/*
 * Copyright (C) 2019 StApps
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
import {
  SCInternalServerErrorResponse,
  SCMethodNotAllowedErrorResponse,
  SCRoute,
  SCValidationErrorResponse,
} from '@openstapps/core';
import {Application, Router} from 'express';
import PromiseRouter from 'express-promise-router';
import {ValidationError} from 'jsonschema';
import {isTestEnvironment, logger, validator} from '../common';
import {isHttpMethod} from './HTTPTypes';

/**
 * Creates a router from a route class (model of a route) and a handler function which implements the logic
 *
 * The given router performs a request and respone validation, sets status codes and checks if the given handler
 * only returns errors that are allowed for the client to see
 *
 * @param routeClass
 * @param handler
 */
export function createRoute<RETURNTYPE>(
  routeClass: SCRoute,
  handler: (validatedBody: any, app: Application, params?: { [parameterName: string]: string }) => Promise<RETURNTYPE>,
): Router {
  // create router
  const router = PromiseRouter({mergeParams: true});

  // create route
  // the given type has no index signature so we have to cast to get the IRouteHandler when a HTTP method is given
  const route = router.route(routeClass.urlFragment);

  // get route parameters (path parameters)
  if (Array.isArray(routeClass.obligatoryParameters) && routeClass.obligatoryParameters.length > 0) {
    routeClass.obligatoryParameters.forEach((parameterName) => {
      router.param(parameterName, async (req, _res, next, parameterValue: string) => {

        if (typeof req.params === 'undefined') {
          req.params = {};
        }

        // set parameter values on request object
        req.params[parameterName] = parameterValue;
        // hand over the request to the next handler (our method route handler)
        next();
      });
    });
  }

  const verb = routeClass.method.toLowerCase();

  // check if route has a valid http verb
  if (isHttpMethod(verb)) {
    // create a route handler for the given HTTP method
    route[verb](async (req, res) => {

      try {
        // validate request
        const requestValidation = validator.validate(req.body, routeClass.requestBodyName);

        if (requestValidation.errors.length > 0) {
          const error = new SCValidationErrorResponse(
            requestValidation.errors,
            isTestEnvironment,
          );
          res.status(error.statusCode);
          res.json(error);
          logger.warn(error);
          return;
        }

        // hand over request to handler with path parameters
        const response = await handler(req.body, req.app, req.params);

        // validate response generated by handler
        const responseErrors: ValidationError[] = validator.validate(response, routeClass.responseBodyName).errors;

        if (responseErrors.length > 0) {
          const validationError = new SCValidationErrorResponse(
            responseErrors,
            isTestEnvironment,
          );
          // The validation error is not caused by faulty user input, but through an error that originates somewhere in
          // the backend, therefor we use this "stacked" error.
          const internalServerError = new SCInternalServerErrorResponse(
            validationError,
            isTestEnvironment,
          );
          res.status(internalServerError.statusCode);
          res.json(internalServerError);
          logger.warn(internalServerError);
          return;
        }

        // set status code
        res.status(routeClass.statusCodeSuccess);

        // respond
        res.json(response);
      } catch (error) {
        // if the error response is allowed on the route
        if (routeClass.errorNames.some((constructorType) => error instanceof constructorType)) {
          // respond with the error from the handler
          res.status(error.statusCode);
          res.json(error);
          logger.warn(error);
        } else {
          // the error is not allowed so something went wrong
          const internalServerError = new SCInternalServerErrorResponse(
            error,
            isTestEnvironment,
          );
          res.status(internalServerError.statusCode);
          res.json(internalServerError);
          logger.error(error);
        }
      }
    });
  } else {
    throw new Error('Invalid HTTP verb in route definition. Please check route definitions in `@openstapps/core`');
  }

  // return a SCMethodNotAllowedErrorResponse on all other HTTP methods
  route.all((_req, res) => {
    const error = new SCMethodNotAllowedErrorResponse(isTestEnvironment);
    res.status(error.statusCode);
    res.json(error);
    logger.warn(error);
  });

  // return router
  return router;
}