@aws-amplify/core/src/Platform/detectFramework.ts

Core category of aws-amplify

// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

import { Framework } from './types';
import { detect } from './detection';

// We want to cache detection since the framework won't change
let frameworkCache: Framework | undefined;

export const frameworkChangeObservers: (() => void)[] = [];

// Setup the detection reset tracking / timeout delays
let resetTriggered = false;
const SSR_RESET_TIMEOUT = 10; // ms
const WEB_RESET_TIMEOUT = 10; // ms
const PRIME_FRAMEWORK_DELAY = 1_000; // ms

export const detectFramework = (): Framework => {
	if (!frameworkCache) {
		frameworkCache = detect();

		if (resetTriggered) {
			// The final run of detectFramework:
			// Starting from this point, the `frameworkCache` becomes "final".
			// So we don't need to notify the observers again so the observer
			// can be removed after the final notice.
			while (frameworkChangeObservers.length) {
				frameworkChangeObservers.pop()?.();
			}
		} else {
			// The first run of detectFramework:
			// Every time we update the cache, call each observer function
			frameworkChangeObservers.forEach(fcn => {
				fcn();
			});
		}

		// Retry once for either Unknown type after a delay (explained below)
		resetTimeout(Framework.ServerSideUnknown, SSR_RESET_TIMEOUT);
		resetTimeout(Framework.WebUnknown, WEB_RESET_TIMEOUT);
	}

	return frameworkCache;
};

/**
 * @internal Setup observer callback that will be called everytime the framework changes
 */
export const observeFrameworkChanges = (fcn: () => void) => {
	// When the `frameworkCache` won't be updated again, we ignore all incoming
	// observers.
	if (resetTriggered) {
		return;
	}

	frameworkChangeObservers.push(fcn);
};

export function clearCache() {
	frameworkCache = undefined;
}

// For a framework type and a delay amount, setup the event to re-detect
//   During the runtime boot, it is possible that framework detection will
//   be triggered before the framework has made modifications to the
//   global/window/etc needed for detection. When no framework is detected
//   we will reset and try again to ensure we don't use a cached
//   non-framework detection result for all requests.
function resetTimeout(framework: Framework, delay: number) {
	if (frameworkCache === framework && !resetTriggered) {
		setTimeout(() => {
			clearCache();
			resetTriggered = true;
			setTimeout(detectFramework, PRIME_FRAMEWORK_DELAY);
		}, delay);
	}
}