import { useCallback, useEffect, useRef } from 'react';

// A lifetime for work begun in one scope. It ends, in the render that sees the change, whenever the scope
// changes - and a return to the same scope is a new lifetime, so work begun before can never resume as if
// current. It also ends while the consumer is unmounted. isLive answers from refs, so a callback held across
// an await asks about now, not about then.
export const useScopeLifetime = (scope: string): { generation: number; isLive: (generation: number) => boolean } => {
    const lifetime = useRef({ scope, generation: 0 });
    const mounted = useRef(true);
    if (lifetime.current.scope !== scope) lifetime.current = { scope, generation: lifetime.current.generation + 1 };
    useEffect(() => {
        mounted.current = true;
        return () => {
            mounted.current = false;
        };
    }, []);
    const isLive = useCallback((generation: number) => mounted.current && lifetime.current.generation === generation, []);
    return { generation: lifetime.current.generation, isLive };
};