"""Synchronization primitives."""

__all__ = ('Lock', 'Event', 'Condition', 'Semaphore', 'BoundedSemaphore')

import collections
import warnings

from . import events
from . import futures
from .coroutines import coroutine


class _ContextManager:
 """Context manager.

 This enables the following idiom for acquiring and releasing a
 lock around a block:

 with (yield from lock):
 <block>

 while failing loudly when accidentally using:

 with lock:
 <block>

 Deprecated, use 'async with' statement:
 async with lock:
 <block>
 """

 def __init__(self, lock):
 self._lock = lock

 def __enter__(self):
 # We have no use for the "as ..." clause in the with
 # statement for locks.
 return None

 def __exit__(self, *args):
 try:
 self._lock.release()
 finally:
 self._lock = None # Crudely prevent reuse.


class _ContextManagerMixin:
 def __enter__(self):
 raise RuntimeError(
 '"yield from" should be used as context manager expression')

 def __exit__(self, *args):
 # This must exist because __enter__ exists, even though that
 # always raises; that's how the with-statement works.
 pass

 @coroutine
 def __iter__(self):
 # This is not a coroutine. It is meant to enable the idiom:
 #
 # with (yield from lock):
 # <block>
 #
 # as an alternative to:
 #
 # yield from lock.acquire()
 # try:
 # <block>
 # finally:
 # lock.release()
 # Deprecated, use 'async with' statement:
 # async with lock:
 # <block>
 warnings.warn("'with (yield from lock)' is deprecated "
 "use 'async with lock' instead",
 DeprecationWarning, stacklevel=2)
 yield from self.acquire()
 return _ContextManager(self)

 async def __acquire_ctx(self):
 await self.acquire()
 return _ContextManager(self)

 def __await__(self):
 warnings.warn("'with await lock' is deprecated "
 "use 'async with lock' instead",
 DeprecationWarning, stacklevel=2)
 # To make "with await lock" work.
 return self.__acquire_ctx().__await__()

 async def __aenter__(self):
 await self.acquire()
 # We have no use for the "as ..." clause in the with
 # statement for locks.
 return None

 async def __aexit__(self, exc_type, exc, tb):
 self.release()


class Lock(_ContextManagerMixin):
 """Primitive lock objects.

 A primitive lock is a synchronization primitive that is not owned
 by a particular coroutine when locked. A primitive lock is in one
 of two states, 'locked' or 'unlocked'.

 It is created in the unlocked state. It has two basic methods,
 acquire() and release(). When the state is unlocked, acquire()
 changes the state to locked and returns immediately. When the
 state is locked, acquire() blocks until a call to release() in
 another coroutine changes it to unlocked, then the acquire() call
 resets it to locked and returns. The release() method should only
 be called in the locked state; it changes the state to unlocked
 and returns immediately. If an attempt is made to release an
 unlocked lock, a RuntimeError will be raised.

 When more than one coroutine is blocked in acquire() waiting for
 the state to turn to unlocked, only one coroutine proceeds when a
 release() call resets the state to unlocked; first coroutine which
 is blocked in acquire() is being processed.

 acquire() is a coroutine and should be called with 'await'.

 Locks also support the asynchronous context management protocol.
 'async with lock' statement should be used.

 Usage:

 lock = Lock()
 ...
 await lock.acquire()
 try:
 ...
 finally:
 lock.release()

 Context manager usage:

 lock = Lock()
 ...
 async with lock:
 ...

 Lock objects can be tested for locking state:

 if not lock.locked():
 await lock.acquire()
 else:
 # lock is acquired
 ...

 """

 def __init__(self, *, loop=None):
 self._waiters = collections.deque()
 self._locked = False
 if loop is not None:
 self._loop = loop
 else:
 self._loop = events.get_event_loop()

 def __repr__(self):
 res = super().__repr__()
 extra = 'locked' if self._locked else 'unlocked'
 if self._waiters:
 extra = f'{extra}, waiters:{len(self._waiters)}'
 return f'<{res[1:-1]} [{extra}]>'

 def locked(self):
 """Return True if lock is acquired."""
 return self._locked

 async def acquire(self):
 """Acquire a lock.

 This method blocks until the lock is unlocked, then sets it to
 locked and returns True.
 """
 if not self._locked and all(w.cancelled() for w in self._waiters):
 self._locked = True
 return True

 fut = self._loop.create_future()
 self._waiters.append(fut)

 # Finally block should be called before the CancelledError
 # handling as we don't want CancelledError to call
 # _wake_up_first() and attempt to wake up itself.
 try:
 try:
 await fut
 finally:
 self._waiters.remove(fut)
 except futures.CancelledError:
 if not self._locked:
 self._wake_up_first()
 raise

 self._locked = True
 return True

 def release(self):
 """Release a lock.

 When the lock is locked, reset it to unlocked, and return.
 If any other coroutines are blocked waiting for the lock to become
 unlocked, allow exactly one of them to proceed.

 When invoked on an unlocked lock, a RuntimeError is raised.

 There is no return value.
 """
 if self._locked:
 self._locked = False
 self._wake_up_first()
 else:
 raise RuntimeError('Lock is not acquired.')

 def _wake_up_first(self):
 """Wake up the first waiter if it isn't done."""
 try:
 fut = next(iter(self._waiters))
 except StopIteration:
 return

 # .done() necessarily means that a waiter will wake up later on and
 # either take the lock, or, if it was cancelled and lock wasn't
 # taken already, will hit this again and wake up a new waiter.
 if not fut.done():
 fut.set_result(True)


class Event:
 """Asynchronous equivalent to threading.Event.

 Class implementing event objects. An event manages a flag that can be set
 to true with the set() method and reset to false with the clear() method.
 The wait() method blocks until the flag is true. The flag is initially
 false.
 """

 def __init__(self, *, loop=None):
 self._waiters = collections.deque()
 self._value = False
 if loop is not None:
 self._loop = loop
 else:
 self._loop = events.get_event_loop()

 def __repr__(self):
 res = super().__repr__()
 extra = 'set' if self._value else 'unset'
 if self._waiters:
 extra = f'{extra}, waiters:{len(self._waiters)}'
 return f'<{res[1:-1]} [{extra}]>'

 def is_set(self):
 """Return True if and only if the internal flag is true."""
 return self._value

 def set(self):
 """Set the internal flag to true. All coroutines waiting for it to
 become true are awakened. Coroutine that call wait() once the flag is
 true will not block at all.
 """
 if not self._value:
 self._value = True

 for fut in self._waiters:
 if not fut.done():
 fut.set_result(True)

 def clear(self):
 """Reset the internal flag to false. Subsequently, coroutines calling
 wait() will block until set() is called to set the internal flag
 to true again."""
 self._value = False

 async def wait(self):
 """Block until the internal flag is true.

 If the internal flag is true on entry, return True
 immediately. Otherwise, block until another coroutine calls
 set() to set the flag to true, then return True.
 """
 if self._value:
 return True

 fut = self._loop.create_future()
 self._waiters.append(fut)
 try:
 await fut
 return True
 finally:
 self._waiters.remove(fut)


class Condition(_ContextManagerMixin):
 """Asynchronous equivalent to threading.Condition.

 This class implements condition variable objects. A condition variable
 allows one or more coroutines to wait until they are notified by another
 coroutine.

 A new Lock object is created and used as the underlying lock.
 """

 def __init__(self, lock=None, *, loop=None):
 if loop is not None:
 self._loop = loop
 else:
 self._loop = events.get_event_loop()

 if lock is None:
 lock = Lock(loop=self._loop)
 elif lock._loop is not self._loop:
 raise ValueError("loop argument must agree with lock")

 self._lock = lock
 # Export the lock's locked(), acquire() and release() methods.
 self.locked = lock.locked
 self.acquire = lock.acquire
 self.release = lock.release

 self._waiters = collections.deque()

 def __repr__(self):
 res = super().__repr__()
 extra = 'locked' if self.locked() else 'unlocked'
 if self._waiters:
 extra = f'{extra}, waiters:{len(self._waiters)}'
 return f'<{res[1:-1]} [{extra}]>'

 async def wait(self):
 """Wait until notified.

 If the calling coroutine has not acquired the lock when this
 method is called, a RuntimeError is raised.

 This method releases the underlying lock, and then blocks
 until it is awakened by a notify() or notify_all() call for
 the same condition variable in another coroutine. Once
 awakened, it re-acquires the lock and returns True.
 """
 if not self.locked():
 raise RuntimeError('cannot wait on un-acquired lock')

 self.release()
 try:
 fut = self._loop.create_future()
 self._waiters.append(fut)
 try:
 await fut
 return True
 finally:
 self._waiters.remove(fut)

 finally:
 # Must reacquire lock even if wait is cancelled
 cancelled = False
 while True:
 try:
 await self.acquire()
 break
 except futures.CancelledError:
 cancelled = True

 if cancelled:
 raise futures.CancelledError

 async def wait_for(self, predicate):
 """Wait until a predicate becomes true.

 The predicate should be a callable which result will be
 interpreted as a boolean value. The final predicate value is
 the return value.
 """
 result = predicate()
 while not result:
 await self.wait()
 result = predicate()
 return result

 def notify(self, n=1):
 """By default, wake up one coroutine waiting on this condition, if any.
 If the calling coroutine has not acquired the lock when this method
 is called, a RuntimeError is raised.

 This method wakes up at most n of the coroutines waiting for the
 condition variable; it is a no-op if no coroutines are waiting.

 Note: an awakened coroutine does not actually return from its
 wait() call until it can reacquire the lock. Since notify() does
 not release the lock, its caller should.
 """
 if not self.locked():
 raise RuntimeError('cannot notify on un-acquired lock')

 idx = 0
 for fut in self._waiters:
 if idx >= n:
 break

 if not fut.done():
 idx += 1
 fut.set_result(False)

 def notify_all(self):
 """Wake up all threads waiting on this condition. This method acts
 like notify(), but wakes up all waiting threads instead of one. If the
 calling thread has not acquired the lock when this method is called,
 a RuntimeError is raised.
 """
 self.notify(len(self._waiters))


class Semaphore(_ContextManagerMixin):
 """A Semaphore implementation.

 A semaphore manages an internal counter which is decremented by each
 acquire() call and incremented by each release() call. The counter
 can never go below zero; when acquire() finds that it is zero, it blocks,
 waiting until some other thread calls release().

 Semaphores also support the context management protocol.

 The optional argument gives the initial value for the internal
 counter; it defaults to 1. If the value given is less than 0,
 ValueError is raised.
 """

 def __init__(self, value=1, *, loop=None):
 if value < 0:
 raise ValueError("Semaphore initial value must be >= 0")
 self._value = value
 self._waiters = collections.deque()
 if loop is not None:
 self._loop = loop
 else:
 self._loop = events.get_event_loop()

 def __repr__(self):
 res = super().__repr__()
 extra = 'locked' if self.locked() else f'unlocked, value:{self._value}'
 if self._waiters:
 extra = f'{extra}, waiters:{len(self._waiters)}'
 return f'<{res[1:-1]} [{extra}]>'

 def _wake_up_next(self):
 while self._waiters:
 waiter = self._waiters.popleft()
 if not waiter.done():
 waiter.set_result(None)
 return

 def locked(self):
 """Returns True if semaphore can not be acquired immediately."""
 return self._value == 0

 async def acquire(self):
 """Acquire a semaphore.

 If the internal counter is larger than zero on entry,
 decrement it by one and return True immediately. If it is
 zero on entry, block, waiting until some other coroutine has
 called release() to make it larger than 0, and then return
 True.
 """
 while self._value <= 0:
 fut = self._loop.create_future()
 self._waiters.append(fut)
 try:
 await fut
 except:
 # See the similar code in Queue.get.
 fut.cancel()
 if self._value > 0 and not fut.cancelled():
 self._wake_up_next()
 raise
 self._value -= 1
 return True

 def release(self):
 """Release a semaphore, incrementing the internal counter by one.
 When it was zero on entry and another coroutine is waiting for it to
 become larger than zero again, wake up that coroutine.
 """
 self._value += 1
 self._wake_up_next()


class BoundedSemaphore(Semaphore):
 """A bounded semaphore implementation.

 This raises ValueError in release() if it would increase the value
 above the initial value.
 """

 def __init__(self, value=1, *, loop=None):
 self._bound_value = value
 super().__init__(value, loop=loop)

 def release(self):
 if self._value >= self._bound_value:
 raise ValueError('BoundedSemaphore released too many times')
 super().release()