join.ts

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

import { assert } from "../../assert/assert.ts";
import { assertPath } from "../_common/assert_path.ts";
import { isPathSeparator } from "./_util.ts";
import { normalize } from "./normalize.ts";

/**
 * Join all given a sequence of `paths`,then normalizes the resulting path.
 * @param paths to be joined and normalized
 */
export function join(...paths: string[]): string {
  if (paths.length === 0) return ".";

  let joined: string | undefined;
  let firstPart: string | null = null;
  for (let i = 0; i < paths.length; ++i) {
    const path = paths[i];
    assertPath(path);
    if (path.length > 0) {
      if (joined === undefined) joined = firstPart = path;
      else joined += `\\${path}`;
    }
  }

  if (joined === undefined) return ".";

  // Make sure that the joined path doesn't start with two slashes, because
  // normalize() will mistake it for an UNC path then.
  //
  // This step is skipped when it is very clear that the user actually
  // intended to point at an UNC path. This is assumed when the first
  // non-empty string arguments starts with exactly two slashes followed by
  // at least one more non-slash character.
  //
  // Note that for normalize() to treat a path as an UNC path it needs to
  // have at least 2 components, so we don't filter for that here.
  // This means that the user can use join to construct UNC paths from
  // a server name and a share name; for example:
  //   path.join('//server', 'share') -> '\\\\server\\share\\')
  let needsReplace = true;
  let slashCount = 0;
  assert(firstPart !== null);
  if (isPathSeparator(firstPart.charCodeAt(0))) {
    ++slashCount;
    const firstLen = firstPart.length;
    if (firstLen > 1) {
      if (isPathSeparator(firstPart.charCodeAt(1))) {
        ++slashCount;
        if (firstLen > 2) {
          if (isPathSeparator(firstPart.charCodeAt(2))) ++slashCount;
          else {
            // We matched a UNC path in the first part
            needsReplace = false;
          }
        }
      }
    }
  }
  if (needsReplace) {
    // Find any more consecutive slashes we need to replace
    for (; slashCount < joined.length; ++slashCount) {
      if (!isPathSeparator(joined.charCodeAt(slashCount))) break;
    }

    // Replace the slashes if needed
    if (slashCount >= 2) joined = `\\${joined.slice(slashCount)}`;
  }

  return normalize(joined);
}