# Adapted with permission from the EdgeDB project;
# license: PSFL.


__all__ = ("TaskGroup",)

from . import events
from . import exceptions
from . import futures
from . import tasks


class TaskGroup:
    """Asynchronous context manager for managing groups of tasks.

    Example use:

        async with asyncio.TaskGroup() as group:
            task1 = group.create_task(some_coroutine(...))
            task2 = group.create_task(other_coroutine(...))
        print("Both tasks have completed now.")

    All tasks are awaited when the context manager exits.

    Any exceptions other than `asyncio.CancelledError` raised within
    a task will cancel all remaining tasks and wait for them to exit.
    The exceptions are then combined and raised as an `ExceptionGroup`.
    """
    def __init__(self):
        self._entered = False
        self._exiting = False
        self._aborting = False
        self._loop = None
        self._parent_task = None
        self._parent_cancel_requested = False
        self._tasks = set()
        self._errors = []
        self._base_error = None
        self._on_completed_fut = None
        self._cancel_on_enter = False

    def __repr__(self):
        info = ['']
        if self._tasks:
            info.append(f'tasks={len(self._tasks)}')
        if self._errors:
            info.append(f'errors={len(self._errors)}')
        if self._aborting:
            info.append('cancelling')
        elif self._entered:
            info.append('entered')

        info_str = ' '.join(info)
        return f'<TaskGroup{info_str}>'

    async def __aenter__(self):
        if self._entered:
            raise RuntimeError(
                f"TaskGroup {self!r} has already been entered")
        if self._loop is None:
            self._loop = events.get_running_loop()
        self._parent_task = tasks.current_task(self._loop)
        if self._parent_task is None:
            raise RuntimeError(
                f'TaskGroup {self!r} cannot determine the parent task')
        self._entered = True
        if self._cancel_on_enter:
            self.cancel()

        return self

    async def __aexit__(self, et, exc, tb):
        tb = None
        try:
            return await self._aexit(et, exc)
        finally:
            # Exceptions are heavy objects that can have object
            # cycles (bad for GC); let's not keep a reference to
            # a bunch of them. It would be nicer to use a try/finally
            # in __aexit__ directly but that introduced some diff noise
            self._parent_task = None
            self._errors = None
            self._base_error = None
            exc = None

    async def _aexit(self, et, exc):
        self._exiting = True

        if (exc is not None and
                self._is_base_error(exc) and
                self._base_error is None):
            self._base_error = exc

        if et is not None and issubclass(et, exceptions.CancelledError):
            propagate_cancellation_error = exc
        else:
            propagate_cancellation_error = None

        if et is not None:
            if not self._aborting:
                # Our parent task is being cancelled:
                #
                #    async with TaskGroup() as g:
                #        g.create_task(...)
                #        await ...  # <- CancelledError
                #
                # or there's an exception in "async with":
                #
                #    async with TaskGroup() as g:
                #        g.create_task(...)
                #        1 / 0
                #
                self._abort()

        # We use while-loop here because "self._on_completed_fut"
        # can be cancelled multiple times if our parent task
        # is being cancelled repeatedly (or even once, when
        # our own cancellation is already in progress)
        while self._tasks:
            if self._on_completed_fut is None:
                self._on_completed_fut = self._loop.create_future()

            try:
                await self._on_completed_fut
            except exceptions.CancelledError as ex:
                if not self._aborting:
                    # Our parent task is being cancelled:
                    #
                    #    async def wrapper():
                    #        async with TaskGroup() as g:
                    #            g.create_task(foo)
                    #
                    # "wrapper" is being cancelled while "foo" is
                    # still running.
                    propagate_cancellation_error = ex
                    self._abort()

            self._on_completed_fut = None

        assert not self._tasks

        if self._base_error is not None:
            try:
                raise self._base_error
            finally:
                exc = None

        if self._parent_cancel_requested:
            # If this flag is set we *must* call uncancel().
            if self._parent_task.uncancel() == 0:
                # If there are no pending cancellations left,
                # don't propagate CancelledError.
                propagate_cancellation_error = None

        # Propagate CancelledError if there is one, except if there
        # are other errors -- those have priority.
        try:
            if propagate_cancellation_error is not None and not self._errors:
                try:
                    raise propagate_cancellation_error
                finally:
                    exc = None
        finally:
            propagate_cancellation_error = None

        if et is not None and not issubclass(et, exceptions.CancelledError):
            self._errors.append(exc)

        if self._errors:
            # If the parent task is being cancelled from the outside
            # of the taskgroup, un-cancel and re-cancel the parent task,
            # which will keep the cancel count stable.
            if self._parent_task.cancelling():
                self._parent_task.uncancel()
                self._parent_task.cancel()
            try:
                raise BaseExceptionGroup(
                    'unhandled errors in a TaskGroup',
                    self._errors,
                ) from None
            finally:
                exc = None

        # Suppress any remaining exception (exceptions deserving to be raised
        # were raised above).
        return True

    def create_task(self, coro, **kwargs):
        """Create a new task in this group and return it.

        Similar to `asyncio.create_task`.
        """
        if not self._entered:
            coro.close()
            raise RuntimeError(f"TaskGroup {self!r} has not been entered")
        if self._exiting and not self._tasks:
            coro.close()
            raise RuntimeError(f"TaskGroup {self!r} is finished")
        if self._aborting:
            coro.close()
            raise RuntimeError(f"TaskGroup {self!r} is shutting down")
        task = self._loop.create_task(coro, **kwargs)

        futures.future_add_to_awaited_by(task, self._parent_task)

        # Always schedule the done callback even if the task is
        # already done (e.g. if the coro was able to complete eagerly),
        # otherwise if the task completes with an exception then it will cancel
        # the current task too early. gh-128550, gh-128588
        self._tasks.add(task)
        task.add_done_callback(self._on_task_done)
        try:
            return task
        finally:
            # gh-128552: prevent a refcycle of
            # task.exception().__traceback__->TaskGroup.create_task->task
            del task

    # Since Python 3.8 Tasks propagate all exceptions correctly,
    # except for KeyboardInterrupt and SystemExit which are
    # still considered special.

    def _is_base_error(self, exc: BaseException) -> bool:
        assert isinstance(exc, BaseException)
        return isinstance(exc, (SystemExit, KeyboardInterrupt))

    def _abort(self):
        self._aborting = True

        for t in self._tasks:
            if not t.done():
                t.cancel()

    def _on_task_done(self, task):
        self._tasks.discard(task)

        futures.future_discard_from_awaited_by(task, self._parent_task)

        if self._on_completed_fut is not None and not self._tasks:
            if not self._on_completed_fut.done():
                self._on_completed_fut.set_result(True)

        if task.cancelled():
            return

        exc = task.exception()
        if exc is None:
            return

        self._errors.append(exc)
        if self._is_base_error(exc) and self._base_error is None:
            self._base_error = exc

        if self._parent_task.done():
            # Not sure if this case is possible, but we want to handle
            # it anyways.
            self._loop.call_exception_handler({
                'message': f'Task {task!r} has errored out but its parent '
                           f'task {self._parent_task} is already completed',
                'exception': exc,
                'task': task,
            })
            return

        if not self._aborting and not self._parent_cancel_requested:
            # If parent task *is not* being cancelled, it means that we want
            # to manually cancel it to abort whatever is being run right now
            # in the TaskGroup.  But we want to mark parent task as
            # "not cancelled" later in __aexit__.  Example situation that
            # we need to handle:
            #
            #    async def foo():
            #        try:
            #            async with TaskGroup() as g:
            #                g.create_task(crash_soon())
            #                await something  # <- this needs to be canceled
            #                                 #    by the TaskGroup, e.g.
            #                                 #    foo() needs to be cancelled
            #        except Exception:
            #            # Ignore any exceptions raised in the TaskGroup
            #            pass
            #        await something_else     # this line has to be called
            #                                 # after TaskGroup is finished.
            self._abort()
            self._parent_cancel_requested = True
            self._parent_task.cancel()

    def cancel(self):
        """Cancel the task group

        `cancel()` will be called on any tasks in the group that aren't yet
        done, as well as the parent (body) of the group.  This will cause the
        task group context manager to exit *without* `asyncio.CancelledError`
        being raised.

        If `cancel()` is called before entering the task group, the group will be
        cancelled upon entry.  This is useful for patterns where one piece of
        code passes an unused TaskGroup instance to another in order to have
        the ability to cancel anything run within the group.

        `cancel()` is idempotent and may be called after the task group has
        already exited.
        """
        if not self._entered:
            self._cancel_on_enter = True
            return
        if self._exiting and not self._tasks:
            return
        if not self._aborting:
            self._abort()
            if self._parent_task and not self._parent_cancel_requested:
                self._parent_cancel_requested = True
                self._parent_task.cancel()
