import mutagen
import mutagen.id3
from mutagen.easyid3 import EasyID3

def popms(id3):
    for k, v in id3.iteritems():
        if k.startswith('POPM'):
            yield k, v

def byte2rating(b):
    if b >= 224: return 5
    if b >= 160: return 4
    if b >= 96: return 3
    if b >= 32: return 2
    if b >= 1: return 1
    return 0

def rating2byte(r):
    if r == 5: return 256
    if r == 4: return 192
    if r == 3: return 128
    if r == 2: return 64
    if r == 1: return 1
    return 0

def rating_get(id3, key):
    try:
        rating = id3['TXXX:RATING']
    except KeyError:
        try:
            _, popm = popms(id3).next()
        except StopIteration:
            return []
        else:
            return [unicode(byte2rating(popm.rating))]
    else:
        return list(rating.text)

def _canconv(r):
    try:
        if int(r) != str(int(r)):
            return False
        return int(r) >= 1 and int(r) <= 5
    except (ValueError, TypeError):
        return False

def rating_set(id3, key, val):
    rating_delete(id3, key)
    if _canconv(val):
        popm = mutagen.id3.POPM()
        popm.email = "Windows Media Player 9 Series"
        popm.count = 0
        popm.rating = rating2byte(int(val))
        id3.add(popm)
    else:
        if 'TXXX:RATING' in id3:
            del(id3['TXXX:RATING'])
        id3.add(mutagen.id3.TXXX(encoding=3, desc='RATING', text=unicode(val)))

def rating_delete(id3, key):
    for k, v in popms(id3):
        del(id3[k])
    if 'TXXX:RATING' in id3:
        del(id3['TXXX:RATING'])

replaygain_tags = ('replaygain_album_gain', 'replaygain_album_peak', \
  'replaygain_track_gain', 'replaygain_track_peak')
for tag in replaygain_tags:
    EasyID3.RegisterTXXXKey(tag, tag)

extra_tags = ('sync', 'totaltracks', 'totaldiscs')
for tag in extra_tags:
    EasyID3.RegisterTXXXKey(tag, tag.upper())

EasyID3.RegisterTextKey('albumartist', 'TPE2')
EasyID3.RegisterKey('rating', rating_get, rating_set, rating_delete)