# Copyright 2014 Google Inc. All rights reserved.
#
# 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.

"""Manipulate access control lists that Cloud Storage provides.

:class:`gcloud.storage.bucket.Bucket` has a getting method that creates
an ACL object under the hood, and you can interact with that using
:func:`gcloud.storage.bucket.Bucket.acl`::

  >>> from gcloud import storage
  >>> client = storage.Client()
  >>> bucket = client.get_bucket(bucket_name)
  >>> acl = bucket.acl

Adding and removing permissions can be done with the following methods
(in increasing order of granularity):

- :func:`ACL.all`
  corresponds to access for all users.
- :func:`ACL.all_authenticated` corresponds
  to access for all users that are signed into a Google account.
- :func:`ACL.domain` corresponds to access on a
  per Google Apps domain (ie, ``example.com``).
- :func:`ACL.group` corresponds to access on a
  per group basis (either by ID or e-mail address).
- :func:`ACL.user` corresponds to access on a
  per user basis (either by ID or e-mail address).

And you are able to ``grant`` and ``revoke`` the following roles:

- **Reading**:
  :func:`_ACLEntity.grant_read` and :func:`_ACLEntity.revoke_read`
- **Writing**:
  :func:`_ACLEntity.grant_write` and :func:`_ACLEntity.revoke_write`
- **Owning**:
  :func:`_ACLEntity.grant_owner` and :func:`_ACLEntity.revoke_owner`

You can use any of these like any other factory method (these happen to
be :class:`_ACLEntity` factories)::

  >>> acl.user('me@example.org').grant_read()
  >>> acl.all_authenticated().grant_write()

You can also chain these ``grant_*`` and ``revoke_*`` methods together
for brevity::

  >>> acl.all().grant_read().revoke_write()

After that, you can save any changes you make with the
:func:`gcloud.storage.acl.ACL.save` method::

  >>> acl.save()

You can alternatively save any existing :class:`gcloud.storage.acl.ACL`
object (whether it was created by a factory method or not) from a
:class:`gcloud.storage.bucket.Bucket`::

  >>> bucket.acl.save(acl=acl)

To get the list of ``entity`` and ``role`` for each unique pair, the
:class:`ACL` class is iterable::

  >>> print list(ACL)
  [{'role': 'OWNER', 'entity': 'allUsers'}, ...]

This list of tuples can be used as the ``entity`` and ``role`` fields
when sending metadata for ACLs to the API.
"""


class _ACLEntity(object):
    """Class representing a set of roles for an entity.

    This is a helper class that you likely won't ever construct
    outside of using the factor methods on the :class:`ACL` object.

    :type entity_type: string
    :param entity_type: The type of entity (ie, 'group' or 'user').

    :type identifier: string
    :param identifier: The ID or e-mail of the entity. For the special
                       entity types (like 'allUsers') this is optional.
    """

    READER_ROLE = 'READER'
    WRITER_ROLE = 'WRITER'
    OWNER_ROLE = 'OWNER'

    def __init__(self, entity_type, identifier=None):
        self.identifier = identifier
        self.roles = set([])
        self.type = entity_type

    def __str__(self):
        if not self.identifier:
            return str(self.type)
        else:
            return '{acl.type}-{acl.identifier}'.format(acl=self)

    def __repr__(self):
        return '<ACL Entity: {acl} ({roles})>'.format(
            acl=self, roles=', '.join(self.roles))

    def get_roles(self):
        """Get the list of roles permitted by this entity.

        :rtype: list of strings
        :returns: The list of roles associated with this entity.
        """
        return self.roles

    def grant(self, role):
        """Add a role to the entity.

        :type role: string
        :param role: The role to add to the entity.
        """
        self.roles.add(role)

    def revoke(self, role):
        """Remove a role from the entity.

        :type role: string
        :param role: The role to remove from the entity.
        """
        if role in self.roles:
            self.roles.remove(role)

    def grant_read(self):
        """Grant read access to the current entity."""
        self.grant(_ACLEntity.READER_ROLE)

    def grant_write(self):
        """Grant write access to the current entity."""
        self.grant(_ACLEntity.WRITER_ROLE)

    def grant_owner(self):
        """Grant owner access to the current entity."""
        self.grant(_ACLEntity.OWNER_ROLE)

    def revoke_read(self):
        """Revoke read access from the current entity."""
        self.revoke(_ACLEntity.READER_ROLE)

    def revoke_write(self):
        """Revoke write access from the current entity."""
        self.revoke(_ACLEntity.WRITER_ROLE)

    def revoke_owner(self):
        """Revoke owner access from the current entity."""
        self.revoke(_ACLEntity.OWNER_ROLE)


class ACL(object):
    """Container class representing a list of access controls."""

    _URL_PATH_ELEM = 'acl'
    _PREDEFINED_QUERY_PARAM = 'predefinedAcl'

    _PREDEFINED_ACLS = frozenset([
        'private',
        'project-private',
        'public-read',
        'public-read-write',
        'authenticated-read',
        'bucket-owner-read',
        'bucket-owner-full-control',
    ])
    """See:
    https://cloud.google.com/storage/docs/access-control#predefined-acl
    """

    loaded = False

    # Subclasses must override to provide these attributes (typically,
    # as properties).
    reload_path = None
    save_path = None

    def __init__(self):
        self.entities = {}

    def _ensure_loaded(self):
        """Load if not already loaded."""
        if not self.loaded:
            self.reload()

    def reset(self):
        """Remove all entities from the ACL, and clear the ``loaded`` flag."""
        self.entities.clear()
        self.loaded = False

    def __iter__(self):
        self._ensure_loaded()

        for entity in self.entities.values():
            for role in entity.get_roles():
                if role:
                    yield {'entity': str(entity), 'role': role}

    def entity_from_dict(self, entity_dict):
        """Build an _ACLEntity object from a dictionary of data.

        An entity is a mutable object that represents a list of roles
        belonging to either a user or group or the special types for all
        users and all authenticated users.

        :type entity_dict: dict
        :param entity_dict: Dictionary full of data from an ACL lookup.

        :rtype: :class:`_ACLEntity`
        :returns: An Entity constructed from the dictionary.
        """
        entity = entity_dict['entity']
        role = entity_dict['role']

        if entity == 'allUsers':
            entity = self.all()

        elif entity == 'allAuthenticatedUsers':
            entity = self.all_authenticated()

        elif '-' in entity:
            entity_type, identifier = entity.split('-', 1)
            entity = self.entity(entity_type=entity_type,
                                 identifier=identifier)

        if not isinstance(entity, _ACLEntity):
            raise ValueError('Invalid dictionary: %s' % entity_dict)

        entity.grant(role)
        return entity

    def has_entity(self, entity):
        """Returns whether or not this ACL has any entries for an entity.

        :type entity: :class:`_ACLEntity`
        :param entity: The entity to check for existence in this ACL.

        :rtype: boolean
        :returns: True of the entity exists in the ACL.
        """
        self._ensure_loaded()
        return str(entity) in self.entities

    def get_entity(self, entity, default=None):
        """Gets an entity object from the ACL.

        :type entity: :class:`_ACLEntity` or string
        :param entity: The entity to get lookup in the ACL.

        :type default: anything
        :param default: This value will be returned if the entity
                        doesn't exist.

        :rtype: :class:`_ACLEntity`
        :returns: The corresponding entity or the value provided
                  to ``default``.
        """
        self._ensure_loaded()
        return self.entities.get(str(entity), default)

    def add_entity(self, entity):
        """Add an entity to the ACL.

        :type entity: :class:`_ACLEntity`
        :param entity: The entity to add to this ACL.
        """
        self._ensure_loaded()
        self.entities[str(entity)] = entity

    def entity(self, entity_type, identifier=None):
        """Factory method for creating an Entity.

        If an entity with the same type and identifier already exists,
        this will return a reference to that entity.  If not, it will
        create a new one and add it to the list of known entities for
        this ACL.

        :type entity_type: string
        :param entity_type: The type of entity to create
                            (ie, ``user``, ``group``, etc)

        :type identifier: string
        :param identifier: The ID of the entity (if applicable).
                           This can be either an ID or an e-mail address.

        :rtype: :class:`_ACLEntity`
        :returns: A new Entity or a reference to an existing identical entity.
        """
        entity = _ACLEntity(entity_type=entity_type, identifier=identifier)
        if self.has_entity(entity):
            entity = self.get_entity(entity)
        else:
            self.add_entity(entity)
        return entity

    def user(self, identifier):
        """Factory method for a user Entity.

        :type identifier: string
        :param identifier: An id or e-mail for this particular user.

        :rtype: :class:`_ACLEntity`
        :returns: An Entity corresponding to this user.
        """
        return self.entity('user', identifier=identifier)

    def group(self, identifier):
        """Factory method for a group Entity.

        :type identifier: string
        :param identifier: An id or e-mail for this particular group.

        :rtype: :class:`_ACLEntity`
        :returns: An Entity corresponding to this group.
        """
        return self.entity('group', identifier=identifier)

    def domain(self, domain):
        """Factory method for a domain Entity.

        :type domain: string
        :param domain: The domain for this entity.

        :rtype: :class:`_ACLEntity`
        :returns: An entity corresponding to this domain.
        """
        return self.entity('domain', identifier=domain)

    def all(self):
        """Factory method for an Entity representing all users.

        :rtype: :class:`_ACLEntity`
        :returns: An entity representing all users.
        """
        return self.entity('allUsers')

    def all_authenticated(self):
        """Factory method for an Entity representing all authenticated users.

        :rtype: :class:`_ACLEntity`
        :returns: An entity representing all authenticated users.
        """
        return self.entity('allAuthenticatedUsers')

    def get_entities(self):
        """Get a list of all Entity objects.

        :rtype: list of :class:`_ACLEntity` objects
        :returns: A list of all Entity objects.
        """
        self._ensure_loaded()
        return list(self.entities.values())

    @property
    def client(self):
        """Abstract getter for the object client."""
        raise NotImplementedError

    def _require_client(self, client):
        """Check client or verify over-ride.

        :type client: :class:`gcloud.storage.client.Client` or ``NoneType``
        :param client: the client to use.  If not passed, falls back to the
                       ``client`` stored on the current ACL.

        :rtype: :class:`gcloud.storage.client.Client`
        :returns: The client passed in or the currently bound client.
        """
        if client is None:
            client = self.client
        return client

    def reload(self, client=None):
        """Reload the ACL data from Cloud Storage.

        :type client: :class:`gcloud.storage.client.Client` or ``NoneType``
        :param client: Optional. The client to use.  If not passed, falls back
                       to the ``client`` stored on the ACL's parent.
        """
        path = self.reload_path
        client = self._require_client(client)

        self.entities.clear()

        found = client.connection.api_request(method='GET', path=path)
        self.loaded = True
        for entry in found.get('items', ()):
            self.add_entity(self.entity_from_dict(entry))

    def _save(self, acl, predefined, client):
        """Helper for :meth:`save` and :meth:`save_predefined`.

        :type acl: :class:`gcloud.storage.acl.ACL`, or a compatible list.
        :param acl: The ACL object to save.  If left blank, this will save
                    current entries.

        :type predefined: string or None
        :param predefined: An identifier for a predefined ACL.  Must be one
                           of the keys in :attr:`_PREDEFINED_ACLS`
                           If passed, `acl` must be None.

        :type client: :class:`gcloud.storage.client.Client` or ``NoneType``
        :param client: Optional. The client to use.  If not passed, falls back
                       to the ``client`` stored on the ACL's parent.
        """
        query_params = {'projection': 'full'}
        if predefined is not None:
            acl = []
            query_params[self._PREDEFINED_QUERY_PARAM] = predefined

        path = self.save_path
        client = self._require_client(client)
        result = client.connection.api_request(
            method='PATCH',
            path=path,
            data={self._URL_PATH_ELEM: list(acl)},
            query_params=query_params)
        self.entities.clear()
        for entry in result.get(self._URL_PATH_ELEM, ()):
            self.add_entity(self.entity_from_dict(entry))
        self.loaded = True

    def save(self, acl=None, client=None):
        """Save this ACL for the current bucket.

        :type acl: :class:`gcloud.storage.acl.ACL`, or a compatible list.
        :param acl: The ACL object to save.  If left blank, this will save
                    current entries.

        :type client: :class:`gcloud.storage.client.Client` or ``NoneType``
        :param client: Optional. The client to use.  If not passed, falls back
                       to the ``client`` stored on the ACL's parent.
        """
        if acl is None:
            acl = self
            save_to_backend = acl.loaded
        else:
            save_to_backend = True

        if save_to_backend:
            self._save(acl, None, client)

    def save_predefined(self, predefined, client=None):
        """Save this ACL for the current bucket using a predefined ACL.

        :type predefined: string
        :param predefined: An identifier for a predefined ACL.  Must be one
                           of the keys in :attr:`_PREDEFINED_ACLS`
                           If passed, `acl` must be None.

        :type client: :class:`gcloud.storage.client.Client` or ``NoneType``
        :param client: Optional. The client to use.  If not passed, falls back
                       to the ``client`` stored on the ACL's parent.
        """
        if predefined not in self._PREDEFINED_ACLS:
            raise ValueError("Invalid predefined ACL: %s" % (predefined,))

        self._save(None, predefined, client)

    def clear(self, client=None):
        """Remove all ACL entries.

        Note that this won't actually remove *ALL* the rules, but it
        will remove all the non-default rules.  In short, you'll still
        have access to a bucket that you created even after you clear
        ACL rules with this method.

        :type client: :class:`gcloud.storage.client.Client` or ``NoneType``
        :param client: Optional. The client to use.  If not passed, falls back
                       to the ``client`` stored on the ACL's parent.
        """
        self.save([], client=client)


class BucketACL(ACL):
    """An ACL specifically for a bucket.

    :type bucket: :class:`gcloud.storage.bucket.Bucket`
    :param bucket: The bucket to which this ACL relates.
    """

    def __init__(self, bucket):
        super(BucketACL, self).__init__()
        self.bucket = bucket

    @property
    def client(self):
        """The client bound to this ACL's bucket."""
        return self.bucket.client

    @property
    def reload_path(self):
        """Compute the path for GET API requests for this ACL."""
        return '%s/%s' % (self.bucket.path, self._URL_PATH_ELEM)

    @property
    def save_path(self):
        """Compute the path for PATCH API requests for this ACL."""
        return self.bucket.path


class DefaultObjectACL(BucketACL):
    """A class representing the default object ACL for a bucket."""

    _URL_PATH_ELEM = 'defaultObjectAcl'
    _PREDEFINED_QUERY_PARAM = 'predefinedDefaultObjectAcl'


class ObjectACL(ACL):
    """An ACL specifically for a Cloud Storage object / blob.

    :type blob: :class:`gcloud.storage.blob.Blob`
    :param blob: The blob that this ACL corresponds to.
    """

    def __init__(self, blob):
        super(ObjectACL, self).__init__()
        self.blob = blob

    @property
    def client(self):
        """The client bound to this ACL's blob."""
        return self.blob.client

    @property
    def reload_path(self):
        """Compute the path for GET API requests for this ACL."""
        return '%s/acl' % self.blob.path

    @property
    def save_path(self):
        """Compute the path for PATCH API requests for this ACL."""
        return self.blob.path
