import { MapOf, PromiseOrValue } from "@implab/core-amd/interfaces";
import { argumentNotEmptyString, isPromise, mixin } from "@implab/core-amd/safe";
import { id as mid } from "module";
import { TraceSource } from "@implab/core-amd/log/TraceSource";

const trace = TraceSource.get(mid);

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

type ResolveCallback<T> = () => PromiseOrValue<T>;

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

function isCallback<T>(v: ResolveCallback<T> | PromiseOrValue<T>): v is ResolveCallback<T> {
    return typeof v === "function";
}

function defaultResolver(module: string) {
    return import(module).then(x => x && x.default ? x.default : x);
}

function chainObjects<T extends object>(o1: T, o2: T) {
    if (!o1)
        return o2;
    if (!o2)
        return o1;

    return mixin(Object.create(o1) as T, o2);
}

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

    private _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 = this._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));
        });
    }

    _loadPackage(localeData: any) {
        if (isCallback(localeData))
            return when(localeData(), data => data && "default" in data ? data.default : data);
        return localeData;
    }
}