// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

import { assertArg } from "../_common/dirname.ts";
import { stripTrailingSeparators } from "../_common/strip_trailing_separators.ts";
import { isPosixPathSeparator } from "./_util.ts";

/**
 * Return the directory path of a `path`.
 * @param path - path to extract the directory from.
 */
export function dirname(path: string): string {
  assertArg(path);

  let end = -1;
  let matchedNonSeparator = false;

  for (let i = path.length - 1; i >= 1; --i) {
    if (isPosixPathSeparator(path.charCodeAt(i))) {
      if (matchedNonSeparator) {
        end = i;
        break;
      }
    } else {
      matchedNonSeparator = true;
    }
  }

  // No matches. Fallback based on provided path:
  //
  // - leading slashes paths
  //     "/foo" => "/"
  //     "///foo" => "/"
  // - no slash path
  //     "foo" => "."
  if (end === -1) {
    return isPosixPathSeparator(path.charCodeAt(0)) ? "/" : ".";
  }

  return stripTrailingSeparators(
    path.slice(0, end),
    isPosixPathSeparator,
  );
}