custom-redirect.js

import errorTemplate from './html/error-template.html'
import { HELPER } from './helper-functions.js'

/**
 * Generates the error page HTML with the given details
 * @param {Object} details - Error details to inject into the template
 * @returns {string} The HTML with injected values
 */
function generateErrorPage(details) {
  return errorTemplate
    .replace('ERROR_CODE', details.errorCode)
    .replace('ERROR_TYPE', details.errorType)
    .replace('ERROR_MESSAGE', details.errorMessage)
    .replace('ERROR_GIF', details.errorGif)
    .replace('ENABLE_REPORT_ERROR', details.enableReportError)
    .replace('REPORT_ERROR_BUTTON_TEXT', details.reportErrorButtonText)
    .replace('REPORT_ERROR_MODAL_HEADER_TEXT', details.reportErrorModalHeaderText)
    .replace('REPORT_ERROR_LABEL_PLACEHOLDER', details.reportErrorLabelPlaceholder)
    .replace('REPORT_ERROR_MODAL_NAME_PLACEHOLDER', details.reportErrorModalNamePlaceholder)
    .replace('REPORT_ERROR_CANCEL_BUTTON_TEXT', details.reportErrorCancelButtonText)
    .replace('REPORT_ERROR_SUBMIT_BUTTON_TEXT', details.reportErrorSubmitButtonText)
    .replace('REPORT_ERROR_SUCCESS_MESSAGE', details.reportErrorSuccessMessage)
    .replace('REPORT_ERROR_FAILURE_MESSAGE', details.reportErrorFailureMessage)
    .replace('REPORT_ERROR_CODE', details.errorCode);
}

/**
 * Creates an HTTP response with specified content
 * @param {string} content - HTML content for the response
 * @param {string} statusCode - HTTP status code
 * @returns {Response} The formatted response
 */
function makeResponse(content, statusCode) {
  return new Response(content, {
    status: parseInt(statusCode, 10),
    headers: {
      'Content-Type': 'text/html',
      'X-Worker-Handled': 'true'
    }
  });
}

/**
 * Builds error details object from an error code and env config
 * @param {number|string} cfCode - The error code or "MAINTENANCE"
 * @param {Object} env - Environment variables
 * @returns {Object} Error details for the template
 */
function getErrorDetails(cfCode, env) {
  const details = {
    errorCode: "500",
    errorType: env.TEXT_GENERIC_ERROR_TYPE,
    errorMessage: env.TEXT_GENERIC_ERROR_MESSAGE,
    errorGif: env.TEXT_GENERIC_ERROR_GIF,
    enableReportError: false,
    reportErrorButtonText: '',
    reportErrorModalHeaderText: '',
    reportErrorLabelPlaceholder: '',
    reportErrorModalNamePlaceholder: '',
    reportErrorCancelButtonText: '',
    reportErrorSubmitButtonText: '',
    reportErrorSuccessMessage: '',
    reportErrorFailureMessage: ''
  };

  if (cfCode === "MAINTENANCE") {
    details.errorCode = "503";
    details.errorType = env.TEXT_MAINTENANCE_TYPE;
    details.errorMessage = env.TEXT_MAINTENANCE_MESSAGE;
    details.errorGif = env.TEXT_MAINTENANCE_GIF;
    return details;
  }

  details.errorCode = cfCode ? cfCode.toString() : "500";
  console.log(`Handling error with code: ${details.errorCode}`);

  const enableReport = env.ENABLE_REPORT_ERROR === true || env.ENABLE_REPORT_ERROR === 'true';
  details.enableReportError = enableReport;
  if (enableReport) {
    details.reportErrorButtonText = env.REPORT_ERROR_BUTTON_TEXT;
    details.reportErrorModalHeaderText = env.REPORT_ERROR_MODAL_HEADER_TEXT;
    details.reportErrorLabelPlaceholder = env.REPORT_ERROR_LABEL_PLACEHOLDER;
    details.reportErrorModalNamePlaceholder = env.REPORT_ERROR_MODAL_NAME_PLACEHOLDER;
    details.reportErrorCancelButtonText = env.REPORT_ERROR_CANCEL_BUTTON_TEXT;
    details.reportErrorSubmitButtonText = env.REPORT_ERROR_SUBMIT_BUTTON_TEXT;
    details.reportErrorSuccessMessage = env.REPORT_ERROR_SUCCESS_MESSAGE;
    details.reportErrorFailureMessage = env.REPORT_ERROR_FAILURE_MESSAGE;
  }

  const containerCodes = env.TEXT_CONTAINER_ERROR_CODE || [];
  const boxCodes = env.TEXT_BOX_ERROR_CODE || [];
  const tunnelCodes = env.TEXT_TUNNEL_ERROR_CODE || [];

  if (containerCodes.includes(cfCode)) {
    details.errorType = env.TEXT_CONTAINER_ERROR_TYPE;
    details.errorMessage = env.TEXT_CONTAINER_ERROR_MESSAGE;
    details.errorGif = env.TEXT_CONTAINER_ERROR_GIF;
  } else if (boxCodes.includes(cfCode)) {
    details.errorType = env.TEXT_BOX_ERROR_TYPE;
    details.errorMessage = env.TEXT_BOX_ERROR_MESSAGE;
    details.errorGif = env.TEXT_BOX_ERROR_GIF;
  } else if (tunnelCodes.includes(cfCode)) {
    details.errorType = env.TEXT_TUNNEL_ERROR_TYPE;
    details.errorMessage = env.TEXT_TUNNEL_ERROR_MESSAGE;
    details.errorGif = env.TEXT_TUNNEL_ERROR_GIF;
  }

  return details;
}

/**
 * Main redirection and error handling function
 * @param {Request} request - Incoming request
 * @param {Response|null} response - Server response if available
 * @param {Error|null} thrownError - Thrown error if present
 * @param {boolean} isMaintenance - Maintenance mode state
 * @param {Object} env - Environment variables
 * @returns {Promise<Response|null>} Appropriate error response or null
 */
export async function c_redirect(request, response, thrownError, isMaintenance, env) {
  // Maintenance mode
  if (isMaintenance) {
    const details = getErrorDetails("MAINTENANCE", env);
    return makeResponse(generateErrorPage(details), details.errorCode);
  }

  // Check if origin is reachable (only if ORIGIN_PING_URL is configured)
  const originUp = await HELPER.isOriginReachable(undefined, env).catch(() => null);

  // Origin confirmed down (originUp === false means the check ran and failed)
  // originUp === null means ORIGIN_PING_URL is not configured, so we skip this check
  if (originUp === false) {
    const details = getErrorDetails(504, env);
    return makeResponse(generateErrorPage(details), details.errorCode);
  }

  // Handle server errors (5xx) from the response
  if (response && response.status >= 500) {
    const details = getErrorDetails(response.status, env);
    return makeResponse(generateErrorPage(details), details.errorCode);
  }

  // Handle thrown errors (fetch failed entirely, e.g. container down / connection refused)
  if (thrownError && !response) {
    const details = getErrorDetails(502, env);
    return makeResponse(generateErrorPage(details), details.errorCode);
  }

  return null;
}