// Gapura RAG — Chat Application Logic
// Handles SSE streaming, file upload, and UI interactions

const DOM = {
    chatContainer: () => document.getElementById('chat-container'),
    messages: () => document.getElementById('messages'),
    welcome: () => document.getElementById('chat-welcome'),
    chatForm: () => document.getElementById('chat-form'),
    chatInput: () => document.getElementById('chat-input'),
    btnSend: () => document.getElementById('btn-send'),
    btnClear: () => document.getElementById('btn-clear-chat'),
    langSelect: () => document.getElementById('lang-select'),
    dropZone: () => document.getElementById('drop-zone'),
    fileInput: () => document.getElementById('file-input'),
    uploadLog: () => document.getElementById('upload-log'),
    statsMini: () => document.getElementById('stats-mini'),
};

const chatHistory = [];

function closeSidebar() {
    document.getElementById('sidebar').classList.remove('open');
    document.getElementById('sidebar-overlay').classList.remove('open');
}

function openSidebar() {
    document.getElementById('sidebar').classList.add('open');
    document.getElementById('sidebar-overlay').classList.add('open');
}

function switchPanel(panelName) {
    document.querySelectorAll('.nav-btn').forEach(b => b.classList.remove('active'));
    document.querySelectorAll('.bottom-nav-btn').forEach(b => b.classList.remove('active'));
    document.querySelectorAll('.panel').forEach(p => p.classList.remove('active'));

    document.querySelectorAll(`[data-panel="${panelName}"]`).forEach(b => b.classList.add('active'));
    const panel = document.getElementById(`panel-${panelName}`);
    if (panel) panel.classList.add('active');
}

// Complexity: Time O(n) | Space O(1) — n = number of nav buttons
function initNavigation() {
    document.querySelectorAll('.nav-btn').forEach(btn => {
        btn.addEventListener('click', () => {
            switchPanel(btn.dataset.panel);
            closeSidebar();
        });
    });

    document.querySelectorAll('.bottom-nav-btn[data-panel]').forEach(btn => {
        btn.addEventListener('click', () => switchPanel(btn.dataset.panel));
    });

    document.getElementById('btn-menu')?.addEventListener('click', openSidebar);
    document.getElementById('btn-close-sidebar')?.addEventListener('click', closeSidebar);
    document.getElementById('sidebar-overlay')?.addEventListener('click', closeSidebar);

    document.getElementById('btn-bottom-settings')?.addEventListener('click', openSidebar);
}

// Complexity: Time O(1) | Space O(1)
function initChatInput() {
    const input = DOM.chatInput();
    const btn = DOM.btnSend();

    input.addEventListener('input', () => {
        btn.disabled = !input.value.trim();
        input.style.height = 'auto';
        input.style.height = Math.min(input.scrollHeight, 120) + 'px';
    });

    input.addEventListener('keydown', (e) => {
        if (e.key === 'Enter' && !e.shiftKey) {
            e.preventDefault();
            if (input.value.trim()) DOM.chatForm().requestSubmit();
        }
    });

    DOM.chatForm().addEventListener('submit', (e) => {
        e.preventDefault();
        const question = input.value.trim();
        if (!question) return;

        input.value = '';
        input.style.height = 'auto';
        btn.disabled = true;
        sendMessage(question);
    });

    DOM.btnClear().addEventListener('click', clearChat);
}

// Complexity: Time O(1) | Space O(1)
function hideWelcome() {
    const welcome = DOM.welcome();
    if (welcome) welcome.classList.add('hidden');
}

function clearChat() {
    DOM.messages().innerHTML = '';
    chatHistory.length = 0;
    const welcome = DOM.welcome();
    if (welcome) welcome.classList.remove('hidden');
}

function appendMessage(role, content) {
    hideWelcome();
    const container = DOM.messages();
    const avatarLabel = role === 'user' ? 'You' : 'AI';

    const msgEl = document.createElement('div');
    msgEl.className = `message ${role}`;
    msgEl.innerHTML = `
        <div class="msg-avatar">${avatarLabel === 'You' ? '👤' : '🏛️'}</div>
        <div class="msg-body">
            <div class="msg-bubble">${escapeHtml(content)}</div>
        </div>
    `;
    container.appendChild(msgEl);
    scrollToBottom();
    return msgEl;
}

function createStreamingMessage() {
    hideWelcome();
    const container = DOM.messages();

    const msgEl = document.createElement('div');
    msgEl.className = 'message assistant';
    msgEl.innerHTML = `
        <div class="msg-avatar">🏛️</div>
        <div class="msg-body">
            <div class="msg-bubble">
                <div class="typing-indicator">
                    <div class="typing-dot"></div>
                    <div class="typing-dot"></div>
                    <div class="typing-dot"></div>
                </div>
            </div>
        </div>
    `;
    container.appendChild(msgEl);
    scrollToBottom();
    return msgEl;
}

function scrollToBottom() {
    const container = DOM.chatContainer();
    requestAnimationFrame(() => {
        container.scrollTop = container.scrollHeight;
    });
}

// Complexity: Time O(n) | Space O(n) — n = response tokens
async function sendMessage(question) {
    appendMessage('user', question);
    chatHistory.push({ role: 'user', content: question });
    const msgEl = createStreamingMessage();
    const bubble = msgEl.querySelector('.msg-bubble');
    const body = msgEl.querySelector('.msg-body');

    const lang = DOM.langSelect().value;
    const historySlice = chatHistory.slice(-10);

    try {
        const response = await fetch('/api/chat', {
            method: 'POST',
            headers: { 'Content-Type': 'application/json' },
            body: JSON.stringify({ question, language: lang, history: historySlice }),
        });

        const reader = response.body.getReader();
        const decoder = new TextDecoder();
        let fullText = '';
        let buffer = '';

        while (true) {
            const { value, done } = await reader.read();
            if (done) break;

            buffer += decoder.decode(value, { stream: true });
            const lines = buffer.split('\n');
            buffer = lines.pop() || '';

            for (const line of lines) {
                if (!line.startsWith('data: ')) continue;
                const raw = line.slice(6).trim();
                if (!raw) continue;

                try {
                    const data = JSON.parse(raw);

                    if (data.type === 'token') {
                        fullText += data.content;
                        bubble.textContent = fullText;
                        scrollToBottom();
                    }

                    if (data.type === 'done' && data.citations?.length) {
                        const citEl = document.createElement('div');
                        citEl.className = 'msg-citations';
                        citEl.innerHTML = `<strong>Sources</strong>` +
                            data.citations.map(c =>
                                `<div class="msg-citation-item">${escapeHtml(c.source)}, Page ${c.page}</div>`
                            ).join('');
                        body.appendChild(citEl);
                    }

                    if (data.type === 'error') {
                        bubble.textContent = `Error: ${data.content}`;
                        bubble.style.color = 'oklch(0.55 0.20 25)';
                    }
                } catch {
                    // skip malformed JSON chunks
                }
            }
        }

        if (!fullText) {
            bubble.textContent = 'No response received.';
        } else {
            chatHistory.push({ role: 'assistant', content: fullText });
        }
    } catch (err) {
        bubble.textContent = `Connection error: ${err.message}`;
        bubble.style.color = 'oklch(0.55 0.20 25)';
    }

    scrollToBottom();
    DOM.btnSend().disabled = !DOM.chatInput().value.trim();
}

function sendHint(el) {
    const text = el.textContent;
    DOM.chatInput().value = text;
    DOM.btnSend().disabled = false;
    DOM.chatForm().requestSubmit();
}

// Complexity: Time O(f) | Space O(f) — f = file count
function initUpload() {
    const zone = DOM.dropZone();
    const input = DOM.fileInput();

    zone.addEventListener('click', () => input.click());

    zone.addEventListener('dragover', (e) => {
        e.preventDefault();
        zone.classList.add('dragover');
    });

    zone.addEventListener('dragleave', () => {
        zone.classList.remove('dragover');
    });

    zone.addEventListener('drop', (e) => {
        e.preventDefault();
        zone.classList.remove('dragover');
        handleFiles(e.dataTransfer.files);
    });

    input.addEventListener('change', () => {
        if (input.files.length) handleFiles(input.files);
        input.value = '';
    });
}

async function handleFiles(fileList) {
    const files = Array.from(fileList).filter(f => f.name.toLowerCase().endsWith('.pdf'));
    if (!files.length) return;

    for (const file of files) {
        const item = addUploadItem(file.name, 'Uploading…', 'pending');

        const formData = new FormData();
        formData.append('file', file);

        try {
            const res = await fetch('/api/upload', {
                method: 'POST',
                body: formData,
            });

            const data = await res.json();

            if (!res.ok) {
                updateUploadItem(item, data.error || 'Upload failed', 'error');
            } else if (data.skipped) {
                updateUploadItem(item, 'Already ingested', 'success');
            } else {
                updateUploadItem(item, `${data.pages} pages → ${data.chunks} chunks`, 'success');
            }
        } catch (err) {
            updateUploadItem(item, err.message, 'error');
        }
    }

    loadStats();
}

function addUploadItem(filename, detail, status) {
    const log = DOM.uploadLog();
    const icons = { pending: '⏳', success: '✅', error: '❌' };

    const el = document.createElement('div');
    el.className = `upload-item ${status}`;
    el.innerHTML = `
        <div class="upload-status">${icons[status]}</div>
        <div class="upload-info">
            <div class="upload-filename">${escapeHtml(filename)}</div>
            <div class="upload-detail">${escapeHtml(detail)}</div>
        </div>
    `;
    log.prepend(el);
    return el;
}

function updateUploadItem(el, detail, status) {
    const icons = { pending: '⏳', success: '✅', error: '❌' };
    el.className = `upload-item ${status}`;
    el.querySelector('.upload-status').textContent = icons[status];
    el.querySelector('.upload-detail').textContent = detail;
}

async function loadStats() {
    try {
        const res = await fetch('/api/stats');
        const data = await res.json();
        DOM.statsMini().innerHTML =
            `📊 ${data.total_vectors} vectors<br>🧠 ${data.embedding_model.split('/').pop()}`;
    } catch {
        DOM.statsMini().textContent = '';
    }
}

function escapeHtml(text) {
    const map = { '&': '&amp;', '<': '&lt;', '>': '&gt;', '"': '&quot;', "'": '&#39;' };
    return text.replace(/[&<>"']/g, c => map[c]);
}

// ── Init ──
document.addEventListener('DOMContentLoaded', () => {
    initNavigation();
    initChatInput();
    initUpload();
    loadStats();
});

// Expose for inline onclick
window.sendHint = sendHint;