#!/usr/bin/env python3

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

from overrides import overrides

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

T = TypeVar('T')


def wait_any(futures: List[SmartFuture], *, callback: Callable = None):
    real_futures = []
    smart_future_by_real_future = {}
    completed_futures = set()
    for _ in futures:
        real_futures.append(_.wrapped_future)
        smart_future_by_real_future[_.wrapped_future] = _
    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)
            yield smart_future_by_real_future[f]
    if callback is not None:
        callback()
    return


def wait_all(futures: List[SmartFuture]) -> None:
    real_futures = [x.wrapped_future for x in futures]
    (done, not_done) = concurrent.futures.wait(
        real_futures, timeout=None, return_when=concurrent.futures.ALL_COMPLETED
    )
    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:
        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)