dplummer/cachext

module Cachext
  module Features
    module Lock
      TimeoutWaitingForLock = Class.new(StandardError)

      def read key, options
        retval = super
        return retval unless retval.nil?

        @lock_info = obtain_lock key, options

        retval = super

        if !retval.nil?
          @config.lock_manager.unlock @lock_info
        end

        retval
      end

      def call_block key, options, &block
        with_heartbeat_extender key.lock_key, options.heartbeat_expires do
          super
        end
      end

      def with_heartbeat_extender lock_key, heartbeat_expires, &block
        done = false
        heartbeat_frequency = heartbeat_expires / 2

        Thread.new do
          loop do
            break if done
            sleep heartbeat_frequency
            break if done
            @config.lock_manager.lock lock_key, (heartbeat_expires * 1000).ceil, extend: @lock_info
          end
        end

        block.call
      ensure
        @config.lock_manager.unlock @lock_info if @lock_info
        done = true
      end

      def obtain_lock key, options
        start_time = Time.now

        until lock_info ||= @config.lock_manager.lock(key.lock_key, (options.heartbeat_expires * 1000).ceil)
          if wait_for_lock(key, start_time) == :timeout
            lock_info = @config.lock_manager.lock(key.lock_key, (options.heartbeat_expires * 1000).ceil)
            raise TimeoutWaitingForLock unless lock_info
          end
        end

        lock_info
      end

      def wait_for_lock key, start_time
        sleep rand(0.01..0.02)

        if Time.now - start_time > @config.max_lock_wait
          :timeout
        end
      end
    end
  end
end