# Copyright (C) 2007 Dan Pascu. See LICENSE for details.
#

"""Helper functions for writing well behaved decorators."""

__all__ = ['decorator', 'preserve_signature']

def decorator(func):
    """A syntactic marker with no other effect than improving readability."""
    return func

def preserve_signature(func):
    """Preserve the original function signature and attributes in decorator wrappers."""
    from inspect import getargspec, formatargspec
    signature  = formatargspec(*getargspec(func))[1:-1]
    parameters = formatargspec(*getargspec(func), **{'formatvalue': lambda value: ""})[1:-1]
    def fix_signature(wrapper):
        code = "def %s(%s): return wrapper(%s)\nnew_wrapper = %s\n" % (func.__name__, signature, parameters, func.__name__)
        exec code in locals(), locals()
        #expression = "lambda %s: wrapper(%s)" % (signature, parameters)
        #new_wrapper = eval(expression, {'wrapper': wrapper})
        new_wrapper.__name__ = func.__name__
        new_wrapper.__doc__ = func.__doc__
        new_wrapper.__module__ = func.__module__
        new_wrapper.__dict__.update(func.__dict__)
        return new_wrapper
    return fix_signature


__usage__ = """
from application.python.decorator import decorator, preserve_signature

# indicate that the next function will be used as a decorator (optional)
@decorator
def print_args(func):
    @preserve_signature(func)
    def wrapper(*args, **kwargs):
        print "arguments:", args, kwargs
        return func(*args, **kwargs)
    return wrapper

@print_args
def foo(x, y, z=7):
    return x + 3*y + z*z

"""