feat(api): GET /api/artists/{id} with nested albums

internal/api/library.go

@@ -91,9 +91,47 @@ func (h *handlers) handleGetAlbum(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, detail)
 }
 
-// handleGetArtist is implemented in Task 8.
+// handleGetArtist implements GET /api/artists/{id}. Returns artist + albums;
+// each album carries its own track_count (one count query per album, same
+// pattern as subsonic). At M1 sizes (albums-per-artist << 100) this is fine.
 func (h *handlers) handleGetArtist(w http.ResponseWriter, r *http.Request) {
-	writeErr(w, http.StatusNotImplemented, "not_implemented", "stub")
+	id, ok := parseUUID(chi.URLParam(r, "id"))
+	if !ok {
+		writeErr(w, http.StatusBadRequest, "bad_request", "invalid artist id")
+		return
+	}
+	q := dbq.New(h.pool)
+	artist, err := q.GetArtistByID(r.Context(), id)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			writeErr(w, http.StatusNotFound, "not_found", "artist not found")
+			return
+		}
+		h.logger.Error("api: get artist failed", "err", err)
+		writeErr(w, http.StatusInternalServerError, "server_error", "lookup failed")
+		return
+	}
+	albums, err := q.ListAlbumsByArtist(r.Context(), id)
+	if err != nil {
+		h.logger.Error("api: list albums by artist failed", "err", err)
+		writeErr(w, http.StatusInternalServerError, "server_error", "lookup failed")
+		return
+	}
+	refs := make([]AlbumRef, 0, len(albums))
+	for _, a := range albums {
+		count, cerr := q.CountTracksByAlbum(r.Context(), a.ID)
+		if cerr != nil {
+			h.logger.Error("api: count tracks failed", "err", cerr)
+			writeErr(w, http.StatusInternalServerError, "server_error", "lookup failed")
+			return
+		}
+		refs = append(refs, albumRefFrom(a, artist.Name, int(count), 0))
+	}
+	detail := ArtistDetail{
+		ArtistRef: artistRefFrom(artist, len(albums)),
+		Albums:    refs,
+	}
+	writeJSON(w, http.StatusOK, detail)
 }
 
 // handleListArtists is implemented in Task 9.

internal/api/library_test.go

@@ -164,3 +164,93 @@ func TestHandleGetAlbum_NotFound(t *testing.T) {
 		t.Errorf("status = %d, want 404", w.Code)
 	}
 }
+
+func TestHandleGetArtist_HappyPath(t *testing.T) {
+	h, pool := testHandlers(t)
+	truncateLibrary(t, pool)
+	artist := seedArtist(t, pool, "Beatles")
+	album1 := seedAlbum(t, pool, artist.ID, "Abbey Road", 1969)
+	album2 := seedAlbum(t, pool, artist.ID, "Let It Be", 1970)
+	seedTrack(t, pool, album1.ID, artist.ID, "Something", 3, 183_000)
+	seedTrack(t, pool, album2.ID, artist.ID, "Get Back", 1, 189_000)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/artists/"+uuidToString(artist.ID), nil)
+	w := httptest.NewRecorder()
+	newLibraryRouter(h).ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d body = %s", w.Code, w.Body.String())
+	}
+	var got ArtistDetail
+	if err := json.Unmarshal(w.Body.Bytes(), &got); err != nil {
+		t.Fatalf("decode: %v body=%s", err, w.Body.String())
+	}
+	if got.Name != "Beatles" {
+		t.Errorf("name = %q", got.Name)
+	}
+	if got.AlbumCount != 2 {
+		t.Errorf("album_count = %d, want 2", got.AlbumCount)
+	}
+	if len(got.Albums) != 2 {
+		t.Fatalf("albums len = %d, want 2", len(got.Albums))
+	}
+	// ListAlbumsByArtist orders by release_date then sort_title; Abbey Road (1969) first.
+	if got.Albums[0].Title != "Abbey Road" {
+		t.Errorf("first album = %q, want Abbey Road", got.Albums[0].Title)
+	}
+	for _, a := range got.Albums {
+		if a.ArtistName != "Beatles" {
+			t.Errorf("album.artist_name = %q", a.ArtistName)
+		}
+		if a.CoverURL == "" {
+			t.Error("album missing cover_url")
+		}
+		if a.TrackCount != 1 {
+			t.Errorf("album.track_count = %d, want 1", a.TrackCount)
+		}
+	}
+}
+
+func TestHandleGetArtist_NoAlbums(t *testing.T) {
+	h, pool := testHandlers(t)
+	truncateLibrary(t, pool)
+	artist := seedArtist(t, pool, "Solo")
+
+	req := httptest.NewRequest(http.MethodGet, "/api/artists/"+uuidToString(artist.ID), nil)
+	w := httptest.NewRecorder()
+	newLibraryRouter(h).ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d", w.Code)
+	}
+	var got ArtistDetail
+	_ = json.Unmarshal(w.Body.Bytes(), &got)
+	if got.Albums == nil {
+		t.Error("albums = nil, want []")
+	}
+	if got.AlbumCount != 0 {
+		t.Errorf("album_count = %d, want 0", got.AlbumCount)
+	}
+}
+
+func TestHandleGetArtist_BadUUID(t *testing.T) {
+	h, _ := testHandlers(t)
+	req := httptest.NewRequest(http.MethodGet, "/api/artists/not-a-uuid", nil)
+	w := httptest.NewRecorder()
+	newLibraryRouter(h).ServeHTTP(w, req)
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("status = %d, want 400", w.Code)
+	}
+}
+
+func TestHandleGetArtist_NotFound(t *testing.T) {
+	h, pool := testHandlers(t)
+	truncateLibrary(t, pool)
+	req := httptest.NewRequest(http.MethodGet,
+		"/api/artists/00000000-0000-0000-0000-000000000001", nil)
+	w := httptest.NewRecorder()
+	newLibraryRouter(h).ServeHTTP(w, req)
+	if w.Code != http.StatusNotFound {
+		t.Errorf("status = %d, want 404", w.Code)
+	}
+}