from boto3.core.constants import DEFAULT_REGION
from boto3.core.constants import NOTHING_PROVIDED
from boto3.core.exceptions import ServerError
from boto3.core.introspection import Introspection
from boto3.utils import six


class ConnectionDetails(object):
    """
    A class that encapsulates the metadata about a given ``Connection``.

    Usually hangs off a ``Connection`` as ``Connection._details``.
    """
    service_name = 'unknown'
    session = None

    def __init__(self, service_name, session):
        """
        Creates a ``ConnectionDetails`` instance.

        :param service_name: The service a given ``Connection`` talks to. Ex.
            ``sqs``, ``sns``, ``dynamodb``, etc.
        :type service_name: string

        :param session: The configured ``Session`` object to refer to.
        :type session: <class boto3.core.session.Session> instance
        """
        super(ConnectionDetails, self).__init__()
        self.service_name = service_name
        self.session = session
        self._api_version = None
        self._loaded_service_data = None

    def __str__(self):
        return u'<{0}: {1} - {2}>'.format(
            self.__class__.__name__,
            self.service_name,
            self.api_version
        )

    @property
    def service_data(self):
        """
        Returns all introspected service data.

        If the data has been previously accessed, a memoized version of the
        data is returned.

        :returns: A dict of introspected service data
        :rtype: dict
        """
        # Lean on the cache first.
        if self._loaded_service_data is not None:
            return self._loaded_service_data

        # We don't have a cache. Build it.
        self._loaded_service_data = self._introspect_service(
            # We care about the ``botocore.session`` here, not the
            # ``boto3.session``.
            self.session.core_session,
            self.service_name
        )
        # Clear out the API version, just in case.
        self._api_version = None
        return self._loaded_service_data

    @property
    def api_version(self):
        """
        Returns API version introspected from the service data.

        If the data has been previously accessed, a memoized version of the
        API version is returned.

        :returns: The service's version
        :rtype: string
        """
        # Lean on the cache first.
        if self._api_version is not None:
            return self._api_version

        # We don't have a cache. Build it.
        self._api_version = self._introspect_api_version(
            self.session.core_session,
            self.service_name
        )
        return self._api_version

    def _introspect_service(self, core_session, service_name):
        # Yes, we could lean on ``self.session|.service_name`` here,
        # but this makes testing/composability easier.
        intro = Introspection(core_session)
        return intro.introspect_service(service_name)

    def _introspect_api_version(self, core_session, service_name):
        intro = Introspection(core_session)
        service = intro.get_service(service_name)
        return service.api_version

    def reload_service_data(self):
        """
        Wipes out & reloads the cached service data.

        :returns: A dict of introspected service data
        :rtype: dict
        """
        self._loaded_service_data = None
        return self.service_data


class Connection(object):
    """
    A common base class for all the ``Connection`` objects.
    """
    def __init__(self, region_name=DEFAULT_REGION):
        """
        Creates a new connection instance.

        :param region_name: (Optional) The name of the region to connect to.
            By default, this is the value from
            ``boto3.core.constants.DEFAULT_REGION``.
        :type region_name: string
        """
        super(Connection, self).__init__()
        self.region_name = region_name

    def __str__(self):
        return u'<{0}: {0}>'.format(
            self.__class__.__name__,
            self.region_name
        )

    def _check_method_params(self, op_params, **kwargs):
        # For now, we don't type-check or anything, just check for required
        # params.
        for param in op_params:
            if param['required'] is True:
                if not param['var_name'] in kwargs:
                    err = "Missing required parameter: '{0}'".format(
                        param['var_name']
                    )
                    raise TypeError(err)

    def _build_service_params(self, op_params, **kwargs):
        # TODO: Maybe build in an extension mechanism (like
        #      ``build_<op_name>_params``)?
        service_params = {}

        for param in op_params:
            value = kwargs.get(param['var_name'], NOTHING_PROVIDED)

            if value is NOTHING_PROVIDED:
                # They didn't give us a value. We should've already checked
                # "required-ness", so just give it a pass & move on.
                continue

            # FIXME: This is weird. I was expecting this to be
            #        ``param['api_name']`` to pass to ``botocore``, but
            #        evidently it expects snake_case here?!
            service_params[param['var_name']] = value

        return service_params

    def _check_for_errors(self, results):
        result_data = results[1]

        if 'Errors' in result_data:
            errs = result_data['Errors']

            if not errs:
                # Skip it if the errors are empty.
                # For instance, S3 will send this key with nothing in it on a
                # successful call.
                return

            if isinstance(errs, (list, tuple)):
                error = errs[0]
            elif hasattr(errs, 'items'):
                error = errs
            else:
                error = {
                    'Message': errs
                }

            raise ServerError(
                code=error.get('Code', 'ConnectionError'),
                message=error.get('Message', 'No details available.'),
                full_response=result_data
            )

    def _post_process_results(self, method_name, output, results):
        # TODO: Maybe build in an extension mechanism (like
        #      ``post_process_<op_name>_results``)?
        return results[1]

    @classmethod
    def connect_to(cls, **kwargs):
        """
        Instantiates the class, passing all ``**kwargs`` along to the
        constructor.

        This is reserved for further extension.

        :returns: An instance of the ``Connection``
        :rtype: <class Connection>
        """
        return cls(**kwargs)

    def _get_operation_data(self, method_name):
        """
        Returns all the introspected operation data for a given method.
        """
        return self._details.service_data[method_name]

    def _get_operation_params(self, method_name):
        return self._get_operation_data(method_name).get('params', [])


class ConnectionFactory(object):
    """
    Builds custom ``Connection`` subclasses based on the service's operations.

    Usage::

        >>> cf = ConnectionFactory()
        >>> S3Connection = cf.construct_for('s3')

    """
    def __init__(self, session, base_connection=Connection,
                 details_class=ConnectionDetails):
        """
        Creates a new ``ConnectionFactory`` instance.

        :param session: The ``Session`` the factory should use.
        :type session: <class boto3.session.Session> instance

        :param base_connection: (Optional) The base class to use when creating
            the connection. By default, this is ``Connection``, but should
            you need to globally change the behavior of all connections,
            you'd simply specify this to provide your own class.
        :type base_connection: <class boto3.core.connection.Connection>

        :param details_class: (Optional) The metadata class used to store things
            like service name & data. By default, this is ``ConnectionDetails``,
            but should you need to globally change the behavior (perhaps
            modifying how the service data is returned), you simply provide
            your own class here.
        :type details_class: <class boto3.core.connection.ConnectionDetails>
        """
        super(ConnectionFactory, self).__init__()
        self.session = session
        self.base_connection = base_connection
        self.details_class = ConnectionDetails

    def __str__(self):
        return self.__class__.__name__

    def construct_for(self, service_name):
        """
        Builds a new, specialized ``Connection`` subclass for a given service.

        This will introspect a service, determine all the API calls it has &
        constructs a brand new class with those methods on it.

        :param service_name: The name of the service to construct a connection
            for. Ex. ``sqs``, ``sns``, ``dynamodb``, etc.
        :type service_name: string

        :returns: A new connection class for that service
        """
        # Construct a new ``ConnectionDetails`` (or similar class) for storing
        # the relevant details about the service & its operations.
        details = self.details_class(service_name, self.session)
        # Make sure the new class gets that ``ConnectionDetails`` instance as a
        # ``cls._details`` attribute.
        attrs = {
            '_details': details,
        }

        # Determine what we should call it.
        klass_name = self._build_class_name(service_name)

        # Construct what the class ought to have on it.
        attrs.update(self._build_methods(details))

        # Create the class.
        return type(
            klass_name,
            (self.base_connection,),
            attrs
        )

    def _build_class_name(self, service_name):
        return '{0}Connection'.format(service_name.capitalize())

    def _build_methods(self, details):
        attrs = {}

        for method_name, op_data in details.service_data.items():
            # First we make expand then we defense it.
            # Construct a brand-new method & assign it on the class.
            attrs[method_name] = self._create_operation_method(method_name, op_data)

        return attrs

    def _generate_docstring(self, op_data):
        docstring = op_data['docs']

        for param_data in op_data['params']:
            param_doc = ":param {0}: {1}\n".format(
                param_data['var_name'],
                param_data.get('docs', 'No documentation available')
            )
            type_doc = ":type {0}: {1}\n".format(
                param_data['var_name'],
                param_data['type']
            )

            docstring += '\n'
            docstring += param_doc
            docstring += type_doc

        docstring += '\n'
        docstring += ':returns: The response data received\n'
        docstring += ':rtype: dict\n'
        return docstring

    def _create_operation_method(factory_self, method_name, orig_op_data):
        if not six.PY3:
            method_name = str(method_name)

        def _new_method(self, **kwargs):
            # Fetch the information about the operation.
            op_data = self._get_operation_data(method_name)

            # Check the parameters.
            self._check_method_params(
                op_data['params'],
                **kwargs
            )

            # Prep the service's parameters.
            service_params = self._build_service_params(
                op_data['params'],
                **kwargs
            )

            # Actually call the service.
            service = self._details.session.get_core_service(
                self._details.service_name
            )
            endpoint = service.get_endpoint(self.region_name)
            op = service.get_operation(
                op_data['api_name']
            )
            results = op.call(endpoint, **service_params)

            # Check for error conditions.
            self._check_for_errors(results)

            # Post-process results here
            post_processed = self._post_process_results(
                method_name,
                op_data['output'],
                results
            )
            return post_processed

        # Swap the name, so it looks right.
        _new_method.__name__ = method_name
        # Assign docstring.
        _new_method.__doc__ = factory_self._generate_docstring(orig_op_data)
        # Return the newly constructed method.
        return _new_method