#    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 copy
import functools
import itertools
import operator

from heat.common import exception
from heat.engine import function
from heat.engine import properties


__all__ = ['ResourceDefinition']


# Field names that can be passed to Template.get_section_name() in order to
# determine the appropriate name for a particular template format.
FIELDS = (
    TYPE, PROPERTIES, METADATA, DELETION_POLICY, UPDATE_POLICY,
    DEPENDS_ON, DESCRIPTION, EXTERNAL_ID,
) = (
    'Type', 'Properties', 'Metadata', 'DeletionPolicy', 'UpdatePolicy',
    'DependsOn', 'Description', 'external_id',
)


class ResourceDefinition(object):
    """A definition of a resource, independent of any template format."""

    class Diff(object):
        """A diff between two versions of the same resource definition."""

        def __init__(self, old_defn, new_defn):
            if not (isinstance(old_defn, ResourceDefinition) and
                    isinstance(new_defn, ResourceDefinition)):
                raise TypeError

            self.old_defn = old_defn
            self.new_defn = new_defn

        def properties_changed(self):
            """Return True if the resource properties have changed."""
            return self.old_defn._properties != self.new_defn._properties

        def metadata_changed(self):
            """Return True if the resource metadata has changed."""
            return self.old_defn._metadata != self.new_defn._metadata

        def update_policy_changed(self):
            """Return True if the resource update policy has changed."""
            return self.old_defn._update_policy != self.new_defn._update_policy

        def __bool__(self):
            """Return True if anything has changed."""
            return (self.properties_changed() or
                    self.metadata_changed() or
                    self.update_policy_changed())

        __nonzero__ = __bool__

    DELETION_POLICIES = (
        DELETE, RETAIN, SNAPSHOT,
    ) = (
        'Delete', 'Retain', 'Snapshot',
    )

    def __init__(self, name, resource_type, properties=None, metadata=None,
                 depends=None, deletion_policy=None, update_policy=None,
                 description=None, external_id=None, condition=None):
        """Initialise with the parsed definition of a resource.

        Any intrinsic functions present in any of the sections should have been
        parsed into Function objects before constructing the definition.

        :param name: The name of the resource (for use in error messages)
        :param resource_type: The resource type
        :param properties: A dictionary of supplied property values
        :param metadata: The supplied metadata
        :param depends: A list of resource names on which this resource depends
        :param deletion_policy: The deletion policy for the resource
        :param update_policy: A dictionary of supplied update policies
        :param description: A string describing the resource
        :param external_id: A uuid of an external resource
        :param condition: A condition name associated with the resource
        """
        self.name = name
        self.resource_type = resource_type
        self.description = description or ''
        self._properties = properties
        self._metadata = metadata
        self._depends = depends
        self._deletion_policy = deletion_policy
        self._update_policy = update_policy
        self._external_id = external_id
        self._condition = condition

        self._hash = hash(self.resource_type)
        self._rendering = None
        self._dep_names = None
        self._all_dep_attrs = None

        assert isinstance(self.description, str)

        if properties is not None:
            assert isinstance(properties, (collections.Mapping,
                                           function.Function))
            self._hash ^= _hash_data(properties)

        if metadata is not None:
            assert isinstance(metadata, (collections.Mapping,
                                         function.Function))
            self._hash ^= _hash_data(metadata)

        if depends is not None:
            assert isinstance(depends, (collections.Sequence,
                                        function.Function))
            assert not isinstance(depends, str)
            self._hash ^= _hash_data(depends)

        if deletion_policy is not None:
            assert deletion_policy in self.DELETION_POLICIES
            self._hash ^= _hash_data(deletion_policy)

        if update_policy is not None:
            assert isinstance(update_policy, (collections.Mapping,
                                              function.Function))
            self._hash ^= _hash_data(update_policy)

        if external_id is not None:
            assert isinstance(external_id, (str,
                                            function.Function))
            self._hash ^= _hash_data(external_id)
            self._deletion_policy = self.RETAIN

        if condition is not None:
            assert isinstance(condition, (str, bool,
                                          function.Function))
            self._hash ^= _hash_data(condition)

        self.set_translation_rules()

    def freeze(self, **overrides):
        """Return a frozen resource definition, with all functions resolved.

        This return a new resource definition with fixed data (containing no
        intrinsic functions). Named arguments passed to this method override
        the values passed as arguments to the constructor.
        """
        if getattr(self, '_frozen', False) and not overrides:
            return self

        def arg_item(attr_name):
            name = attr_name.lstrip('_')
            if name in overrides:
                value = overrides[name]
                if not value and getattr(self, attr_name) is None:
                    value = None
            else:
                value = function.resolve(getattr(self, attr_name))

            return name, value

        args = ('name', 'resource_type', '_properties', '_metadata',
                '_depends', '_deletion_policy', '_update_policy',
                'description', '_external_id', '_condition')

        defn = type(self)(**dict(arg_item(a) for a in args))
        defn._frozen = True
        return defn

    def reparse(self, stack, template):
        """Reinterpret the resource definition in the context of a new stack.

        This returns a new resource definition, with all of the functions
        parsed in the context of the specified stack and template.

        Any conditions are *not* included - it is assumed that the resource is
        being interpreted in any context that it should be enabled in that
        context.
        """
        assert not getattr(self, '_frozen', False
                           ), "Cannot re-parse a frozen definition"

        def reparse_snippet(snippet):
            return template.parse(stack, copy.deepcopy(snippet))

        return type(self)(
            self.name, self.resource_type,
            properties=reparse_snippet(self._properties),
            metadata=reparse_snippet(self._metadata),
            depends=reparse_snippet(self._depends),
            deletion_policy=reparse_snippet(self._deletion_policy),
            update_policy=reparse_snippet(self._update_policy),
            external_id=reparse_snippet(self._external_id),
            condition=None)

    def validate(self):
        """Validate intrinsic functions that appear in the definition."""
        function.validate(self._properties, PROPERTIES)
        function.validate(self._metadata, METADATA)
        function.validate(self._depends, DEPENDS_ON)
        function.validate(self._deletion_policy, DELETION_POLICY)
        function.validate(self._update_policy, UPDATE_POLICY)
        function.validate(self._external_id, EXTERNAL_ID)

    def dep_attrs(self, resource_name, load_all=False):
        """Iterate over attributes of a given resource that this references.

        Return an iterator over dependent attributes for specified
        resource_name in resources' properties and metadata fields.
        """
        if self._all_dep_attrs is None and load_all:
            attr_map = collections.defaultdict(set)
            atts = itertools.chain(function.all_dep_attrs(self._properties),
                                   function.all_dep_attrs(self._metadata))
            for res_name, att_name in atts:
                attr_map[res_name].add(att_name)
            self._all_dep_attrs = attr_map

        if self._all_dep_attrs is not None:
            return self._all_dep_attrs[resource_name]

        return itertools.chain(function.dep_attrs(self._properties,
                                                  resource_name),
                               function.dep_attrs(self._metadata,
                                                  resource_name))

    def required_resource_names(self):
        """Return a set of names of all resources on which this depends.

        Note that this is done entirely in isolation from the rest of the
        template, so the resource names returned may refer to resources that
        don't actually exist, or would have strict_dependency=False. Use the
        dependencies() method to get validated dependencies.
        """
        if self._dep_names is None:
            explicit_depends = [] if self._depends is None else self._depends

            def path(section):
                return '.'.join([self.name, section])

            prop_deps = function.dependencies(self._properties,
                                              path(PROPERTIES))
            metadata_deps = function.dependencies(self._metadata,
                                                  path(METADATA))
            implicit_depends = map(lambda rp: rp.name,
                                   itertools.chain(prop_deps,
                                                   metadata_deps))

            # (ricolin) External resource should not depend on any other
            # resources. This operation is not allowed for now.
            if self.external_id():
                if explicit_depends:
                    raise exception.InvalidExternalResourceDependency(
                        external_id=self.external_id(),
                        resource_type=self.resource_type
                    )
                self._dep_names = set()
            else:
                self._dep_names = set(itertools.chain(explicit_depends,
                                                      implicit_depends))
        return self._dep_names

    def dependencies(self, stack):
        """Return the Resource objects in given stack on which this depends."""
        def get_resource(res_name):
            if res_name not in stack:
                if res_name in stack.defn.all_rsrc_names():
                    # The resource is conditionally defined, allow dependencies
                    # on it
                    return
                raise exception.InvalidTemplateReference(resource=res_name,
                                                         key=self.name)
            res = stack[res_name]
            if getattr(res, 'strict_dependency', True):
                return res

        return filter(None, map(get_resource, self.required_resource_names()))

    def set_translation_rules(self, rules=None, client_resolve=True):
        """Helper method to update properties with translation rules."""
        self._rules = rules or []
        self._client_resolve = client_resolve

    def properties(self, schema, context=None):
        """Return a Properties object representing the resource properties.

        The Properties object is constructed from the given schema, and may
        require a context to validate constraints.
        """
        props = properties.Properties(schema, self._properties or {},
                                      function.resolve, context=context,
                                      section=PROPERTIES,
                                      rsrc_description=self.description)
        props.update_translation(self._rules, self._client_resolve)
        return props

    def deletion_policy(self):
        """Return the deletion policy for the resource.

        The policy will be one of those listed in DELETION_POLICIES.
        """
        return function.resolve(self._deletion_policy) or self.DELETE

    def update_policy(self, schema, context=None):
        """Return a Properties object representing the resource update policy.

        The Properties object is constructed from the given schema, and may
        require a context to validate constraints.
        """
        props = properties.Properties(schema, self._update_policy or {},
                                      function.resolve, context=context,
                                      section=UPDATE_POLICY)
        props.update_translation(self._rules, self._client_resolve)
        return props

    def metadata(self):
        """Return the resource metadata."""
        return function.resolve(self._metadata) or {}

    def external_id(self):
        """Return the external resource id."""
        return function.resolve(self._external_id)

    def condition(self):
        """Return the name of the conditional inclusion rule, if any.

        Returns None if the resource is included unconditionally.
        """
        return function.resolve(self._condition)

    def render_hot(self):
        """Return a HOT snippet for the resource definition."""
        if self._rendering is None:
            attrs = {
                'type': 'resource_type',
                'properties': '_properties',
                'metadata': '_metadata',
                'deletion_policy': '_deletion_policy',
                'update_policy': '_update_policy',
                'depends_on': '_depends',
                'external_id': '_external_id',
                'condition': '_condition'
            }

            def rawattrs():
                """Get an attribute with function objects stripped out."""
                for key, attr in attrs.items():
                    value = getattr(self, attr)
                    if value is not None:
                        yield key, copy.deepcopy(value)

            self._rendering = dict(rawattrs())

        return self._rendering

    def __sub__(self, previous):
        """Calculate the difference between this definition and a previous one.

        Return a Diff object that can be used to establish differences between
        this definition and a previous definition of the same resource.
        """
        if not isinstance(previous, ResourceDefinition):
            return NotImplemented

        return self.Diff(previous, self)

    def __eq__(self, other):
        """Compare this resource definition for equality with another.

        Two resource definitions are considered to be equal if they can be
        generated from the same template snippet. The name of the resource is
        ignored, as are the actual values that any included functions resolve
        to.
        """
        if not isinstance(other, ResourceDefinition):
            return NotImplemented

        return self.render_hot() == other.render_hot()

    def __ne__(self, other):
        """Compare this resource definition for inequality with another.

        See __eq__() for the definition of equality.
        """
        equal = self.__eq__(other)
        if equal is NotImplemented:
            return NotImplemented

        return not equal

    def __hash__(self):
        """Return a hash value for this resource definition.

        Resource definitions that compare equal will have the same hash. (In
        particular, the resource name is *not* taken into account.) See
        the __eq__() method for the definition of equality.
        """
        return self._hash

    def __repr__(self):
        """Return a string representation of the resource definition."""

        def arg_repr(arg_name):
            return '='.join([arg_name, repr(getattr(self, '_%s' % arg_name))])

        args = ('properties', 'metadata', 'depends',
                'deletion_policy', 'update_policy', 'condition')
        data = {
            'classname': type(self).__name__,
            'name': repr(self.name),
            'type': repr(self.resource_type),
            'args': ', '.join(arg_repr(n) for n in args)
        }
        return '%(classname)s(%(name)s, %(type)s, %(args)s)' % data


def _hash_data(data):
    """Return a stable hash value for an arbitrary parsed-JSON data snippet."""
    if isinstance(data, function.Function):
        data = copy.deepcopy(data)

    if not isinstance(data, str):
        if isinstance(data, collections.Sequence):
            return hash(tuple(_hash_data(d) for d in data))

        if isinstance(data, collections.Mapping):
            item_hashes = (hash(k) ^ _hash_data(v) for k, v in data.items())
            return functools.reduce(operator.xor, item_hashes, 0)

    return hash(data)
