/**
 * Mutual exclude for JavaScript.
 *
 * @module mutex
 */

/**
 * @callback mutex
 * @param {function():void} cb Only executed when this mutex is not in the current stack
 * @param {function():void} [elseCb] Executed when this mutex is in the current stack
 */

/**
 * Creates a mutual exclude function with the following property:
 *
 * ```js
 * const mutex = createMutex()
 * mutex(() => {
 *   // This function is immediately executed
 *   mutex(() => {
 *     // This function is not executed, as the mutex is already active.
 *   })
 * })
 * ```
 *
 * @return {mutex} A mutual exclude function
 * @public
 */
export const createMutex = () => {
  let token = true
  return (f, g) => {
    if (token) {
      token = false
      try {
        f()
      } finally {
        token = true
      }
    } else if (g !== undefined) {
      g()
    }
  }
}