import { MapOf, PromiseOrValue } from "@implab/core-amd/interfaces";
import { argumentNotEmptyString, isPromise, mixin } from "@implab/core-amd/safe";

export type LocaleProvider<T> = () => PromiseOrValue<T | {default: T}>;

function when<T, T2>(value: PromiseOrValue<T>, cb: (v: T) => PromiseOrValue<T2>): PromiseOrValue<T2> {
    return isPromise(value) ?
        value.then(cb) :
        cb(value);
}

const loadPackage = <T extends object>(localeData: LocaleProvider<Partial<T>> | undefined) => 
    localeData ?
        when(localeData(), data => data && "default" in data ? data.default : data) :
        undefined;

const chainObjects = <T extends object>(o1: T, o2: Partial<T> | undefined): T =>
    o2 ? mixin(Object.create(o1) as T, o2) : o1;

export class NlsBundle<T extends object> {
    private readonly _locales: MapOf<LocaleProvider<Partial<T>>>;

    private readonly _default: T;

    private _cache: MapOf<PromiseOrValue<T>>;

    constructor(defNls: T, locales?: MapOf<LocaleProvider<Partial<T>>>) {
        this._default = defNls;
        this._locales = locales || {};
        this._cache = {};
    }

    getLocale(locale: string) {
        argumentNotEmptyString(locale, "locale");
        const _loc = locale;

        // en-US => ["en", "en-US"]
        const locales = _loc.split(/-|_/).map((x, i, a) => a.slice(0, i + 1).join("-"));
        return this._resolveLocale(locales);
    }

    _resolveLocale(locales: string[]): PromiseOrValue<T> {
        if (!locales.length)
            return this._default;

        const locale = locales.pop();
        if (!locale)
            throw new Error("The locale can't be empty");

        if (this._cache[locale])
            return this._cache[locale];

        const data = loadPackage(this._locales[locale]);
        const parent = this._resolveLocale(locales);

        return this._cache[locale] = when(data, x => {
            return when(parent, y => this._cache[locale] = chainObjects(y, x));
        });
    }
}