Add tool to fetch album art from the Cover Art Archive

diff --git a/caa-fetcher.py b/caa-fetcher.py
new file mode 100755 (executable)
index 0000000..5c23107
--- /dev/null
+++ b/caa-fetcher.py
@@ -0,0 +1,75 @@
+#!/usr/bin/env python
+#
+# Copyright © 2018 Nick Bowler
+#
+# Tool to fetch album art for a release from the Cover Art Archive.
+#
+# License WTFPL2: Do What The Fuck You Want To Public License, version 2.
+# This is free software: you are free to do what the fuck you want to.
+# There is NO WARRANTY, to the extent permitted by law.
+
+from pathlib import Path
+import musicbrainzngs
+import argparse
+import tempfile
+import sys
+import os
+
+progname = "caa-fetcher"
+version = "0"
+musicbrainzngs.set_useragent(progname, version)
+
+parser = argparse.ArgumentParser(
+    description='Download album artwork from the Cover Art Archive'
+)
+
+class VersionAction(argparse.Action):
+    def __init__(self, **kw):
+        super().__init__(nargs=0, help="show a version message and exit", **kw)
+    def __call__(self, parser, namespace, values, option_string=None):
+        print("%s %s" % (progname, version))
+        print('''Copyright © 2018 Nick Bowler
+License WTFPL2: Do What The Fuck You Want To Public License, version 2.
+This is free software: you are free to do what the fuck you want to.
+There is NO WARRANTY, to the extent permitted by law.''')
+        sys.exit(0)
+parser.add_argument('--version', action=VersionAction)
+
+parser.add_argument('-o', '--output-directory', metavar='DIR',
+                    help='''downloaded files are written to DIR, which is
+                            created if it does not exists.  Default: .''')
+parser.add_argument('-r', '--release-mbid', metavar='MBID', required=True)
+args = parser.parse_args()
+
+# TODO: allow the naming scheme to be configured...
+name_format = "{num:02d}"
+
+covers = musicbrainzngs.get_image_list(args.release_mbid)
+if len(covers["images"]) == 0:
+    print("release has no cover art, nothing to do")
+    sys.exit()
+
+if args.output_directory:
+    Path(args.output_directory).mkdir(parents=True, exist_ok=True)
+    os.chdir(args.output_directory)
+
+failed = False
+for c in covers["images"]:
+    (_,ext) = os.path.splitext(c["image"])
+    outname = (name_format + "{0}").format(ext,
+        num = (covers["images"].index(c) + 1)
+    )
+
+    if Path(outname).exists():
+        print("%s already exists, skipping..." % outname)
+        continue
+
+    outfile = tempfile.NamedTemporaryFile(suffix=ext, dir=".")
+    rc = os.spawnlp(os.P_WAIT, 'wget', 'wget', '-O', outfile.name, c["image"])
+    if rc:
+        failed = True
+    os.link(outfile.name, outname)
+    outfile.close()
+
+if failed:
+    sys.exit(1)