Since we couldn't be bothered to register models elsewhere
    our definitions need to be extracted from the parameters.
    We require an 'id' field for the schema to be correctly
    added to the definitions list.

def _extract_definitions(alist, level=None):
    """
    Since we couldn't be bothered to register models elsewhere
    our definitions need to be extracted from the parameters.
    We require an 'id' field for the schema to be correctly
    added to the definitions list.
    """

    def _extract_array_defs(source):
        # extract any definitions that are within arrays
        # this occurs recursively
        ret = []
        items = source.get('items')
        if items is not None and 'schema' in items:
            ret += _extract_definitions([items], level+1)
        return ret

    # for tracking level of recursion
    if level is None:
        level = 0

    defs = list()
    if alist is not None:
        for item in alist:
            schema = item.get("schema")
            if schema is not None:
                schema_id = schema.get("id")
                if schema_id is not None:
                    defs.append(schema)
                    ref = {"$ref": "#/definitions/{}".format(schema_id)}

                    # only add the reference as a schema if we are in a response or
                    # a parameter i.e. at the top level
                    # directly ref if a definition is used within another definition
                    if level == 0:
                        item['schema'] = ref
                    else:
                        item.update(ref)
                        del item['schema']

                # extract any definitions that are within properties
                # this occurs recursively
                properties = schema.get('properties')
                if properties is not None:
                    defs += _extract_definitions(properties.values(), level+1)

                defs += _extract_array_defs(schema)

            defs += _extract_array_defs(item)

    return defs