import { computed, observable } from 'mobx';
import { lazyObservable } from 'mobx-utils';
import { decorator_compatibility } from './utils';

const getPrivateStore = (obj: any, key: symbol) => {
    let store = obj[key];
    if (!store) store = obj[key] = {};
    return store;
}

const LAZY_PROPS = Symbol('lazyObservable collection');

/**
 * A decorator form of mobx-utils' lazyObservable.
 * May decorate a property, using it's value as the initialValue
 * @param callback 
 */
export const LazyObservable = <S, T = any>(callback: (this: S, sink: (newValue: T) => void, self: S) => void) => decorator_compatibility({
    legacy(target, propertyKey, descriptor) {
        const makeLazyObservable = (self, defaultValue?) => lazyObservable((sink) => callback.call(self, sink, self), defaultValue);
        return computed(target, propertyKey as any, {
            set(value: T) {
                const state = getPrivateStore(this, LAZY_PROPS);
                if (typeof value == 'object') value = observable(value);
                state[propertyKey] = makeLazyObservable(this, value)
            },
            ...(descriptor || {}),
            get() {
                const state = getPrivateStore(this, LAZY_PROPS);
                const lazy = state[propertyKey] = state[propertyKey] || makeLazyObservable(this);
                return lazy.current();
            },
        })
    },
    // stage3(value, context) {
    //     // TODO
    // },
});