const boot = document.getElementById('boot');
const title = document.getElementById('boot-title');
const detail = document.getElementById('boot-detail');
const progress = document.getElementById('boot-progress');
const retry = document.getElementById('boot-retry');
const formatBytes = bytes => (bytes / 1024 / 1024).toFixed(1) + ' MB';
let entries = new Map();
let failed = false;
let lastPaint = 0;

export function beginLoading(files, message = '正在载入三维场景') {
 entries = new Map(files.map(file => [file, {stage:'waiting', loaded:0, total:0}]));
 failed = false;
 boot.hidden = false;
 boot.dataset.state = 'loading';
 boot.setAttribute('aria-busy', 'true');
 title.textContent = message;
 detail.textContent = '正在检查本地资源缓存';
 progress.hidden = false;
 progress.removeAttribute('value');
 retry.hidden = true;
 lastPaint = 0;
}

export function reportProgress(update) {
 if (failed || !entries.has(update.file)) return;
 entries.set(update.file, update);
 // Large streamed files can emit hundreds of chunks in a frame.
 if (update.stage === 'download' && performance.now() - lastPaint < 100) return;
 lastPaint = performance.now();
 const values = [...entries.values()];
 const done = values.filter(item => item.stage === 'ready').length;
 const loaded = values.reduce((sum, item) => sum + item.loaded, 0);
 const cached = values.filter(item => item.stage === 'cache').length;
 const parsing = values.some(item => item.stage === 'parse');
 const downloading = values.some(item => item.stage === 'download');
 progress.max = Math.max(1, values.length);
 progress.value = done;
 title.textContent = `正在载入场景资源 ${done} / ${values.length}`;
 detail.textContent = `${parsing ? '正在解析模型' : downloading ? '正在下载资源' : cached ? '正在读取本地缓存' : '正在准备场景'} · 已读取 ${formatBytes(loaded)}`;
}

export function finishLoading() {
 if (failed) return;
 boot.setAttribute('aria-busy', 'false');
 boot.hidden = true;
}

export function failLoading(error) {
 failed = true;
 boot.hidden = false;
 boot.dataset.state = 'error';
 boot.setAttribute('aria-busy', 'false');
 title.textContent = '场景资源加载失败';
 detail.textContent = '部分资源未能载入，请检查网络后重试。' + (error?.message ? '（' + error.message + '）' : '');
 progress.hidden = true;
 retry.hidden = false;
}

retry.addEventListener('click', () => window.location.reload());