from __future__ import absolute_import

import importlib
import os
import re
import warnings

from anyjson import deserialize
from kombu.utils import cached_property

from celery.datastructures import DictAttribute
from celery.exceptions import ImproperlyConfigured
from celery.utils import get_cls_by_name
from celery.utils import import_from_cwd as _import_from_cwd

BUILTIN_MODULES = frozenset(["celery.task"])

ERROR_ENVVAR_NOT_SET = (
"""The environment variable %r is not set,
and as such the configuration could not be loaded.
Please set this variable and make it point to
a configuration module.""")


class BaseLoader(object):
    """The base class for loaders.

    Loaders handles,

        * Reading celery client/worker configurations.

        * What happens when a task starts?
            See :meth:`on_task_init`.

        * What happens when the worker starts?
            See :meth:`on_worker_init`.

        * What modules are imported to find tasks?

    """
    builtin_modules = BUILTIN_MODULES
    configured = False
    error_envvar_not_set = ERROR_ENVVAR_NOT_SET
    override_backends = {}
    worker_initialized = False

    _conf = None

    def __init__(self, app=None, **kwargs):
        from celery.app import app_or_default
        self.app = app_or_default(app)

    def on_task_init(self, task_id, task):
        """This method is called before a task is executed."""
        pass

    def on_process_cleanup(self):
        """This method is called after a task is executed."""
        pass

    def on_worker_init(self):
        """This method is called when the worker (:program:`celeryd`)
        starts."""
        pass

    def import_task_module(self, module):
        return self.import_from_cwd(module)

    def import_module(self, module):
        return importlib.import_module(module)

    def import_from_cwd(self, module, imp=None):
        return _import_from_cwd(module,
                self.import_module if imp is None else imp)

    def import_default_modules(self):
        imports = set(list(self.conf.get("CELERY_IMPORTS") or ()))
        return [self.import_task_module(module)
                    for module in imports | self.builtin_modules]

    def init_worker(self):
        if not self.worker_initialized:
            self.worker_initialized = True
            self.on_worker_init()

    def config_from_envvar(self, variable_name, silent=False):
        module_name = os.environ.get(variable_name)
        if not module_name:
            if silent:
                return False
            raise ImproperlyConfigured(self.error_envvar_not_set % module_name)
        return self.config_from_object(module_name, silent=silent)

    def config_from_object(self, obj, silent=False):
        if isinstance(obj, basestring):
            try:
                if "." in obj:
                    obj = get_cls_by_name(obj, imp=self.import_from_cwd)
                else:
                    obj = self.import_from_cwd(obj)
            except (ImportError, AttributeError):
                if silent:
                    return False
                raise
        if not hasattr(obj, "__getitem__"):
            obj = DictAttribute(obj)
        self._conf = obj
        return True

    def cmdline_config_parser(self, args, namespace="celery",
                re_type=re.compile(r"\((\w+)\)"),
                extra_types={"json": deserialize},
                override_types={"tuple": "json",
                                "list": "json",
                                "dict": "json"}):
        from celery.app.defaults import Option, NAMESPACES
        namespace = namespace.upper()
        typemap = dict(Option.typemap, **extra_types)

        def getarg(arg):
            """Parse a single configuration definition from
            the command line."""

            ## find key/value
            # ns.key=value|ns_key=value (case insensitive)
            key, value = arg.split('=', 1)
            key = key.upper().replace(".", "_")

            ## find namespace.
            # .key=value|_key=value expands to default namespace.
            if key[0] == '_':
                ns, key = namespace, key[1:]
            else:
                # find namespace part of key
                ns, key = key.split('_', 1)

            ns_key = (ns and ns + "_" or "") + key

            # (type)value makes cast to custom type.
            cast = re_type.match(value)
            if cast:
                type_ = cast.groups()[0]
                type_ = override_types.get(type_, type_)
                value = value[len(cast.group()):]
                value = typemap[type_](value)
            else:
                try:
                    value = NAMESPACES[ns][key].to_python(value)
                except ValueError, exc:
                    # display key name in error message.
                    raise ValueError("%r: %s" % (ns_key, exc))
            return ns_key, value

        return dict(map(getarg, args))

    def mail_admins(self, subject, body, fail_silently=False,
            sender=None, to=None, host=None, port=None,
            user=None, password=None, timeout=None, use_ssl=False):
        try:
            message = self.mail.Message(sender=sender, to=to,
                                        subject=subject, body=body)
            mailer = self.mail.Mailer(host=host, port=port,
                                      user=user, password=password,
                                      timeout=timeout, use_ssl=use_ssl)
            mailer.send(message)
        except Exception, exc:
            if not fail_silently:
                raise
            warnings.warn(self.mail.SendmailWarning(
                "Mail could not be sent: %r %r" % (
                    exc, {"To": to, "Subject": subject})))

    @property
    def conf(self):
        """Loader configuration."""
        if self._conf is None:
            self._conf = self.read_configuration()
        return self._conf

    @cached_property
    def mail(self):
        return self.import_module("celery.utils.mail")
