module Picky

  # This is very optional.
  # Only load if the user wants it.
  #
  module Interfaces

    # This is an interface that provides the user of
    # Picky with the possibility to change parameters
    # while the Application is running.
    #
    # Important Note: This will only work in Master/Child configurations.
    #
    class LiveParameters

      def initialize
        @child, @parent = IO.pipe
        start_master_process_thread
      end

      # This runs a thread that listens to child processes.
      #
      def start_master_process_thread
        # This thread is stopped in the children.
        #
        Thread.new do
          loop do
            IO.select([@child], nil, nil, 2) or next
            result = @child.gets ';;;'
            pid, configuration_hash = eval result
            next unless Hash === configuration_hash
            next if configuration_hash.empty?
            exclaim "Trying to update MASTER configuration."
            try_updating_configuration_with configuration_hash
            kill_each_worker_except pid

            # Fails hard on an error.
            #
          end
        end
      end

      # TODO This needs to be webserver agnostic.
      #
      def worker_pids
        Unicorn::HttpServer::WORKERS.keys
      end

      # Taken from Unicorn.
      #
      def kill_each_worker_except pid
        worker_pids.each do |wpid|
          next if wpid == pid
          kill_worker :KILL, wpid
        end
      end
      def kill_worker signal, wpid
        Process.kill signal, wpid
        exclaim "Killing worker ##{wpid} with signal #{signal}."
      rescue Errno::ESRCH
        remove_worker wpid
      end
      # TODO This needs to be Webserver agnostic.
      #
      def remove_worker wpid
        worker = Unicorn::HttpServer::WORKERS.delete(wpid) and worker.tmp.close rescue nil
      end

      # Updates any parameters with the ones given and
      # returns the updated params.
      #
      # The params are a strictly defined hash of:
      #   * querying_removes_characters: Regexp
      #   * querying_stopwords:          Regexp
      #   * querying_splits_text_on:     Regexp
      #
      # This first tries to update in the child process,
      # and if successful, in the parent process
      #
      def parameters configuration_hash
        close_child
        exclaim "Trying to update worker child configuration." unless configuration_hash.empty?
        try_updating_configuration_with configuration_hash
        write_parent configuration_hash
        extract_configuration
      rescue CouldNotUpdateConfigurationError => e
        # I need to die such that my broken config is never used.
        #
        exclaim "Child process #{Process.pid} performs harakiri because of broken config."
        harakiri
        { e.config_key => :ERROR }
      end
      # Kills itself, but still answering the request honorably.
      #
      def harakiri
        Process.kill :QUIT, Process.pid
      end
      # Write the parent.
      #
      # Note: The ;;; is the end marker for the message.
      #
      def write_parent configuration_hash
        @parent.write "#{[Process.pid, configuration_hash]};;;"
      end
      # Close the child if it isn't yet closed.
      #
      def close_child
        @child.close unless @child.closed?
      end

      class CouldNotUpdateConfigurationError < StandardError
        attr_reader :config_key
        def initialize config_key, message
          super message
          @config_key = config_key
        end
      end

      # Tries updating the configuration in the child process or parent process.
      #
      def try_updating_configuration_with configuration_hash
        current_key = nil
        begin
          configuration_hash.each_pair do |key, new_value|
            exclaim "  Setting #{key} with #{new_value}."
            current_key = key
            send :"#{key}=", new_value
          end
        rescue StandardError => e
          # Catch any error and reraise as config error.
          #
          raise CouldNotUpdateConfigurationError.new current_key, e.message
        end
      end

      def extract_configuration
        {
          querying_removes_characters: querying_removes_characters,
          querying_stopwords:          querying_stopwords,
          querying_splits_text_on:     querying_splits_text_on
        }
      end

      # TODO Move to Interface object.
      #
      def querying_removes_characters
        regexp = Tokenizer.query_default.instance_variable_get :@removes_characters_regexp
        regexp && regexp.source
      end
      def querying_removes_characters= new_value
        Tokenizer.query_default.instance_variable_set(:@removes_characters_regexp, %r{#{new_value}})
      end
      def querying_stopwords
        regexp = Tokenizer.query_default.instance_variable_get :@remove_stopwords_regexp
        regexp && regexp.source
      end
      def querying_stopwords= new_value
        Tokenizer.query_default.instance_variable_set(:@remove_stopwords_regexp, %r{#{new_value}})
      end
      def querying_splits_text_on
        splits = Tokenizer.query_default.instance_variable_get :@splits_text_on
        splits && splits.respond_to?(:source) ? splits.source : splits
      end
      def querying_splits_text_on= new_value
        splits = Tokenizer.query_default.instance_variable_get :@splits_text_on
        if splits.respond_to?(:source)
          Tokenizer.query_default.instance_variable_set(:@splits_text_on, %r{#{new_value}})
        else
          Tokenizer.query_default.instance_variable_set(:@splits_text_on, new_value)
        end
      end

      #
      #
      def to_s
        "Suckerfish Live Interface (Use the picky-live gem to introspect)"
      end

    end

  end

  # Aka.
  #
  LiveParameters = Interfaces::LiveParameters

end