allow selecting a CD drive from the command line

Add -d/--drive command-line option to arver and arver-discinfo. The new
option allows selecting the CD drive to read the TOC from.

The implementation follows the path of least resistance: get_disc_info()
was changed to accept two arguments instead of one, and its internal
logic became more complicated.

This should be simplified in the long run. Refactoring should also take
into account creating DiscInfo object with -t/--track-lengths option.

arver/__init__.py

@@ -1,5 +1,5 @@
 """Main ARver package."""
 
 APPNAME = 'ARver'
-VERSION = 'v1.4.0.dev1'
+VERSION = 'v1.4.0.dev2'
 URL = 'https://github.com/arcctgx/ARver'

arver/arver_discinfo.py

@@ -16,10 +16,17 @@ def _parse_args():
         derived from MusicBrainz disc ID. Fetch and display AccurateRip data
         of the disc.""")
 
-    parser.add_argument('-i',
-                        '--disc-id',
-                        metavar='disc_id',
-                        help='get disc TOC from MusicBrainz by disc ID')
+    toc_source = parser.add_mutually_exclusive_group()
+
+    toc_source.add_argument('-d',
+                            '--drive',
+                            metavar='device_path',
+                            help='read disc TOC from a CD in specified drive (e.g. /dev/sr0)')
+
+    toc_source.add_argument('-i',
+                            '--disc-id',
+                            metavar='disc_id',
+                            help='get disc TOC from MusicBrainz by disc ID query')
 
     parser.add_argument('-v', '--version', action='version', version=version_string())
 
@@ -28,7 +35,7 @@ def _parse_args():
 
 def main():
     args = _parse_args()
-    disc = get_disc_info(args.disc_id)
+    disc = get_disc_info(args.drive, args.disc_id)
 
     if disc is None:
         print('Failed to get disc info, exiting.')

arver/arver_main.py

@@ -36,6 +36,11 @@ def _parse_args():
 
     toc_source = parser.add_mutually_exclusive_group()
 
+    toc_source.add_argument('-d',
+                            '--drive',
+                            metavar='device_path',
+                            help='read disc TOC from a CD in specified drive (e.g. /dev/sr0)')
+
     toc_source.add_argument('-i',
                             '--disc-id',
                             metavar='disc_id',
@@ -87,7 +92,7 @@ def main():
     if args.track_lengths:
         disc = DiscInfo.from_track_lengths(rip.track_frames(), args.pregap_length, args.data_length)
     else:
-        disc = get_disc_info(args.disc_id)
+        disc = get_disc_info(args.drive, args.disc_id)
 
     if disc is None:
         print('Failed to get disc info, exiting.')

arver/disc/info.py

@@ -384,21 +384,26 @@ def fetch_accuraterip_data(self) -> None:
         self.accuraterip_data = fetcher.fetch()
 
 
-def get_disc_info(disc_id: Optional[str]) -> Optional[DiscInfo]:
+def get_disc_info(drive: Optional[str], disc_id: Optional[str]) -> Optional[DiscInfo]:
     """
-    Helper function for obtaining disc information.
-    If disc_id is None read CD TOC from the CD in drive.
-    Otherwise get TOC from specified MusicBrainz disc ID.
-    """
-    if disc_id is None:
-        disc_info = DiscInfo.from_cd()
-    else:
-        disc_info = DiscInfo.from_disc_id(disc_id)
+    Helper function for obtaining DiscInfo object.
 
-    if disc_info is None:
-        if disc_id is None:
+    drive   | disc ID | TOC source
+    --------|---------|------------------
+    None    | None    | default device
+    defined | None    | specified device
+    None    | defined | disc ID query
+    """
+    if (drive is None and disc_id is None) or drive is not None:
+        disc_info = DiscInfo.from_cd(drive)
+        if disc_info is None:
             print('Could not read disc. Is there a CD in the drive?')
-        else:
+        return disc_info
+
+    if disc_id is not None:
+        disc_info = DiscInfo.from_disc_id(disc_id)
+        if disc_info is None:
             print(f'Could not look up disc ID "{disc_id}", is it correct?')
+        return disc_info
 
-    return disc_info
+    return None