Discogs (and other individual plugins) should return a penalty between
0.0 and 0.1, which will be multiplied by the general source weight. This
allows individual plugins to be weighted against relative to each other,
and amplified together against other penalty categories (track, title,
etc.)
Some albums have a single disc with positions like I, II, III, IV, etc.
Previously beets thought each track on these albums was a new medium.
Now we assume that if there is no explicit medium index and the ordinal
of an alpha medium does not appear to be sequential (e.g. A, B, C) that
the medium is actually the medium index.
This is a refactor of the plugin developed by `imenem`.
- Pass `artist`, `album` and `va_likely` to `candidates()` so that
plugins don't have to work this out from `items` all over again.
- Pass `artist` and `title` to `item_candidates()`.
- Silence spurious `urllib3` info log lines.
- Use a proper "beets" user agent with `discogs_client`.
- Remove `abstract_search` plugin. It seems unnecessary. How many
music databases are there? How many will beets support? How much
common code might there be between them? We can add some abstraction
if or when more databases are supported.
- Derive more AlbumInfo and TrackInfo properties from discogs Release
objects, especially album ID so that beets doesn't just use the first
release and think all subsequent releases are duplicates.
- Add basic documentation, doc strings and code comments.
- Sanitise search query. Remove non-word characters and medium info that
might filter out good search results.
- Use artist `join` strings from discogs Release object when an album
or track has multiple artists.
- Don't rely on discogs track position, which is unreliable. But tracks
are in order, so we can recalculate medium and medium_index as long as
we can extract a consistent medium across tracks from the position.
- Add "various" as a known signal to indicate various artists.
- Prevent `chroma` plugin from returning a a huge track distance for any
track that is missing an ID (e.g. all discog tracks).
- `TrackInfo.index` should be the release index (calculated by beets),
not the medium index (derived from discogs track position).
- Add `AlbumInfo.data_source`. It's "Unknown" by default which is shown
in red when displaying a suggested or selected match. The built in
auto tagger sets it to "MusicBrainz" which is shown in green. Anything
else (e.g. "Discogs") is shown in yellow.
- Remove double spaces from album titles (bad data from Discogs).
This slight modification to the selection algorithm avoids the situation in
which too many objects are chosen for a given artist and fewer than N objects
are eventually returned. We do this by implementing "selection without
replacement" literally: we choose objects one at a time and pop them from the
population when they are selected.
The main change here, aside from documentation/naming updates, is that we skip
"duplicates" that arise from albums/tracks that are missing their MBIDs.
