#
# 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-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)

    # Magic.
    t_parameter = self.parse_t_parameter(page_data)
    
    video_url = "http://www.youtube.com/get_video?video_id=#{video_id}&t=#{t_parameter}"

    # Figure out which formats are available, and if any are,
    # choose the best one.
    available_formats = get_available_formats(page_data)
    desired_format = get_desired_format(available_formats)
    
    if not desired_format.nil?
      # 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 stick the format parameter on the end of the URL.
      video_url = video_url + "&fmt=#{desired_format}"
    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;

  # 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()
    # Return nil if we get no matches below.
    video_id = nil
    
    # 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)
    video_id = second_form_matches[1] if not (second_form_matches.nil? ||
                                              second_form_matches.length < 2)
    
    return video_id
  end


  # Parse out the "t" parameter from the video's page. I'm not sure
  # what "t" stands for, but it's located in some JSON, and is required
  # for the final video URL to work.
  def parse_t_parameter(page_data)
    t_parameter = nil
    
    t_parameter_regex = /\"t\"\:[[:space:]]\"([^\"]+?)\"/
    matches = t_parameter_regex.match(page_data)
    t_parameter = matches[1] if not (matches.nil? || matches.length < 2)

    return t_parameter
  end
  

  def get_available_formats(page_data)
    # Parse the list of available formats from the "fmt_list" Flash
    # variable.
    available_formats = []
    fmt_list_regex = /\"fmt_list\"\:[[:space:]]\"([^\"]+?)\"/
    matches = fmt_list_regex.match(page_data)

    if matches.nil?
      return nil
    else
      fmts_string = CGI::unescape(matches[1])

      fmts_string.split(',').each do |fmt|
        # Each "fmt" will look something like,
        #
        #   35/640000/9/0/115
        #
        # with the format identifier coming before the first slash.
        first_slash_idx = fmt.index('/')
        available_formats << fmt[0...first_slash_idx].to_i
      end
      
    end
    
    return available_formats
  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)
  end
  
end