class Jekyll::PaginateV2::Generator::PaginationIndexer

def self.index_posts_by(all_posts, index_key)
  return nil if all_posts.nil?
  return all_posts if index_key.nil?
  index = {}
  all_posts.each do |post|
    next if post.data.nil?
    next if !post.data.has_key?(index_key)
    next if post.data[index_key].nil?
    next if post.data[index_key].size <= 0
    next if post.data[index_key].to_s.strip.length == 0
    
    # Only tags and categories come as premade arrays, locale does not, so convert any data

    # elements that are strings into arrays

    post_data = post.data[index_key]
    if post_data.is_a?(String)
      post_data = post_data.split(/;|,|\s/)
    end
    
    post_data.each do |key|
      key = key.to_s.downcase.strip
      # If the key is a delimetered list of values 

      # (meaning the user didn't use an array but a string with commas)

      key.split(/;|,/).each do |k_split|
        k_split = k_split.to_s.downcase.strip #Clean whitespace and junk

        if !index.has_key?(k_split)
          index[k_split.to_s] = []
        end
        index[k_split.to_s] << post
      end
    end
  end
  return index
end # function index_posts_by

def self.intersect_arrays(first, *rest)
  return nil if first.nil?
  return nil if rest.nil?
  
  intersect = first
  rest.each do |item|
    return [] if item.nil?
    intersect = intersect & item
  end
  return intersect
end #function intersect_arrays

def self.read_config_value_and_filter_posts(config, config_key, posts, source_posts)
  return nil if posts.nil?
  return nil if source_posts.nil? # If the source is empty then simply don't do anything

  return posts if config.nil?
  return posts if !config.has_key?(config_key)
  return posts if config[config_key].nil?
  
  # Get the filter values from the config (this is the cat/tag/locale values that should be filtered on)

  config_value = config[config_key]
  
  # If we're dealing with a delimitered string instead of an array then let's be forgiving

  if( config_value.is_a?(String))
    config_value = config_value.split(/;|,/)
  end
    
  # Now for all filter values for the config key, let's remove all items from the posts that

  # aren't common for all collections that the user wants to filter on

  config_value.each do |key|
    key = key.to_s.downcase.strip
    posts = PaginationIndexer.intersect_arrays(posts, source_posts[key])
  end
  
  # The fully filtered final post list

  return posts
end #function read_config_value_and_filter_posts