#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

import collections
import warnings

import six

from heat.common.i18n import _
from heat.engine import constraints as constr
from heat.engine import support


class Schema(constr.Schema):
    """
    Simple schema class for attributes.

    Schema objects are serialisable to dictionaries following a superset of
    the HOT input Parameter schema using dict().
    """

    KEYS = (
        DESCRIPTION,
    ) = (
        'description',
    )

    CACHE_MODES = (
        CACHE_LOCAL,
        CACHE_NONE
    ) = (
        'cache_local',
        'cache_none'
    )

    def __init__(self, description=None,
                 support_status=support.SupportStatus(),
                 cache_mode=CACHE_LOCAL):
        self.description = description
        self.support_status = support_status
        self.cache_mode = cache_mode

    def __getitem__(self, key):
        if key == self.DESCRIPTION:
            if self.description is not None:
                return self.description

        raise KeyError(key)

    @classmethod
    def from_attribute(cls, schema_dict):
        """
        Return a Property Schema corresponding to a Attribute Schema.
        """
        if isinstance(schema_dict, cls):
            return schema_dict
        warnings.warn('<name>: <description> schema definition is deprecated. '
                      'Use <name>: attributes.Schema(<description>) instead.',
                      DeprecationWarning)
        return cls(schema_dict)


def schemata(schema):
    """
    Return dictionary of Schema objects for given dictionary of schemata.
    """
    return dict((n, Schema.from_attribute(s)) for n, s in schema.items())


class Attribute(object):
    """
    An Attribute schema.
    """

    def __init__(self, attr_name, schema):
        """
        Initialise with a name and description.

        :param attr_name: the name of the attribute
        :param schema: attribute schema
        """
        self.name = attr_name
        self.schema = Schema.from_attribute(schema)

    def support_status(self):
        return self.schema.support_status

    def as_output(self, resource_name):
        """
        Return an Output schema entry for a provider template with the given
        resource name.

        :param resource_name: the logical name of the provider resource
        :returns: This attribute as a template 'Output' entry
        """
        return {
            "Value": '{"Fn::GetAtt": ["%s", "%s"]}' % (resource_name,
                                                       self.name),
            "Description": self.schema.description
        }


class Attributes(collections.Mapping):
    """Models a collection of Resource Attributes."""

    def __init__(self, res_name, schema, resolver):
        self._resource_name = res_name
        self._resolver = resolver
        self._attributes = Attributes._make_attributes(schema)
        self.reset_resolved_values()

    def reset_resolved_values(self):
        self._resolved_values = {}

    @staticmethod
    def _make_attributes(schema):
        return dict((n, Attribute(n, d)) for n, d in schema.items())

    @staticmethod
    def as_outputs(resource_name, resource_class):
        """
        :param resource_name: logical name of the resource
        :param resource_class: resource implementation class
        :returns: The attributes of the specified resource_class as a template
                  Output map
        """
        schema = resource_class.attributes_schema
        attribs = Attributes._make_attributes(schema).items()

        return dict((n, att.as_output(resource_name)) for n, att in attribs)

    @staticmethod
    def schema_from_outputs(json_snippet):
        if json_snippet:
            return dict((k, Schema(v.get("Description")))
                        for k, v in json_snippet.items())
        return {}

    def __getitem__(self, key):
        if key not in self:
            raise KeyError(_('%(resource)s: Invalid attribute %(key)s') %
                           dict(resource=self._resource_name, key=key))

        attrib = self._attributes.get(key)
        if attrib.schema.cache_mode == Schema.CACHE_NONE:
            return self._resolver(key)

        if key in self._resolved_values:
            return self._resolved_values[key]

        value = self._resolver(key)
        if value is not None:
            # only store if not None, it may resolve to an actual value
            # on subsequent calls
            self._resolved_values[key] = value
        return value

    def __len__(self):
        return len(self._attributes)

    def __contains__(self, key):
        return key in self._attributes

    def __iter__(self):
        return iter(self._attributes)

    def __repr__(self):
        return ("Attributes for %s:\n\t" % self._resource_name +
                '\n\t'.join(self._attributes.values()))


def select_from_attribute(attribute_value, path):
    '''
    Select an element from an attribute value.

    :param attribute_value: the attribute value.
    :param path: a list of path components to select from the attribute.
    :returns: the selected attribute component value.
    '''
    def get_path_component(collection, key):
        if not isinstance(collection, (collections.Mapping,
                                       collections.Sequence)):
            raise TypeError(_("Can't traverse attribute path"))

        if not isinstance(key, (six.string_types, int)):
            raise TypeError(_('Path components in attributes must be strings'))

        return collection[key]

    try:
        return reduce(get_path_component, path, attribute_value)
    except (KeyError, IndexError, TypeError):
        return None
