require 'thread'
require 'concurrent/utilities'
require 'concurrent/atomic/condition'

module Concurrent

  # Old school kernel-style event reminiscent of Win32 programming in C++.
  #
  # When an `Event` is created it is in the `unset` state. Threads can choose to
  # `#wait` on the event, blocking until released by another thread. When one
  # thread wants to alert all blocking threads it calls the `#set` method which
  # will then wake up all listeners. Once an `Event` has been set it remains set.
  # New threads calling `#wait` will return immediately. An `Event` may be
  # `#reset` at any time once it has been set.
  #
  # @see http://msdn.microsoft.com/en-us/library/windows/desktop/ms682655.aspx
  class Event

    # Creates a new `Event` in the unset state. Threads calling `#wait` on the
    # `Event` will block.
    def initialize
      @set = false
      @mutex = Mutex.new
      @condition = Condition.new
    end

    # Is the object in the set state?
    #
    # @return [Boolean] indicating whether or not the `Event` has been set
    def set?
      @mutex.lock
      result = @set
      @mutex.unlock

      result
    end

    # Trigger the event, setting the state to `set` and releasing all threads
    # waiting on the event. Has no effect if the `Event` has already been set.
    #
    # @return [Boolean] should always return `true`
    def set
      @mutex.lock
      unless @set
        @set = true
        @condition.broadcast
      end
      @mutex.unlock

      true
    end

    def try?
      @mutex.lock

      if @set
        result = false
      else
        @set = true
        @condition.broadcast
        result = true
      end

      @mutex.unlock

      result
    end

    # Reset a previously set event back to the `unset` state.
    # Has no effect if the `Event` has not yet been set.
    #
    # @return [Boolean] should always return `true`
    def reset
      @mutex.lock
      @set = false
      @mutex.unlock

      true
    end

    # Wait a given number of seconds for the `Event` to be set by another
    # thread. Will wait forever when no `timeout` value is given. Returns
    # immediately if the `Event` has already been set.
    #
    # @return [Boolean] true if the `Event` was set before timeout else false
    def wait(timeout = nil)
      @mutex.lock

      unless @set
        remaining = Condition::Result.new(timeout)
        while !@set && remaining.can_wait?
          remaining = @condition.wait(@mutex, remaining.remaining_time)
        end
      end

      result = @set

      @mutex.unlock

      result
    end
  end
end