const EXTERNAL_HYDRATION_PROMISE = Symbol.for('octane.external-hydration-promise');

type ExternalHydrationThenable<T> = PromiseLike<T> & {
	[EXTERNAL_HYDRATION_PROMISE]: true;
	status?: ThenableStatus;
	value?: T;
	reason?: unknown;
};

type ThenableStatus = 'pending' | 'fulfilled' | 'rejected';

const externalHydrationThenables = new WeakMap<object, ExternalHydrationThenable<unknown>>();

/**
 * Wrap a router-owned promise so Octane still schedules its suspense boundary,
 * while TanStack's serializer remains the only owner of its hydration value.
 */
export function toExternalHydrationThenable<T>(thenable: PromiseLike<T>): PromiseLike<T> {
	const key = thenable as object;
	const existing = externalHydrationThenables.get(key);
	if (existing) {
		return existing as ExternalHydrationThenable<T>;
	}

	let localStatus: ThenableStatus | undefined;
	let localValue: T | undefined;
	let localReason: unknown;
	let hasLocalValue = false;
	let hasLocalReason = false;

	const externalThenable: ExternalHydrationThenable<T> = {
		[EXTERNAL_HYDRATION_PROMISE]: true,
		get status() {
			return localStatus ?? readThenableStatus(thenable);
		},
		set status(status) {
			localStatus = status;
		},
		get value(): T | undefined {
			return hasLocalValue ? localValue : readThenableProperty<T>(thenable, 'value');
		},
		set value(value: T | undefined) {
			hasLocalValue = true;
			localValue = value;
		},
		get reason(): unknown {
			return hasLocalReason ? localReason : readThenableProperty<unknown>(thenable, 'reason');
		},
		set reason(reason) {
			hasLocalReason = true;
			localReason = reason;
		},
		then(onfulfilled, onrejected) {
			return thenable.then(onfulfilled, onrejected);
		},
	};
	externalHydrationThenables.set(key, externalThenable);
	return externalThenable;
}

function readThenableStatus(thenable: PromiseLike<unknown>) {
	const status = readThenableProperty(thenable, 'status');
	return status === 'pending' || status === 'fulfilled' || status === 'rejected'
		? status
		: undefined;
}

function readThenableProperty<T>(
	thenable: PromiseLike<unknown>,
	property: 'status' | 'value' | 'reason',
): T | undefined {
	try {
		return (thenable as PromiseLike<unknown> & Record<string, T>)[property];
	} catch {
		return undefined;
	}
}