import { computed, IComputedValue, isObservableArray } from "mobx";

export function getOrCreateComputed(obj: any, key: string, options: () => { get(): any; set(data: any): void }) {
    let result: IComputedValue<any>;
    if (!Object.prototype.hasOwnProperty.call(obj, key)) {
        const { get, set } = options();
        obj[key] = result = computed(get, set);
    } else {
        result = obj[key];
    }
    return result;
}

export function isArray(obj: any) {
    return Array.isArray(obj) || isObservableArray(obj);
}

export function hasJsonProperty(obj: any) {
    return obj && typeof obj === "object" && ("json" in obj);
}

export function canLoadInto(obj: any) {
    return hasJsonProperty(obj) || (obj && isArray(obj));
}

export function save(obj: any): any {    
    return hasJsonProperty(obj) ? obj.json : obj;
}

export function load(obj: any, data: any) {
    if (data === "undefined" || !obj) {
        return;
    }

    if (!canLoadInto(obj)) {
        throw new Error("Can only load JSON into an object with a json property, or an array");
    }

    if (hasJsonProperty(obj)) {
        obj.json = data;
        return;
    }

    if (isArray(obj)) {
        // Plain array data, so just replace everything
        if (isArray(data)) {            
            obj.splice.apply(obj, [0, obj.length].concat(data));
        } else {
            obj.length = 0;
        }
        return;
    }
}