"""Caching decorator"""
import inspect
import logging
import time

from decorator import decorator
from paste.deploy.converters import asbool

from pylons.decorators.util import get_pylons
    
log = logging.getLogger(__name__)

def beaker_cache(key="cache_default", expire="never", type=None,
                 query_args=False,
                 cache_headers=('content-type', 'content-length'),
                 invalidate_on_startup=False, 
                 cache_response=True, **b_kwargs):
    """Cache decorator utilizing Beaker. Caches action or other
    function that returns a pickle-able object as a result.

    Optional arguments:

    ``key``
        None - No variable key, uses function name as key
        "cache_default" - Uses all function arguments as the key
        string - Use kwargs[key] as key
        list - Use [kwargs[k] for k in list] as key
    ``expire``
        Time in seconds before cache expires, or the string "never". 
        Defaults to "never"
    ``type``
        Type of cache to use: dbm, memory, file, memcached, or None for
        Beaker's default
    ``query_args``
        Uses the query arguments as the key, defaults to False
    ``cache_headers``
        A tuple of header names indicating response headers that
        will also be cached.
    ``invalidate_on_startup``
        If True, the cache will be invalidated each time the application
        starts or is restarted.
    ``cache_response``
        Determines whether the response at the time beaker_cache is used
        should be cached or not, defaults to True.
        
        .. note::
            When cache_response is set to False, the cache_headers
            argument is ignored as none of the response is cached.

    If cache_enabled is set to False in the .ini file, then cache is
    disabled globally.

    """
    if invalidate_on_startup:
        starttime = time.time()
    else:
        starttime = None
    cache_headers = set(cache_headers)

    def wrapper(func, *args, **kwargs):
        """Decorator wrapper"""
        pylons = get_pylons(args)
        log.debug("Wrapped with key: %s, expire: %s, type: %s, query_args: %s",
                  key, expire, type, query_args)
        enabled = pylons.config.get("cache_enabled", "True")
        if not asbool(enabled):
            log.debug("Caching disabled, skipping cache lookup")
            return func(*args, **kwargs)

        if key:
            key_dict = kwargs.copy()
            key_dict.update(_make_dict_from_args(func, args))
            if query_args:
                key_dict.update(pylons.request.GET.mixed())
            
            if key != "cache_default":
                if isinstance(key, list):
                    key_dict = dict((k, key_dict[k]) for k in key)
                else:
                    key_dict = {key: key_dict[key]}
        else:
            key_dict = None

        self = None
        if args:
            self = args[0]
        namespace, cache_key = create_cache_key(func, key_dict, self)

        if type:
            b_kwargs['type'] = type
        
        cache_obj = getattr(pylons.app_globals, 'cache', None)
        if not cache_obj:
            cache_obj = getattr(pylons, 'cache', None)
        if not cache_obj:
            raise Exception('No cache object found')
        my_cache = cache_obj.get_cache(namespace, **b_kwargs)
            
        if expire == "never":
            cache_expire = None
        else:
            cache_expire = expire
        
        def create_func():
            log.debug("Creating new cache copy with key: %s, type: %s",
                      cache_key, type)
            result = func(*args, **kwargs)
            glob_response = pylons.response
            headers = glob_response.headerlist
            status = glob_response.status
            full_response = dict(headers=headers, status=status,
                                 cookies=None, content=result)
            return full_response
        
        response = my_cache.get_value(cache_key, createfunc=create_func,
                                      expiretime=cache_expire,
                                      starttime=starttime)
        if cache_response:
            glob_response = pylons.response
            glob_response.headerlist = [header for header in response['headers']
                                        if header[0].lower() in cache_headers]
            glob_response.status = response['status']

        return response['content']
    return decorator(wrapper)

def create_cache_key(func, key_dict=None, self=None):
    """Get a cache namespace and key used by the beaker_cache decorator.
    
    Example::
        from pylons import cache
        from pylons.decorators.cache import create_cache_key
        namespace, key = create_cache_key(MyController.some_method)
        cache.get_cache(namespace).remove(key)
            
    """
    kls = None
    if hasattr(func, 'im_func'):
        kls = func.im_class
        func = func.im_func
        cache_key = func.__name__
    else:
        cache_key = func.__name__
    if key_dict:
        cache_key += " " + " ".join("%s=%s" % (k, v)
                                    for k, v in key_dict.iteritems())

    if not kls and self:
        kls = getattr(self, '__class__', None)
    
    if kls:
        return '%s.%s' % (kls.__module__, kls.__name__), cache_key
    else:
        return func.__module__, cache_key

def _make_dict_from_args(func, args):
    """Inspects function for name of args"""
    args_keys = {}
    for i, arg in enumerate(inspect.getargspec(func)[0]):
        if arg != "self":
            args_keys[arg] = args[i]
    return args_keys
