feat: add MusicBrainz fallback to !similar and !tags commands

Remove early return on missing Last.fm API key. Both commands now
fall back to MusicBrainz (mb_search_artist -> mb_artist_tags ->
mb_find_similar_recordings) when no API key is configured or when
Last.fm returns empty results. Same pattern used by discover_similar.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/lastfm.py

@@ -198,9 +198,6 @@ async def cmd_similar(bot, message):
         !similar play <artist> Queue a similar track for named artist
     """
     api_key = _get_api_key(bot)
-    if not api_key:
-        await bot.reply(message, "Last.fm API key not configured")
-        return
 
     parts = message.text.split(None, 2)
     # !similar play [artist]
@@ -223,38 +220,86 @@ async def cmd_similar(bot, message):
             await bot.reply(message, "Nothing playing and no artist given")
             return
 
-    # Try track-level similarity first if we have both artist + title
+    # -- Last.fm path --
     similar = []
-    if artist and title:
-        similar = await loop.run_in_executor(
-            None, _get_similar_tracks, api_key, artist, title,
-        )
+    similar_artists = []
+    if api_key:
+        # Try track-level similarity first if we have both artist + title
+        if artist and title:
+            similar = await loop.run_in_executor(
+                None, _get_similar_tracks, api_key, artist, title,
+            )
+        # Fall back to artist-level similarity
+        if not similar:
+            search_artist = artist or title
+            similar_artists = await loop.run_in_executor(
+                None, _get_similar_artists, api_key, search_artist,
+            )
 
-    # Fall back to artist-level similarity
-    if not similar:
+    # -- MusicBrainz fallback --
+    mb_results = []
+    if not similar and not similar_artists:
         search_artist = artist or title
-        similar_artists = await loop.run_in_executor(
-            None, _get_similar_artists, api_key, search_artist,
-        )
-        if not similar_artists:
-            await bot.reply(message, f"No similar artists found for '{search_artist}'")
+        try:
+            from plugins._musicbrainz import (
+                mb_artist_tags,
+                mb_find_similar_recordings,
+                mb_search_artist,
+            )
+            mbid = await loop.run_in_executor(
+                None, mb_search_artist, search_artist,
+            )
+            if mbid:
+                tags = await loop.run_in_executor(None, mb_artist_tags, mbid)
+                if tags:
+                    mb_results = await loop.run_in_executor(
+                        None, mb_find_similar_recordings, search_artist,
+                        tags, 20,
+                    )
+        except Exception:
+            log.warning("lastfm: MusicBrainz fallback failed", exc_info=True)
+
+    # -- Track-level results (Last.fm) --
+    if similar:
+        if play_mode:
+            pick = random.choice(similar[:10])
+            pick_artist = pick.get("artist", {}).get("name", "")
+            pick_title = pick.get("name", "")
+            search = f"{pick_artist} {pick_title}".strip()
+            if not search:
+                await bot.reply(message, "No playable result found")
+                return
+            message.text = f"!play {search}"
+            music_mod = bot.registry._modules.get("music")
+            if music_mod:
+                await music_mod.cmd_play(bot, message)
             return
 
+        lines = [f"Similar to {artist} - {title}:"]
+        for t in similar[:8]:
+            t_artist = t.get("artist", {}).get("name", "")
+            t_name = t.get("name", "?")
+            match = _fmt_match(t.get("match", ""))
+            suffix = f" ({match})" if match else ""
+            lines.append(f"  {t_artist} - {t_name}{suffix}")
+        await bot.long_reply(message, lines, label="similar tracks")
+        return
+
+    # -- Artist-level results (Last.fm) --
+    if similar_artists:
+        search_artist = artist or title
         if play_mode:
-            # Pick a random similar artist and search YouTube
             pick = random.choice(similar_artists[:10])
             pick_name = pick.get("name", "")
             if not pick_name:
                 await bot.reply(message, "No playable result found")
                 return
-            # Inject a !play command with a YouTube search
             message.text = f"!play {pick_name}"
             music_mod = bot.registry._modules.get("music")
             if music_mod:
                 await music_mod.cmd_play(bot, message)
             return
 
-        # Display similar artists
         lines = [f"Similar to {search_artist}:"]
         for a in similar_artists[:8]:
             name = a.get("name", "?")
@@ -264,30 +309,27 @@ async def cmd_similar(bot, message):
         await bot.long_reply(message, lines, label="similar artists")
         return
 
-    # Track-level results
-    if play_mode:
-        pick = random.choice(similar[:10])
-        pick_artist = pick.get("artist", {}).get("name", "")
-        pick_title = pick.get("name", "")
-        search = f"{pick_artist} {pick_title}".strip()
-        if not search:
-            await bot.reply(message, "No playable result found")
+    # -- MusicBrainz results --
+    if mb_results:
+        search_artist = artist or title
+        if play_mode:
+            pick = random.choice(mb_results[:10])
+            search = f"{pick['artist']} {pick['title']}".strip()
+            message.text = f"!play {search}"
+            music_mod = bot.registry._modules.get("music")
+            if music_mod:
+                await music_mod.cmd_play(bot, message)
             return
-        message.text = f"!play {search}"
-        music_mod = bot.registry._modules.get("music")
-        if music_mod:
-            await music_mod.cmd_play(bot, message)
+
+        lines = [f"Similar to {search_artist}:"]
+        for r in mb_results[:8]:
+            lines.append(f"  {r['artist']} - {r['title']}")
+        await bot.long_reply(message, lines, label="similar tracks")
         return
 
-    # Display similar tracks
-    lines = [f"Similar to {artist} - {title}:"]
-    for t in similar[:8]:
-        t_artist = t.get("artist", {}).get("name", "")
-        t_name = t.get("name", "?")
-        match = _fmt_match(t.get("match", ""))
-        suffix = f" ({match})" if match else ""
-        lines.append(f"  {t_artist} - {t_name}{suffix}")
-    await bot.long_reply(message, lines, label="similar tracks")
+    # Nothing found
+    search_artist = artist or title
+    await bot.reply(message, f"No similar artists found for '{search_artist}'")
 
 
 @command("tags", help="Music: !tags [artist] -- show genre tags")
@@ -299,9 +341,6 @@ async def cmd_tags(bot, message):
         !tags <artist>     Tags for named artist
     """
     api_key = _get_api_key(bot)
-    if not api_key:
-        await bot.reply(message, "Last.fm API key not configured")
-        return
 
     parts = message.text.split(None, 1)
     query = parts[1].strip() if len(parts) > 1 else ""
@@ -318,9 +357,28 @@ async def cmd_tags(bot, message):
             await bot.reply(message, "Nothing playing and no artist given")
             return
 
-    tags = await loop.run_in_executor(
-        None, _get_top_tags, api_key, artist,
-    )
+    # -- Last.fm path --
+    tags = []
+    if api_key:
+        tags = await loop.run_in_executor(
+            None, _get_top_tags, api_key, artist,
+        )
+
+    # -- MusicBrainz fallback --
+    if not tags:
+        try:
+            from plugins._musicbrainz import mb_artist_tags, mb_search_artist
+            mbid = await loop.run_in_executor(None, mb_search_artist, artist)
+            if mbid:
+                mb_tags = await loop.run_in_executor(
+                    None, mb_artist_tags, mbid,
+                )
+                if mb_tags:
+                    await bot.reply(message, f"{artist}: {', '.join(mb_tags)}")
+                    return
+        except Exception:
+            log.warning("lastfm: MusicBrainz tag fallback failed",
+                        exc_info=True)
 
     if not tags:
         await bot.reply(message, f"No tags found for '{artist}'")

tests/test_lastfm.py

@@ -339,12 +339,56 @@ class TestFmtMatch:
 
 
 class TestCmdSimilar:
-    def test_no_api_key(self):
+    def test_no_api_key_mb_fallback(self):
+        """No API key falls back to MusicBrainz for similar results."""
         bot = _FakeBot(api_key="")
         msg = _Msg(text="!similar Tool")
-        with patch.dict("os.environ", {}, clear=True):
+        mb_picks = [{"artist": "MB Artist", "title": "MB Song"}]
+        with patch.dict("os.environ", {}, clear=True), \
+             patch("plugins._musicbrainz.mb_search_artist",
+                   return_value="mbid-123"), \
+             patch("plugins._musicbrainz.mb_artist_tags",
+                   return_value=["rock", "metal"]), \
+             patch("plugins._musicbrainz.mb_find_similar_recordings",
+                   return_value=mb_picks):
             asyncio.run(_mod.cmd_similar(bot, msg))
-        assert any("not configured" in r for r in bot.replied)
+        assert any("Similar to Tool" in r for r in bot.replied)
+        assert any("MB Artist" in r for r in bot.replied)
+
+    def test_no_api_key_mb_no_results(self):
+        """No API key + MusicBrainz returns nothing shows 'no similar'."""
+        bot = _FakeBot(api_key="")
+        msg = _Msg(text="!similar Tool")
+        with patch.dict("os.environ", {}, clear=True), \
+             patch("plugins._musicbrainz.mb_search_artist",
+                   return_value=None):
+            asyncio.run(_mod.cmd_similar(bot, msg))
+        assert any("No similar artists" in r for r in bot.replied)
+
+    def test_no_api_key_play_mode(self):
+        """No API key + play mode delegates to cmd_play via MB results."""
+        bot = _FakeBot(api_key="")
+        msg = _Msg(text="!similar play Tool")
+        mb_picks = [{"artist": "MB Band", "title": "MB Track"}]
+        play_called = []
+
+        async def fake_play(b, m):
+            play_called.append(m.text)
+
+        music_mod = MagicMock()
+        music_mod.cmd_play = fake_play
+        bot.registry._modules["music"] = music_mod
+
+        with patch.dict("os.environ", {}, clear=True), \
+             patch("plugins._musicbrainz.mb_search_artist",
+                   return_value="mbid-123"), \
+             patch("plugins._musicbrainz.mb_artist_tags",
+                   return_value=["rock"]), \
+             patch("plugins._musicbrainz.mb_find_similar_recordings",
+                   return_value=mb_picks):
+            asyncio.run(_mod.cmd_similar(bot, msg))
+        assert len(play_called) == 1
+        assert "MB Band" in play_called[0]
 
     def test_no_artist_nothing_playing(self):
         bot = _FakeBot()
@@ -468,12 +512,29 @@ class TestCmdSimilar:
 
 
 class TestCmdTags:
-    def test_no_api_key(self):
+    def test_no_api_key_mb_fallback(self):
+        """No API key falls back to MusicBrainz for tags."""
         bot = _FakeBot(api_key="")
         msg = _Msg(text="!tags Tool")
-        with patch.dict("os.environ", {}, clear=True):
+        with patch.dict("os.environ", {}, clear=True), \
+             patch("plugins._musicbrainz.mb_search_artist",
+                   return_value="mbid-123"), \
+             patch("plugins._musicbrainz.mb_artist_tags",
+                   return_value=["rock", "progressive metal", "art rock"]):
             asyncio.run(_mod.cmd_tags(bot, msg))
-        assert any("not configured" in r for r in bot.replied)
+        assert any("Tool:" in r for r in bot.replied)
+        assert any("rock" in r for r in bot.replied)
+        assert any("progressive metal" in r for r in bot.replied)
+
+    def test_no_api_key_mb_no_results(self):
+        """No API key + MusicBrainz returns nothing shows 'no tags'."""
+        bot = _FakeBot(api_key="")
+        msg = _Msg(text="!tags Obscure")
+        with patch.dict("os.environ", {}, clear=True), \
+             patch("plugins._musicbrainz.mb_search_artist",
+                   return_value=None):
+            asyncio.run(_mod.cmd_tags(bot, msg))
+        assert any("No tags found" in r for r in bot.replied)
 
     def test_no_artist_nothing_playing(self):
         bot = _FakeBot()