"""Proof of concept: integrate tkinter, asyncio and async iterator.

Terry Jan Reedy, 2016 July 25
"""

import asyncio
import tkinter as tk
import datetime


class atimer():
    """Yield ticks (None) at intervals.

    If tick0, yield initial tick.
    If n, stop after n + tick0 ticks.
    """

    def __init__(self, interval, n=0, tick0=False):
        self.interval = interval
        self.tick0 = tick0
        self.end_time = loop.time() + (n + .9) * interval if n else 0

    async def __aiter__(self):
        return self

    async def __anext__(self):
        if self.tick0:
            self.tick0 = False
            return
        await asyncio.sleep(self.interval)
        if not self.end_time or (loop.time() <= self.end_time):
            return
        else:
            raise StopAsyncIteration


class App(tk.Tk):
    
    def __init__(self, loop, interval=.01):
        super().__init__()
        self.loop = loop
        self.interval = interval
        self.protocol("WM_DELETE_WINDOW", self.close)
        self.create_widgets()
        self.tasks = []
        self.tasks.append(loop.create_task(self.clock(1)))
        self.tasks.append(loop.create_task(
                self.bg_flip(self.hello, 'light red', .217)))
        self.updater()

    def create_widgets(self):
        self.hello = tk.Label(self, text='Hello World', bg='white')
        self.dtime = tk.Label(self)
        self.hello.pack()
        self.dtime.pack()

    async def clock(self, interval):
        async for tick in atimer(interval, tick0=True):
            self.dtime['text'] = datetime.datetime.now()

    async def bg_flip(self, widget, color, interval):
        async for tick in atimer(interval):
            bg = widget['bg']
            widget['bg'] = color if bg == 'white' else 'white'

    def updater(self):
        self.update()
        self.loop.call_later(self.interval, self.updater)

    def close(self):
        for task in self.tasks:
            task.cancel()
        self.loop.stop()
        self.destroy()


loop = asyncio.get_event_loop()
app = App(loop)
loop.run_forever()
loop.close()