# Copyright (c) 2004-5 Marek Hnilica. All rights reserved.
# Module that searches for information in Windows Media Audio files.
# Distributed under GPL version 2, or (at your option) later


# I don't have read any single document about wma file format and about the
# method how are tags stored in it. I probably have lowered ability of searching
# on Internet.. Result of night with hexa-editor analyzing few WMA files is
# presented here. Documents or (better...) patches would be greatly appreciated.
# TODO: Get information about total time of the track
import string,os.path
class TagError:
	def __init__(self, err):
		self.err=err
	def __str__(self):
		return self.err

def null_rem(text):
	text=string.replace(text,'\x00','')
	return text
def Tag(filename):
	if not os.path.exists(filename):
		raise TagError,'File %s does not exist.' % filename
	null=chr(0)
	[AlbumString,YearString,GenreString,TrackString,kbpsString]=['','','','','']
	
	for i in list('WM/AlbumTitle'):
		AlbumString+=i+chr(0)
	AlbumString=AlbumString[:-1]
	
	for i in list('WM/Year'):
		YearString+=i+chr(0)
	YearString=YearString[:-1]
 	
	for i in list('WM/Genre'):
		GenreString+=i+chr(0)
	GenreString=GenreString[:-1]
 	
	for i in list('WM/TrackNumber'):
		TrackString+=i+chr(0)
	TrackString=TrackString[:-1]
 	
	for i in list('kbps'):
		kbpsString+=i+chr(0)
	kbpsString=kbpsString[:-1]
	

# Following string is, as it looks, very important - it somewhat
# introduces tag information. It's contained in file either twice or
# three-times (or more, but it's not useful for us):
# Twice: In this case there is no frame in the file about Title/Artist/Comment
# Thrice: Title/Artist/Comment frames are used
# It appears for first at the very beginning of the file - byte 13 (0x0d)
# Position of second occurence depends on many factors like padding, etc.
# If there is a third occurence, then (3?) bytes after second appearance
# signifies, how long the tag is. Bytes after the third
# occurence indicates how long the audia data is. For reasons, of which I cannot
# explain any single one, the final size of data is that number minus 16 (0x10)

	# 1 M bytes to analyze should be more than enough.
	TagString=chr(0x62)+chr(0xce)+chr(0x6c)
	try:
		WmaFile=open(filename,'rb')
	except:
		raise TagError,'Error opening file %s' %filename
	if os.path.getsize(filename) >= 1000000:
		buff=WmaFile.read(1000000)
	else:
		buff=WmaFile.read()

	AlbumPosition=string.find(buff,AlbumString)
	if AlbumPosition>0:
		AlbumSize=ord(buff[(AlbumPosition+len(AlbumString)+5)])+(ord(buff[(AlbumPosition+len(AlbumString)+6)])*0x100)
		Album=buff[AlbumPosition+len(AlbumString)+7:AlbumPosition+len(AlbumString)+7+AlbumSize]
	else:
		Album=''

	YearPosition=string.find(buff,YearString)
	if YearPosition>0:
		YearSize=ord(buff[(YearPosition+len(YearString)+5)])+(ord(buff[(YearPosition+len(YearString)+6)])*0x100)
		Year=buff[YearPosition+len(YearString)+7:YearPosition+len(YearString)+7+YearSize]
	else:
		Year=''

	GenrePosition=string.find(buff,GenreString)
	if GenrePosition>0:
		GenreSize=ord(buff[(GenrePosition+len(GenreString)+5)])+(ord(buff[(GenrePosition+len(GenreString)+6)])*0x100)
		Genre=buff[GenrePosition+len(GenreString)+7:GenrePosition+len(GenreString)+7+GenreSize]
	else:
		Genre=''

	TrackPosition=string.find(buff,TrackString)
	if TrackPosition>0:
		TrackSize=ord(buff[(TrackPosition+len(TrackString)+5)])+(ord(buff[(TrackPosition+len(TrackString)+6)])*0x100)
		Track=buff[TrackPosition+len(TrackString)+7:TrackPosition+len(TrackString)+7+TrackSize]
		if buff[TrackPosition+len(TrackString)+3]!=null:
			FirstPos=TrackPosition+len(TrackString)+7
			Track=str(ord(buff[FirstPos])+ord(buff[FirstPos+1])*0x100+ord(buff[FirstPos+2])*0x10000)
	else:
		Track=''

	kbpsPosition=string.find(buff,kbpsString)
	if kbpsPosition>0:
		Bitrate=buff[kbpsPosition-9:kbpsPosition-3]
	else:
		Bitrate=''

	Bitrate=null_rem(Bitrate)
	Album=null_rem(Album)
	Year=null_rem(Year)
	Genre=null_rem(Genre)
	Track=null_rem(Track)
	WmaFile.close()
	if string.count(buff,TagString) >= 3:
		buff=buff[16:]
		TagStartPosition=string.find(buff,TagString)

# If it's more than 3 bytes - sorry; It shouldn't be a big defect since three
# bytes are sufficient enough for about 16 megs of tag...moreover, there
# are five frames in this order: 1) Title 2) Artist 3) Copyright 4) Comment
# 5) something mysterious :o/ it might be a flag or something; all ot them
# are described by two bytes, so maximum we can have is FFFF*5=4FFFFB.

		StringSizeBytes=buff[TagStartPosition+3:TagStartPosition+7]
		TagSize=ord(StringSizeBytes[0])+(ord(StringSizeBytes[1])*0x100)+(ord(StringSizeBytes[2])*0x10000)
		try:
			Tag=buff[TagStartPosition+11:TagStartPosition+3+TagSize]
		except:
			raise TagError,"Exception during getting information from %s" %filename
		TitleSize=ord(Tag[0])+(ord(Tag[1])*0x100)
		ArtistSize=ord(Tag[2])+(ord(Tag[3])*0x100)
		CopySize=ord(Tag[4])+(ord(Tag[5])*0x100)
		CommentSize=ord(Tag[6])+(ord(Tag[7])*0x100)
		Title=Tag[10:TitleSize+10]
		Artist=Tag[10+TitleSize:10+TitleSize+ArtistSize]
		Comment=Tag[10+TitleSize+ArtistSize+CopySize:10+TitleSize+ArtistSize+CopySize+CommentSize]
	else:
		Title=''
		Artist=''
		Comment=''
	Title=null_rem(Title)
	Artist=null_rem(Artist)
	Comment=null_rem(Comment)
	try:
		Bitrate=int(Bitrate)
	except:
		Bitrate=None
	return (Title,Album,Artist,Year,Genre,Track,Comment,Bitrate)