InterfaceHelper.js

'use strict'

class InterfaceHelper {
	static #initiated = false

	static preInit() {
		if (InterfaceHelper.#initiated) {
			console.error('InterfaceHelper is already initiated.')
			return
		}
		InterfaceHelper.#initiated = true

		const globalStyle = document.createElement('link')
		globalStyle.rel = 'stylesheet'
		globalStyle.href = '/global.css'
		document.head.prepend(globalStyle)

		const fallbackStyle = document.createElement('style')
		fallbackStyle.textContent = 'html { background-color: var(--main-background-color); }'
		document.head.prepend(fallbackStyle)
	}

	/** Coordinator shell: popup opener or `/join` parent. */
	static #target() {
		return globalThis.opener ?? globalThis.parent
	}

	/** First ping after init is applied (same as legacy `postMessage(null)`; coordinator accepts `Arena-Interface-Ready` too). */
	static signalReady() {
		const t = InterfaceHelper.#target()
		if (t) {
			t.postMessage(null, '*')
		}
	}

	/**
	 * Send a normal interface reply to the arena coordinator.
	 * @param {object} payload
	 * @param {unknown} payload.value
	 * @param {{ toRespond: number, toTerminate: number }} [payload.executionSteps]
	 * @param {unknown} [payload.console]
	 */
	static respond(payload) {
		const t = InterfaceHelper.#target()
		if (!t) {
			return
		}
		const executionSteps = payload.executionSteps ?? { toRespond: 0, toTerminate: 0 }
		t.postMessage({
			type: 'Response',
			response: {
				value: payload.value,
				executionSteps,
				...(payload.console ? { console: payload.console } : {}),
			},
		}, '*')
	}
}

globalThis.InterfaceHelper = InterfaceHelper
InterfaceHelper.preInit()