# Copyright 2021-2022 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# -----------------------------------------------------------------------------
# Imports
# -----------------------------------------------------------------------------
import asyncio
import logging
import traceback
import collections
from contextlib import ExitStack
import sys
from typing import (
    Awaitable,
    Callable,
    ContextManager,
    Mapping,
    Optional,
    Set,
    Tuple,
    TypeVar,
)
import functools
from pyee import EventEmitter

from .colors import color

# -----------------------------------------------------------------------------
# Logging
# -----------------------------------------------------------------------------
logger = logging.getLogger(__name__)


# -----------------------------------------------------------------------------
def setup_event_forwarding(emitter, forwarder, event_name):
    def emit(*args, **kwargs):
        forwarder.emit(event_name, *args, **kwargs)

    emitter.on(event_name, emit)


# -----------------------------------------------------------------------------
def composite_listener(cls):
    """
    Decorator that adds a `register` and `deregister` method to a class, which
    registers/deregisters all methods named `on_<event_name>` as a listener for
    the <event_name> event with an emitter.
    """
    # pylint: disable=protected-access

    def register(self, emitter):
        for method_name in dir(cls):
            if method_name.startswith('on_'):
                emitter.on(method_name[3:], getattr(self, method_name))

    def deregister(self, emitter):
        for method_name in dir(cls):
            if method_name.startswith('on_'):
                emitter.remove_listener(method_name[3:], getattr(self, method_name))

    cls._bumble_register_composite = register
    cls._bumble_deregister_composite = deregister
    return cls


# -----------------------------------------------------------------------------
_T = TypeVar('_T')


class AbortableEventEmitter(EventEmitter):
    def abort_on(self, event: str, awaitable: Awaitable[_T]) -> Awaitable[_T]:
        """
        Set a coroutine or future to abort when an event occur.
        """
        future = asyncio.ensure_future(awaitable)
        if future.done():
            return future

        def on_event(*_):
            if future.done():
                return
            msg = f'abort: {event} event occurred.'
            if isinstance(future, asyncio.Task):
                # python < 3.9 does not support passing a message on `Task.cancel`
                if sys.version_info < (3, 9, 0):
                    future.cancel()
                else:
                    future.cancel(msg)
            else:
                future.set_exception(asyncio.CancelledError(msg))

        def on_done(_):
            self.remove_listener(event, on_event)

        self.on(event, on_event)
        future.add_done_callback(on_done)
        return future


# -----------------------------------------------------------------------------
class CompositeEventEmitter(AbortableEventEmitter):
    def __init__(self):
        super().__init__()
        self._listener = None

    @property
    def listener(self):
        return self._listener

    @listener.setter
    def listener(self, listener):
        # pylint: disable=protected-access
        if self._listener:
            # Call the deregistration methods for each base class that has them
            for cls in self._listener.__class__.mro():
                if hasattr(cls, '_bumble_register_composite'):
                    cls._bumble_deregister_composite(listener, self)
        self._listener = listener
        if listener:
            # Call the registration methods for each base class that has them
            for cls in listener.__class__.mro():
                if hasattr(cls, '_bumble_deregister_composite'):
                    cls._bumble_register_composite(listener, self)


# -----------------------------------------------------------------------------
class AsyncRunner:
    class WorkQueue:
        def __init__(self, create_task=True):
            self.queue = None
            self.task = None
            self.create_task = create_task

        def enqueue(self, coroutine):
            # Create a task now if we need to and haven't done so already
            if self.create_task and self.task is None:
                self.task = asyncio.create_task(self.run())

            # Lazy-create the coroutine queue
            if self.queue is None:
                self.queue = asyncio.Queue()

            # Enqueue the work
            self.queue.put_nowait(coroutine)

        async def run(self):
            while True:
                item = await self.queue.get()
                try:
                    await item
                except Exception as error:
                    logger.warning(
                        f'{color("!!! Exception in work queue:", "red")} {error}'
                    )

    # Shared default queue
    default_queue = WorkQueue()

    # Shared set of running tasks
    running_tasks: Set[Awaitable] = set()

    @staticmethod
    def run_in_task(queue=None):
        """
        Function decorator used to adapt an async function into a sync function
        """

        def decorator(func):
            @functools.wraps(func)
            def wrapper(*args, **kwargs):
                coroutine = func(*args, **kwargs)
                if queue is None:
                    # Create a task to run the coroutine
                    async def run():
                        try:
                            await coroutine
                        except Exception:
                            logger.warning(
                                f'{color("!!! Exception in wrapper:", "red")} '
                                f'{traceback.format_exc()}'
                            )

                    asyncio.create_task(run())
                else:
                    # Queue the coroutine to be awaited by the work queue
                    queue.enqueue(coroutine)

            return wrapper

        return decorator

    @staticmethod
    def spawn(coroutine):
        """
        Spawn a task to run a coroutine in a "fire and forget" mode.

        Using this method instead of just calling `asyncio.create_task(coroutine)`
        is necessary when you don't keep a reference to the task, because `asyncio`
        only keeps weak references to alive tasks.
        """
        task = asyncio.create_task(coroutine)
        AsyncRunner.running_tasks.add(task)
        task.add_done_callback(AsyncRunner.running_tasks.remove)


# -----------------------------------------------------------------------------
class FlowControlAsyncPipe:
    """
    Asyncio pipe with flow control. When writing to the pipe, the source is
    paused (by calling a function passed in when the pipe is created) if the
    amount of queued data exceeds a specified threshold.
    """

    def __init__(
        self,
        pause_source,
        resume_source,
        write_to_sink=None,
        drain_sink=None,
        threshold=0,
    ):
        self.pause_source = pause_source
        self.resume_source = resume_source
        self.write_to_sink = write_to_sink
        self.drain_sink = drain_sink
        self.threshold = threshold
        self.queue = collections.deque()  # Queue of packets
        self.queued_bytes = 0  # Number of bytes in the queue
        self.ready_to_pump = asyncio.Event()
        self.paused = False
        self.source_paused = False
        self.pump_task = None

    def start(self):
        if self.pump_task is None:
            self.pump_task = asyncio.create_task(self.pump())

        self.check_pump()

    def stop(self):
        if self.pump_task is not None:
            self.pump_task.cancel()
            self.pump_task = None

    def write(self, packet):
        self.queued_bytes += len(packet)
        self.queue.append(packet)

        # Pause the source if we're over the threshold
        if self.queued_bytes > self.threshold and not self.source_paused:
            logger.debug(f'pausing source (queued={self.queued_bytes})')
            self.pause_source()
            self.source_paused = True

        self.check_pump()

    def pause(self):
        if not self.paused:
            self.paused = True
            if not self.source_paused:
                self.pause_source()
                self.source_paused = True
            self.check_pump()

    def resume(self):
        if self.paused:
            self.paused = False
            if self.source_paused:
                self.resume_source()
                self.source_paused = False
            self.check_pump()

    def can_pump(self):
        return self.queue and not self.paused and self.write_to_sink is not None

    def check_pump(self):
        if self.can_pump():
            self.ready_to_pump.set()
        else:
            self.ready_to_pump.clear()

    async def pump(self):
        while True:
            # Wait until we can try to pump packets
            await self.ready_to_pump.wait()

            # Try to pump a packet
            if self.can_pump():
                packet = self.queue.pop()
                self.write_to_sink(packet)
                self.queued_bytes -= len(packet)

                # Drain the sink if we can
                if self.drain_sink:
                    await self.drain_sink()

                # Check if we can accept more
                if self.queued_bytes <= self.threshold and self.source_paused:
                    logger.debug(f'resuming source (queued={self.queued_bytes})')
                    self.source_paused = False
                    self.resume_source()

            self.check_pump()


# -----------------------------------------------------------------------------
def event_emitter_once_for_group(
    emitter: EventEmitter,
    handlers: Mapping[str, Callable],
    context: Optional[ContextManager] = None,
) -> None:
    """
    Register event listeners as a group, with optional context manager.

    For each entry in the map, an event listener is registered with the emitter.
    When any of the event names in the handlers map is emitted by the emitter,
    the corresponding handler is invoked, then all of the listeners are removed from
    the emitter.
    If a context manager is specified, it will be entered prior to registering the
    listeners, and exited when any of the events is emitted.

    Args:
      emitter:
        The event emitter with which to register the event listeners.
      handlers:
        A map that associates an event name with an event handler.
      context:
        A context manager to manager resources, or None if not needed.
    """
    event_emitters_once_for_group(
        {(emitter, event_name): handler for event_name, handler in handlers.items()},
        context,
    )


# -----------------------------------------------------------------------------
def event_emitters_once_for_group(
    handlers: Mapping[Tuple[EventEmitter, str], Callable],
    context: Optional[ContextManager] = None,
) -> None:
    """
    Register event listeners as a group, with optional context manager.

    Similar to event_emitter_once_for_group, but instead of registering the listeners
    with a single emitter, each event may by associate with a different emitter.

    Args:
      handlers:
        A map that associates an (emitter, event_name) pair with an event handler.
      context:
        A context manager to manager resources, or None if not needed.
    """
    # Setup an exit stack to enter and exit the context, if any.
    if context is not None:
        exit_stack = ExitStack()
        exit_stack.enter_context(context)
    else:
        exit_stack = None

    def on_event(handler, *args, **kwargs) -> None:
        # Invoke the handler.
        handler(*args, **kwargs)

        # Release the context, if any.
        if exit_stack is not None:
            exit_stack.close()

        # Remove all listeners.
        for (emitter, event_name), listener in listeners.items():
            emitter.remove_listener(event_name, listener)

    listeners = {
        (emitter, event_name): emitter.on(
            event_name, functools.partial(on_event, handler)
        )
        for (emitter, event_name), handler in handlers.items()
    }