# frozen_string_literal: true

# Copyright, 2017, by Samuel G. D. Williams. <http://www.codeotaku.com>
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

require 'fiber'
require_relative 'node'

module Async
	# A synchronization primitive, which allows fibers to wait until a particular condition is (edge) triggered.
	# @public Since `stable-v1`.
	class Condition
		def initialize
			@waiting = []
		end
		
		Queue = Struct.new(:fiber) do
			def transfer(*arguments)
				fiber&.transfer(*arguments)
			end
			
			def alive?
				fiber&.alive?
			end
			
			def nullify
				self.fiber = nil
			end
		end
		
		private_constant :Queue
		
		# Queue up the current fiber and wait on yielding the task.
		# @returns [Object]
		def wait
			queue = Queue.new(Fiber.current)
			@waiting << queue
			
			Fiber.scheduler.transfer
		ensure
			queue.nullify
		end
		
		# Is any fiber waiting on this notification?
		# @returns [Boolean]
		def empty?
			@waiting.empty?
		end
		
		# Signal to a given task that it should resume operations.
		# @parameter value [Object | Nil] The value to return to the waiting fibers.
		def signal(value = nil)
			waiting = @waiting
			@waiting = []
			
			waiting.each do |fiber|
				Fiber.scheduler.resume(fiber, value) if fiber.alive?
			end
			
			return nil
		end
	end
end