const API = '';
let currentSession = null;

// DOM
const sessionList = document.getElementById('session-list');
const messages = document.getElementById('messages');
const emptyState = document.getElementById('empty-state');
const inputArea = document.getElementById('input-area');
const inputMessage = document.getElementById('input-message');
const btnSend = document.getElementById('btn-send');
const btnNewSession = document.getElementById('btn-new-session');
const btnClear = document.getElementById('btn-clear');
const btnDelete = document.getElementById('btn-delete');
const btnMenu = document.getElementById('btn-menu');
const chatTitle = document.getElementById('chat-title');
const statsEl = document.getElementById('stats');

// ---- API helpers ----
async function api(path, opts = {}) {
    const res = await fetch(API + path, {
        headers: { 'Content-Type': 'application/json' },
        ...opts,
    });
    return res.json();
}

// ---- Sessions ----
async function loadSessions() {
    const sessions = await api('/api/sessions');
    sessionList.innerHTML = sessions.map(s => `
        <div class="session-item ${currentSession?.id === s.id ? 'active' : ''}"
             data-id="${s.id}" onclick="selectSession('${s.id}')">
            <span class="title">${esc(s.title)}</span>
            <span class="time">${formatTime(s.updated_at)}</span>
        </div>
    `).join('');
}

async function createSession() {
    const s = await api('/api/sessions', { method: 'POST', body: '{}' });
    currentSession = s;
    await loadSessions();
    showChat();
}

async function selectSession(id) {
    const sessions = await api('/api/sessions');
    currentSession = sessions.find(s => s.id === id) || null;
    if (!currentSession) return;
    await loadSessions();
    await loadMessages(id);
    showChat();
}

async function deleteSession() {
    if (!currentSession) return;
    if (!confirm('Xóa phiên này?')) return;
    await api(`/api/sessions/${currentSession.id}`, { method: 'DELETE' });
    currentSession = null;
    await loadSessions();
    showEmpty();
}

async function clearMessages() {
    if (!currentSession) return;
    if (!confirm('Xóa lịch sử chat trong phiên này?')) return;
    await api(`/api/sessions/${currentSession.id}/clear`, { method: 'POST' });
    await loadMessages(currentSession.id);
}

async function loadMessages(sessionId) {
    const msgs = await api(`/api/sessions/${sessionId}/messages`);
    messages.innerHTML = '';
    if (msgs.length === 0) {
        messages.innerHTML = `<div class="empty-state"><p>Gõ câu hỏi bên dưới để bắt đầu</p></div>`;
        return;
    }
    msgs.forEach(m => appendMessage(m.role, m.content, m.sources));
    scrollToBottom();
}

// ---- Chat ----
async function sendMessage() {
    const text = inputMessage.value.trim();
    if (!text || !currentSession) return;

    inputMessage.value = '';
    autoResize();
    appendMessage('user', text);
    scrollToBottom();

    // Typing indicator
    const typingEl = document.createElement('div');
    typingEl.className = 'message assistant';
    typingEl.innerHTML = `<div class="bubble"><div class="typing-indicator"><span></span><span></span><span></span></div></div>`;
    messages.appendChild(typingEl);
    scrollToBottom();
    btnSend.disabled = true;

    try {
        const data = await api(`/api/sessions/${currentSession.id}/messages`, {
            method: 'POST',
            body: JSON.stringify({ content: text }),
        });

        typingEl.remove();
        appendMessage('assistant', data.content, data.sources);
        scrollToBottom();
        loadSessions();
    } catch (e) {
        typingEl.remove();
        appendMessage('assistant', 'Lỗi kết nối: ' + e.message);
        scrollToBottom();
    } finally {
        btnSend.disabled = false;
        inputMessage.focus();
    }
}

function appendMessage(role, content, sources = null) {
    // Remove empty state if present
    const empty = messages.querySelector('.empty-state');
    if (empty) empty.remove();

    const div = document.createElement('div');
    div.className = `message ${role}`;

    let html = `<div class="bubble">${esc(content)}</div>`;

    if (sources && sources.length > 0) {
        html += `<div class="sources">`;
        sources.forEach(s => {
            html += `<a class="source-chip" href="${esc(s.url)}" target="_blank" title="${esc(s.title)}">${esc(s.title.substring(0, 40))}</a>`;
        });
        html += `</div>`;
    }

    div.innerHTML = html;
    messages.appendChild(div);
}

// ---- UI state ----
function showChat() {
    emptyState.style.display = 'none';
    inputArea.style.display = 'block';
    chatTitle.textContent = currentSession?.title || '';
    btnClear.style.display = currentSession ? '' : 'none';
    btnDelete.style.display = currentSession ? '' : 'none';
}

function showEmpty() {
    emptyState.style.display = 'flex';
    inputArea.style.display = 'none';
    chatTitle.textContent = 'Chọn hoặc tạo phiên mới';
    btnClear.style.display = 'none';
    btnDelete.style.display = 'none';
    messages.innerHTML = '';
    messages.appendChild(emptyState);
}

function scrollToBottom() {
    messages.scrollTop = messages.scrollHeight;
}

function autoResize() {
    inputMessage.style.height = 'auto';
    inputMessage.style.height = Math.min(inputMessage.scrollHeight, 120) + 'px';
}

// ---- Stats ----
async function loadStats() {
    try {
        const s = await api('/api/stats');
        statsEl.innerHTML = `Chunks: ${s.chunks_indexed} | Phiên: ${s.sessions} | Tin nhắn: ${s.messages}`;
    } catch {}
}

// ---- Util ----
function esc(str) {
    if (!str) return '';
    const d = document.createElement('div');
    d.textContent = str;
    return d.innerHTML;
}

function formatTime(iso) {
    if (!iso) return '';
    const d = new Date(iso);
    const now = new Date();
    const diff = now - d;
    if (diff < 60000) return 'vừa xong';
    if (diff < 3600000) return Math.floor(diff / 60000) + ' phút';
    if (diff < 86400000) return Math.floor(diff / 3600000) + ' giờ';
    return d.toLocaleDateString('vi-VN', { day: '2-digit', month: '2-digit' });
}

// ---- Events ----
btnNewSession.onclick = createSession;
btnClear.onclick = clearMessages;
btnDelete.onclick = deleteSession;
btnSend.onclick = sendMessage;

btnMenu.onclick = () => {
    document.getElementById('sidebar').classList.toggle('open');
};

inputMessage.addEventListener('input', autoResize);
inputMessage.addEventListener('keydown', e => {
    if (e.key === 'Enter' && !e.shiftKey) {
        e.preventDefault();
        sendMessage();
    }
});

// Close sidebar on mobile when clicking outside
document.querySelector('.main').addEventListener('click', () => {
    document.getElementById('sidebar').classList.remove('open');
});

// Init
loadSessions().then(loadStats);