Everything now uses bog-standard Python dataclasses, with Pydantic
providing validation and type conversion through separate classes using
its type adapter feature. It's also possible to define your classes
using Pydantic's own model type directly, making the type adapter
unnecessary, but I didn't want to do things that way because no actual
validation is needed when constructing a Song instance for example.
Having Pydantic do its thing only on-demand was preferable.
I tried a number of validation libraries before settling on Pydantic for
this. It's not the fastest option out there (msgspec is I think), but it
makes adding support for third-party types like yarl.URL really easy, it
generates a nice clean JSON Schema which is easy enough to adjust to my
requirements through its GenerateJsonSchema hooks, and raw speed isn't
all that important anyway since this is a single-user desktop program
that reads its configuration file once on startup.
Also, MessagePack is now mandatory if you're caching to an external
service. It just didn't make a whole lot sense to explicitly install
mpd-now-playable's Redis or Memcached support and then use pickling with
them.
With all this fussing around done, I'm probably finally ready to
actually use that configuration file to configure new features! Yay!
python-mpd2 unreliably returns either a single value or a list of
values for commands like currentsong, which is super fun if you're
trying to write type stubs for it that statically describe its
behaviour. Whee.
Anyway, I ended up changing my internal song model to always use lists
for tags like artist and genre which are likely to have multiple values.
There's some finagling involved in massaging python-mpd2's output into
lists every time. However it's much nicer to work with an object that
always has a list of artists, even if it's a list of one or zero
artists, rather than an object that can have a single artist, a list of
multiple artists, or a null. So it's worth it.
The MPNowPlayingInfoCenter in MacOS only works with single string values
for these tags, not lists, so we have to join the artists and such into
a single string for its consumption. I'm using commas for the separator
at the moment, but I may make this a config option later on if there's
interest.
The new config file currently only configures the same options that were
already available through environment variables. However I have ideas
for additional features that would be much nicer to support using a
structured configuration format like TOML rather than environment
variables, so config files exist now!
The previous environment variables are still supported and will be used
if you don't have a config file. I plan to keep supporting the MPD_HOST
and MPD_PORT environment variables forever since they're shared with
other MPD clients such as mpc, but I may eventually drop the environment
variables specific to mpd-now-playable in a future release.
I still don't totally understand when MusicBrainz uses a track ID and
when it uses a release track ID - they're both displayed as the
"MusicBrainz Track ID" tag in Picard, despite being treated as different
tags by everything else - but supporting both is easy enough.
