Builds a path utility that allows replacing parameters in a given path template.

build-path.ts

type PathParams<T extends string> =
  T extends `${infer _}:${infer Param}/${infer Rest}`
    ? { [K in keyof PathParams<Rest> | Param]: string }
    : T extends `${infer _}:${infer Param}`
      ? Record<Param, string>
      : void;

/**
 * Builds a path utility that allows replacing parameters in a given path template.
 *
 * @template T - The path template string.
 * @param path - The path template containing path parameters prefixed with `:`.
 * @returns A tuple where the first element is the original path,
 * and the second element is a function that replaces parameters with provided values.
 */
function buildPath<T extends string>(path: T) {
  /**
   * Replaces parameters in the path with actual values.
   *
   * @param params - The object containing values for path parameters.
   * @returns The final path with parameters replaced.
   * @throws If a required parameter is missing.
   */
  const pathWithParams = (params: PathParams<T>) => {
    return path.replace(/:([^/]+)/g, (_, key) => {
      if (typeof params === 'object' && !(key in params)) {
        throw new Error(`Missing parameter: ${key}`);
      }
      return String(params[key as keyof typeof params]);
    });
  };

  return [path, pathWithParams] as const;
}

/**
 * Generates an object mapping paths to functions that replace parameters.
 *
 * @template T - An array of path template strings.
 * @param paths - An array of path templates.
 * @returns An object where keys are paths
 * and values are functions that generate the final URL by replacing parameters.
 *
 * @example ```ts
 * const API_ENDPOINTS = buildPaths([
 *   '/posts/',
 *   '/posts/:postId/',
 *   '/posts/:postId/comments/:commentId/',
 * ]);
 *
 * console.log(API_ENDPOINTS['/posts/']()); // "/posts/"
 * console.log(API_ENDPOINTS['/posts/:postId/']({ postId: '123' })); // "/posts/123/"
 * console.log(API_ENDPOINTS['/posts/:postId/comments/:commentId/']({ postId: '123', commentId: '456' })); // "/posts/123/comments/456/"
 * ```
 */
function buildPaths<T extends string[]>(paths: T) {
  return Object.fromEntries(paths.map(buildPath)) as unknown as Readonly<{
    [Key in T[number]]: (params: PathParams<Key>) => string;
  }>;
}

export { buildPaths };