external.py

import hashlib
import os
import subprocess
import urllib
import urllib2
from lxml import etree
from djrandom import utils


class AlbumImageDiskCache(object):
    """Cache album art on disk.

    Files are saved and converted to JPEG using Imagemagick.  Negative
    matches are saved as empty files.
    """

    def __init__(self, root):
        self.root = root

    def _path(self, artist, album):
        album_hash = hashlib.sha1('%s|%s' % (artist, album)).hexdigest()
        return utils.generate_path(self.root, album_hash)

    def has(self, artist, album):
        return os.path.exists(self._path(artist, album))

    def get(self, artist, album):
        path = self._path(artist, album)
        if os.path.getsize(path) == 0:
            return None
        return path

    def set_negative_match(self, artist, album):
        open(self._path(artist, album), 'w').close()

    def download(self, artist, album, url):
        """Download url and convert to JPEG."""
        path = self._path(artist, album)
        tmpf = path + '.tmp'
        with open(tmpf, 'w') as fd:
            fd.write(urllib2.urlopen(url).read())
        subprocess.call(
            ['/usr/bin/convert', tmpf, '-quality', '75', 'jpeg:%s' % path])
        os.unlink(tmpf)


class AlbumImageRetriever(object):

    def __init__(self, api_key, cache_root):
        self.api_key = api_key
        self.cache = AlbumImageDiskCache(cache_root)

    def _get_album_info(self, artist, album):
        args = {'method': 'album.getInfo',
                'artist': artist,
                'album': album,
                'api_key': self.api_key}
        request = urllib2.urlopen(
            'http://ws.audioscrobbler.com/2.0/?%s' % urllib.urlencode(args))
        return etree.fromstring(request.read())

    def get_album_image(self, artist, album):
        if not self.cache.has(artist, album):
            try:
                xml = self._get_album_info(artist, album)
                xp = etree.XPath('album/image[@size="extralarge"]')
                img = xp(xml)
                if img:
                    self.cache.download(artist, album, img[0].text)
                else:
                    self.cache.set_negative_match(artist, album)
            except:
                return None
        return self.cache.get(artist, album)


if __name__ == '__main__':
    import sys
    api_key, artist, album = sys.argv[1:]
    air = AlbumImageRetriever(api_key, '/var/tmp/album-image-cache')
    print air.get_album_image(artist, album)