// Import libs
import express from 'express';

// Import shared helpers
import currentUser from '../currentUser';

// Constants
const CLIENT_ID = 'client_id';
const CLIENT_SECRET = 'client_secret';

/*------------------------------------------------------------------------*/
/*                                 Helpers                                */
/*------------------------------------------------------------------------*/

/**
 * Generate an oauth code
 * @author Gabe Abrams
 * @param id userId
 * @returns oauth code
 */
const genCode = (id: number): string => {
  return `simulated-oauth-code-for-${id}`;
};

/**
 * Generate a refresh token
 * @author Gabe Abrams
 * @param id userId
 * @returns refresh token
 */
const genRefreshToken = (id: number): string => {
  return `simulated-refresh-token-for-${id}`;
};

/**
 * Parse a refresh token to get the user's id
 * @author Gabe Abrams
 * @param code refresh token
 * @returns user's id
 */
const refreshTokenToId = (code: string): number => {
  const parts = code.split('-');
  if (parts.length !== 5) {
    return null;
  }
  return Number.parseInt(parts[4]);
};

/*------------------------------------------------------------------------*/
/*                              Global Logic                              */
/*------------------------------------------------------------------------*/

// Keep track of token expiry
const tokenExpiry = new Map<string, number>(); // token => ms expiry timestamp

/**
 * Reset an access token's expiry time
 * @author Gabe Abrams
 * @param token user's token
 */
const resetTokenExpiry = (token: string) => {
  tokenExpiry.set(token, Date.now() + 3600000);
};

/**
 * Check if an access token is valid
 * @author Gabe Abrams
 * @param token access token
 * @returns true if the token is valid
 */
const tokenIsValid = (token: string): boolean => {
  const expiry = tokenExpiry.get(token);
  return (
    expiry
    && (expiry > Date.now())
  );
};

/*------------------------------------------------------------------------*/
/*                                 Routes                                 */
/*------------------------------------------------------------------------*/

/**
 * Initializes simulated LTI launch functionality
 * @param app the express app to add routes to
 */
const initOAuth = (app: express.Application) => {

  /**
   * Replace Canvas's default oauth endpoint
   * @author Gabe Abrams
   */
  app.get(
    '/login/oauth2/auth',
    (req, res) => {
      const { state } = req.query;
      const redirectURI = String(req.query.redirect_uri);

      // Detect and complain about unknown clients
      if (CLIENT_ID !== req.query.client_id) {
        return res.send('while(1);{"error":"invalid_client","error_description":"unknown client"}');
      }

      // Detect and complain about invalid redirectURI
      if (!redirectURI || !redirectURI.startsWith('https://localhost')) {
        return res.send('while(1);{"error":"invalid_request","error_description":"redirect_uri does not match client settings"}');
      }

      // Detect and complain about invalid code
      if (req.query.response_type !== 'code') {
        return res.redirect(`${redirectURI}?error=unsupported_response_type&error_description=Only+response_type%3Dcode+is+permitted`);
      }

      // Get the current user
      const user = currentUser.get();
      if (!user) {
        return res.send('while(1);{"error":"invalid_client","error_description":"unknown client"}');
      }
      const { id } = user;

      // Generate a code
      const code = genCode(id);

      // Show authorize page
      res.render(
        `${__dirname}/authorizePage`,
        {
          name: (
            (user && user.profile && user.profile.name)
              ? user.profile.name
              : 'a test user'
          ),
          cancelURL: `${redirectURI}?error=access_denied`,
          approveURL: `${redirectURI}?code=${code}&state=${state}`,
        },
      );
    }
  );

  /**
   * Replace Canvas's default token swap endpoint
   * @author Gabe Abrams
   */
  app.post('/login/oauth2/token', (req, res) => {
    // Handle code-based authorization request
    if (req.body.grant_type === 'authorization_code') {
      if (CLIENT_ID !== req.body.client_id) {
        return res.status(401).json({
          error: 'invalid_client',
          error_description: 'unknown client',
        });
      }
      if (CLIENT_SECRET !== req.body.client_secret) {
        return res.status(401).json({
          error: 'invalid_client',
          error_description: 'invalid client',
        });
      }

      // Make sure the code is valid
      const user = currentUser.get();
      if (!user) {
        return res.status(401).json({
          error: 'invalid_client',
          error_description: 'unknown client',
        });
      }
      const {
        id,
        token,
        profile,
      } = user;
      if (genCode(id) !== req.body.code) {
        return res.status(400).json({
          error: 'invalid_grant',
          error_description: 'authorization_code not found',
        });
      }

      // Reset the expiry time
      resetTokenExpiry(token);

      // Generate a refresh token
      const refreshToken = genRefreshToken(id);

      // Respond to the request
      return res.json({
        access_token: token,
        refresh_token: refreshToken,
        expires_in: 3600,
        token_type: 'Bearer',
        user:
          {
            id,
            name: profile.name,
            global_id: null,
            effective_locale: 'en',
          },
      });
    }

    // Handle refresh token request
    if (req.body.grant_type === 'refresh_token') {
      // Make sure the credentials are valid
      if (CLIENT_ID !== req.body.client_id) {
        return res.status(401).json({
          error: 'invalid_client',
          error_description: 'unknown client',
        });
      }
      if (CLIENT_SECRET !== req.body.client_secret) {
        return res.status(401).json({
          error: 'invalid_client',
          error_description: 'invalid client',
        });
      }

      // Parse the refresh token
      const id = refreshTokenToId(req.body.refresh_token);
      if (!id) {
        return res.status(400).json({
          error: 'invalid_grant',
          error_description: 'authorization_code not found',
        });
      }

      // Get the access token
      const user = currentUser.get(id);
      if (!user) {
        return res.status(401).json({
          error: 'invalid_client',
          error_description: 'invalid client',
        });
      }
      const { token, profile } = user;

      // Reset expiry
      resetTokenExpiry(token);

      // Respond to request
      return res.json({
        access_token: token,
        expires_in: 3600,
        token_type: 'Bearer',
        user:
          {
            id,
            name: profile.name,
            global_id: null,
            effective_locale: 'en',
          },
      });
    }

    // Must be an invalid grant type
    return res.status(500).send('Invalid grant type');
  });

  /**
   * Middleware to simulate expiration of token
   * @author Gabe Abrams
   */
  app.all(
    '*',
    (req, res, next) => {
      if (req.body.access_token && !tokenIsValid(req.body.access_token)) {
        req.body.access_token = 'invalid_access_token';
      }
      next();
    },
  );
};

export default initOAuth;