"""Support for tasks, coroutines and the scheduler."""
from __future__ import print_function

__all__ = ['coroutine', 'Task',
           'iscoroutinefunction', 'iscoroutine',
           'FIRST_COMPLETED', 'FIRST_EXCEPTION', 'ALL_COMPLETED',
           'wait', 'wait_for', 'as_completed', 'sleep', 'async',
           'gather', 'shield', 'Return',
           ]

import collections
import functools
import linecache
import traceback
try:
    from weakref import WeakSet
except ImportError:
    # Python 2.6
    from .py27_weakrefset import WeakSet

from . import events
from . import executor
from . import futures
from .locks import Lock, Condition, Semaphore
from .coroutine import Return, coroutine, iscoroutinefunction, iscoroutine

@coroutine
def lock_coroutine(lock):
    cm = yield lock.acquire()
    raise Return(cm)


class Task(futures.Future):
    """A coroutine wrapped in a Future."""

    # An important invariant maintained while a Task not done:
    #
    # - Either _fut_waiter is None, and _step() is scheduled;
    # - or _fut_waiter is some Future, and _step() is *not* scheduled.
    #
    # The only transition from the latter to the former is through
    # _wakeup().  When _fut_waiter is not None, one of its callbacks
    # must be _wakeup().

    # Weak set containing all tasks alive.
    _all_tasks = WeakSet()

    # Dictionary containing tasks that are currently active in
    # all running event loops.  {EventLoop: Task}
    _current_tasks = {}

    @classmethod
    def current_task(cls, loop=None):
        """Return the currently running task in an event loop or None.

        By default the current task for the current event loop is returned.

        None is returned when called not in the context of a Task.
        """
        if loop is None:
            loop = events.get_event_loop()
        return cls._current_tasks.get(loop)

    @classmethod
    def all_tasks(cls, loop=None):
        """Return a set of all tasks for an event loop.

        By default all tasks for the current event loop are returned.
        """
        if loop is None:
            loop = events.get_event_loop()
        return set(t for t in cls._all_tasks if t._loop is loop)

    def __init__(self, coro, loop=None):
        assert iscoroutine(coro), repr(coro)  # Not a coroutine function!
        super(Task, self).__init__(loop=loop)
        self._coro = iter(coro)  # Use the iterator just in case.
        self._fut_waiter = None
        self._must_cancel = False
        self._loop.call_soon(self._step)
        self.__class__._all_tasks.add(self)

    def __repr__(self):
        res = super(Task, self).__repr__()
        if (self._must_cancel and
            self._state == futures._PENDING and
            '<PENDING' in res):
            res = res.replace('<PENDING', '<CANCELLING', 1)
        i = res.find('<')
        if i < 0:
            i = len(res)
        res = res[:i] + '(<{0}>)'.format(self._coro.__name__) + res[i:]
        return res

    def get_stack(self, limit=None):
        """Return the list of stack frames for this task's coroutine.

        If the coroutine is active, this returns the stack where it is
        suspended.  If the coroutine has completed successfully or was
        cancelled, this returns an empty list.  If the coroutine was
        terminated by an exception, this returns the list of traceback
        frames.

        The frames are always ordered from oldest to newest.

        The optional limit gives the maximum nummber of frames to
        return; by default all available frames are returned.  Its
        meaning differs depending on whether a stack or a traceback is
        returned: the newest frames of a stack are returned, but the
        oldest frames of a traceback are returned.  (This matches the
        behavior of the traceback module.)

        For reasons beyond our control, only one stack frame is
        returned for a suspended coroutine.
        """
        frames = []
        f = self._coro.gi_frame
        if f is not None:
            while f is not None:
                if limit is not None:
                    if limit <= 0:
                        break
                    limit -= 1
                frames.append(f)
                f = f.f_back
            frames.reverse()
        elif self._exception is not None:
            tb = self._exception.__traceback__
            while tb is not None:
                if limit is not None:
                    if limit <= 0:
                        break
                    limit -= 1
                frames.append(tb.tb_frame)
                tb = tb.tb_next
        return frames

    def print_stack(self, limit=None, file=None):
        """Print the stack or traceback for this task's coroutine.

        This produces output similar to that of the traceback module,
        for the frames retrieved by get_stack().  The limit argument
        is passed to get_stack().  The file argument is an I/O stream
        to which the output goes; by default it goes to sys.stderr.
        """
        extracted_list = []
        checked = set()
        for f in self.get_stack(limit=limit):
            lineno = f.f_lineno
            co = f.f_code
            filename = co.co_filename
            name = co.co_name
            if filename not in checked:
                checked.add(filename)
                linecache.checkcache(filename)
            line = linecache.getline(filename, lineno, f.f_globals)
            extracted_list.append((filename, lineno, name, line))
        exc = self._exception
        if not extracted_list:
            print('No stack for %r' % self, file=file)
        elif exc is not None:
            print('Traceback for %r (most recent call last):' % self,
                  file=file)
        else:
            print('Stack for %r (most recent call last):' % self,
                  file=file)
        traceback.print_list(extracted_list, file=file)
        if exc is not None:
            for line in traceback.format_exception_only(exc.__class__, exc):
                print(line, file=file, end='')

    def cancel(self):
        if self.done():
            return False
        if self._fut_waiter is not None:
            if self._fut_waiter.cancel():
                # Leave self._fut_waiter; it may be a Task that
                # catches and ignores the cancellation so we may have
                # to cancel it again later.
                return True
        # It must be the case that self._step is already scheduled.
        self._must_cancel = True
        return True

    def _step(self, value=None, exc=None):
        assert not self.done(), \
            '_step(): already done: {0!r}, {1!r}, {2!r}'.format(self, value, exc)
        if self._must_cancel:
            if not isinstance(exc, futures.CancelledError):
                exc = futures.CancelledError()
            self._must_cancel = False
        coro = self._coro
        self._fut_waiter = None

        self.__class__._current_tasks[self._loop] = self
        # Call either coro.throw(exc) or coro.send(value).
        try:
            if exc is not None:
                result = coro.throw(exc)
            elif value is not None:
                result = coro.send(value)
            else:
                result = next(coro)
        except Return as exc:
            exc.raised = True
            self.set_result(exc.value)
        except StopIteration:
            self.set_result(None)
        except futures.CancelledError as exc:
            super(Task, self).cancel()  # I.e., Future.cancel(self).
        except Exception as exc:
            self.set_exception(exc)
        except BaseException as exc:
            self.set_exception(exc)
            raise
        else:
            if iscoroutine(result):
                result = async(result, loop=self._loop)
            # FIXME: faster check. common base class? hasattr?
            elif isinstance(result, (Lock, Condition, Semaphore)):
                result = Task(lock_coroutine(result), loop=self._loop)

            if isinstance(result, futures.Future):
                # Yielded Future must come from Future.__iter__().
                result.add_done_callback(self._wakeup)
                self._fut_waiter = result
                if self._must_cancel:
                    if self._fut_waiter.cancel():
                        self._must_cancel = False
            elif result is None:
                # Bare yield relinquishes control for one event loop iteration.
                self._loop.call_soon(self._step)
            else:
                # Yielding something else is an error.
                self._loop.call_soon(
                    self._step, None,
                    RuntimeError(
                        'Task got bad yield: {0!r}'.format(result)))
        finally:
            self.__class__._current_tasks.pop(self._loop)
        self = None

    def _wakeup(self, future):
        try:
            value = future.result()
        except Exception as exc:
            # This may also be a cancellation.
            self._step(None, exc)
        else:
            self._step(value, None)
        self = None  # Needed to break cycles when an exception occurs.


# wait() and as_completed() similar to those in PEP 3148.

# Export symbols in asyncio.tasks for compatibility with Tulip
FIRST_COMPLETED = executor.FIRST_COMPLETED
FIRST_EXCEPTION = executor.FIRST_EXCEPTION
ALL_COMPLETED = executor.ALL_COMPLETED


@coroutine
def wait(fs, loop=None, timeout=None, return_when=ALL_COMPLETED):
    """Wait for the Futures and coroutines given by fs to complete.

    Coroutines will be wrapped in Tasks.

    Returns two sets of Future: (done, pending).

    Usage:

        done, pending = yield asyncio.wait(fs)

    Note: This does not raise TimeoutError! Futures that aren't done
    when the timeout occurs are returned in the second set.
    """
    if not fs:
        raise ValueError('Set of coroutines/Futures is empty.')

    if loop is None:
        loop = events.get_event_loop()

    fs = set(async(f, loop=loop) for f in set(fs))

    if return_when not in (FIRST_COMPLETED, FIRST_EXCEPTION, ALL_COMPLETED):
        raise ValueError('Invalid return_when value: {0}'.format(return_when))
    result = yield _wait(fs, timeout, return_when, loop)
    raise Return(result)


def _release_waiter(waiter, value=True, *args):
    if not waiter.done():
        waiter.set_result(value)


@coroutine
def wait_for(fut, timeout, loop=None):
    """Wait for the single Future or coroutine to complete, with timeout.

    Coroutine will be wrapped in Task.

    Returns result of the Future or coroutine.  When a timeout occurs,
    it cancels the task and raises TimeoutError.  To avoid the task
    cancellation, wrap it in shield().

    Usage:

        result = yield asyncio.wait_for(fut, 10.0)

    """
    if loop is None:
        loop = events.get_event_loop()

    if timeout is None:
        raise Return((yield fut))

    waiter = futures.Future(loop=loop)
    timeout_handle = loop.call_later(timeout, _release_waiter, waiter, False)
    cb = functools.partial(_release_waiter, waiter, True)

    fut = async(fut, loop=loop)
    fut.add_done_callback(cb)

    try:
        if (yield waiter):
            raise Return(fut.result())
        else:
            fut.remove_done_callback(cb)
            fut.cancel()
            raise futures.TimeoutError()
    finally:
        timeout_handle.cancel()


@coroutine
def _wait(fs, timeout, return_when, loop):
    """Internal helper for wait() and _wait_for().

    The fs argument must be a collection of Futures.
    """
    assert fs, 'Set of Futures is empty.'
    waiter = futures.Future(loop=loop)
    timeout_handle = None
    if timeout is not None:
        timeout_handle = loop.call_later(timeout, _release_waiter, waiter)
    non_local = {'counter': len(fs)}

    def _on_completion(f):
        non_local['counter'] -= 1
        if (non_local['counter'] <= 0 or
            return_when == FIRST_COMPLETED or
            return_when == FIRST_EXCEPTION and (not f.cancelled() and
                                                f.exception() is not None)):
            if timeout_handle is not None:
                timeout_handle.cancel()
            if not waiter.done():
                waiter.set_result(False)

    for f in fs:
        f.add_done_callback(_on_completion)

    try:
        yield waiter
    finally:
        if timeout_handle is not None:
            timeout_handle.cancel()

    done, pending = set(), set()
    for f in fs:
        f.remove_done_callback(_on_completion)
        if f.done():
            done.add(f)
        else:
            pending.add(f)
    raise Return(done, pending)


# This is *not* a @coroutine!  It is just an iterator (yielding Futures).
def as_completed(fs, loop=None, timeout=None):
    """Return an iterator whose values, when waited for, are Futures.

    This differs from PEP 3148; the proper way to use this is:

        for f in as_completed(fs):
            result = yield f  # The 'yield from' may raise.
            # Use result.

    Raises TimeoutError if the timeout occurs before all Futures are
    done.

    Note: The futures 'f' are not necessarily members of fs.
    """
    loop = loop if loop is not None else events.get_event_loop()
    deadline = None if timeout is None else loop.time() + timeout
    todo = set(async(f, loop=loop) for f in set(fs))
    completed = collections.deque()

    @coroutine
    def _wait_for_one():
        while not completed:
            timeout = None
            if deadline is not None:
                timeout = deadline - loop.time()
                if timeout < 0:
                    raise futures.TimeoutError()
            done, pending = yield _wait(
                todo, timeout, FIRST_COMPLETED, loop)
            # Multiple callers might be waiting for the same events
            # and getting the same outcome.  Dedupe by updating todo.
            for f in done:
                if f in todo:
                    todo.remove(f)
                    completed.append(f)
        f = completed.popleft()
        raise Return(f.result())  # May raise.

    for _ in range(len(todo)):
        yield _wait_for_one()


@coroutine
def sleep(delay, result=None, loop=None):
    """Coroutine that completes after a given time (in seconds)."""
    future = futures.Future(loop=loop)
    h = future._loop.call_later(delay, future.set_result, result)
    try:
        result = yield future
        raise Return(result)
    finally:
        h.cancel()


def async(coro_or_future, loop=None):
    """Wrap a coroutine in a future.

    If the argument is a Future, it is returned directly.
    """
    if isinstance(coro_or_future, futures.Future):
        if loop is not None and loop is not coro_or_future._loop:
            raise ValueError('loop argument must agree with Future')
        return coro_or_future
    elif iscoroutine(coro_or_future):
        return Task(coro_or_future, loop=loop)
    else:
        raise TypeError('A Future or coroutine is required')


class _GatheringFuture(futures.Future):
    """Helper for gather().

    This overrides cancel() to cancel all the children and act more
    like Task.cancel(), which doesn't immediately mark itself as
    cancelled.
    """

    def __init__(self, children, loop=None):
        super(_GatheringFuture, self).__init__(loop=loop)
        self._children = children

    def cancel(self):
        if self.done():
            return False
        for child in self._children:
            child.cancel()
        return True


def gather(*coros_or_futures, **kw):
    """Return a future aggregating results from the given coroutines
    or futures.

    All futures must share the same event loop.  If all the tasks are
    done successfully, the returned future's result is the list of
    results (in the order of the original sequence, not necessarily
    the order of results arrival).  If *return_exceptions* is True,
    exceptions in the tasks are treated the same as successful
    results, and gathered in the result list; otherwise, the first
    raised exception will be immediately propagated to the returned
    future.

    Cancellation: if the outer Future is cancelled, all children (that
    have not completed yet) are also cancelled.  If any child is
    cancelled, this is treated as if it raised CancelledError --
    the outer Future is *not* cancelled in this case.  (This is to
    prevent the cancellation of one child to cause other children to
    be cancelled.)
    """
    loop = kw.pop('loop', None)
    return_exceptions = kw.pop('return_exceptions', False)
    if kw:
        raise TypeError("unexpected keyword")

    arg_to_fut = dict((arg, async(arg, loop=loop))
                      for arg in set(coros_or_futures))
    children = [arg_to_fut[arg] for arg in coros_or_futures]
    n = len(children)
    if n == 0:
        outer = futures.Future(loop=loop)
        outer.set_result([])
        return outer
    if loop is None:
        loop = children[0]._loop
    for fut in children:
        if fut._loop is not loop:
            raise ValueError("futures are tied to different event loops")
    outer = _GatheringFuture(children, loop=loop)
    non_local = {'nfinished': 0}
    results = [None] * n

    def _done_callback(i, fut):
        if outer._state != futures._PENDING:
            if fut._exception is not None:
                # Mark exception retrieved.
                fut.exception()
            return
        if fut._state == futures._CANCELLED:
            res = futures.CancelledError()
            if not return_exceptions:
                outer.set_exception(res)
                return
        elif fut._exception is not None:
            res = fut.exception()  # Mark exception retrieved.
            if not return_exceptions:
                outer.set_exception(res)
                return
        else:
            res = fut._result
        results[i] = res
        non_local['nfinished'] += 1
        if non_local['nfinished'] == n:
            outer.set_result(results)

    for i, fut in enumerate(children):
        fut.add_done_callback(functools.partial(_done_callback, i))
    return outer


def shield(arg, loop=None):
    """Wait for a future, shielding it from cancellation.

    The statement

        res = yield shield(something())

    is exactly equivalent to the statement

        res = yield something()

    *except* that if the coroutine containing it is cancelled, the
    task running in something() is not cancelled.  From the POV of
    something(), the cancellation did not happen.  But its caller is
    still cancelled, so the yield-from expression still raises
    CancelledError.  Note: If something() is cancelled by other means
    this will still cancel shield().

    If you want to completely ignore cancellation (not recommended)
    you can combine shield() with a try/except clause, as follows:

        try:
            res = yield shield(something())
        except CancelledError:
            res = None
    """
    inner = async(arg, loop=loop)
    if inner.done():
        # Shortcut.
        return inner
    loop = inner._loop
    outer = futures.Future(loop=loop)

    def _done_callback(inner):
        if outer.cancelled():
            # Mark inner's result as retrieved.
            inner.cancelled() or inner.exception()
            return
        if inner.cancelled():
            outer.cancel()
        else:
            exc = inner.exception()
            if exc is not None:
                outer.set_exception(exc)
            else:
                outer.set_result(inner.result())

    inner.add_done_callback(_done_callback)
    return outer
