def exposure_additional_keywords(
            self, layer_mode_key=None, layer_geometry_key=None,
            exposure_key=None):
        """Return additional_keywords for exposure.

        :param layer_mode_key: The layer mode key
        :type layer_mode_key: str

        :param layer_geometry_key: The layer geometry key
        :type layer_geometry_key: str

        :param exposure_key: The hazard key
        :type exposure_key: str

        :returns: List of additional keywords
        :rtype: list
        """
        additional_keywords = []
        for impact_function in self.impact_functions:
            if_additional_keywords = impact_function.metadata().\
                exposure_additional_keywords(
                    layer_mode_key=layer_mode_key,
                    layer_geometry_key=layer_geometry_key,
                    exposure_key=exposure_key)
            if if_additional_keywords:
                add_to_list(additional_keywords, if_additional_keywords)

        return additional_keywords

    def raster_hazards_classifications_for_layer(
            self, hazard_key, layer_geometry_key, layer_mode_key,
            hazard_category_key):
        """Get continuous hazard units.
        :param hazard_key: The hazard key
        :type hazard_key: str

        :param layer_geometry_key: The layer geometry key
        :type layer_geometry_key: str

        :param layer_mode_key: The layer mode key
        :type layer_mode_key: str

        :param hazard_category_key: The hazard category key
        :type hazard_category_key: str

        :returns: List of raster_hazards_classifications
        :rtype: list
        """
        raster_hazards_classifications = []
        for impact_function in self.impact_functions:
            if_vector_hazards_classifications = impact_function.metadata().\
                raster_hazards_classifications_for_layer(
                    hazard_key, layer_geometry_key, layer_mode_key,
                    hazard_category_key)
            if if_vector_hazards_classifications:
                add_to_list(
                    raster_hazards_classifications,
                    if_vector_hazards_classifications)

        return raster_hazards_classifications

    def exposure_class_fields(
            self, layer_mode_key=None, layer_geometry_key=None,
            exposure_key=None):
        """Return list of exposure class field.

        :param layer_mode_key: The layer mode key
        :type layer_mode_key: str

        :param layer_geometry_key: The layer geometry key
        :type layer_geometry_key: str

        :param exposure_key: The exposure key
        :type exposure_key: str

        :returns: List of exposure class field.
        :rtype: list
        """
        result = []
        for impact_function in self.impact_functions:
            if_exposure_class_field = impact_function.metadata(). \
                exposure_class_fields(
                    layer_mode_key=layer_mode_key,
                    layer_geometry_key=layer_geometry_key,
                    exposure_key=exposure_key)
            if if_exposure_class_field:
                add_to_list(result, if_exposure_class_field)

        return result

    def available_hazards(self, hazard_category_key, ascending=True):
        """available_hazards from hazard_category_key

        :param hazard_category_key: The hazard category key
        :type hazard_category_key: str

        :param ascending: Sort ascending or not.
        :type ascending: bool

        :returns: List of available hazards
        :rtype: list
        """

        hazards = []
        for impact_function in self.impact_functions:
            if_hazards = impact_function.metadata(). \
                available_hazards(hazard_category_key)
            if if_hazards:
                add_to_list(hazards, if_hazards)

        # make it sorted
        if ascending and hazards:
            hazards = sorted(hazards, key=lambda k: k['key'])

        return hazards

    def exposure_units_for_layer(
            self, exposure_key, layer_geometry_key, layer_mode_key):
        """Get hazard categories form layer_geometry_key

        :param exposure_key: The exposure key
        :type exposure_key: str

        :param layer_geometry_key: The geometry key
        :type layer_geometry_key: str

        :param layer_mode_key: The layer mode key
        :type layer_mode_key: str

        :returns: List of exposure unit
        :rtype: list
        """
        exposure_units = []
        for impact_function in self.impact_functions:
            if_exposure_units = impact_function.metadata().\
                exposure_units_for_layer(
                    exposure_key, layer_geometry_key, layer_mode_key)
            if if_exposure_units:
                add_to_list(exposure_units, if_exposure_units)

        return exposure_units

    def continuous_hazards_units_for_layer(
            self, hazard_key, layer_geometry_key, layer_mode_key,
            hazard_category_key):
        """Get continuous hazard units.
        :param hazard_key: The hazard key
        :type hazard_key: str

        :param layer_geometry_key: The layer geometry key
        :type layer_geometry_key: str

        :param layer_mode_key: The layer mode key
        :type layer_mode_key: str

        :param hazard_category_key: The hazard category key
        :type hazard_category_key: str

        :returns: List of continuous hazard unit
        :rtype: list
        """
        continuous_hazards_units = []
        for impact_function in self.impact_functions:
            if_continuous_hazard_units = impact_function.metadata().\
                continuous_hazards_units_for_layer(
                    hazard_key, layer_geometry_key, layer_mode_key,
                    hazard_category_key)
            if if_continuous_hazard_units:
                add_to_list(
                    continuous_hazards_units, if_continuous_hazard_units)

        return continuous_hazards_units

    def get_available_exposures(self, impact_function=None, ascending=True):
        """Return a list of valid available exposures for an impact function.

        If impact_function is None, return all available exposures

        .. versionadded:: 2.2

        :param impact_function: Impact Function object.
        :type impact_function: FunctionProvider

        :param ascending: Sort ascending or not.
        :type ascending: bool

        :returns: A list of exposures full metadata.
        :rtype: list
        """

        exposures = []
        if impact_function is None:
            for impact_function in self.impact_functions:
                add_to_list(exposures, impact_function.metadata().get_exposures())

        else:
            # noinspection PyUnresolvedReferences
            exposures = impact_function.metadata().get_exposures()

        # make it sorted
        if ascending:
            exposures = sorted(exposures, key=lambda k: k["id"])

        return exposures

    def hazard_additional_keywords(
            self, layer_mode_key=None, layer_geometry_key=None,
            hazard_category_key=None, hazard_key=None):
        """Return additional_keywords for hazard.

        :param layer_mode_key: The layer mode key
        :type layer_mode_key: str

        :param layer_geometry_key: The layer geometry key
        :type layer_geometry_key: str

        :param hazard_category_key: The hazard category key
        :type hazard_category_key: str

        :param hazard_key: The hazard key
        :type hazard_key: str

        :returns: List of additional keywords
        :rtype: list
        """
        additional_keywords = []
        for impact_function in self.impact_functions:
            if_additional_keywords = impact_function.metadata().\
                hazard_additional_keywords(
                    layer_mode_key=layer_mode_key,
                    layer_geometry_key=layer_geometry_key,
                    hazard_category_key=hazard_category_key,
                    hazard_key=hazard_key)
            if if_additional_keywords:
                add_to_list(additional_keywords, if_additional_keywords)

        return additional_keywords

    def available_hazard_layer_modes(
            self, hazard_key, hazard_geometry_key, hazard_category_key):
        """Return all available layer_mode.

        :param hazard_key: The hazard key
        :type hazard_key: str

        :param hazard_geometry_key: The hazard geometry key
        :type hazard_geometry_key: str

        :param hazard_category_key: The hazard category key
        :type hazard_category_key: str

        :returns: List of layer_mode
        :rtype: list
        """
        layer_modes = []
        for impact_function in self.impact_functions:
            if_hazard_layer_mode = impact_function.metadata().\
                available_hazard_layer_mode(
                    hazard_key, hazard_geometry_key, hazard_category_key)
            if if_hazard_layer_mode:
                add_to_list(layer_modes, if_hazard_layer_mode)

        return layer_modes

    def allowed_data_types(cls, subcategory):
        """Get the list of allowed data types for a subcategory.

        Example usage::

            foo = IF()
            meta = IF.metadata
            ubar = meta.allowed_data_types('structure')
            ubar
            > ['polygon']

        In the above example it does not show ‘numeric’ as the request is
        specific to the structure subcategory for that IF (using the IF
        declaration at the top of this file as the basis for IF())

        Passing a subcategory is required otherwise the context of the
        data_type(s) would be ambiguous (i.e. whether they can be used as
        exposure or hazards).

        :param subcategory: Required subcategory which will be used to subset
            the allowed data_types.
        :type subcategory: str

        :returns: A list of one or more strings is returned.
        :rtype: list
        """
        result = []
        metadata_dict = cls.as_dict()
        categories = metadata_dict['categories']
        if subcategory in [x['id'] for x in cls.allowed_subcategories(
                'exposure')]:
            # implementation logic that returns the allowed data_types for
            # exposure layer with subcategory as passed in to this method

            layer_constraints = categories['exposure']['layer_constraints']
            for layer_constraint in layer_constraints:
                result = add_to_list(result, layer_constraint['data_type'])
        elif subcategory in [x['id'] for x in cls.allowed_subcategories(
                'hazard')]:
            # implementation logic that returns the allowed data_types for
            # hazard layer with subcategory as passed in to this method
            layer_constraints = categories['hazard']['layer_constraints']
            for layer_constraint in layer_constraints:
                result = add_to_list(result, layer_constraint['data_type'])
        else:
            # raise Exception('Invalid subcategory.')
            # TODO (ismailsunni): create custom exception to catch since it
            # will called by all impact function
            pass

        return result

    def allowed_units(cls, subcategory, data_type):
        """Get the list of allowed units for a subcategory and data_type.

        .. note:: One data_type could be  used by more than one subcategory,
            so we need to explicitly pass the subcategory to this function.

        Example usage::

            foo = IF()
            meta = IF.metadata
            ubar = meta.allowed_data_types('structure')
            ubar
            > ['polygon']


        :param subcategory: Required subcategory which will be used to subset
            the allowed data_types.
        :type subcategory: str

        :param data_type: Required data_type which will be used to subset the
            allowed units.
        :type data_type: str

        :returns: A list of one or more strings is returned.
        :rtype: list
        """
        # pass  # must implement here
        result = []
        if data_type not in cls.allowed_data_types(subcategory):
            return result
        metadata_dict = cls.as_dict()
        categories = metadata_dict['categories']
        if subcategory in [x['id'] for x in cls.allowed_subcategories(
                'exposure')]:
            # implementation logic that returns the allowed data_types for
            # exposure layer with subcategory as passed in to this method

            result = add_to_list(result, categories['exposure']['units'])
        elif subcategory in [x['id'] for x in cls.allowed_subcategories(
                'hazard')]:
            # implementation logic that returns the allowed data_types for
            # hazard layer with subcategory as passed in to this method
            result = add_to_list(result, categories['hazard']['units'])
        else:
            # raise Exception('Invalid subcategory.')
            # TODO (ismailsunni): create custom exception to catch since it
            # will called by all impact function
            pass

        return result

    def purposes_for_layer(self, layer_geometry_key):
        """Get purposes of a layer geometry id.

        :param layer_geometry_key: The geometry id
        :type layer_geometry_key: str

        """
        layer_purposes = []
        for impact_function in self.impact_functions:
            if_layer_purposes = impact_function.metadata().purposes_for_layer(
                layer_geometry_key)
            if if_layer_purposes:
                add_to_list(layer_purposes, if_layer_purposes)

        return layer_purposes

    def allowed_units(self, subcategory, data_type):
        """Determine allowed units from all impact functions.


        It uses subcategory and data_type as a filter.

        .. note:: One data_type could be  used by more than one subcategory,
            so we need to explicitly pass the subcategory to this function.

        :param subcategory: Required subcategory which will be used to subset
            the allowed data_types.
        :type subcategory: str

        :param data_type: Required data_type which will be used to subset the
            allowed units.
        :type data_type: str

        :returns: A list of one or more strings is returned.
        :rtype: list
        """
        result = []
        for impact_function in self.impact_functions:
            my_allowed_units = impact_function.metadata().allowed_units(subcategory, data_type)
            result = add_to_list(result, my_allowed_units)
        return result

    def available_exposure_constraints(self, exposure_key):
        """Get exposure constraints for exposure_key.

        :param exposure_key: The exposure key
        :type exposure_key: str

        :returns: List of tuple of layer_mode and layer_geometry
        :rtype: list
        """
        exposure_constraints = []
        for impact_function in self.impact_functions:
            if_exposure_constraints = impact_function.metadata(). \
                available_exposure_constraints(exposure_key)
            if if_exposure_constraints:
                add_to_list(exposure_constraints, if_exposure_constraints)

        return exposure_constraints

    def exposures_for_layer(self, layer_geometry_key):
        """Get hazard categories form layer_geometry_key

        :param layer_geometry_key: The geometry id
        :type layer_geometry_key: str

        :returns: List of hazard
        :rtype: list
        """
        exposures = []
        for impact_function in self.impact_functions:
            if_exposures = impact_function.metadata().exposures_for_layer(
                layer_geometry_key)
            if if_exposures:
                add_to_list(exposures, if_exposures)

        return exposures

 def test_add_to_list(self):
     """Test for add_to_list function
     """
     list_original = ['a', 'b', ['a'], {'a': 'b'}]
     list_a = ['a', 'b', ['a'], {'a': 'b'}]
     # add same immutable element
     list_b = add_to_list(list_a, 'b')
     assert list_b == list_original
     # add list
     list_b = add_to_list(list_a, ['a'])
     assert list_b == list_original
     # add same mutable element
     list_b = add_to_list(list_a, {'a': 'b'})
     assert list_b == list_original
     # add new mutable element
     list_b = add_to_list(list_a, 'c')
     assert len(list_b) == (len(list_original) + 1)
     assert list_b[-1] == 'c'

    def categories_for_layer(cls, layer_type, data_type):
        """Determine the valid categories for a layer.

        This method is used to determine if a given layer can be used as a
        hazard, exposure or aggregation layer.

        In the returned the values are categories (if any) applicable for that
        layer_type and data_type.

        :param layer_type: The type for this layer. Valid values would be,
            'raster' or 'vector'.
        :type layer_type: str

        :param data_type: The data_type for this layer. Valid possibilities
            would be 'numeric' (for raster), point, line, polygon (for
            vectors).
        :type data_type: str

        :returns: A list as per the example above where each value represents
            a valid category.
        :rtype: list
        """
        layer_constraints = {
            'layer_type': layer_type,
            'data_type': data_type
        }
        result = []

        exposure_layer_constraints = cls.allowed_layer_constraints('exposure')
        exposure_layer_constraints = [
            cls.simplify_layer_constraint(e) for e in
            exposure_layer_constraints]

        hazard_layer_constraints = cls.allowed_layer_constraints('hazard')
        hazard_layer_constraints = [
            cls.simplify_layer_constraint(e) for e in
            hazard_layer_constraints]

        if layer_constraints in exposure_layer_constraints:
            result = add_to_list(result, 'exposure')
        if layer_constraints in hazard_layer_constraints:
            result = add_to_list(result, 'hazard')
        return result

    def allowed_layer_constraints(cls, category=None):
        """Determine allowed layer constraints.

        It is optionally filtered by category.

        Example usage::

            foo = IF()
            meta = IF.metadata
            ubar = meta.allowed_layer_constraints('exposure')
            ubar
            >  [
                {
                    'layer_type': 'vector',
                    'data_type': 'polygon'
                },
                {
                    'layer_type': 'raster',
                    'data_type': 'numeric'
                }
            ]

        :param category: Optional category which will be used to subset the
            allowed layer_constraints. If omitted, all supported
            layer_constraints will be returned (for both hazard and exposure).
            Default is None.
        :type category: str

        :returns: A list of one or more dictionary is returned.
        :rtype: list
        """
        result = []
        if category is None:
            result = add_to_list(result,
                                 cls.allowed_layer_constraints('hazard'))
            result = add_to_list(
                result, cls.allowed_layer_constraints('exposure'))
            return result

        else:
            metadata_dict = cls.as_dict()
            categories = metadata_dict['categories']
            return categories[category]['layer_constraints']

    def categories_for_layer(self, layer_type, data_type):
        """Return a list of valid categories for a layer.

        This method is used to determine if a given layer can be used as a
        hazard, exposure or aggregation layer.

        Example usage::

            foo  = categories_for_layer('vector', 'polygon')
            print foo

        Would output this::

            ['hazard', 'exposure', 'aggregation']

        While passing a vector point layer::

            foo  = units_for_layer('vector', 'point')
            print foo

        Might return this::

            ['hazard', 'exposure']

        In the returned the values are categories (if any) applicable for that
        layer_type and data_type.

        :param layer_type: The type for this layer. Valid values would be,
            'raster' or 'vector'.
        :type layer_type: str

        :param data_type: The data_type for this layer. Valid possibilities
            would be 'numeric' (for raster), point, line, polygon
            (for vectors).
        :type data_type: str

        :returns: A list as per the example above where each value represents
            a valid category.
        :rtype: list
        """
        result = []
        for impact_function in self.impact_functions:
            categories = impact_function.metadata()\
                .categories_for_layer(layer_type, data_type)
            result = add_to_list(result, categories)
        categories_definitions = []
        for category in result:
            if category == 'hazard':
                categories_definitions.append(hazard_definition)
            elif category == 'exposure':
                categories_definitions.append(exposure_definition)
            else:
                raise Exception('Unsupported categories')
        return categories_definitions

    def hazards_for_layer(self, layer_geometry_key, hazard_category_key=None):
        """Get hazard categories form layer_geometry_key

        :param layer_geometry_key: The geometry id
        :type layer_geometry_key: str

        :param hazard_category_key: The hazard category
        :type hazard_category_key: str

        :returns: List of hazard
        :rtype: list
        """
        hazards = []
        for impact_function in self.impact_functions:
            if_hazards = impact_function.metadata().hazards_for_layer(
                layer_geometry_key, hazard_category_key)
            if if_hazards:
                add_to_list(hazards, if_hazards)

        return hazards