/**
 * Lazy Loader - Dynamic script loading with dependency management
 * Enables code splitting for heavy libraries (Chart.js, Cropper.js, etc.)
 */
class LazyLoader {
    constructor() {
        this._loaded = {};   // url -> Promise
        this._ready = {};    // name -> boolean
    }

    /**
     * Load a script dynamically
     * @param {string} url - Script URL
     * @param {string} globalName - Global variable name to check for existence
     * @returns {Promise}
     */
    loadScript(url, globalName = null) {
        if (this._loaded[url]) return this._loaded[url];

        this._loaded[url] = new Promise((resolve, reject) => {
            // Already available globally?
            if (globalName && window[globalName]) {
                this._ready[globalName] = true;
                resolve(window[globalName]);
                return;
            }

            const script = document.createElement('script');
            script.src = url;
            script.async = true;
            script.onload = () => {
                if (globalName) this._ready[globalName] = true;
                resolve(globalName ? window[globalName] : true);
            };
            script.onerror = () => {
                delete this._loaded[url];
                reject(new Error(`Failed to load: ${url}`));
            };
            document.head.appendChild(script);
        });

        return this._loaded[url];
    }

    /**
     * Load CSS dynamically
     */
    loadCSS(url) {
        if (document.querySelector(`link[href="${url}"]`)) return Promise.resolve();
        return new Promise((resolve, reject) => {
            const link = document.createElement('link');
            link.rel = 'stylesheet';
            link.href = url;
            link.onload = resolve;
            link.onerror = reject;
            document.head.appendChild(link);
        });
    }

    /**
     * Check if a library is ready
     */
    isReady(name) { return !!this._ready[name]; }

    /**
     * Wait for a library to be available (polls window[name])
     */
    waitFor(name, timeout = 10000) {
        if (window[name]) return Promise.resolve(window[name]);
        return new Promise((resolve, reject) => {
            const start = Date.now();
            const check = () => {
                if (window[name]) { this._ready[name] = true; resolve(window[name]); return; }
                if (Date.now() - start > timeout) { reject(new Error(`${name} not loaded after ${timeout}ms`)); return; }
                setTimeout(check, 50);
            };
            check();
        });
    }
}

// Singleton
const lazyLoader = new LazyLoader();
window.lazyLoader = lazyLoader;

// Predefined lazy-load bundles
const LAZY_BUNDLES = {
    charts: () => Promise.all([
        lazyLoader.loadScript('https://cdn.jsdelivr.net/npm/chart.js@4', 'Chart'),
        lazyLoader.loadScript('https://cdn.jsdelivr.net/npm/chartjs-adapter-date-fns@3'),
        lazyLoader.loadScript('https://cdn.jsdelivr.net/npm/chartjs-plugin-annotation@3'),
    ]),
    cropper: () => lazyLoader.loadCSS('https://cdn.jsdelivr.net/npm/cropperjs@1/dist/cropper.min.css')
        .then(() => lazyLoader.loadScript('https://cdn.jsdelivr.net/npm/cropperjs@1', 'Cropper')),
};

window.LAZY_BUNDLES = LAZY_BUNDLES;