/** x0
 * Lazy web pages.
 * 
 * [x0-mods] - modules to load
 * [x0-module-root] - set module src root
 */

if (window['x0']) {
    throw new Error("window.x0 already declared.", window.x0);
}

class x0 {
    #rootElement;
    #cfg = {
        moduleSource: "./x0/modules/",
        modules: [],
        init: true
    }
    #hooks = {
        moduleRemove: {}
    }
    #moduleStorage = {};

    constructor(rootElement = document.querySelector("html")) {
        this.#rootElement = rootElement;
        
        this.#updateConfig();
        if (this.#cfg.init)
            this.#updateScriptElements();
    }

    #getAttribute(name, level) {
        return this.#rootElement.getAttribute(`x${level ?? ''}-${name}`)
    }

    #updateConfig() {
        this.#cfg.moduleSource = this.#getAttribute("module-root", 0) ?? this.#cfg.moduleSource;
        this.#cfg.modules = this.#getAttribute("mods", 0)?.split(",") ?? this.#cfg.modules;
        this.#cfg.init = (this.#getAttribute("init", 0) ?? "true") == "true"
    }

    #updateScriptElements() {
        this.#cfg.modules
            .forEach(m => {
                if (this.#rootElement.querySelector(`[x0-m="${m}"]`)) return;
                let script = document.createElement("script");
                script.src = this.#cfg.moduleSource + m + ".js";
                script.setAttribute("x0-m", m);
                this.#rootElement.appendChild(script);
            })

        this.#rootElement
            .querySelectorAll("[x0-m]")
            .forEach(e => {
                if (!this.#cfg.modules.includes(e.getAttribute("x0-m"))) {
                    this.#removeModule(e.getAttribute("x0-m"));
                    e.remove();
                }
            })
    }

    #removeModule(module) {
        if (this.#hooks.moduleRemove[module])
            this.#hooks.moduleRemove[module](this.#moduleStorage[module] ?? {}); // run module remove hook
        if (this.#moduleStorage[module])
            this.#moduleStorage[module] = undefined;
    }

    registerModuleRemoveHook(module, callback) {
        if (this.#hooks.moduleRemove[module]) return null;
        this.#hooks.moduleRemove[module] = callback;
    }

    /** registerStorage
     * Register a storage.
     * This can only happen once per module.
     */
    registerStorage(module) {
        if (this.#moduleStorage[module]) return null;
        this.#moduleStorage[module] = {};
        return this.#moduleStorage[module];
    }

    update() {
        this.#updateConfig();
        this.#updateScriptElements();
    }
}

window.x0 = new x0();