Complete Text refactoring, document FileSystem complexity

Co-authored-by: dmichon-msft <26827560+dmichon-msft@users.noreply.github.com>

Author: Copilot

libraries/node-core-library/src/fileSystem/errorChecks.ts

@@ -0,0 +1,74 @@
+// Copyright (c) Microsoft Corporation. All rights reserved. Licensed under the MIT license.
+// See LICENSE in the project root for license information.
+
+/**
+ * Returns true if the error object indicates the file or folder already exists (`EEXIST`).
+ * @public
+ */
+export function isExistError(error: Error): boolean {
+  return isErrnoException(error) && error.code === 'EEXIST';
+}
+
+/**
+ * Returns true if the error object indicates the file or folder does not exist (`ENOENT` or `ENOTDIR`)
+ * @public
+ */
+export function isNotExistError(error: Error): boolean {
+  return isFileDoesNotExistError(error) || isFolderDoesNotExistError(error);
+}
+
+/**
+ * Returns true if the error object indicates the file does not exist (`ENOENT`).
+ * @public
+ */
+export function isFileDoesNotExistError(error: Error): boolean {
+  return isErrnoException(error) && error.code === 'ENOENT';
+}
+
+/**
+ * Returns true if the error object indicates the folder does not exist (`ENOTDIR`).
+ * @public
+ */
+export function isFolderDoesNotExistError(error: Error): boolean {
+  return isErrnoException(error) && error.code === 'ENOTDIR';
+}
+
+/**
+ * Returns true if the error object indicates the target is a directory (`EISDIR`).
+ * @public
+ */
+export function isDirectoryError(error: Error): boolean {
+  return isErrnoException(error) && error.code === 'EISDIR';
+}
+
+/**
+ * Returns true if the error object indicates the target is not a directory (`ENOTDIR`).
+ * @public
+ */
+export function isNotDirectoryError(error: Error): boolean {
+  return isErrnoException(error) && error.code === 'ENOTDIR';
+}
+
+/**
+ * Returns true if the error object indicates that the `unlink` system call failed
+ * due to a permissions issue (`EPERM`).
+ * @public
+ */
+export function isUnlinkNotPermittedError(error: Error): boolean {
+  return isErrnoException(error) && error.code === 'EPERM' && error.syscall === 'unlink';
+}
+
+/**
+ * Detects if the provided error object is a `NodeJS.ErrnoException`
+ * @public
+ */
+export function isErrnoException(error: Error): error is NodeJS.ErrnoException {
+  const typedError: NodeJS.ErrnoException = error;
+  // Don't check for `path` because the syscall may not have a path.
+  // For example, when invoked with a file descriptor.
+  return (
+    typeof typedError.code === 'string' &&
+    typeof typedError.errno === 'number' &&
+    typeof typedError.syscall === 'string'
+  );
+}