source: frontend/node_modules/pirates/lib/index.js

'use strict';

/* (c) 2015 Ari Porad (@ariporad) <http://ariporad.com>. License: ariporad.mit-license.org */
const BuiltinModule = require('module');
const path = require('path');

const nodeModulesRegex = /^(?:.*[\\/])?node_modules(?:[\\/].*)?$/;
// Guard against poorly-mocked module constructors.
const Module =
  module.constructor.length > 1 ? module.constructor : BuiltinModule;

const HOOK_RETURNED_NOTHING_ERROR_MESSAGE =
  '[Pirates] A hook returned a non-string, or nothing at all! This is a' +
  ' violation of intergalactic law!\n' +
  '--------------------\n' +
  'If you have no idea what this means or what Pirates is, let me explain: ' +
  'Pirates is a module that makes it easy to implement require hooks. One of' +
  " the require hooks you're using uses it. One of these require hooks" +
  " didn't return anything from it's handler, so we don't know what to" +
  ' do. You might want to debug this.';

/**
 * @param {string} filename The filename to check.
 * @param {string[]} exts The extensions to hook. Should start with '.' (ex. ['.js']).
 * @param {Matcher|null} matcher A matcher function, will be called with path to a file. Should return truthy if the file should be hooked, falsy otherwise.
 * @param {boolean} ignoreNodeModules Auto-ignore node_modules. Independent of any matcher.
 */
function shouldCompile(filename, exts, matcher, ignoreNodeModules) {
  if (typeof filename !== 'string') {
    return false;
  }
  if (exts.indexOf(path.extname(filename)) === -1) {
    return false;
  }

  const resolvedFilename = path.resolve(filename);

  if (ignoreNodeModules && nodeModulesRegex.test(resolvedFilename)) {
    return false;
  }
  if (matcher && typeof matcher === 'function') {
    return !!matcher(resolvedFilename);
  }

  return true;
}

/**
 * @callback Hook The hook. Accepts the code of the module and the filename.
 * @param {string} code
 * @param {string} filename
 * @returns {string}
 */
/**
 * @callback Matcher A matcher function, will be called with path to a file.
 *
 * Should return truthy if the file should be hooked, falsy otherwise.
 * @param {string} path
 * @returns {boolean}
 */
/**
 * @callback RevertFunction Reverts the hook when called.
 * @returns {void}
 */
/**
 * @typedef {object} Options
 * @property {Matcher|null} [matcher=null] A matcher function, will be called with path to a file.
 *
 * Should return truthy if the file should be hooked, falsy otherwise.
 *
 * @property {string[]} [extensions=['.js']] The extensions to hook. Should start with '.' (ex. ['.js']).
 * @property {string[]} [exts=['.js']] The extensions to hook. Should start with '.' (ex. ['.js']).
 *
 * @property {string[]} [extension=['.js']] The extensions to hook. Should start with '.' (ex. ['.js']).
 * @property {string[]} [ext=['.js']] The extensions to hook. Should start with '.' (ex. ['.js']).
 *
 * @property {boolean} [ignoreNodeModules=true] Auto-ignore node_modules. Independent of any matcher.
 */

/**
 * Add a require hook.
 *
 * @param {Hook} hook The hook. Accepts the code of the module and the filename. Required.
 * @param {Options} [opts] Options
 * @returns {RevertFunction} The `revert` function. Reverts the hook when called.
 */
function addHook(hook, opts = {}) {
  let reverted = false;
  const loaders = [];
  const oldLoaders = [];
  let exts;

  // We need to do this to fix #15. Basically, if you use a non-standard extension (ie. .jsx), then
  // We modify the .js loader, then use the modified .js loader for as the base for .jsx.
  // This prevents that.
  const originalJSLoader = Module._extensions['.js'];

  const matcher = opts.matcher || null;
  const ignoreNodeModules = opts.ignoreNodeModules !== false;
  exts = opts.extensions || opts.exts || opts.extension || opts.ext || ['.js'];
  if (!Array.isArray(exts)) {
    exts = [exts];
  }

  exts.forEach((ext) => {
    if (typeof ext !== 'string') {
      throw new TypeError(`Invalid Extension: ${ext}`);
    }
    const oldLoader = Module._extensions[ext] || originalJSLoader;
    oldLoaders[ext] = Module._extensions[ext];

    loaders[ext] = Module._extensions[ext] = function newLoader(mod, filename) {
      let compile;
      if (!reverted) {
        if (shouldCompile(filename, exts, matcher, ignoreNodeModules)) {
          compile = mod._compile;
          mod._compile = function _compile(code) {
            // reset the compile immediately as otherwise we end up having the
            // compile function being changed even though this loader might be reverted
            // Not reverting it here leads to long useless compile chains when doing
            // addHook -> revert -> addHook -> revert -> ...
            // The compile function is also anyway created new when the loader is called a second time.
            mod._compile = compile;
            const newCode = hook(code, filename);
            if (typeof newCode !== 'string') {
              throw new Error(HOOK_RETURNED_NOTHING_ERROR_MESSAGE);
            }

            return mod._compile(newCode, filename);
          };
        }
      }

      oldLoader(mod, filename);
    };
  });
  return function revert() {
    if (reverted) return;
    reverted = true;

    exts.forEach((ext) => {
      // if the current loader for the extension is our loader then unregister it and set the oldLoader again
      // if not we cannot do anything as we cannot remove a loader from within the loader-chain
      if (Module._extensions[ext] === loaders[ext]) {
        if (!oldLoaders[ext]) {
          delete Module._extensions[ext];
        } else {
          Module._extensions[ext] = oldLoaders[ext];
        }
      }
    });
  };
}

exports.addHook = addHook;