# -*- coding: utf-8 -*-
# @Time    : 2018/12/15 18:55
# @File    : coroutine.py


#一個簡單的 Coroutine 框架


import socket			# on top of TCP
import time
from selectors import DefaultSelector, EVENT_WRITE, EVENT_READ
# select: System Call -----> watch the readiness of a unix-file(socket) i/o
# only socket is possible in Windows
# non-blocking socket


selector = DefaultSelector()


class Future:				# ~=Promise, return the caller scope a promise
							# about something in the future
	def __init__(self):
		self.callbacks = []

	def resolve(self):		# on future event callback
		for func in self.callbacks:
			func()


class Task:					# responsible for calling next() on generators
							# in charge of the async functions
	def __init__(self, gen, eventLoop):
		self.gen = gen
		self.step()

	def step(self):			# go to next step/next yield
		try:
			f = next(self.gen)
			f.callbacks.append(self.step)
		except StopIteration as e:
			# Task is finished
			eventLoop.n_task -= 1


class EventLoop:
	def __init__(self):
		self.n_task = 0

	def add_task(self, generator):
		self.n_task += 1
		Task(generator, self)

	def start(self):
		while self.n_task > 0:
			events = selector.select()
			for event, mask in events:
				f = event.data
				f.resolve()


def pause(s, event):
	f = Future()
	selector.register(s.fileno(), event, data=f)
	yield f		# pause this function

def resume(s):
	selector.unregister(s.fileno())

def async_await(s, event):
	yield from pause(s, event)
	resume(s)

def async_get(path):
	s = socket.socket()
	s.setblocking(False)
	try:
		s.connect(('localhost', 3000))
	except BlockingIOError as e:
		print(e)

	yield from async_await(s, EVENT_WRITE)

	request = 'GET %s HTTP/1.0\r\n\r\n' % path
	s.send(request.encode())

	totalReceived = []
	while True:
		yield from async_await(s, EVENT_READ)

		received = s.recv(1000)
		if received:
			totalReceived.append(received)
		else:
			body = (b''.join(totalReceived)).decode()
			print('--------------------------------------')
			print(body)
			print('--------------------------------------', 'Byte Received:', len(body), '\n\n')
			return


if __name__ == '__main__':
	start = time.time()
	eventLoop = EventLoop()

	for i in range(50):
		eventLoop.add_task(async_get('/super-slow'))

	eventLoop.start()

	print('%.1f sec' % (time.time() - start))