class Array
  def to_filters(hook=nil)
    Filter::FILTER_MAP.values_at(*(self.map{|o| o.to_sym})).reject{|f| f.nil?}.map{|k| Kernel.const_get(k)}.select do |k|
      hook.nil? || k.hooks?(hook)
    end
  end
  
  def each_filter(hook=nil, &b)
    to_filters(hook).each{|f| b.call(f)}
  end
end

module Filter
  FILTER_MAP = {
    :reverse => :ReverseFilter,
    :pound => :ToPoundOrNotToPoundFilter,
    :twitter => :TwitterFilter,
    :lastfmdescription => :LastFmDescriptionFilter,
    :tumblrdescription => :TumblrDescriptionFilter,
  }

  def self.current_filters
    @@current_filters
  end

  def self.current_filters=(new_current_filters)
    @@current_filters = new_current_filters
  end

  def self.options
    h = {}
    self::FILTER_MAP.each do |key, klass|
      h[key.to_s] = Kernel.const_get(klass).describe
    end
    h
  end
  
  def describe
    self::DESCRIPTION
  end
  
  def hooks?(hook)
    self::HOOK == hook
  end
  
  ## Redefine these in new filters
  HOOK = nil
  DESCRIPTION = nil
  def run_filter
    #...
  end
end

module ReverseFilter
  extend Filter
  HOOK = :after_feeds_pulled
  DESCRIPTION = "Entries displayed in reverse chronological order."
  def run_filter
    reverse!
  end
end

module TwitterFilter
  extend Filter
  HOOK = :feed_after_grab_items
  DESCRIPTION = "Make twitter titles prettier."
  def run_filter
    if url =~ /twitter.com/
      @links.map do |link|
        link.description = link.title.gsub(/^[a-zA-Z0-9]+: /, '') \
          + link.date_published.strftime(" (%a %b %e, %l%p)").downcase
        link.title = '#'
        link
      end
    end
  end
end

module TumblrDescriptionFilter
  extend Filter
  HOOK = :feed_after_grab_items
  DESCRIPTION = "Make tumblr titles prettier."
  def run_filter
    if @normalized_feed.respond_to? :generator
      if @normalized_feed.generator =~ /Tumblr/
        @links.map{|l| l.title = '#'; l}
      end
    end
  end
end

module LastFmDescriptionFilter
  extend Filter
  HOOK = :feed_after_grab_items
  DESCRIPTION = "Clean up useless info from Last.fm recent tracks"
  def run_filter
    if url =~ /ws.audioscrobbler.com.*recenttracks.rss/
      @links.map{|l| l.description = ''; l}
    end
  end
end

module ToPoundOrNotToPoundFilter
  # I call it "hash" or "number sign" rather than "pound", but I love this function name
  extend Filter
  HOOK = :descriptive_feed_item
  DESCRIPTION = "Instead of a '#' title placeholder, skip it."
  def run_filter
    @title = '' if @title == '#'
  end
end