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