const languages = require("./languages.js").languages;
const phrasebook = require("./phrasebook.js").phrasebook;
const selector = require("./selector.js").selector;
const autotranslate = require("./autotranslate.js").autotranslate;

/**
 * This class is responsible for saving and loading user language preferences
 * in the browser localStorage. It is not avairable, when using library in
 * the NodeJS enviroment.
 */
class preferences {
    /**
     * @var {languages}
     * This store loaded languages object.
     */
    #languages;

    /**
     * @var {?selector}
     * This store selector for preferences.
     */
    #selector;

    /**
     * @var {?autotranslate}
     * This store autotranslator, or null.
     */
    #autotranslate;

    /**
     * This create new language preferences manager from loaded languages
     * object.
     *
     * @throws {Error} - When trying to use it in NodeJS.
     * 
     * @param {languages} target - loaded languages object.
     */
    constructor(target) {
        NODE: throw new Error("It could be used only in browser.");
        this.#selector = null;
        this.#autotranslate = null;
        this.#languages = target;
    }

    /**
     * This return name of language key in localStorage.
     * 
     * @returns {string} - Name of key in localStorage.
     */
    get #setting_name() {
        return "cx_libtranslate_lang";
    }

    /**
     * This return current saved language name, or null if any language
     * is not selected yet.
     * 
     * @returns {?string} - Saved language or null.
     */
    get #state() {
        return localStorage.getItem(this.#setting_name);
    }

    /**
     * This return selector, which could being used in the ui.
     * 
     * @returns {selector} - New UI selector of the languages.
     */
    get selector() {
        if (this.#selector !== null) {
            return this.#selector;
        }

        this.#selector = new selector(this.#languages)
        .set_selection(this.current)
        .add_listener(target => {
            this.update(target); 
        })
        .add_listener(async target => { 
            if (this.#autotranslate === null) {
                return;
            }

            this.#reload_autotranslate();
        });

        return this.#selector;
    }

    async #reload_autotranslate() {
        const connected = this.#autotranslate.is_connected;

        if (connected) {
            this.#autotranslate.disconnect();
        }

        this.#autotranslate = null;
        const created = await this.get_autotranslate();
        
        if (connected) {
            created.connect();
        }
    }

    /**
     * This load phrasebook for selected language, create autotranslate
     * for it, and returns it. Autotranslate is cached in this object.
     * 
     * @returns {autotranslate} - Autotranslate for phrasebook.
     */
    async get_autotranslate() {
        if (this.#autotranslate !== null) {
            return this.#autotranslate;
        }

        const phrasebook = await this.load_choosen_phrasebook();
        this.#autotranslate = new autotranslate(phrasebook);
        this.#autotranslate.update();

        return this.#autotranslate;
    }

    /**
     * This save new selected language name to localStorage, or remove it 
     * from there if null given.
     * 
     * @param {?string} content - Name of selected language or null.
     */
    set #state(content) {
        if (content === null) {
            localStorage.removeItem(this.#setting_name);
            return;
        }

        localStorage.setItem(this.#setting_name, content);
    }

    /**
     * This return current language from localStorage. When any language is
     * not loaded yet, then return default language. It also check that value
     * value from localStorage, and if it not avairable in languages storage,
     * then also return default language.
     * 
     * @return {string} - Name of the current language.
     */
    get current() {
        const saved = this.#state;

        if (saved === null) {
            return this.#languages.default;
        }

        if (this.#languages.has(saved)) {
            return saved;
        }

        return this.#languages.default;
    }

    /**
     * This load phrasebook for current selected language.
     * 
     * @returns {phrasebook} - Phrasebook for current language.
     */
    async load_choosen_phrasebook() {
        return await this.#languages.select(this.current);
    }

    /**
     * This return loaded languages container.
     * 
     * @returns {languages} - Languages container.
     */
    get languages() {
        return this.#languages;
    }

    /**
     * This set new language for user. It also check that language exists 
     * in the language container. When not exists, throws error.
     * 
     * @throws {Error} - When language not exists in container.
     * 
     * @param {string} name - New language to select.
     * @returns {preferences} - This object to chain.
     */
    update(name) {
        DEBUG: if (!this.#languages.has(name)) {
            let error = "Can not set language \"" + name + "\" ";
            error += "because not exists in languages container.";

            throw new Error(error);
        }

        this.#state = name;
        return this;
    }
}

exports.preferences = preferences;