All files / path / windows / normalize.ts

// Copyright 2018-2025 the Deno authors. MIT license.
// This module is browser compatible.

import { assertArg } from "../_common/normalize.ts";
import { CHAR_COLON } from "../_common/constants.ts";
import { normalizeString } from "../_common/normalize_string.ts";
import { isPathSeparator, isWindowsDeviceRoot } from "./_util.ts";
import { fromFileUrl } from "./from_file_url.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/windows/normalize";
 * import { assertEquals } from "@std/assert";
 *
 * assertEquals(normalize("C:\\foo\\..\\bar"), "C:\\bar");
 * assertEquals(normalize(new URL("file:///C:/foo/../bar")), "C:\\bar");
 * ```
 *
 * @param path The path to normalize
 * @returns The normalized path
 */
export function normalize(path: string | URL): string {
  if (path instanceof URL) {
    path = fromFileUrl(path);
  }
  assertArg(path);

  const len = path.length;
  let rootEnd = 0;
  let device: string | undefined;
  let isAbsolute = false;
  const code = path.charCodeAt(0);

  // Try to match a root
  if (len > 1) {
    if (isPathSeparator(code)) {
      // Possible UNC root

      // If we started with a separator, we know we at least have an absolute
      // path of some kind (UNC or otherwise)
      isAbsolute = true;

      if (isPathSeparator(path.charCodeAt(1))) {
        // Matched double path separator at beginning
        let j = 2;
        let last = j;
        // Match 1 or more non-path separators
        for (; j < len; ++j) {
          if (isPathSeparator(path.charCodeAt(j))) break;
        }
        if (j < len && j !== last) {
          const firstPart = path.slice(last, j);
          // Matched!
          last = j;
          // Match 1 or more path separators
          for (; j < len; ++j) {
            if (!isPathSeparator(path.charCodeAt(j))) break;
          }
          if (j < len && j !== last) {
            // Matched!
            last = j;
            // Match 1 or more non-path separators
            for (; j < len; ++j) {
              if (isPathSeparator(path.charCodeAt(j))) break;
            }
            if (j === len) {
              // We matched a UNC root only
              // Return the normalized version of the UNC root since there
              // is nothing left to process

              return `\\\\${firstPart}\\${path.slice(last)}\\`;
            } else if (j !== last) {
              // We matched a UNC root with leftovers

              device = `\\\\${firstPart}\\${path.slice(last, j)}`;
              rootEnd = j;
            }
          }
        }
      } else {
        rootEnd = 1;
      }
    } else if (isWindowsDeviceRoot(code)) {
      // Possible device root

      if (path.charCodeAt(1) === CHAR_COLON) {
        device = path.slice(0, 2);
        rootEnd = 2;
        if (len > 2) {
          if (isPathSeparator(path.charCodeAt(2))) {
            // Treat separator following drive name as an absolute path
            // indicator
            isAbsolute = true;
            rootEnd = 3;
          }
        }
      }
    }
  } else if (isPathSeparator(code)) {
    // `path` contains just a path separator, exit early to avoid unnecessary
    // work
    return "\\";
  }

  let tail: string;
  if (rootEnd < len) {
    tail = normalizeString(
      path.slice(rootEnd),
      !isAbsolute,
      "\\",
      isPathSeparator,
    );
  } else {
    tail = "";
  }
  if (tail.length === 0 && !isAbsolute) tail = ".";
  if (tail.length > 0 && isPathSeparator(path.charCodeAt(len - 1))) {
    tail += "\\";
  }
  if (device === undefined) {
    if (isAbsolute) {
      if (tail.length > 0) return `\\${tail}`;
      else return "\\";
    }
    return tail;
  } else if (isAbsolute) {
    if (tail.length > 0) return `${device}\\${tail}`;
    else return `${device}\\`;
  }
  return device + tail;
}