"""
Basic Concept:
--------------

All concurrency is expressed by some means of coroutines.
This is the lowest possible exposable interface.

A coroutine is a structure that controls a sequence
of continuations in time. It contains a frame object
that is a restartable stack chain. This frame object
is updated on every switch.

The frame can be None. Either the coroutine is not yet
bound, or it is the current coroutine of some costate.
See below. XXX rewrite a definition of these terms.

There is always a notation of a "current" and a "last"
coroutine. Current has no frame and represents the
running program. last is needed to keep track of the
coroutine that receives a new frame chain after a switch.

A costate object holds last and current.
There are different coroutine concepts existing in
parallel, like plain interp-level coroutines and
app-level structures like coroutines, greenlets and
tasklets.
Every concept is associated with its own costate object.
This allows for peaceful co-existence of many concepts.
The type of a switch is determined by the target's costate.
"""

from pypy.rlib.rstack import yield_current_frame_to_caller, resume_point
from pypy.rlib.objectmodel import we_are_translated

try:
    from greenlet import greenlet
    main_greenlet = greenlet.getcurrent()
except (ImportError, ValueError):
    def greenlet(*args, **kwargs):
        raise NotImplementedError("need either greenlets or a translated version of pypy")

class FrameChain(object):
    """Greenlet-based emulation of the primitive rstack 'frames' of RPython"""

    def __init__(self, thunk=None):
        if thunk:
            self.greenlet = greenlet(thunk)
        else:
            self.greenlet = greenlet.getcurrent()

    def switch(self):
        last = FrameChain()
        return self.greenlet.switch(last)

import sys, os

def make_coroutine_classes(baseclass):
    class BaseCoState(object):
        def __init__(self):
            self.current = self.main = None

        def __repr__(self):
            "NOT_RPYTHON"
            # for debugging only
            return '<%s current=%r>' % (self.__class__.__name__, self.current)

        def update(self, new):
            syncstate.leaving = self.current
            syncstate.entering = new
            self.current = new
            frame, new.frame = new.frame, None
            return frame


    class CoState(BaseCoState):
        def __init__(self):
            BaseCoState.__init__(self)
            self.current = self.main = Coroutine(self)

    class CoroutineDamage(SystemError):
        pass


    class SyncState(object):
        def __init__(self):
            self.reset()

        def reset(self):
            self.default_costate = None
            self.leaving = None
            self.entering = None
            self.things_to_do = False
            self.temp_exc = None
            self.to_delete = []

        def switched(self, incoming_frame):
            left = syncstate.leaving
            entered = syncstate.entering
            syncstate.leaving = syncstate.entering = None
            if left is not None:   # mostly to work around an annotation problem;
                                   # should not really be None
                left.frame = incoming_frame
                left.goodbye()
            if entered is not None:
                entered.hello()
            if self.things_to_do:
                self._do_things_to_do()

        def push_exception(self, exc):
            self.things_to_do = True
            self.temp_exc = exc

        def check_for_zombie(self, obj):
            return co in self.to_delete

        def postpone_deletion(self, obj):
            self.to_delete.append(obj)
            self.things_to_do = True

        def _do_things_to_do(self):
            if self.temp_exc is not None:
                # somebody left an unhandled exception and switched to us.
                # this both provides default exception handling and the
                # way to inject an exception, like CoroutineExit.
                e, self.temp_exc = self.temp_exc, None
                self.things_to_do = bool(self.to_delete)
                raise e
            while self.to_delete:
                delete, self.to_delete = self.to_delete, []
                for obj in delete:
                    obj.parent = obj.costate.current
                    obj._kill_finally()
            else:
                self.things_to_do = False

        def _freeze_(self):
            self.reset()
            return False

    syncstate = SyncState()


    class CoroutineExit(SystemExit):
        # XXX SystemExit's __init__ creates problems in bookkeeper.
        def __init__(self):
            pass

    class AbstractThunk(object):
        def call(self):
            raise NotImplementedError("abstract base class")


    class Coroutine(baseclass):
        def __init__(self, state=None):
            self.frame = None
            if state is None:
                state = self._get_default_costate()
            self.costate = state
            self.parent = None
            self.thunk = None

        def __repr__(self):
            'NOT_RPYTHON'
            # just for debugging
            if hasattr(self, '__name__'):
                return '<Coro %s frame=%r %s>' % (self.__name__, self.frame, self.thunk is not None)
            else:
                return '<coro frame=%r %s>' % (self.frame, self.thunk is not None)

        def _get_default_costate():
            state = syncstate.default_costate
            if state is None:
                state = syncstate.default_costate = CoState()
            return state
        _get_default_costate = staticmethod(_get_default_costate)

        def _get_default_parent(self):
            return self.costate.current

        def bind(self, thunk):
            assert isinstance(thunk, AbstractThunk)
            if self.frame is not None:
                raise CoroutineDamage
            if self.parent is None:
                self.parent = self._get_default_parent()
            assert self.parent is not None
            self.thunk = thunk
            if we_are_translated():
                self.frame = self._bind()
            else:
                self.frame = self._greenlet_bind()

        def _greenlet_bind(self):
            weak = [self]
            def _greenlet_execute(incoming_frame):
                try:
                    chain2go2next = weak[0]._execute(incoming_frame)
                except:
                    # no exception is supposed to get out of _execute()
                    # better report it directly into the main greenlet then,
                    # and hidden to prevent catching
                    main_greenlet.throw(AssertionError(
                        "unexpected exception out of Coroutine._execute()",
                        *sys.exc_info()))
                    assert 0
                del weak[0]
                greenlet.getcurrent().parent = chain2go2next.greenlet
                return None   # as the result of the FrameChain.switch()
            chain = FrameChain(_greenlet_execute)
            return chain

        def _bind(self):
            state = self.costate
            incoming_frame = yield_current_frame_to_caller()
            self = state.current
            return self._execute(incoming_frame)

        def _execute(self, incoming_frame):
            state = self.costate
            try:
                try:
                    try:
                        exc = None
                        thunk = self.thunk
                        self.thunk = None
                        syncstate.switched(incoming_frame)
                        thunk.call()
                        resume_point("coroutine__bind", state)
                    except Exception, e:
                        exc = e
                        raise
                finally:
                    # warning! we must reload the 'self' from the costate,
                    # because after a clone() the 'self' of both copies
                    # point to the original!
                    self = state.current
                    self.finish(exc)
            except CoroutineExit:
                # ignore a shutdown exception
                pass
            except Exception, e:
                # redirect all unhandled exceptions to the parent
                syncstate.push_exception(e)
            while self.parent is not None and self.parent.frame is None:
                # greenlet behavior is fine
                self.parent = self.parent.parent
            return state.update(self.parent)

        def switch(self):
            if self.frame is None:
                # considered a programming error.
                # greenlets and tasklets have different ideas about this.
                raise CoroutineDamage
            state = self.costate
            incoming_frame = state.update(self).switch()
            resume_point("coroutine_switch", state, returns=incoming_frame)
            syncstate.switched(incoming_frame)

        def kill(self):
            if self.frame is None:
                return
            state = self.costate
            syncstate.push_exception(CoroutineExit())
            # careful here - if setting self.parent to state.current would
            # create a loop, break it.  The assumption is that 'self'
            # will die, so that state.current's chain of parents can be
            # modified to skip 'self' without too many people noticing.
            p = state.current
            if p is self or self.parent is None:
                pass  # killing the current of the main - don't change any parent
            else:
                while p.parent is not None:
                    if p.parent is self:
                        p.parent = self.parent
                        break
                    p = p.parent
                self.parent = state.current
            self.switch()

        def _kill_finally(self):
            try:
                self._userdel()
            except Exception:
                pass # maybe print a warning?
            self.kill()

        __already_postponed = False
    
        def __del__(self):
            # provide the necessary clean-up
            # note that AppCoroutine has to take care about this
            # as well, including a check for user-supplied __del__.
            # Additionally note that in the context of __del__, we are
            # not in the position to issue a switch.
            # we defer it completely.
            
            # it is necessary to check whether syncstate is None because CPython
            # sets it to None when it cleans up the modules, which will lead to
            # very strange effects

            if not we_are_translated():
                # we need to make sure that we postpone each coroutine only once on
                # top of CPython, because this resurrects the coroutine and CPython
                # calls __del__ again, thus postponing and resurrecting the
                # coroutine once more :-(
                if self.__already_postponed:
                    return
                self.__already_postponed = True
            if syncstate is not None:
                syncstate.postpone_deletion(self)

        # coroutines need complete control over their __del__ behaviour. In
        # particular they need to care about calling space.userdel themselves
        handle_del_manually = True

        def _userdel(self):
            # override this for exposed coros
            pass

        def is_alive(self):
            return self.frame is not None or self is self.costate.current

        def is_zombie(self):
            return self.frame is not None and syncstate.check_for_zombie(self)

        def getcurrent():
            costate = Coroutine._get_default_costate()
            return costate.current
        getcurrent = staticmethod(getcurrent)

        def getmain():
            costate = Coroutine._get_default_costate()
            return costate.main
        getmain = staticmethod(getmain)

        def hello(self):
            "Called when execution is transferred into this coroutine."

        def goodbye(self):
            "Called just after execution is transferred away from this coroutine."

        def finish(self, exc=None):
            "stephan forgot me"

    return locals()

# _________________________________________________