"""Parameters management."""

import copy

from modoboa.lib import exceptions, form_utils, signals
from modoboa.lib.sysutils import guess_extension_name


class NotDefined(exceptions.ModoboaException):
    """Custom exception for undefined parameters."""

    http_code = 404

    def __init__(self, app, name=None):
        self.app = app
        self.name = name

    def __str__(self):
        if self.name is None:
            return "Application {} not registered".format(self.app)
        return "Parameter {} not defined for app {}".format(
            self.name, self.app)


class Registry(object):
    """A registry for parameters."""

    def __init__(self):
        """Constructor."""
        self._registry = {
            "global": {},
            "user": {}
        }

    def add(self, level, formclass, label):
        """Add a new class containing parameters."""
        self._registry[level][formclass.app] = {
            "label": label, "formclass": formclass, "defaults": {}
        }

    def _load_default_values(self, level):
        """Load default values."""
        for _app, data in list(self._registry[level].items()):
            form = data["formclass"](load_values_from_db=False)
            for name, field in list(form.fields.items()):
                if isinstance(field, form_utils.SeparatorField):
                    continue
                data["defaults"][name] = field.initial

    def get_forms(self, level, *args, **kwargs):
        """Return form instances for all app of the given level."""
        sorted_apps = []
        first_app = kwargs.pop("first_app", "core")
        if first_app in self._registry[level]:
            sorted_apps.append(first_app)
        sorted_apps += sorted(
            (
                a for a in self._registry[level]
                if a != first_app
            ),
            key=lambda a: self._registry[level][a]["label"]
        )
        result = []
        for app in sorted_apps:
            data = self._registry[level][app]
            if not data["formclass"].has_access(**kwargs):
                continue
            result.append({
                "app": app,
                "label": data["label"],
                "form": data["formclass"](*args, **kwargs)
            })
        return result

    def exists(self, level, app, parameter=None):
        """Check if parameter exists."""
        parameters = self._registry[level]
        result = app in parameters
        if parameter:
            result = result and parameter in parameters[app]["defaults"]
        return result

    def get_default(self, level, app, parameter):
        """Retrieve default value for parameter."""
        if app not in self._registry[level]:
            raise NotDefined(app)
        if parameter not in self._registry[level][app]["defaults"]:
            raise NotDefined(app, parameter)
        return self._registry[level][app]["defaults"][parameter]

    def get_defaults(self, level, app):
        """Retrieve default values for application."""
        if app not in self._registry[level]:
            raise NotDefined(app)
        return self._registry[level][app]["defaults"]


registry = Registry()


class Manager(object):
    """A manager for parameters."""

    def __init__(self, level, parameters):
        """Constructor."""
        self._level = level
        self._parameters = parameters
        registry._load_default_values(level)

    def get_value(self, parameter, app=None, raise_exception=True):
        """Return the value associated to the specified parameter."""
        if app is None:
            app = guess_extension_name()
        # Compat. with the old way...
        parameter = parameter.lower()
        try:
            default = registry.get_default(self._level, app, parameter)
        except NotDefined:
            if raise_exception:
                raise
            return None
        if app in self._parameters:
            return self._parameters[app].get(parameter, default)
        return default

    def get_values(self, app=None):
        """Return all values for the given level/app."""
        if app is None:
            app = guess_extension_name()
        values = registry.get_defaults(self._level, app)
        for parameter, value in list(values.items()):
            if app in self._parameters:
                value = self._parameters[app].get(parameter, value)
            yield (parameter, value)

    def set_value(self, parameter, value, app=None):
        """Set parameter for the given app."""
        if app is None:
            app = guess_extension_name()
        if not registry.exists(self._level, app, parameter):
            raise NotDefined(app, parameter)
        if app not in self._parameters:
            self._parameters[app] = copy.deepcopy(
                registry.get_defaults(self._level, app))
        self._parameters[app][parameter] = value

    def set_values(self, values, app=None):
        """Set/update values for the given app."""
        if app is None:
            app = guess_extension_name()
        if not registry.exists(self._level, app):
            raise NotDefined(app)
        if app not in self._parameters:
            self._parameters[app] = copy.deepcopy(
                registry.get_defaults(self._level, app))
        self._parameters[app].update(values)


def get_localconfig():
    """Retrieve current LocalConfig instance."""
    from modoboa.core import models as core_models
    request = signals.get_request()
    if request:
        return request.localconfig
    return core_models.LocalConfig.objects.first()


def get_global_parameter(name, app=None, **kwargs):
    """Retrieve a global parameter.

    This is a shortcut to use when a LocalConfig instance is not
    available (ie. when no request object is available).

    A ``NotDefined`` exception if the parameter doesn't exist.

    :param name: the parameter's name
    :param app: the application owning the parameter
    :return: the corresponding value
    """
    if app is None:
        app = guess_extension_name()
    return get_localconfig().parameters.get_value(name, app=app, **kwargs)


def get_global_parameters(app, **kwargs):
    """Retrieve global parameters of a given app.

    This is a shortcut to use when a LocalConfig instance is not
    available (ie. when no request object is available).

    A ``NotDefined`` exception if the parameter doesn't exist.

    :param name: the parameter's name
    :param app: the application owning the parameter
    :return: the corresponding value

    """
    return get_localconfig().parameters.get_values(app, **kwargs)


def apply_to_django_settings():
    """Apply global parameters to Django settings module."""
    for form in registry.get_forms("global"):
        form["form"].to_django_settings()