All files / path / windows / dirname.ts

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

import { assertArg } from "../_common/dirname.ts";
import { CHAR_COLON } from "../_common/constants.ts";
import { stripTrailingSeparators } from "../_common/strip_trailing_separators.ts";
import {
  isPathSeparator,
  isPosixPathSeparator,
  isWindowsDeviceRoot,
} from "./_util.ts";
import { fromFileUrl } from "./from_file_url.ts";

/**
 * Return the directory path of a `path`.
 *
 * @example Usage
 * ```ts
 * import { dirname } from "@std/path/windows/dirname";
 * import { assertEquals } from "@std/assert";
 *
 * assertEquals(dirname("C:\\foo\\bar\\baz.ext"), "C:\\foo\\bar");
 * assertEquals(dirname(new URL("file:///C:/foo/bar/baz.ext")), "C:\\foo\\bar");
 * ```
 *
 * @param path The path to get the directory from.
 * @returns The directory path.
 */
export function dirname(path: string | URL): string {
  if (path instanceof URL) {
    path = fromFileUrl(path);
  }
  assertArg(path);

  const len = path.length;
  let rootEnd = -1;
  let end = -1;
  let matchedSlash = true;
  let offset = 0;
  const code = path.charCodeAt(0);

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

      rootEnd = offset = 1;

      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) {
          // 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 path;
            }
            if (j !== last) {
              // We matched a UNC root with leftovers

              // Offset by 1 to include the separator after the UNC root to
              // treat it as a "normal root" on top of a (UNC) root
              rootEnd = offset = j + 1;
            }
          }
        }
      }
    } else if (isWindowsDeviceRoot(code)) {
      // Possible device root

      if (path.charCodeAt(1) === CHAR_COLON) {
        rootEnd = offset = 2;
        if (len > 2) {
          if (isPathSeparator(path.charCodeAt(2))) rootEnd = offset = 3;
        }
      }
    }
  } else if (isPathSeparator(code)) {
    // `path` contains just a path separator, exit early to avoid
    // unnecessary work
    return path;
  }

  for (let i = len - 1; i >= offset; --i) {
    if (isPathSeparator(path.charCodeAt(i))) {
      if (!matchedSlash) {
        end = i;
        break;
      }
    } else {
      // We saw the first non-path separator
      matchedSlash = false;
    }
  }

  if (end === -1) {
    if (rootEnd === -1) return ".";
    else end = rootEnd;
  }
  return stripTrailingSeparators(path.slice(0, end), isPosixPathSeparator);
}