feat(lidarr): MusicBrainz track-to-album resolver

Add musicbrainz_best_album() that resolves an artist+track pair to its
best studio album via the MusicBrainz search API, with a 1 req/sec
courtesy rate-limiter. Prefers plain studio albums over compilations,
singles, and live releases; falls back to any release group when no
studio album is found. Never raises — returns None on any failure.

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

musicfetch

@@ -12,6 +12,7 @@ import os
 import re
 import subprocess
 import sys
+import time
 from concurrent.futures import ThreadPoolExecutor
 from dataclasses import dataclass, field
 from typing import Optional
@@ -126,6 +127,69 @@ def _artist_to_hit(artist: dict) -> Hit:
     )
 
 
+MUSICBRAINZ_URL = "https://musicbrainz.org/ws/2"
+MB_HEADERS = {"User-Agent": "musicfetch/2.0 (https://github.com/; personal music fetcher)"}
+_mb_last_call = 0.0
+
+
+def _mb_rate_limit():
+    """Courtesy ~1 req/sec to MusicBrainz."""
+    global _mb_last_call
+    elapsed = time.time() - _mb_last_call
+    if elapsed < 1.0:
+        time.sleep(1.0 - elapsed)
+    _mb_last_call = time.time()
+
+
+def _mb_artist_credit(credit) -> str:
+    """First credited artist name only (ignore featured/secondary)."""
+    if credit and isinstance(credit, list) and isinstance(credit[0], dict):
+        return credit[0].get("name") or (credit[0].get("artist") or {}).get("name", "")
+    return ""
+
+
+def musicbrainz_best_album(artist: str, track: str, timeout: int = 8) -> Optional[dict]:
+    """Resolve 'artist - track' to its best studio album via MusicBrainz.
+    Returns {album_title, artist, year, rg_mbid} or None. Never raises."""
+    query = f'artist:"{artist}" AND recording:"{track}"'
+    try:
+        _mb_rate_limit()
+        resp = requests.get(
+            f"{MUSICBRAINZ_URL}/recording",
+            params={"query": query, "fmt": "json", "limit": 10},
+            headers=MB_HEADERS, timeout=timeout,
+        )
+        resp.raise_for_status()
+        data = resp.json()
+    except Exception as e:  # noqa: BLE001 — degrade to fallback on any failure
+        dbg(f"MusicBrainz lookup failed: {e}")
+        return None
+
+    # candidate = (is_studio, date_sortkey, title, artist, year, mbid)
+    candidates = []
+    for rec in data.get("recordings", []):
+        rec_artist = _mb_artist_credit(rec.get("artist-credit"))
+        for rel in rec.get("releases", []):
+            rg = rel.get("release-group") or {}
+            title = rg.get("title") or rel.get("title") or ""
+            if not title:
+                continue
+            mbid = rg.get("id") or ""
+            primary = rg.get("primary-type") or ""
+            secondary = rg.get("secondary-types") or []
+            date = rel.get("date") or rg.get("first-release-date") or ""
+            is_studio = primary == "Album" and not secondary
+            candidates.append((is_studio, date or "9999", title, rec_artist, date[:4], mbid))
+
+    if not candidates:
+        return None
+    pool = [c for c in candidates if c[0]] or candidates
+    pool.sort(key=lambda c: c[1])  # earliest date first
+    _, _, title, art, year, mbid = pool[0]
+    dbg(f"MusicBrainz resolved '{artist} - {track}' -> '{title}' ({year}) mbid={mbid}")
+    return {"album_title": title, "artist": art or artist, "year": year, "rg_mbid": mbid}
+
+
 def _split_query(query: str) -> tuple[str, Optional[str]]:
     """Split a Shazam-style 'Artist - Track' on the first ' - '.
     Returns (artist, track) or (term, None) when there is no separator."""

tests/test_musicbrainz.py

@@ -0,0 +1,79 @@
+import server.mf  # noqa: F401
+import musicfetch_core as mf
+
+
+class _FakeResp:
+    def __init__(self, payload):
+        self._payload = payload
+    def raise_for_status(self):
+        pass
+    def json(self):
+        return self._payload
+
+
+MB_PAYLOAD = {
+    "recordings": [
+        {
+            "artist-credit": [{"name": "Daft Punk"}],
+            "releases": [
+                {"date": "2001",
+                 "release-group": {"id": "single-mbid", "title": "Harder, Better, Faster, Stronger",
+                                   "primary-type": "Single", "secondary-types": []}},
+                {"date": "2002",
+                 "release-group": {"id": "comp-mbid", "title": "Musique, Vol. 1",
+                                   "primary-type": "Album", "secondary-types": ["Compilation"]}},
+                {"date": "2001",
+                 "release-group": {"id": "48117b90-a16e-34ca-a514-19c702df1158",
+                                   "title": "Discovery", "primary-type": "Album",
+                                   "secondary-types": []}},
+            ],
+        }
+    ]
+}
+
+
+def test_picks_studio_album_over_single_and_comp(monkeypatch):
+    monkeypatch.setattr(mf.requests, "get", lambda *a, **k: _FakeResp(MB_PAYLOAD))
+    monkeypatch.setattr(mf.time, "sleep", lambda *_: None)
+    out = mf.musicbrainz_best_album("Daft Punk", "Harder Better Faster Stronger")
+    assert out["album_title"] == "Discovery"
+    assert out["artist"] == "Daft Punk"
+    assert out["year"] == "2001"
+    assert out["rg_mbid"] == "48117b90-a16e-34ca-a514-19c702df1158"
+
+
+def test_returns_none_on_empty(monkeypatch):
+    monkeypatch.setattr(mf.requests, "get", lambda *a, **k: _FakeResp({"recordings": []}))
+    monkeypatch.setattr(mf.time, "sleep", lambda *_: None)
+    assert mf.musicbrainz_best_album("Nobody", "Nothing") is None
+
+
+def test_returns_none_on_exception(monkeypatch):
+    def boom(*a, **k):
+        raise mf.requests.exceptions.RequestException("network down")
+    monkeypatch.setattr(mf.requests, "get", boom)
+    monkeypatch.setattr(mf.time, "sleep", lambda *_: None)
+    assert mf.musicbrainz_best_album("Daft Punk", "Discovery") is None
+
+
+def test_falls_back_to_any_releasegroup_when_no_studio(monkeypatch):
+    payload = {"recordings": [{"artist-credit": [{"name": "X"}], "releases": [
+        {"date": "2010", "release-group": {"id": "live1", "title": "Live Thing",
+                                           "primary-type": "Album", "secondary-types": ["Live"]}},
+    ]}]}
+    monkeypatch.setattr(mf.requests, "get", lambda *a, **k: _FakeResp(payload))
+    monkeypatch.setattr(mf.time, "sleep", lambda *_: None)
+    out = mf.musicbrainz_best_album("X", "Y")
+    assert out["album_title"] == "Live Thing"
+
+
+def test_first_artist_credit_only(monkeypatch):
+    payload = {"recordings": [{"artist-credit": [{"name": "SLVMLORD"}, {"name": "Travis Bradley"}],
+                              "releases": [{"date": "2025",
+                                            "release-group": {"id": "x", "title": "Album X",
+                                                              "primary-type": "Album",
+                                                              "secondary-types": []}}]}]}
+    monkeypatch.setattr(mf.requests, "get", lambda *a, **k: _FakeResp(payload))
+    monkeypatch.setattr(mf.time, "sleep", lambda *_: None)
+    out = mf.musicbrainz_best_album("SLVMLORD", "Under My Skin")
+    assert out["artist"] == "SLVMLORD"