from decorator import FunctionMaker

from .pool import runInDBPool

from .utils import WithSession

import inspect

class DBDefer(object):

    '''a twisted sqlalchemy connector this Decorator adds a session parameter, with a valid session connection'''

    def __init__(self, engine, autocommit=False):

        self.autocommit=autocommit

        self.engine = engine

    def __call__(self, func):

        @runInDBPool

        def wrapper(func,*a, **kw):

            pos = argspec.args.index("session")

            ab=list(a[:pos])

            ae=list(a[pos:])

            with WithSession(self.engine, self.autocommit) as session:

                al = ab+[session]+ae

                return func(*al, **kw)

        caller=func

        argspec = inspect.getargspec(caller)

        args =[i for i in argspec.args if i != "session" ]

        sargs=", ".join(args)        

        evaldict = caller.func_globals.copy()

        evaldict['_call_'] = func

        evaldict['decorator'] = wrapper

        wrap = FunctionMaker.create(

              '%s(%s)' % (caller.__name__, sargs), 

              'return decorator(_call_, %s)' % sargs,

              evaldict, defaults=argspec.defaults, undecorated=caller, __wrapped__=caller,

              doc=caller.__doc__, module=caller.__module__, addsource=True)

        return wrap

dbdefer=DBDefer(None)

def setEngine(engine,autocommit=False): 

    dbdefer.engine = engine

    dbdefer.autocommit = autocommit