`urllib.urlretrieve` was using the correct extension in most cases -- I think
when the URL ended with .jpg -- but not in every case. This was leading to files
named just "cover" and not "cover.jpg" or something else sensible. In
particular, proxied URLs don't have .jpg extensions. This generates the filename
manually so the source image always has an extension.
Searching for `convert` or PIL has non-negligible performance overhead, so it's
preferable to only do it when really necessary. This way, the search is only
performed when ArtResizer.shared is accessed for the first time.
An earlier commit broke the call to art_for_album here (too few arguments).
I've also now propagated the maxwidth setting for the command to match the
import hook.
Fixed a number of issues with the changes to fetchart:
- Remove redundant fetches. This was making the Amazon source download every
image twice even when art resizing was not enabled!
- Restore local_only switch in plugin hook, which got lost in the shuffle at
some point.
- Don't replace the original image file in-place; use a temporary file instead.
This would clobber the original source image on the filesystem with the
downscaled version!
The previous method was to change self.__class__ dynamically to make __init__
instantiate different classes. This new way, which uses bare functions instead
of separate functor-like classes, instead just forwards the resize() call to
a module-global implementation based on self.method.
Additionally, the semantics of ArtResizer have changed. Clients now *always*
call resize() and proxy_url(), regardless of method. The method makes *one* of
these a no-op. This way, clients need not manually inspect which method is
being used.
artresizer.py instances an ArtResizer object that uses internally the PIL; ImageMagick
or a web proxy service to perform the resizing operations.
Because embedart works on input images located on filesystem it requires PIL or ImageMagick, whereas
fetchart is able to do the job with the fallback webproxy resizer.
This necessitated a slight refactoring in the plugin event handling mechanism.
Rather than loading all handlers up front and storing them in a module-scope
structure, we now scan for event handlers at every send(). This is probably
very slightly less efficient but allows for more flexible logic.
