module Clockwork
  class Manager
    class NoHandlerDefined < RuntimeError; end

    attr_reader :config

    def initialize
      @events = []
      @callbacks = {}
      @config = default_configuration
      @handler = nil
      @mutex = Mutex.new
      @condvar = ConditionVariable.new
      @finish = false
    end

    def thread_available?
      Thread.list.select { |t| t['creator'] == self }.count < config[:max_threads]
    end

    def configure
      yield(config)
      if config[:sleep_timeout] < 1
        config[:logger].warn 'sleep_timeout must be >= 1 second'
      end
    end

    def default_configuration
      { :sleep_timeout => 1, :logger => Logger.new(STDOUT), :thread => false, :max_threads => 10 }
    end

    def handler(&block)
      @handler = block if block_given?
      raise NoHandlerDefined unless @handler
      @handler
    end

    def error_handler(&block)
      @error_handler = block if block_given?
      @error_handler
    end

    def on(event, options={}, &block)
      raise "Unsupported callback #{event}" unless [:before_tick, :after_tick, :before_run, :after_run].include?(event.to_sym)
      (@callbacks[event.to_sym]||=[]) << block
    end

    def every(period, job='unnamed', options={}, &block)
      if job.is_a?(Hash) and options.empty?
        options = job
        job = "unnamed"
      end
      if options[:at].respond_to?(:each)
        every_with_multiple_times(period, job, options, &block)
      else
        register(period, job, block, options)
      end
    end

    def fire_callbacks(event, *args)
      @callbacks[event].nil? || @callbacks[event].all? { |h| h.call(*args) }
    end

    def run
      log "Starting clock for #{@events.size} events: [ #{@events.map(&:to_s).join(' ')} ]"

      sig_read, sig_write = IO.pipe

      (%w[INT TERM HUP] & Signal.list.keys).each do |sig|
        trap sig do
          sig_write.puts(sig)
        end
      end

      run_tick_loop

      while io = IO.select([sig_read])
        sig = io.first[0].gets.chomp
        handle_signal(sig)
      end
    end

    def handle_signal(sig)
      logger.debug "Got #{sig} signal"
      case sig
      when 'INT'
        shutdown
      when 'TERM'
        # Heroku sends TERM signal, and waits 10 seconds before exit
        graceful_shutdown
      when 'HUP'
        graceful_shutdown
      end
    end

    def shutdown
      logger.info 'Shutting down'
      stop_tick_loop
      exit(0)
    end

    def graceful_shutdown
      logger.info 'Gracefully shutting down'
      stop_tick_loop
      wait_tick_loop_finishes
      exit(0)
    end

    def stop_tick_loop
      @finish = true
    end

    def wait_tick_loop_finishes
      @mutex.synchronize do # wait by synchronize
        @condvar.signal
      end
    end

    def run_tick_loop
      Thread.new do
        @mutex.synchronize do
          until @finish
            tick
            interval = config[:sleep_timeout] - Time.now.subsec + 0.001
            @condvar.wait(@mutex, interval) if interval > 0
          end
        end
      end
    end

    def tick(t=Time.now)
      if (fire_callbacks(:before_tick))
        events = events_to_run(t)
        events.each do |event|
          if (fire_callbacks(:before_run, event, t))
            event.run(t)
            fire_callbacks(:after_run, event, t)
          end
        end
      end
      fire_callbacks(:after_tick)
      events
    end

    def logger
      config[:logger]
    end

    def log_error(e)
      config[:logger].error(e)
    end

    def handle_error(e)
      error_handler.call(e) if error_handler
    end

    def log(msg)
      config[:logger].info(msg)
    end

    private
    def events_to_run(t)
      @events.select{ |event| event.run_now?(t) }
    end

    def register(period, job, block, options)
      event = Event.new(self, period, job, block || handler, options)
      @events << event
      event
    end

    def every_with_multiple_times(period, job, options={}, &block)
      each_options = options.clone
      options[:at].each do |at|
        each_options[:at] = at
        register(period, job, block, each_options)
      end
    end
  end
end