Source code for zsl.utils.resource_helper

"""
:mod:`zsl.utils.resource_helper`
--------------------------------

Helper module for resource management.
"""
# TODO describe what model resource is and use cases
import importlib
import logging
from typing import Callable, Dict, List, Union

from flask import request

from zsl import Config, Injected, Zsl, inject
from zsl.db.model import AppModel
from zsl.interface.resource import ResourceResult
from zsl.resource.model_resource import ModelResource
from zsl.utils.string_helper import underscore_to_camelcase
from zsl.utils.task_helper import instantiate




class MethodNotImplementedException(Exception):
    """Exception raised on missing method"""
    pass





def parse_resource_path(path):
    """Split the path to its elements.

    :param path: URL path
    :type path: str
    :return: name and rest of the path
    :rtype: tuple(str, list(str))
    """
    splits = path.split('/')

    return splits[0], splits[1:]





def get_method(resource, method):
    """Test and return a method by name on resource.

    :param resource: resource object
    :type resource: object
    :param method: method name
    :type method: str
    :return: bounded method
    :raises MethodNotImplementedException: when method not found
    """
    if hasattr(resource, method) and callable(getattr(resource, method)):
        return getattr(resource, method)
    else:
        raise MethodNotImplementedException()





@inject(config=Config)
def get_resource_task(resource_path, config=Injected):
    # type: (str, Config) -> Callable[[str, Dict, Dict], Union[List[AppModel], AppModel, ResourceResult]]
    """Search and return a bounded method for given path.

    :param resource_path: resource path
    :type resource_path: str
    :param config: current configuration, injected
    :type config: Config
    :return: bounded method or None when not found
    :raises NameError: when can't find given resource by path
    """
    class_name = underscore_to_camelcase(resource_path) + 'Resource'

    resource_packages = config['RESOURCE_PACKAGES'] if 'RESOURCE_PACKAGES' in config else (config['RESOURCE_PACKAGE'],)

    resource = None
    for resource_package in resource_packages:
        module_name = "{0}.{1}".format(resource_package, resource_path)

        try:
            module = importlib.import_module(module_name)

            try:
                cls = getattr(module, class_name)

                resource = instantiate(cls)
                break
            except AttributeError:
                raise NameError("Can't find resource [{0}]".format(resource_path))

        except ImportError:

            # try to find __exposer__
            try:
                exposer = importlib.import_module(resource_package + '.__exposer__')

                resource = exposer.get_resource(class_name)
                break
            except Exception as e:
                logging.error("Can not load resource {0} [{1}].".format(resource_path, e))
                pass

    if resource is None:
        raise NameError("Can't find resource [{0}]".format(resource_path))

    try:
        if request.method == 'POST':
            return get_method(resource, 'create')

        elif request.method == 'GET':
            return get_method(resource, 'read')

        elif request.method == 'PUT' or request.method == 'PATCH':
            return get_method(resource, 'update')

        elif request.method == 'DELETE':
            return get_method(resource, 'delete')

        else:
            logging.error("Invalid request method [%s] is requested for path [%s]", request.method, resource_path)

    except MethodNotImplementedException:
        logging.error(
            "MethodNotImplementedException raised for method [%s] and path [%s]",
            request.method,
            resource_path
        )
        return None





@inject(app=Zsl)
def create_model_resource(resource_map, name, app=Injected):
    """Create a model resource from a dict ``resource_map``
    {'resource name': ('model package', 'model class')}

    :param resource_map: dict with resource descriptions
    :type resource_map: dict(str, tuple(str))
    :param name: name of the concrete resource
    :param app: current application, injected
    :type app: Zsl
    :return: instantiated model resource
    """
    try:
        resource_description = resource_map[name]
        if len(resource_description) == 2:
            module_name, model_name = resource_map[name]
            resource_class = ModelResource
        elif len(resource_description) == 3:
            module_name, model_name, resource_class = resource_map[name]
        else:
            raise ImportError("Invalid resource description for resource '{0}'".format(name))
    except KeyError:
        raise ImportError("Missing resource description for resource '{0}'".format(name))

    module = importlib.import_module(module_name)
    model_cls = getattr(module, model_name)

    return app.injector.create_object(resource_class, {'model_cls': model_cls})