#
# Copyright Michael Orlitzky
#
# http://michael.orlitzky.com/
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# http://www.fsf.org/licensing/licenses/gpl.html
#

require 'src/website'
require 'cgi'

class Youtube < Website

  VALID_YOUTUBE_URL_REGEX = /^(http:\/\/)?([a-z0-9]+\.)?youtube\.com\/((watch\?v=)|(v\/)|([a-z]+\#[a-z]\/[a-z]\/[0-9]\/))[a-z0-9_\-]+(\&.*)?\#?$/i

  def self.owns_url?(url)
    return url =~ VALID_YOUTUBE_URL_REGEX
  end


  def initialize(url)
    super

    # The @format variable just caches the format of the video we're
    # downloading. Storing it will prevent us from having to calculate
    # it twice.
    @format = 0
  end


  def get_video_url()
    video_id = self.parse_video_id()

    # The video's URL (the "page data" URL) may be different from the
    # URL that was passed to the program. We support the /v/video_id
    # URL format, but that is *not* the main video page where we can
    # retrieve the "t" parameter. We can only get that from the
    # /watch?v=video_id form.
    page_data_url = "http://www.youtube.com/watch?v=#{video_id}"
    page_data = self.get_page_data(page_data_url)

    begin
      # Get the URL map from the page.
      fmt_url_map = get_format_url_map(page_data)

      # Figure out which formats are available, and if any are,
      # choose the best one.
      available_formats = fmt_url_map.keys()
      desired_format = get_desired_format(available_formats)

      # First we cache the format so that when we're asked for the
      # video filename later, we don't have to recompute the format.
      @format = desired_format

      # And then use whatever URL is available for the desired format.
      # We assume that all available formats will have an entry in the
      # fmt_url_map hash.
      video_url = fmt_url_map[desired_format]
      return video_url
    rescue StandardError => e
      # If at first you do not succeed, maybe someone decided to
      # change some shit. This alternate method parses
      # url_encoded_fmt_stream_map.
      fmt_streams = get_fmt_stream_list(page_data)
      video_url = self.choose_best_fmt_stream_url(fmt_streams)

      # The "itag" parameter makes the 403 happen.
      video_url.gsub!(/itag=\d+&/, '')
    end

    return video_url
  end


  def get_video_filename()
    # The format -> extension mapping is available on Wikipedia:
    #
    #   http://en.wikipedia.org/wiki/YouTube#Quality_and_codecs
    #
    # The default extension is .flv.
    extension = '.flv'

    if [18, 22, 35, 37].include?(@format)
      extension = '.mp4'
    elsif (@format == 17)
      extension = '.3gp'
    end

    return (self.parse_video_id() + extension)
  end


  protected;

  def choose_best_fmt_stream_url(fmt_stream_urls)
    # Take a list, generated by get_fmt_stream_list(), and choose the
    # best URL out of the bunch based on the video format.
    fmt_stream_urls.each do |fs|
      if fs =~ /video\/mp4/ and fs =~ /quality=large/
        return fs
      elsif fs =~ /quality=large/
        return fs
      elsif fs =~ /video\/mp4/
        return fs
      else
        return fs
      end
    end
  end


  def unicode_unescape(string)
    # Unescape sequences like '\u0026'.
    # Ok, only '\u0026' for now.
    return string.gsub('\u0026', '&')
  end


  def get_fmt_stream_list(page_data)
    # This is another (new?) method of embedding the video URLs.
    # The url_encoded_fmt_stream_map variable contains a list of URLs
    # in the form url=foo1,url=foo2...
    #
    # It looks like the first one in the list is the highest
    # quality?  Let's just take that one for now.
    fmt_stream_regex = /\"url_encoded_fmt_stream_map\": \"(.+?)\"/

    matches = fmt_stream_regex.match(page_data)

    if (matches.nil? || matches.length < 2)
      raise StandardError.new("Could not parse the url_encoded_fmt_stream_map Flash variable.")
    end

    urlstring = matches[1]
    urlstring.gsub!('url=', '')
    urls = urlstring.split(',')

    urls.each_index do |idx|
      urls[idx] = self.unicode_unescape(urls[idx])
      urls[idx] = CGI::unescape(urls[idx])
      # Strip off everything after the first space in the URL.
      # I don't know why this works, but if we leave the space
      # in (encoded, even), Youtube throws us 403 errors.
      urls[idx].gsub!(/ .+$/, '')
    end

    return urls
  end


  # Get the video id from the URL. Should be relatively easy,
  # unless Youtube supports some URL formats of which I'm unaware.
  def parse_video_id()
    # Both URLs are fairly easy to parse if you handle
    # them one at a time. The only tricky situation is when
    # parameters like "&hl=en" are tacked on to the end.
    # We'll call /watch?v=video_id the "first form."
    first_form_video_id_regex = /v=([0-9a-z_\-]+)/i
    first_form_matches = first_form_video_id_regex.match(@url)
    return first_form_matches[1] if not (first_form_matches.nil? ||
                                         first_form_matches.length < 2)

    # First form didn't work? Try the second.
    second_form_video_id_regex = /\/v\/([0-9a-z_\-]+)/i
    second_form_matches = second_form_video_id_regex.match(@url)
    return second_form_matches[1] if not (second_form_matches.nil? ||
                                          second_form_matches.length < 2)

    # ...and the third.
    third_form_video_id_regex = /\/([[:alnum:]]+)$/i
    third_form_matches = third_form_video_id_regex.match(@url)
    return third_form_matches[1] if not (third_form_matches.nil? ||
                                         third_form_matches.length < 2)

    # If we made it here, we couldn't figure out the video id. Yes,
    # this is fatal, since we don't know where the video file is
    # located.
    raise StandardError.new("Could not parse the video id.")
  end



  def get_format_url_map(page_data)
    # Youtube has implemented a new fmt_url_map that (perhaps
    # unsurprisingly) maps formats to video URLs. This makes it
    # easyish to parse the video URLs.
    url_map = {}
    url_map_regex = /fmt_url_map=([^&\"]+)/

    matches = url_map_regex.match(page_data)

    if (matches.nil? || matches.length < 1)
      raise StandardError.new("Could not parse the fmt_url_map Flash variable.")
    end

    # The map is stored entirely in one Flash variable. The format is
    # key|value,key|value,...
    maptext = CGI::unescape(matches[1])
    entries = maptext.split(',')
    entries.each do |entry|
      key = entry.split('|')[0].to_i
      value = entry.split('|')[1]
      url_map[key] = value
    end

    if (url_map.length < 1)
      raise StandardError.new("Could not find any valid format URLs.")
    end

    return url_map
  end


  def get_desired_format(available_formats)
    # Check for the presence of formats, in order of preference
    # (quality). That is, we check for the best formats first. As soon
    # as a format is found to be available, we return it as the
    # desired format, since the first format we find is going to be
    # the best available format.
    return 37 if available_formats.include?(37)
    return 22 if available_formats.include?(22)
    return 35 if available_formats.include?(35)
    return 18 if available_formats.include?(18)
    return 34 if available_formats.include?(34)
    return 17 if available_formats.include?(17)

    # Available formats can't be empty (we would have raised an error
    # in get_available_formats), so if there's some unknown format
    # here we might as well return it as a last resort.
    return available_formats[0]
  end

end