'''Proof of concept 2: integrate tkinter and async iterator.

Terry Jan Reedy, 2016 July 19
Run with 'python -i' or from IDLE editor to keep tk window alive.

This version uses async for loop and async timer to update tk label.
See tkloop.py for other comments.
'''

import asyncio as aio
import tkinter as tk
import datetime
import threading

# On Windows, need proactor for subprocess functions
EventLoop = aio.SelectorEventLoop
# Following gets aio.SelectorEventLoop
# EventLoop = type(aio.get_event_loop())

class TkEventLoop(EventLoop):
    def __init__(self, root):
        self.root = root
        super().__init__()

    def run_forever(self):  # copy with 1 new line for proof of concept
        """Run until stop() is called."""
        self._check_closed()
        if self.is_running():
            raise RuntimeError('Event loop is running.')
        self._set_coroutine_wrapper(self._debug)
        self._thread_id = threading.get_ident()
        try:
            while True:
                self._run_once()  # can block indefinitely
                self.root.update()  # new line
                if self._stopping:
                    break
        finally:
            self._stopping = False
            self._thread_id = None
            self._set_coroutine_wrapper(False)

root = tk.Tk()
loop = TkEventLoop(root)
aio.set_event_loop(loop)


class atimer():
    "Yield n or n+1 ticks (None) at intervals."

    def __init__(self, n, interval, tick0=False):
        "Yield initial tick if tick0."
        self.interval = interval
        self.tick0 = tick0
        self.end_time = loop.time() + (n + .9) * interval

    async def __aiter__(self): 
        return self

    async def __anext__(self):
        if self.tick0:
            self.tick0 = False
            return
        await aio.sleep(self.interval)
        if loop.time() <= self.end_time:
            return
        else:
            raise StopAsyncIteration

def flipbg(widget, color):
    bg = widget['bg']
    print('click', bg, loop.time())
    widget['bg'] = color if bg == 'white' else 'white'

async def display_date(n, interval):
    hello = tk.Label(root, text='Hello World', bg='white')
    flipper = tk.Button(root, text='Change hello background', bg='yellow',
                        command=lambda: flipbg(hello, 'red'))
    label = tk.Label(root)
    hello.pack()
    flipper.pack()
    label.pack()
    root.update()
    async for tick in atimer(n, interval, tick0=True):
        print(datetime.datetime.now())
        label['text'] = datetime.datetime.now()

loop.run_until_complete(display_date(10, 1.0))
loop.close()