from django.core.files.storage import Storage
from django.conf import settings
from django.utils.deconstruct import deconstructible

'''
TODO: Create a signal to remove instances from cache if modified
'''

import logging
logger = logging.getLogger(__name__)

@deconstructible
class MultiStorage(Storage):
    ''' Django storage class that proxies multiple storage classes.

    Uses a name prefix to determine store e.g. 'images:foo/bar.jpg'
    '''

    DELIM = ":"

    def __init__(self, config=None):
        self.config = config or getattr(settings, 'BRING_YOUR_OWN_STORAGE', {})
        self._cache = {}

    def get_storage(self, name):
        if name not in self._cache:
            config = self.config[name]
            self._cache[name] = get_storage_class(config['storage'])(**config['settings'])
        return self._cache[name]

    def split(self, name):
        try:
            storage, p = name.split(self.DELIM, 1)
            return storage, p
        except ValueError:
            raise ValueError(f"Bad storage path [{name}]")

    def join(self, storage, name):
        return self.DELIM.join((storage, name))

    def _proxy(self, method, name, *args, **kwargs):
        storage, p = self.split(name)
        result =  getattr(self.get_storage(storage), method)(p, *args, **kwargs)
        logger.debug("Proxy: %s(%r, *%r, **%r) => %r", method, name, args, kwargs, result)
        return result

    def _proxy_name(self, method, name, *args, **kwargs):
        storage, p = self.split(name)
        result = getattr(self.get_storage(storage), method)(p, *args, **kwargs)
        logger.debug("Proxy: %s(%r, *%r, **%r) => %s:%s", method, name, args, kwargs, storage, result)
        return self.join(storage, result)

    def _open(self, name, mode='rb'):
        return self._proxy('open', name, mode)

    def save(self, name, content, max_length=None):
        return self._proxy_name('save', name, content, max_length)

    def exists(self, name):
        return self._proxy('exists', name)

    def delete(self, name):
        return self._proxy('delete', name)

    def url(self, name):
        return self._proxy('url', name)

    def get_accessed_time(self, name):
        return self._proxy('get_accessed_time', name)

    def get_alternative_name(self, file_root, file_ext):
        return self._proxy_name('get_alternative_name', file_root, file_ext)

    def get_available_name(self, name, max_length=None):
        return self._proxy_name('get_available_name', name, max_length)

    def get_modified_time(self, name):
        return self._proxy('get_modified_time', name)


class BYOStorage(MultiStorage):
    ''' Database driven Bring-Your-Own-Storage

    Multiple storages can 
    '''

    def get_storage(self, name):
        if name not in self._cache:

            # use storage from config by default
            if name in self.config:
                return super(BYOStorage, self).get_storage(name)

            from .models import UserStorage
            obj = UserStorage.objects.get(name=name)
            self._cache[name] = obj.instance()
        return self._cache[name]