std/path/posix/normalize.ts

// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

import { assertArg } from "../_common/normalize.ts";
import { normalizeString } from "../_common/normalize_string.ts";
import { isPosixPathSeparator } from "./_util.ts";

/**
 * Normalize the `path`, resolving `'..'` and `'.'` segments.
 * Note that resolving these segments does not necessarily mean that all will be eliminated.
 * A `'..'` at the top-level will be preserved, and an empty path is canonically `'.'`.
 *
 * @example Usage
 * ```ts
 * import { normalize } from "@std/path/posix/normalize";
 * import { assertEquals } from "@std/assert";
 *
 * const path = normalize("/foo/bar//baz/asdf/quux/..");
 * assertEquals(path, "/foo/bar/baz/asdf");
 * ```
 *
 * @example Working with URLs
 *
 * Note: This function will remove the double slashes from a URL's scheme.
 * Hence, do not pass a full URL to this function. Instead, pass the pathname of
 * the URL.
 *
 * ```ts
 * import { normalize } from "@std/path/posix/normalize";
 * import { assertEquals } from "@std/assert";
 *
 * const url = new URL("https://deno.land");
 * url.pathname = normalize("//std//assert//.//mod.ts");
 * assertEquals(url.href, "https://deno.land/std/assert/mod.ts");
 *
 * url.pathname = normalize("std/assert/../async/retry.ts");
 * assertEquals(url.href, "https://deno.land/std/async/retry.ts");
 * ```
 *
 * Note: If you are working with file URLs,
 * use the new version of `normalize` from `@std/path/posix/unstable-normalize`.
 *
 * @param path The path to normalize.
 * @returns The normalized path.
 */
export function normalize(path: string): string {
  assertArg(path);

  const isAbsolute = isPosixPathSeparator(path.charCodeAt(0));
  const trailingSeparator = isPosixPathSeparator(
    path.charCodeAt(path.length - 1),
  );

  // Normalize the path
  path = normalizeString(path, !isAbsolute, "/", isPosixPathSeparator);

  if (path.length === 0 && !isAbsolute) path = ".";
  if (path.length > 0 && trailingSeparator) path += "/";

  if (isAbsolute) return `/${path}`;
  return path;
}