Support fetching cover art images from the Cover Art Archive

Add option `--cover-art` to `whipper cd rip` command which accepts three values:
- `file`: save the downloaded cover image as standalone file in the rip folder (named `cover.jpg`)
- `embed`: embed the download cover image into all the ripped audio tracks (no standalone file will be kept)
- `complete`: save standalone cover image as standalone file and embed it into all the ripped audio tracks (`file` + `embed`)

Every cover art is fetched from the Cover Art Archive as JPEG thumbnail with a maximum dimension of 500px.
Other supported values for the thumbnails are 250, 500 and 1200 (currently only some images have a corresponding 1200px sized thumbnail).

This feature introduces an optional dependency on the `Pillow` module which is required for the decoding of the cover file (required by the `embed` and `complete` option values).

Problem:
- EmbedPicTureTask shouldn't be a task.

Signed-off-by: ABCbum <kimlong221002@gmail.com>
Co-authored-by: JoeLametta <JoeLametta@users.noreply.github.com>
Signed-off-by: JoeLametta <JoeLametta@users.noreply.github.com>

whipper/command/cd.py

@@ -20,6 +20,7 @@
 
 import argparse
 import cdio
+import importlib.util
 import os
 import glob
 import logging
@@ -290,6 +291,14 @@ Log files will log the path to tracks relative to this directory.
                                  help="whether to continue ripping if "
                                  "the disc is a CD-R",
                                  default=False)
+        self.parser.add_argument('-C', '--cover-art',
+                                 action="store", dest="fetch_cover_art",
+                                 help="Fetch cover art and save it as "
+                                 "standalone file, embed into FLAC files "
+                                 "or perform both actions: file, embed, "
+                                 "complete option values respectively",
+                                 choices=['file', 'embed', 'complete'],
+                                 default=None)
 
     def handle_arguments(self):
         self.options.output_directory = os.path.expanduser(
@@ -342,6 +351,19 @@ Log files will log the path to tracks relative to this directory.
             logger.info("creating output directory %s", dirname)
             os.makedirs(dirname)
 
+        self.coverArtPath = None
+        if (self.options.fetch_cover_art in {"embed", "complete"} and
+                importlib.util.find_spec("PIL") is None):
+            logger.warning("the cover art option '%s' won't be honored "
+                           "because the 'pillow' module isn't available",
+                           self.options.fetch_cover_art)
+        elif self.options.fetch_cover_art in {"file", "embed", "complete"}:
+            self.coverArtPath = self.program.getCoverArt(
+                                    dirname,
+                                    self.program.metadata.mbid)
+        if self.options.fetch_cover_art == "file":
+            self.coverArtPath = None  # NOTE: avoid image embedding (hacky)
+
         # FIXME: turn this into a method
         def _ripIfNotRipped(number):
             logger.debug('ripIfNotRipped for track %d', number)
@@ -412,7 +434,8 @@ Log files will log the path to tracks relative to this directory.
                                               what='track %d of %d%s' % (
                                                   number,
                                                   len(self.itable.tracks),
-                                                  extra))
+                                                  extra),
+                                              coverArtPath=self.coverArtPath)
                         break
                     # FIXME: catching too general exception (Exception)
                     except Exception as e:
@@ -474,6 +497,11 @@ Log files will log the path to tracks relative to this directory.
                 continue
             _ripIfNotRipped(i + 1)
 
+        if (self.options.fetch_cover_art == "embed" and
+                self.coverArtPath is not None):
+            logger.debug('deleting cover art file at: %r', self.coverArtPath)
+            os.remove(self.coverArtPath)
+
         logger.debug('writing cue file for %r', discName)
         self.program.writeCue(discName)