from __future__ import division, absolute_import, unicode_literals
import errno
import functools


__all__ = ('decorator', 'memoize', 'interruptable')


def decorator(caller, func=None):
    """
    Create a new decorator

    decorator(caller) converts a caller function into a decorator;
    decorator(caller, func) decorates a function using a caller.

    """
    if func is None:
        # return a decorator
        @functools.wraps(caller)
        def _decorator(f, *args, **opts):
            @functools.wraps(f)
            def _caller(*args, **opts):
                return caller(f, *args, **opts)
            return _caller
        _decorator.func = caller
        return _decorator
    else:
        # return a decorated function
        @functools.wraps(func)
        def _decorated(*args, **opts):
            return caller(func, *args, **opts)
        _decorated.func = func
        return _decorated


def memoize(func):
    """
    A decorator for memoizing function calls

    http://en.wikipedia.org/wiki/Memoization

    """
    func.cache = {}
    return decorator(_memoize, func)


def _memoize(func, *args, **opts):
    """Implements memoized cache lookups"""
    if opts:  # frozenset is used to ensure hashability
        key = args, frozenset(opts.items())
    else:
        key = args
    cache = func.cache  # attribute added by memoize
    try:
        result = cache[key]
    except KeyError:
        result = cache[key] = func(*args, **opts)
    return result


@decorator
def interruptable(func, *args, **opts):
    """Handle interruptable system calls

    OSX and others are known to interrupt system calls

        http://en.wikipedia.org/wiki/PCLSRing
        http://en.wikipedia.org/wiki/Unix_philosophy#Worse_is_better

    The @interruptable decorator handles this situation

    """
    while True:
        try:
            result = func(*args, **opts)
        except IOError as e:
            if e.errno == errno.EINTR:
                continue
            raise e
        except OSError as e:
            if e.errno in (errno.EINTR, errno.EINVAL):
                continue
            raise e
        else:
            break
    return result
