+	dir := t.TempDir()
+	writeMP3(t, dir, "03 - Third.mp3")
+	writeMP3(t, dir, "01 - First.mp3")
+	writeMP3(t, dir, "02 - Second.mp3")
+
+	if _, err := WriteDir(dir, Metadata{Album: "A"}); err != nil {
+		t.Fatalf("WriteDir: %v", err)
+	}
+	_, track, ok := Read(filepath.Join(dir, "03 - Third.mp3"))
+	if !ok {
+		t.Fatal("tags not readable")
+	}
+	if track != 3 {
+		t.Errorf("track = %d, want 3 (from a \"3/3\" frame)", track)
+	}
+}
+
+// ID3v2 is an MP3 convention; writing it into other containers produces
+// something no player reads, so other formats are skipped rather than corrupted.
+func TestWriteDir_SkipsNonMP3(t *testing.T) {
+	dir := t.TempDir()
+	writeMP3(t, dir, "01 - One.mp3")
+	if err := os.WriteFile(filepath.Join(dir, "02 - Two.opus"), []byte("not an mp3"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, "cover.jpg"), []byte("jpeg"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	results, err := WriteDir(dir, Metadata{Album: "A"})
+	if err != nil {
+		t.Fatalf("WriteDir: %v", err)
+	}
+	if len(results) != 1 || !strings.HasSuffix(results[0].File, ".mp3") {
+		t.Errorf("got %+v, want only the mp3", results)
+	}
+}
+
+func TestWriteDir_MissingDirectoryIsAnError(t *testing.T) {
+	if _, err := WriteDir(filepath.Join(t.TempDir(), "nope"), Metadata{}); err == nil {
+		t.Error("expected an error for a missing directory")
+	}
+}
+
+// A file with no track prefix should still get its metadata; only the track
+// number is absent.
+func TestWriteDir_HandlesUnnumberedFiles(t *testing.T) {
+	dir := t.TempDir()
+	writeMP3(t, dir, "Introduction.mp3")
+
+	results, err := WriteDir(dir, Metadata{Album: "Course", Artist: "Someone"})
+	if err != nil {
+		t.Fatalf("WriteDir: %v", err)
+	}
+	if results[0].Err != nil {
+		t.Fatalf("tagging failed: %v", results[0].Err)
+	}
+	title, track, ok := Read(filepath.Join(dir, "Introduction.mp3"))
+	if !ok || title != "Introduction" {
+		t.Errorf("title = %q ok = %v, want the filename stem", title, ok)
+	}
+	if track != 0 {
+		t.Errorf("track = %d, want 0 for an unnumbered file", track)
+	}
+}
+
+// Re-running the tagger must be safe; the pipeline is meant to be resumable.
+func TestWriteDir_IsIdempotent(t *testing.T) {
+	dir := t.TempDir()
+	writeMP3(t, dir, "01 - One.mp3")
+	md := Metadata{Album: "A", Artist: "B"}
+
+	for i := 0; i < 3; i++ {
+		if _, err := WriteDir(dir, md); err != nil {
+			t.Fatalf("pass %d: %v", i, err)
+		}
+	}
+	title, track, ok := Read(filepath.Join(dir, "01 - One.mp3"))
+	if !ok || title != "One" || track != 1 {
+		t.Errorf("after 3 passes: title=%q track=%d ok=%v", title, track, ok)
+	}
+}