Refactor musicbrainz to reduce cognitive complexity

[snejus]

MusicBrainz Plugin Refactor

Summary

A broad internal refactor of beetsplug/musicbrainz.py and its test suite. No user-facing behaviour changes are intended. The goal is to make parsing logic easier to understand, test, and maintain.

This PR halves the cognitive complexity in musicbrainz plugin:

Before

$ complexipy beetsplug/musicbrainz.py
🧠 Total Cognitive Complexity: 181
1 file analyzed in 0.0116 seconds

After

$ complexipy beetsplug/musicbrainz.py
🧠 Total Cognitive Complexity: 93
1 file analyzed in 0.0097 seconds

---

Production Code Changes

Parsing Decomposition

The monolithic album_info method is broken into focused @staticmethod helpers, each returning a typed TypedDict:

Method	Responsibility
_parse_artist_credits	Replaces _flatten_artist_credit / _multi_artist_credit
_parse_release_group	albumtype, original_year, etc.
_parse_label_infos	label, catalognum
_parse_genres	Genre list
_parse_external_ids	Third-party IDs from URL relations
_parse_work_relations	Composer / lyricist credits
_parse_artist_relations	Arranger / remixer credits
get_tracks_from_medium	Per-medium track iteration

Each helper returns a typed TypedDict, making the data contract explicit and the code easier to compose with **kwargs unpacking into AlbumInfo / TrackInfo.

Other Simplifications

• _set_date_str (mutable, side-effecting) is replaced by _get_date, a pure function returning (year, month, day).
• _preferred_release_event and _preferred_alias are simplified.
• Three @cached_property entries (ignored_media, ignore_data_tracks, ignore_video_tracks) are moved up to sit with other class-level properties.

---

Test Infrastructure Changes

Factory Layer (test/plugins/factories/musicbrainz.py)

factory-boy / pytest-factoryboy are added as test dependencies. A new factory module introduces composable, deterministic factories:

• AliasFactory, ArtistFactory, ArtistCreditFactory
• RecordingFactory, TrackFactory, MediumFactory
• ReleaseGroupFactory, ReleaseFactory

Factories use a shared _IdFactory base class that generates stable, predictable UUIDs (00000000-0000-0000-0000-000000001001, etc.) based on an id_base + index pair. This makes assertions on IDs readable and deterministic without hard-coded magic strings.

Before:

recording = {
    "title": "foo",
    "id": "bar",
    "length": 42,
    "artist_credit": [{"artist": {"name": "some-artist", "id": "some-id", ...}, ...}],
    ...
}

After:

recording = recording_factory(title="foo", length=42)

Test Consolidation

Many small single-field assertion tests that each constructed an identical release are collapsed into a single test_parse_release snapshot assertion, covering all AlbumInfo fields at once. This reduces redundant fixture setup and makes it immediately obvious what the full output of album_info looks like for a default release.

The hand-rolled _make_release / _make_recording helpers are removed entirely, replaced by composable factory calls using factory-boy's __ double-underscore traversal syntax:

# Before
release = self._make_release(date="1987-03-31")

# After
release = release_factory(release_group__first_release_date="1987-03-31")

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[Copilot]

Pull request overview

grug see PR try break big MusicBrainz parse monster into small helpers, plus new test factories, to make brain hurt less. Goal say “no user-facing change”, but grug spot few behavior leaks and test factory sharp edge.

Changes:

• Split MusicBrainzPlugin.album_info parsing into smaller helpers and add TypedDict contracts.
• Add factory-boy based factories for MusicBrainz payloads and refactor tests to use them (plus one snapshot-style assertion).
• Add pytest-factoryboy dependency (and lockfile updates).

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
beetsplug/musicbrainz.py	Refactor parsing into helpers; new date/alias logic; new medium/track iteration helper.
test/plugins/test_musicbrainz.py	Switch tests to new factories and consolidate many assertions into one snapshot-style test.
test/plugins/factories/musicbrainz.py	New deterministic-ish payload factories for MusicBrainz structures.
test/plugins/factories/init.py	New package marker for factories.
pyproject.toml	Add pytest-factoryboy dependency.
poetry.lock	Lock dependency graph for new test deps.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.99%. Comparing base (ff9f93e) to head (0a40300).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6530   +/-   ##
=======================================
  Coverage   70.99%   70.99%           
=======================================
  Files         150      150           
  Lines       19124    19124           
  Branches     3078     3078           
=======================================
  Hits        13577    13577           
  Misses       4896     4896           
  Partials      651      651           

Files with missing lines	Coverage Δ
beetsplug/_utils/musicbrainz.py	97.29% <100.00%> (ø)

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[aereaux]

I haven't had a chance to look too closely at the code but at least on my library this doesn't cause any unexpected tagging changes!