feat: add track lookup by ISRC

Deezer's API supports GET /track/isrc:{isrc} as an alternative to
GET /track/{trackId}, letting callers look up a track directly by its
ISRC (International Standard Recording Code) instead of Deezer's own
numeric ID. This is the standard way cross-platform music tools match
the same recording across services that use different internal IDs.

Adds TrackService.getTrackByIsrc and TrackRequestFactory.getTrackByIsrc,
reusing the existing unauthenticated SimpleDeezerRequest wrapper (this
endpoint needs no access token, same as getTrack). Includes unit test,
WireMock-backed integration test, and a bruno-collection request for
manual testing, following the project's existing conventions.

Author: user4me

bruno-collection/opencollection.yml

@@ -33,6 +33,8 @@ request:
       value: "605632582"
     - name: track-id
       value: "541999"
+    - name: track-isrc
+      value: "USRC18207933"
 bundled: false
 extensions:
   ignore:

bruno-collection/track/get-track-by-isrc.yml

@@ -0,0 +1,15 @@
+info:
+  name: get-track-by-isrc
+  type: http
+  seq: 3
+
+http:
+  method: GET
+  url: "{{api-host}}/track/isrc:{{track-isrc}}"
+  auth: inherit
+
+settings:
+  encodeUrl: true
+  timeout: 0
+  followRedirects: true
+  maxRedirects: 5

src/integrationTest/java/io/github/yvasyliev/dz4j/TrackIT.java

@@ -45,6 +45,20 @@ void shouldReturnTrack(long trackId, String file) throws IOException {
         assertEquals(expected, deezerClient.track().getTrack(trackId));
     }
 
+    @Test
+    void shouldReturnTrackByIsrc() throws IOException {
+        var isrc = "USRC18207933";
+        var body = read("/response/track/get-track-maneater.json");
+        var expected = MAPPER.readValue(body, Track.class);
+
+        stubFor(get(urlPathTemplate("/track/isrc:{isrc}"))
+                .withPathParam("isrc", equalTo(isrc))
+                .willReturn(okJson(body))
+        );
+
+        assertEquals(expected, deezerClient.track().getTrackByIsrc(isrc));
+    }
+
     @Test
     void shouldUpdateTrack() throws IOException {
         var trackId = 541999L;

src/main/java/io/github/yvasyliev/dz4j/factory/TrackRequestFactory.java

@@ -4,6 +4,7 @@
 import io.github.yvasyliev.dz4j.model.Track;
 import io.github.yvasyliev.dz4j.request.DeezerRequest;
 import io.github.yvasyliev.dz4j.request.IdDeezerRequest;
+import io.github.yvasyliev.dz4j.request.SimpleDeezerRequest;
 import io.github.yvasyliev.dz4j.request.UpdateTrackDeezerRequest;
 import io.github.yvasyliev.dz4j.service.TrackService;
 import lombok.RequiredArgsConstructor;
@@ -26,6 +27,16 @@ public DeezerRequest<Track> getTrack(long trackId) {
         return new IdDeezerRequest<>(trackId, trackService::getTrack);
     }
 
+    /**
+     * Creates a request to get a track by its ISRC (International Standard Recording Code).
+     *
+     * @param isrc track ISRC
+     * @return request to get a track
+     */
+    public DeezerRequest<Track> getTrackByIsrc(String isrc) {
+        return new SimpleDeezerRequest<>(() -> trackService.getTrackByIsrc(isrc));
+    }
+
     /**
      * Creates a request to update a track.
      *

src/main/java/io/github/yvasyliev/dz4j/service/TrackService.java

@@ -24,6 +24,15 @@ public interface TrackService {
     @RequestLine("GET /track/{trackId}")
     CompletableFuture<Track> getTrack(@Param("trackId") long trackId);
 
+    /**
+     * Returns a track by its ISRC (International Standard Recording Code).
+     *
+     * @param isrc the track's ISRC
+     * @return a track
+     */
+    @RequestLine("GET /track/isrc:{isrc}")
+    CompletableFuture<Track> getTrackByIsrc(@Param("isrc") String isrc);
+
     /**
      * Updates a user's track information.
      *

src/test/java/io/github/yvasyliev/dz4j/factory/TrackRequestFactoryTest.java

@@ -34,6 +34,18 @@ void testGetTrack() {
         assertEquals(expected, actual);
     }
 
+    @Test
+    void testGetTrackByIsrc() {
+        var isrc = "USRC18207933";
+        var expected = Track.builder().isrc(isrc).build();
+
+        when(trackService.getTrackByIsrc(isrc)).thenReturn(CompletableFuture.completedFuture(expected));
+
+        var actual = trackRequestFactory.getTrackByIsrc(isrc).execute();
+
+        assertEquals(expected, actual);
+    }
+
     @Test
     void testUpdateTrack() {
         var trackId = 123L;