# Test asyncio.gather() function, featres that are not implemented.

try:
    import asyncio
except ImportError:
    print("SKIP")
    raise SystemExit


async def foo():
    return 42


try:
    foo().__await__
except AttributeError:
    print("SKIP")
    raise SystemExit


def custom_handler(loop, context):
    print(repr(context["exception"]))


async def task(id):
    print("task start", id)
    await asyncio.sleep(0.01)
    print("task end", id)
    return id


async def gather_task(t0, t1):
    print("gather_task start")
    await asyncio.gather(t0, t1)
    print("gather_task end")


async def main():
    loop = asyncio.get_event_loop()
    loop.set_exception_handler(custom_handler)

    # Test case where can't wait on a task being gathered.
    tasks = [asyncio.create_task(task(1)), asyncio.create_task(task(2))]
    gt = asyncio.create_task(gather_task(tasks[0], tasks[1]))
    await asyncio.sleep(0)  # let the gather start
    try:
        await tasks[0]  # can't await because this task is part of the gather
    except RuntimeError as er:
        print(repr(er))
    await gt

    print("====")

    # Test case where can't gather on a task being waited.
    tasks = [asyncio.create_task(task(1)), asyncio.create_task(task(2))]
    asyncio.create_task(gather_task(tasks[0], tasks[1]))
    await tasks[0]  # wait on this task before the gather starts
    await tasks[1]


asyncio.run(main())