# see http://www.xiph.org/ogg/vorbis/docs.html for documentation on vorbis format
# http://www.xiph.org/vorbis/doc/v-comment.html
# http://www.xiph.org/vorbis/doc/framing.html
# 
# License: ruby

require "iconv"

class Hash 
   ### lets you specify hash["key"] as hash.key
   ### this came from CodingInRuby on RubyGarden
   ### http://www.rubygarden.org/ruby?CodingInRuby 
   def method_missing(meth,*args) 
     if /=$/=~(meth=meth.id2name) then
       self[meth[0...-1]] = (args.length<2 ? args[0] : args)
     else
       self[meth]
     end
   end
end
					    
# Raised on any kind of error related to ruby-ogginfo
class OggInfoError < StandardError ; end

class OggInfo
  VERSION = "0.4.2"
  CHECKSUM_TABLE = [
    0x00000000,0x04c11db7,0x09823b6e,0x0d4326d9,
    0x130476dc,0x17c56b6b,0x1a864db2,0x1e475005,
    0x2608edb8,0x22c9f00f,0x2f8ad6d6,0x2b4bcb61,
    0x350c9b64,0x31cd86d3,0x3c8ea00a,0x384fbdbd,
    0x4c11db70,0x48d0c6c7,0x4593e01e,0x4152fda9,
    0x5f15adac,0x5bd4b01b,0x569796c2,0x52568b75,
    0x6a1936c8,0x6ed82b7f,0x639b0da6,0x675a1011,
    0x791d4014,0x7ddc5da3,0x709f7b7a,0x745e66cd,
    0x9823b6e0,0x9ce2ab57,0x91a18d8e,0x95609039,
    0x8b27c03c,0x8fe6dd8b,0x82a5fb52,0x8664e6e5,
    0xbe2b5b58,0xbaea46ef,0xb7a96036,0xb3687d81,
    0xad2f2d84,0xa9ee3033,0xa4ad16ea,0xa06c0b5d,
    0xd4326d90,0xd0f37027,0xddb056fe,0xd9714b49,
    0xc7361b4c,0xc3f706fb,0xceb42022,0xca753d95,
    0xf23a8028,0xf6fb9d9f,0xfbb8bb46,0xff79a6f1,
    0xe13ef6f4,0xe5ffeb43,0xe8bccd9a,0xec7dd02d,
    0x34867077,0x30476dc0,0x3d044b19,0x39c556ae,
    0x278206ab,0x23431b1c,0x2e003dc5,0x2ac12072,
    0x128e9dcf,0x164f8078,0x1b0ca6a1,0x1fcdbb16,
    0x018aeb13,0x054bf6a4,0x0808d07d,0x0cc9cdca,
    0x7897ab07,0x7c56b6b0,0x71159069,0x75d48dde,
    0x6b93dddb,0x6f52c06c,0x6211e6b5,0x66d0fb02,
    0x5e9f46bf,0x5a5e5b08,0x571d7dd1,0x53dc6066,
    0x4d9b3063,0x495a2dd4,0x44190b0d,0x40d816ba,
    0xaca5c697,0xa864db20,0xa527fdf9,0xa1e6e04e,
    0xbfa1b04b,0xbb60adfc,0xb6238b25,0xb2e29692,
    0x8aad2b2f,0x8e6c3698,0x832f1041,0x87ee0df6,
    0x99a95df3,0x9d684044,0x902b669d,0x94ea7b2a,
    0xe0b41de7,0xe4750050,0xe9362689,0xedf73b3e,
    0xf3b06b3b,0xf771768c,0xfa325055,0xfef34de2,
    0xc6bcf05f,0xc27dede8,0xcf3ecb31,0xcbffd686,
    0xd5b88683,0xd1799b34,0xdc3abded,0xd8fba05a,
    0x690ce0ee,0x6dcdfd59,0x608edb80,0x644fc637,
    0x7a089632,0x7ec98b85,0x738aad5c,0x774bb0eb,
    0x4f040d56,0x4bc510e1,0x46863638,0x42472b8f,
    0x5c007b8a,0x58c1663d,0x558240e4,0x51435d53,
    0x251d3b9e,0x21dc2629,0x2c9f00f0,0x285e1d47,
    0x36194d42,0x32d850f5,0x3f9b762c,0x3b5a6b9b,
    0x0315d626,0x07d4cb91,0x0a97ed48,0x0e56f0ff,
    0x1011a0fa,0x14d0bd4d,0x19939b94,0x1d528623,
    0xf12f560e,0xf5ee4bb9,0xf8ad6d60,0xfc6c70d7,
    0xe22b20d2,0xe6ea3d65,0xeba91bbc,0xef68060b,
    0xd727bbb6,0xd3e6a601,0xdea580d8,0xda649d6f,
    0xc423cd6a,0xc0e2d0dd,0xcda1f604,0xc960ebb3,
    0xbd3e8d7e,0xb9ff90c9,0xb4bcb610,0xb07daba7,
    0xae3afba2,0xaafbe615,0xa7b8c0cc,0xa379dd7b,
    0x9b3660c6,0x9ff77d71,0x92b45ba8,0x9675461f,
    0x8832161a,0x8cf30bad,0x81b02d74,0x857130c3,
    0x5d8a9099,0x594b8d2e,0x5408abf7,0x50c9b640,
    0x4e8ee645,0x4a4ffbf2,0x470cdd2b,0x43cdc09c,
    0x7b827d21,0x7f436096,0x7200464f,0x76c15bf8,
    0x68860bfd,0x6c47164a,0x61043093,0x65c52d24,
    0x119b4be9,0x155a565e,0x18197087,0x1cd86d30,
    0x029f3d35,0x065e2082,0x0b1d065b,0x0fdc1bec,
    0x3793a651,0x3352bbe6,0x3e119d3f,0x3ad08088,
    0x2497d08d,0x2056cd3a,0x2d15ebe3,0x29d4f654,
    0xc5a92679,0xc1683bce,0xcc2b1d17,0xc8ea00a0,
    0xd6ad50a5,0xd26c4d12,0xdf2f6bcb,0xdbee767c,
    0xe3a1cbc1,0xe760d676,0xea23f0af,0xeee2ed18,
    0xf0a5bd1d,0xf464a0aa,0xf9278673,0xfde69bc4,
    0x89b8fd09,0x8d79e0be,0x803ac667,0x84fbdbd0,
    0x9abc8bd5,0x9e7d9662,0x933eb0bb,0x97ffad0c,
    0xafb010b1,0xab710d06,0xa6322bdf,0xa2f33668,
    0xbcb4666d,0xb8757bda,0xb5365d03,0xb1f740b4 
  ]

  attr_reader :channels, :samplerate, :bitrate, :nominal_bitrate, :length
  
  # +tag+ is a hash containing the vorbis tag like "Artist", "Title", and the like
  attr_reader :tag

  # create new instance of OggInfo, using +charset+ to convert tags to
  def initialize(filename, charset = "utf-8")
    @filename = filename
    @charset = charset
    @file = File.new(@filename, "rb")

    frames = (1..2).collect { |i| OggInfo.read_frame(@file) }
    extract_vorbis_infos(frames[0])
    extract_tag(frames[1])
    convert_tag_charset("utf-8", @charset)
    @original_tag = @tag.dup
    @length = get_length
    @bitrate = @file.stat.size.to_f*8/@length
    @file.close
  end

  # "block version" of ::new()
  def self.open(*args)
    m = self.new(*args)
    ret = nil
    if block_given?
      begin
        ret = yield(m)
      ensure
        m.close
      end
    else
      ret = m
    end
    ret
  end

  # commits any tags to file
  def close
    if @tag != @original_tag
      cmd = %w{vorbiscomment -w} 
      convert_tag_charset(@charset, "utf-8")

      @tag.each do |k,v|
        cmd.concat(["-t", k.upcase+"="+v])
      end
      cmd << @filename
      system(*cmd)
    end
  end

  # check the presence of a tag
  def hastag?
    !@tag.empty?
  end
  
  def to_s
    "channels #{@channels} samplerate #{@samplerate} bitrate #{@nominal_bitrate} bitrate #{@bitrate} length #{@length} #{@tag.inspect}"
  end

  # read an ogg frame from the +file+
  def self.read_frame(file)
    frame = {}

    frame[:file_position] = file.pos

    return nil if file.eof?
    chunk = file.read(27)
    raise OggInfoError if file.eof?

    capture_pattern,
    frame[:version],
    frame[:header_type], 
    frame[:granule_pos], 
    frame[:bitstream_serial_number], 
    frame[:page_sequence_number],
    frame[:checksum],
    frame[:page_segments] = chunk.unpack("a4CCQNNNC")

    if capture_pattern != "OggS"
      raise(OggInfoError, "bad magic number '#{capture_pattern}'")
    end
    
    segment_sizes = file.read(frame[:page_segments]).unpack("C*")
    frame[:body_size] = segment_sizes.inject(0) { |sum, i| sum += i }
    frame[:header_size] = 27 + frame[:page_segments]
    frame[:size] = frame[:header_size] + frame[:body_size]
    file.seek(frame[:body_size], IO::SEEK_CUR)
    frame
  end

  # compute the checksum of a given +frame+ from a given +file+, you can compare it with frame[:checksum].
  def self.checksum(file, frame)
    original_pos = file.pos
    file.seek(frame[:file_position])
    data = file.read(frame[:size])
    data[22] = data[23] = data[24] = data[25] = 0

    crc = 0
    data.each_byte do |byte|
      crc = (crc << 8)^CHECKSUM_TABLE[((crc >> 24)&0xff) ^ byte]
      crc = crc & 0xffffffff
    end

    # "reverse" it
    crc = [crc].pack("V").unpack("N").first
    file.seek(original_pos)
    crc
  end

private
  def extract_vorbis_infos(frame)
    @file.seek(frame[:file_position] + frame[:header_size] + 1 ) # seek after "vorbis"
    vorbis_string, vorbis_version, @channels, @samplerate, upper_bitrate, @nominal_bitrate, lower_bitrate = @file.read(27).unpack("a6VCV4")
    if @nominal_bitrate == 0
      if upper_bitrate == 2**32 - 1 or lower_bitrate == 2**32 - 1 
	@nominal_bitrate = 0
      else
	@nominal_bitrate = (upper_bitrate + lower_bitrate)/2
      end
    end
  end

  def extract_tag(frame)
    @file.seek(frame[:file_position] + frame[:header_size] + 1 + "vorbis".size)
    vendor_length = @file.read(4).unpack("V").first
    @vendor = @file.read(vendor_length)

    @tag = {}
    tag_size = @file.read(4).unpack("V")[0]

    tag_size.times do |i|
      size = @file.read(4).unpack("V")[0]
      comment = @file.read(size)
      key, val = comment.split(/=/, 2)
      @tag[key.downcase] = val
    end
  end

  def get_length
    @file.seek(0)
    last_frame = nil
    begin
      while f = OggInfo.read_frame(@file) 
        last_frame = f
      end
    rescue OggInfoError
    end
    last_frame[:granule_pos].to_f / @samplerate
  end

  def convert_tag_charset(from_charset, to_charset)
    return if from_charset == to_charset
    Iconv.open(to_charset, from_charset) do |ic|
      @tag.each do |k, v|
        @tag[k] = ic.iconv(v)
      end
    end
  end
end