site/node_modules/zwitch/index.js

/**
 * @callback Handler
 *   Handle a value, with a certain ID field set to a certain value.
 *   The ID field is passed to `zwitch`, and it’s value is this function’s
 *   place on the `handlers` record.
 * @param {...any} parameters
 *   Arbitrary parameters passed to the zwitch.
 *   The first will be an object with a certain ID field set to a certain value.
 * @returns {any}
 *   Anything!
 */

/**
 * @callback UnknownHandler
 *   Handle values that do have a certain ID field, but it’s set to a value
 *   that is not listed in the `handlers` record.
 * @param {unknown} value
 *   An object with a certain ID field set to an unknown value.
 * @param {...any} rest
 *   Arbitrary parameters passed to the zwitch.
 * @returns {any}
 *   Anything!
 */

/**
 * @callback InvalidHandler
 *   Handle values that do not have a certain ID field.
 * @param {unknown} value
 *   Any unknown value.
 * @param {...any} rest
 *   Arbitrary parameters passed to the zwitch.
 * @returns {void|null|undefined|never}
 *   This should crash or return nothing.
 */

/**
 * @template {InvalidHandler} [Invalid=InvalidHandler]
 * @template {UnknownHandler} [Unknown=UnknownHandler]
 * @template {Record<string, Handler>} [Handlers=Record<string, Handler>]
 * @typedef Options
 *   Configuration (required).
 * @property {Invalid} [invalid]
 *   Handler to use for invalid values.
 * @property {Unknown} [unknown]
 *   Handler to use for unknown values.
 * @property {Handlers} [handlers]
 *   Handlers to use.
 */

const own = {}.hasOwnProperty

/**
 * Handle values based on a field.
 *
 * @template {InvalidHandler} [Invalid=InvalidHandler]
 * @template {UnknownHandler} [Unknown=UnknownHandler]
 * @template {Record<string, Handler>} [Handlers=Record<string, Handler>]
 * @param {string} key
 *   Field to switch on.
 * @param {Options<Invalid, Unknown, Handlers>} [options]
 *   Configuration (required).
 * @returns {{unknown: Unknown, invalid: Invalid, handlers: Handlers, (...parameters: Parameters<Handlers[keyof Handlers]>): ReturnType<Handlers[keyof Handlers]>, (...parameters: Parameters<Unknown>): ReturnType<Unknown>}}
 */
export function zwitch(key, options) {
  const settings = options || {}

  /**
   * Handle one value.
   *
   * Based on the bound `key`, a respective handler will be called.
   * If `value` is not an object, or doesn’t have a `key` property, the special
   * “invalid” handler will be called.
   * If `value` has an unknown `key`, the special “unknown” handler will be
   * called.
   *
   * All arguments, and the context object, are passed through to the handler,
   * and it’s result is returned.
   *
   * @this {unknown}
   *   Any context object.
   * @param {unknown} [value]
   *   Any value.
   * @param {...unknown} parameters
   *   Arbitrary parameters passed to the zwitch.
   * @property {Handler} invalid
   *   Handle for values that do not have a certain ID field.
   * @property {Handler} unknown
   *   Handle values that do have a certain ID field, but it’s set to a value
   *   that is not listed in the `handlers` record.
   * @property {Handlers} handlers
   *   Record of handlers.
   * @returns {unknown}
   *   Anything.
   */
  function one(value, ...parameters) {
    /** @type {Handler|undefined} */
    let fn = one.invalid
    const handlers = one.handlers

    if (value && own.call(value, key)) {
      // @ts-expect-error Indexable.
      const id = String(value[key])
      // @ts-expect-error Indexable.
      fn = own.call(handlers, id) ? handlers[id] : one.unknown
    }

    if (fn) {
      return fn.call(this, value, ...parameters)
    }
  }

  one.handlers = settings.handlers || {}
  one.invalid = settings.invalid
  one.unknown = settings.unknown

  // @ts-expect-error: matches!
  return one
}