const fs = require('fs');
const express = require('express');
const anotherModule = require('./another-module');

int Start(int argc, char** argv) {
  InitializationResult result = InitializeOncePerProcess(argc, argv);
  if (result.early_return) {
    return result.exit_code;
  }
  {
    Isolate::CreateParams params;
    const std::vector<size_t>* indices = nullptr;
    const EnvSerializeInfo* env_info = nullptr;
    bool use_node_snapshot =
        per_process::cli_options->per_isolate->node_snapshot;
    if (use_node_snapshot) {
      v8::StartupData* blob = NodeMainInstance::GetEmbeddedSnapshotBlob();
      if (blob != nullptr) {
        params.snapshot_blob = blob;
        indices = NodeMainInstance::GetIsolateDataIndices();
        env_info = NodeMainInstance::GetEnvSerializeInfo();
      }
    }
    uv_loop_configure(uv_default_loop(), UV_METRICS_IDLE_TIME);
    NodeMainInstance main_instance(&params,
                                   uv_default_loop(),
                                   per_process::v8_platform.Platform(),
                                   result.args,
                                   result.exec_args,
                                   indices);
    result.exit_code = main_instance.Run(env_info);
  }
  TearDownOncePerProcess();
  return result.exit_code;
}

int NodeMainInstance::Run(const EnvSerializeInfo* env_info) {
  Locker locker(isolate_);
  Isolate::Scope isolate_scope(isolate_);
  HandleScope handle_scope(isolate_);
  int exit_code = 0;
  DeleteFnPtr<Environment, FreeEnvironment> env =
      CreateMainEnvironment(&exit_code, env_info);
  CHECK_NOT_NULL(env);
  Context::Scope context_scope(env->context());
  Run(&exit_code, env.get());
  return exit_code;
}

Environment* CreateEnvironment(
    IsolateData* isolate_data,
    Local<Context> context,
    const std::vector<std::string>& args,
    const std::vector<std::string>& exec_args,
    EnvironmentFlags::Flags flags,
    ThreadId thread_id,
    std::unique_ptr<InspectorParentHandle> inspector_parent_handle) {
  Isolate* isolate = context->GetIsolate();
  HandleScope handle_scope(isolate);
  Context::Scope context_scope(context);
  // TODO(addaleax): This is a much better place for parsing per-Environment
  // options than the global parse call.
  Environment* env = new Environment(
      isolate_data, context, args, exec_args, nullptr, flags, thread_id);
#if HAVE_INSPECTOR
  if (inspector_parent_handle) {
    env->InitializeInspector(
        std::move(static_cast<InspectorParentHandleImpl*>(
            inspector_parent_handle.get())->impl));
  } else {
    env->InitializeInspector({});
  }
#endif
  if (env->RunBootstrapping().IsEmpty()) {
    FreeEnvironment(env);
    return nullptr;
  }
  return env;
}

MaybeLocal<Value> Environment::RunBootstrapping() {
  EscapableHandleScope scope(isolate_);
  CHECK(!has_run_bootstrapping_code());
  if (BootstrapInternalLoaders().IsEmpty()) {
    return MaybeLocal<Value>();
  }
  Local<Value> result;
  if (!BootstrapNode().ToLocal(&result)) {
    return MaybeLocal<Value>();
  }
  // Make sure that no request or handle is created during bootstrap -
  // if necessary those should be done in pre-execution.
  // Usually, doing so would trigger the checks present in the ReqWrap and
  // HandleWrap classes, so this is only a consistency check.
  CHECK(req_wrap_queue()->IsEmpty());
  CHECK(handle_wrap_queue()->IsEmpty());
  DoneBootstrapping();
  return scope.Escape(result);
}

function nativeModuleRequire(id) {
  if (id === loaderId) {
    return loaderExports;
  }
  const mod = NativeModule.map.get(id);
  // Can't load the internal errors module from here, have to use a raw error.
  // eslint-disable-next-line no-restricted-syntax
  if (!mod) throw new TypeError(`Missing internal module '${id}'`);
  return mod.compileForInternalLoader();
}
const loaderExports = {
  internalBinding,
  NativeModule,
  require: nativeModuleRequire
};
return loaderExports;

int NodeMainInstance::Run(const EnvSerializeInfo* env_info) {
  Locker locker(isolate_);
  Isolate::Scope isolate_scope(isolate_);
  HandleScope handle_scope(isolate_);
  int exit_code = 0;
  DeleteFnPtr<Environment, FreeEnvironment> env =
      CreateMainEnvironment(&exit_code, env_info);
  CHECK_NOT_NULL(env);
  Context::Scope context_scope(env->context());
  Run(&exit_code, env.get());
  return exit_code;
}

void NodeMainInstance::Run(int* exit_code, Environment* env) {
  if (*exit_code == 0) {
    LoadEnvironment(env, StartExecutionCallback{});
    *exit_code = SpinEventLoop(env).FromMaybe(1);
  }
  ResetStdio();
  // TODO(addaleax): Neither NODE_SHARED_MODE nor HAVE_INSPECTOR really
  // make sense here.
#if HAVE_INSPECTOR && defined(__POSIX__) && !defined(NODE_SHARED_MODE)
  struct sigaction act;
  memset(&act, 0, sizeof(act));
  for (unsigned nr = 1; nr < kMaxSignal; nr += 1) {
    if (nr == SIGKILL || nr == SIGSTOP || nr == SIGPROF)
      continue;
    act.sa_handler = (nr == SIGPIPE) ? SIG_IGN : SIG_DFL;
    CHECK_EQ(0, sigaction(nr, &act, nullptr));
  }
#endif
#if defined(LEAK_SANITIZER)
  __lsan_do_leak_check();
#endif
}

MaybeLocal<Value> LoadEnvironment(
    Environment* env,
    StartExecutionCallback cb) {
  env->InitializeLibuv();
  env->InitializeDiagnostics();
  return StartExecution(env, cb);
}

MaybeLocal<Value> StartExecution(Environment* env, StartExecutionCallback cb) {
  // 已省略其他運(yùn)行方式，我們只看 `node index.js` 這種情況，不影響我們理解模塊系統(tǒng)
  if (!first_argv.empty() && first_argv != "-") {
    return StartExecution(env, "internal/main/run_main_module");
  }
}

'use strict';
const {
  prepareMainThreadExecution
} = require('internal/bootstrap/pre_execution');
prepareMainThreadExecution(true);
markBootstrapComplete();
// Note: this loads the module through the ESM loader if the module is
// determined to be an ES module. This hangs from the CJS module loader
// because we currently allow monkey-patching of the module loaders
// in the preloaded scripts through require('module').
// runMain here might be monkey-patched by users in --require.
// XXX: the monkey-patchability here should probably be deprecated.
require('internal/modules/cjs/loader').Module.runMain(process.argv[1]);

(function(require, /* 其他入?yún)?*/) {
  // 這里是 internal/main/run_main_module.js 的文件內(nèi)容
})();

function initializeCJSLoader() {
  const CJSLoader = require('internal/modules/cjs/loader');
  if (!noGlobalSearchPaths) {
    CJSLoader.Module._initPaths();
  }
  // TODO(joyeecheung): deprecate this in favor of a proper hook?
  CJSLoader.Module.runMain =
    require('internal/modules/run_main').executeUserEntryPoint;
}

function executeUserEntryPoint(main = process.argv[1]) {
  const resolvedMain = resolveMainPath(main);
  const useESMLoader = shouldUseESMLoader(resolvedMain);
  if (useESMLoader) {
    runMainESM(resolvedMain || main);
  } else {
    // Module._load is the monkey-patchable CJS module loader.
    Module._load(main, null, true);
  }
}

// `_load` 函數(shù)檢查請(qǐng)求文件的緩存
// 1. 如果模塊已經(jīng)存在，返回已緩存的 exports 對(duì)象
// 2. 如果模塊是內(nèi)置模塊，通過調(diào)用 `NativeModule.prototype.compileForPublicLoader()`
//    獲取內(nèi)置模塊的 exports 對(duì)象，compileForPublicLoader 函數(shù)是有白名單的，只能獲取公開
//    內(nèi)置模塊的 exports。
// 3. 以上兩者皆為否，創(chuàng)建新的 Module 對(duì)象并保存到緩存中，然后通過它加載文件并返回其 exports。
// request：請(qǐng)求的模塊，比如 `fs`，`./another-module`，'@pipcook/core' 等
// parent：父模塊，如在 `a.js` 中 `require('b.js')`，那么這里的 request 為 'b.js',
           parent 為 `a.js` 對(duì)應(yīng)的 Module 對(duì)象
// isMain: 除入口文件為 `true` 外，其他模塊都為 `false`
Module._load = function(request, parent, isMain) {
  let relResolveCacheIdentifier;
  if (parent) {
    debug('Module._load REQUEST %s parent: %s', request, parent.id);
    // relativeResolveCache 是模塊路徑緩存，
    // 用于加速父模塊所在目錄下的所有模塊請(qǐng)求當(dāng)前模塊時(shí)
    // 可以直接查詢到實(shí)際路徑，而不需要通過 _resolveFilename 查找文件
    relResolveCacheIdentifier = `${parent.path}\x00${request}`;
    const filename = relativeResolveCache[relResolveCacheIdentifier];
    if (filename !== undefined) {
      const cachedModule = Module._cache[filename];
      if (cachedModule !== undefined) {
        updateChildren(parent, cachedModule, true);
        if (!cachedModule.loaded)
          return getExportsForCircularRequire(cachedModule);
        return cachedModule.exports;
      }
      delete relativeResolveCache[relResolveCacheIdentifier];
    }
  }
	// 嘗試查找模塊文件路徑，找不到模塊拋出異常
  const filename = Module._resolveFilename(request, parent, isMain);
  // 如果是內(nèi)置模塊，從 `NativeModule` 加載
  if (StringPrototypeStartsWith(filename, 'node:')) {
    // Slice 'node:' prefix
    const id = StringPrototypeSlice(filename, 5);
    const module = loadNativeModule(id, request);
    if (!module?.canBeRequiredByUsers) {
      throw new ERR_UNKNOWN_BUILTIN_MODULE(filename);
    }
    return module.exports;
  }
	// 如果緩存中已存在，將當(dāng)前模塊 push 到父模塊的 children 字段
  const cachedModule = Module._cache[filename];
  if (cachedModule !== undefined) {
    updateChildren(parent, cachedModule, true);
    // 處理循環(huán)引用
    if (!cachedModule.loaded) {
      const parseCachedModule = cjsParseCache.get(cachedModule);
      if (!parseCachedModule || parseCachedModule.loaded)
        return getExportsForCircularRequire(cachedModule);
      parseCachedModule.loaded = true;
    } else {
      return cachedModule.exports;
    }
  }
	// 嘗試從內(nèi)置模塊加載
  const mod = loadNativeModule(filename, request);
  if (mod?.canBeRequiredByUsers) return mod.exports;
  // Don't call updateChildren(), Module constructor already does.
  const module = cachedModule || new Module(filename, parent);
  if (isMain) {
    process.mainModule = module;
    module.id = '.';
  }
	// 將 module 對(duì)象加入緩存
  Module._cache[filename] = module;
  if (parent !== undefined) {
    relativeResolveCache[relResolveCacheIdentifier] = filename;
  }
  // 嘗試加載模塊，如果加載失敗則刪除緩存中的 module 對(duì)象，
  // 同時(shí)刪除父模塊的 children 內(nèi)的 module 對(duì)象。
  let threw = true;
  try {
    module.load(filename);
    threw = false;
  } finally {
    if (threw) {
      delete Module._cache[filename];
      if (parent !== undefined) {
        delete relativeResolveCache[relResolveCacheIdentifier];
        const children = parent?.children;
        if (ArrayIsArray(children)) {
          const index = ArrayPrototypeIndexOf(children, module);
          if (index !== -1) {
            ArrayPrototypeSplice(children, index, 1);
          }
        }
      }
    } else if (module.exports &&
               !isProxy(module.exports) &&
               ObjectGetPrototypeOf(module.exports) ===
                 CircularRequirePrototypeWarningProxy) {
      ObjectSetPrototypeOf(module.exports, ObjectPrototype);
    }
  }
	// 返回 exports 對(duì)象
  return module.exports;
};

Module.prototype.load = function(filename) {
  debug('load %j for module %j', filename, this.id);
  assert(!this.loaded);
  this.filename = filename;
  this.paths = Module._nodeModulePaths(path.dirname(filename));
  const extension = findLongestRegisteredExtension(filename);
  // allow .mjs to be overridden
  if (StringPrototypeEndsWith(filename, '.mjs') && !Module._extensions['.mjs'])
    throw new ERR_REQUIRE_ESM(filename, true);
  Module._extensions[extension](this, filename);
  this.loaded = true;
  const esmLoader = asyncESM.esmLoader;
  // Create module entry at load time to snapshot exports correctly
  const exports = this.exports;
  // Preemptively cache
  if ((module?.module === undefined ||
       module.module.getStatus() < kEvaluated) &&
      !esmLoader.cjsCache.has(this))
    esmLoader.cjsCache.set(this, exports);
};

const wrapper = [
  '(function (exports, require, module, __filename, __dirname) { ',
  '\n});',
];

Module.prototype.require = function(id) {
  validateString(id, 'id');
  if (id === '') {
    throw new ERR_INVALID_ARG_VALUE('id', id,
                                    'must be a non-empty string');
  }
  requireDepth++;
  try {
    return Module._load(id, this, /* isMain */ false);
  } finally {
    requireDepth--;
  }
};