119 lines
3.7 KiB
Plaintext
119 lines
3.7 KiB
Plaintext
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/**
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* @callback Handler
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* Handle a value, with a certain ID field set to a certain value.
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* The ID field is passed to `zwitch`, and it’s value is this function’s
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* place on the `handlers` record.
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* @param {...any} parameters
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* Arbitrary parameters passed to the zwitch.
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* The first will be an object with a certain ID field set to a certain value.
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* @returns {any}
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* Anything!
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*/
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/**
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* @callback UnknownHandler
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* Handle values that do have a certain ID field, but it’s set to a value
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* that is not listed in the `handlers` record.
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* @param {unknown} value
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* An object with a certain ID field set to an unknown value.
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* @param {...any} rest
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* Arbitrary parameters passed to the zwitch.
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* @returns {any}
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* Anything!
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*/
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/**
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* @callback InvalidHandler
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* Handle values that do not have a certain ID field.
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* @param {unknown} value
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* Any unknown value.
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* @param {...any} rest
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* Arbitrary parameters passed to the zwitch.
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* @returns {void|null|undefined|never}
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* This should crash or return nothing.
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*/
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/**
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* @template {InvalidHandler} [Invalid=InvalidHandler]
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* @template {UnknownHandler} [Unknown=UnknownHandler]
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* @template {Record<string, Handler>} [Handlers=Record<string, Handler>]
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* @typedef Options
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* Configuration (required).
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* @property {Invalid} [invalid]
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* Handler to use for invalid values.
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* @property {Unknown} [unknown]
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* Handler to use for unknown values.
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* @property {Handlers} [handlers]
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* Handlers to use.
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*/
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const own = {}.hasOwnProperty
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/**
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* Handle values based on a field.
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*
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* @template {InvalidHandler} [Invalid=InvalidHandler]
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* @template {UnknownHandler} [Unknown=UnknownHandler]
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* @template {Record<string, Handler>} [Handlers=Record<string, Handler>]
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* @param {string} key
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* Field to switch on.
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* @param {Options<Invalid, Unknown, Handlers>} [options]
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* Configuration (required).
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* @returns {{unknown: Unknown, invalid: Invalid, handlers: Handlers, (...parameters: Parameters<Handlers[keyof Handlers]>): ReturnType<Handlers[keyof Handlers]>, (...parameters: Parameters<Unknown>): ReturnType<Unknown>}}
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*/
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export function zwitch(key, options) {
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const settings = options || {}
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/**
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* Handle one value.
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*
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* Based on the bound `key`, a respective handler will be called.
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* If `value` is not an object, or doesn’t have a `key` property, the special
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* “invalid” handler will be called.
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* If `value` has an unknown `key`, the special “unknown” handler will be
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* called.
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*
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* All arguments, and the context object, are passed through to the handler,
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* and it’s result is returned.
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*
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* @this {unknown}
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* Any context object.
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* @param {unknown} [value]
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* Any value.
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* @param {...unknown} parameters
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* Arbitrary parameters passed to the zwitch.
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* @property {Handler} invalid
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* Handle for values that do not have a certain ID field.
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* @property {Handler} unknown
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* Handle values that do have a certain ID field, but it’s set to a value
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* that is not listed in the `handlers` record.
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* @property {Handlers} handlers
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* Record of handlers.
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* @returns {unknown}
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* Anything.
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*/
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function one(value, ...parameters) {
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/** @type {Handler|undefined} */
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let fn = one.invalid
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const handlers = one.handlers
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if (value && own.call(value, key)) {
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// @ts-expect-error Indexable.
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const id = String(value[key])
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// @ts-expect-error Indexable.
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fn = own.call(handlers, id) ? handlers[id] : one.unknown
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}
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if (fn) {
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return fn.call(this, value, ...parameters)
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}
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}
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one.handlers = settings.handlers || {}
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one.invalid = settings.invalid
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one.unknown = settings.unknown
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// @ts-expect-error: matches!
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return one
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}
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