#!/usr/bin/env python3

# © Copyright 2021-2022, Scott Gasch

"""A future that can be treated like the result that it contains and
will not block until it is used.  At that point, if the underlying
value is not yet available, it will block until it becomes
available.

"""

from __future__ import annotations
import concurrent
import concurrent.futures as fut
import logging
from typing import Callable, List, Set, TypeVar

from overrides import overrides

import id_generator

# This module is commonly used by others in here and should avoid
# taking any unnecessary dependencies back on them.
from deferred_operand import DeferredOperand

logger = logging.getLogger(__name__)

T = TypeVar('T')


def wait_any(
    futures: List[SmartFuture],
    *,
    callback: Callable = None,
    log_exceptions: bool = True,
):
    real_futures = []
    smart_future_by_real_future = {}
    completed_futures: Set[fut.Future] = set()
    for x in futures:
        assert isinstance(x, SmartFuture)
        real_futures.append(x.wrapped_future)
        smart_future_by_real_future[x.wrapped_future] = x

    while len(completed_futures) != len(real_futures):
        newly_completed_futures = concurrent.futures.as_completed(real_futures)
        for f in newly_completed_futures:
            if callback is not None:
                callback()
            completed_futures.add(f)
            if log_exceptions and not f.cancelled():
                exception = f.exception()
                if exception is not None:
                    logger.warning('Future 0x%x raised an unhandled exception and exited.', id(f))
                    logger.exception(exception)
                    raise exception
            yield smart_future_by_real_future[f]
    if callback is not None:
        callback()


def wait_all(
    futures: List[SmartFuture],
    *,
    log_exceptions: bool = True,
) -> None:
    real_futures = []
    for x in futures:
        assert isinstance(x, SmartFuture)
        real_futures.append(x.wrapped_future)

    (done, not_done) = concurrent.futures.wait(
        real_futures, timeout=None, return_when=concurrent.futures.ALL_COMPLETED
    )
    if log_exceptions:
        for f in real_futures:
            if not f.cancelled():
                exception = f.exception()
                if exception is not None:
                    logger.warning('Future 0x%x raised an unhandled exception and exited.', id(f))
                    logger.exception(exception)
                    raise exception
    assert len(done) == len(real_futures)
    assert len(not_done) == 0


class SmartFuture(DeferredOperand):
    """This is a SmartFuture, a class that wraps a normal Future and can
    then be used, mostly, like a normal (non-Future) identifier.

    Using a FutureWrapper in expressions will block and wait until
    the result of the deferred operation is known.
    """

    def __init__(self, wrapped_future: fut.Future) -> None:
        assert isinstance(wrapped_future, fut.Future)
        self.wrapped_future = wrapped_future
        self.id = id_generator.get("smart_future_id")

    def get_id(self) -> int:
        return self.id

    def is_ready(self) -> bool:
        return self.wrapped_future.done()

    # You shouldn't have to call this; instead, have a look at defining a
    # method on DeferredOperand base class.
    @overrides
    def _resolve(self, timeout=None) -> T:
        return self.wrapped_future.result(timeout)