const express = require('express');
const session = require('express-session');
const bcrypt = require('bcryptjs');
const multer = require('multer');
const rateLimit = require('express-rate-limit');
const crypto = require('crypto');
const fs = require('fs');
const path = require('path');

const PORT = process.env.PORT || 3210;
// 127.0.0.1 by default: on a VPS, Nginx fronts this with TLS and is the only
// thing that should be reachable from outside. On the old local-Windows setup
// this was 0.0.0.0 for LAN access; set HOST=0.0.0.0 explicitly if you still
// need that. COOKIE_SECURE should be "true" once you're behind real HTTPS.
const HOST = process.env.HOST || '127.0.0.1';
const COOKIE_SECURE = process.env.COOKIE_SECURE === 'true';
const DATA_FILE = path.join(__dirname, 'data.json');
const PID_FILE = path.join(__dirname, 'server.pid');
const FRONTEND_DIST = path.join(__dirname, '..', 'frontend', 'dist');
const UPLOADS_DIR = path.join(__dirname, 'uploads');
const AUTH_FILE = path.join(__dirname, 'auth.json');
const DEFAULT_USERNAME = 'admin';
const DEFAULT_PASSWORD = 'admin123';

if (!fs.existsSync(UPLOADS_DIR)) fs.mkdirSync(UPLOADS_DIR, { recursive: true });

/* --------------------------------- auth ---------------------------------- */

function loadAuth() {
  if (!fs.existsSync(AUTH_FILE)) {
    const auth = { username: DEFAULT_USERNAME, passwordHash: bcrypt.hashSync(DEFAULT_PASSWORD, 10) };
    fs.writeFileSync(AUTH_FILE, JSON.stringify(auth, null, 2), 'utf8');
    return auth;
  }
  try {
    return JSON.parse(fs.readFileSync(AUTH_FILE, 'utf8'));
  } catch (e) {
    const auth = { username: DEFAULT_USERNAME, passwordHash: bcrypt.hashSync(DEFAULT_PASSWORD, 10) };
    fs.writeFileSync(AUTH_FILE, JSON.stringify(auth, null, 2), 'utf8');
    return auth;
  }
}
function saveAuth(auth) {
  fs.writeFileSync(AUTH_FILE, JSON.stringify(auth, null, 2), 'utf8');
}

/* ------------------------------ secret / crypto -------------------------- */
// Used to encrypt the DeepSeek API key (and anything else sensitive) at
// rest, so it isn't sitting around the filesystem as plain text.

const SECRET_KEY_FILE = path.join(__dirname, '.secret-key');
function getSecretKey() {
  if (!fs.existsSync(SECRET_KEY_FILE)) {
    const key = crypto.randomBytes(32);
    fs.writeFileSync(SECRET_KEY_FILE, key.toString('base64'), { encoding: 'utf8', mode: 0o600 });
    return key;
  }
  return Buffer.from(fs.readFileSync(SECRET_KEY_FILE, 'utf8').trim(), 'base64');
}
const SECRET_KEY = getSecretKey();

function encrypt(text) {
  if (!text) return '';
  const iv = crypto.randomBytes(12);
  const cipher = crypto.createCipheriv('aes-256-gcm', SECRET_KEY, iv);
  const encrypted = Buffer.concat([cipher.update(text, 'utf8'), cipher.final()]);
  const tag = cipher.getAuthTag();
  return Buffer.concat([iv, tag, encrypted]).toString('base64');
}
function decrypt(b64) {
  if (!b64) return '';
  try {
    const buf = Buffer.from(b64, 'base64');
    const iv = buf.subarray(0, 12);
    const tag = buf.subarray(12, 28);
    const encrypted = buf.subarray(28);
    const decipher = crypto.createDecipheriv('aes-256-gcm', SECRET_KEY, iv);
    decipher.setAuthTag(tag);
    return Buffer.concat([decipher.update(encrypted), decipher.final()]).toString('utf8');
  } catch (e) {
    return '';
  }
}

/* --------------------------------- AI config ------------------------------ */

const AI_CONFIG_FILE = path.join(__dirname, 'ai-config.json');
// Lets you point this at a different OpenAI-compatible endpoint if needed
// (e.g. testing against a mock server); defaults to the real DeepSeek API.
const DEEPSEEK_API_BASE = process.env.DEEPSEEK_API_BASE || 'https://api.deepseek.com';

function loadAiConfig() {
  try {
    const raw = JSON.parse(fs.readFileSync(AI_CONFIG_FILE, 'utf8'));
    return { apiKey: decrypt(raw.apiKeyEnc || '') };
  } catch (e) {
    return { apiKey: '' };
  }
}
function saveAiConfig(apiKey) {
  fs.writeFileSync(AI_CONFIG_FILE, JSON.stringify({ apiKeyEnc: encrypt(apiKey) }, null, 2), 'utf8');
}

const REGION_LABELS = {
  africa: 'Africa', middle_east: 'Middle East', australia: 'Australia/Oceania',
  europe: 'Europe', sea: 'Southeast Asia', other: 'Other',
};

function buildCustomerContext(c) {
  const lines = [];
  lines.push(`Company: ${c.company || '(unknown / not on file)'}`);
  if (c.contact) lines.push(`Contact person: ${c.contact}`);
  const place = [c.country, REGION_LABELS[c.region]].filter(Boolean).join(', ');
  if (place) lines.push(`Location: ${place}`);
  if (c.productLines && c.productLines.length) lines.push(`Product interest: ${c.productLines.join(', ')}`);
  if (c.productLinesNote) lines.push(`Specific model interest: ${c.productLinesNote}`);
  if (c.lastContact) lines.push(`Last contact date: ${c.lastContact}`);
  if (c.notes) lines.push(`Notes on file: ${c.notes}`);
  if (c.isVip) lines.push('This is a VIP / priority customer — extra attentive tone.');
  return lines.join('\n');
}

async function callDeepSeek(apiKey, messages) {
  const resp = await fetch(`${DEEPSEEK_API_BASE}/chat/completions`, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Authorization: `Bearer ${apiKey}`,
    },
    body: JSON.stringify({
      model: 'deepseek-v4-flash',
      messages,
      temperature: 0.7,
      max_tokens: 600,
    }),
  });
  if (!resp.ok) {
    const errText = await resp.text().catch(() => '');
    throw new Error(`DeepSeek API error ${resp.status}: ${errText.slice(0, 200)}`);
  }
  const data = await resp.json();
  const content = data.choices && data.choices[0] && data.choices[0].message && data.choices[0].message.content;
  if (!content) throw new Error('DeepSeek API returned an empty response');
  return content;
}

/* ------------------------------ data file ------------------------------ */

function readData() {
  try {
    return JSON.parse(fs.readFileSync(DATA_FILE, 'utf8'));
  } catch (e) {
    return {};
  }
}

function writeData(data) {
  // write to a temp file then rename, avoids corrupting data.json if the
  // process is killed mid-write
  const tmp = DATA_FILE + '.tmp';
  fs.writeFileSync(tmp, JSON.stringify(data, null, 2), 'utf8');
  fs.renameSync(tmp, DATA_FILE);
}

// only allow simple ids (our customer ids are like "c_169..._ab12c"),
// this keeps the upload path from ever escaping the uploads/ folder
function safeId(id) {
  return /^[A-Za-z0-9_-]+$/.test(id) ? id : null;
}

/* --------------------------------- app ---------------------------------- */

const app = express();

// behind Nginx, Express needs this to read X-Forwarded-* correctly —
// otherwise req.ip is always Nginx's own address (breaks rate limiting)
// and the "secure" cookie flag can't tell the request was HTTPS.
app.set('trust proxy', 1);

app.use(express.json({ limit: '10mb' }));
app.use(session({
  secret: crypto.randomBytes(32).toString('hex'),
  resave: false,
  saveUninitialized: false,
  cookie: {
    httpOnly: true,
    sameSite: 'lax',
    secure: COOKIE_SECURE,
    maxAge: 30 * 24 * 60 * 60 * 1000, // 30 days
  },
}));

function requireAuth(req, res, next) {
  if (req.session && req.session.authed) return next();
  res.status(401).json({ error: 'not authenticated' });
}

const loginLimiter = rateLimit({
  windowMs: 15 * 60 * 1000,
  max: 5,
  standardHeaders: true,
  legacyHeaders: false,
  message: { error: 'too many login attempts, please try again in a few minutes' },
});

/* -------------------------------- auth api ------------------------------- */

app.post('/api/auth/login', loginLimiter, (req, res) => {
  const body = req.body || {};
  const username = body.username || '';
  const password = body.password || '';
  const auth = loadAuth();
  if (username === auth.username && bcrypt.compareSync(password, auth.passwordHash)) {
    req.session.authed = true;
    req.session.username = username;
    return res.json({ ok: true, username });
  }
  res.status(401).json({ error: 'invalid credentials' });
});

app.post('/api/auth/logout', (req, res) => {
  if (req.session) {
    req.session.destroy(() => res.json({ ok: true }));
  } else {
    res.json({ ok: true });
  }
});

app.get('/api/auth/check', (req, res) => {
  const authed = !!(req.session && req.session.authed);
  res.json({ authed, username: authed ? req.session.username : null });
});

app.post('/api/auth/change-password', requireAuth, (req, res) => {
  const body = req.body || {};
  const currentPassword = body.currentPassword || '';
  const newPassword = body.newPassword || '';
  const auth = loadAuth();
  if (!bcrypt.compareSync(currentPassword, auth.passwordHash)) {
    return res.status(400).json({ error: 'current password is incorrect' });
  }
  if (newPassword.length < 4) {
    return res.status(400).json({ error: 'new password is too short' });
  }
  auth.passwordHash = bcrypt.hashSync(newPassword, 10);
  saveAuth(auth);
  res.json({ ok: true });
});

/* ------------------------------ storage api ------------------------------ */

app.get('/api/storage/:key', requireAuth, (req, res) => {
  const data = readData();
  const key = req.params.key;
  if (!(key in data)) return res.status(404).json({ error: 'not found' });
  res.json({ value: data[key] });
});

app.put('/api/storage/:key', requireAuth, (req, res) => {
  const data = readData();
  data[req.params.key] = req.body.value;
  writeData(data);
  res.json({ ok: true });
});

/* --------------------------------- ai api --------------------------------- */

app.get('/api/ai-config', requireAuth, (req, res) => {
  const cfg = loadAiConfig();
  res.json({ hasKey: !!cfg.apiKey });
});

app.put('/api/ai-config', requireAuth, (req, res) => {
  const apiKey = ((req.body && req.body.apiKey) || '').trim();
  if (!apiKey) return res.status(400).json({ error: 'apiKey is required' });
  saveAiConfig(apiKey);
  res.json({ ok: true });
});

app.delete('/api/ai-config', requireAuth, (req, res) => {
  try { fs.unlinkSync(AI_CONFIG_FILE); } catch (e) {}
  res.json({ ok: true });
});

app.post('/api/ai-config/test', requireAuth, async (req, res) => {
  const cfg = loadAiConfig();
  if (!cfg.apiKey) return res.status(400).json({ error: 'no API key configured' });
  try {
    const content = await callDeepSeek(cfg.apiKey, [{ role: 'user', content: 'Reply with exactly: OK' }]);
    res.json({ ok: true, reply: content.trim() });
  } catch (e) {
    res.status(400).json({ error: e.message });
  }
});

const aiLimiter = rateLimit({
  windowMs: 10 * 60 * 1000,
  max: 30,
  standardHeaders: true,
  legacyHeaders: false,
  message: { error: 'too many AI requests, please slow down' },
});

app.post('/api/ai/draft', requireAuth, aiLimiter, async (req, res) => {
  const body = req.body || {};
  const customerId = body.customerId;
  const channel = body.channel;
  if (!customerId || !['email', 'whatsapp'].includes(channel)) {
    return res.status(400).json({ error: 'invalid request' });
  }
  const cfg = loadAiConfig();
  if (!cfg.apiKey) return res.status(400).json({ error: 'DeepSeek API key not configured' });

  const data = readData();
  let customers = [];
  try { customers = JSON.parse(data['crm:customers'] || '[]'); } catch (e) {}
  const customer = customers.find((c) => c.id === customerId);
  if (!customer) return res.status(404).json({ error: 'customer not found' });

  const context = buildCustomerContext(customer);
  const systemPrompt = 'You are a sales assistant helping a B2B export salesperson at a Chinese power-equipment company (UPS systems, rectifiers, solar inverters, battery storage) write natural, professional follow-up outreach to overseas customers. Always write in English. Never sound like a generic template, reference specifics from the customer info given. Output only the requested content, with no meta-commentary, explanations, or markdown formatting.';

  const userPrompt = channel === 'email'
    ? `Customer info:\n${context}\n\nWrite a short, warm but professional follow-up email to this customer. Respond in EXACTLY this format with no extra text:\nSUBJECT: <subject line>\nBODY:\n<email body, 3-5 short paragraphs max, sign off with "[Your name]">`
    : `Customer info:\n${context}\n\nWrite a short, casual WhatsApp message to check in with this customer (2-4 sentences, friendly tone, no formal greeting like "Dear", a light emoji is fine if it feels natural). Respond with ONLY the message text, nothing else.`;

  try {
    const content = await callDeepSeek(cfg.apiKey, [
      { role: 'system', content: systemPrompt },
      { role: 'user', content: userPrompt },
    ]);
    if (channel === 'email') {
      const subjectMatch = content.match(/SUBJECT:\s*(.+)/i);
      const bodyMatch = content.match(/BODY:\s*([\s\S]*)/i);
      res.json({
        subject: subjectMatch ? subjectMatch[1].trim() : 'Following up',
        body: bodyMatch ? bodyMatch[1].trim() : content.trim(),
      });
    } else {
      res.json({ body: content.trim() });
    }
  } catch (e) {
    res.status(502).json({ error: e.message });
  }
});

/* ------------------------- communication attachments ------------------------- */

const upload = multer({
  storage: multer.diskStorage({
    destination: (req, file, cb) => {
      const cid = safeId(req.params.customerId);
      if (!cid) return cb(new Error('invalid customer id'));
      const dir = path.join(UPLOADS_DIR, cid);
      fs.mkdirSync(dir, { recursive: true });
      cb(null, dir);
    },
    filename: (req, file, cb) => {
      const ts = Date.now();
      const rand = Math.random().toString(36).slice(2, 8);
      const ext = path.extname(file.originalname).slice(0, 10);
      cb(null, `${ts}_${rand}${ext}`);
    },
  }),
  limits: { fileSize: 25 * 1024 * 1024 }, // 25MB per file
});

app.post('/api/uploads/:customerId', requireAuth, (req, res) => {
  if (!safeId(req.params.customerId)) return res.status(400).json({ error: 'invalid customer id' });
  upload.single('file')(req, res, (err) => {
    if (err) return res.status(400).json({ error: err.message });
    if (!req.file) return res.status(400).json({ error: 'no file received' });
    res.json({ fileName: req.file.filename, originalName: req.file.originalname, size: req.file.size });
  });
});

app.delete('/api/uploads/:customerId/:fileName', requireAuth, (req, res) => {
  const cid = safeId(req.params.customerId);
  const fname = req.params.fileName;
  const isSafeFile = fname && !fname.includes('..') && !fname.includes('/') && !fname.includes('\\');
  if (!cid || !isSafeFile) return res.status(400).json({ error: 'invalid request' });
  fs.unlink(path.join(UPLOADS_DIR, cid, fname), () => {
    // a missing file is also treated as success, so clicking delete twice never errors
    res.json({ ok: true });
  });
});

app.use('/uploads', requireAuth, express.static(UPLOADS_DIR));

app.use(express.static(FRONTEND_DIST));
app.get('*', (req, res) => {
  res.sendFile(path.join(FRONTEND_DIST, 'index.html'));
});

/* ------------------------------- bootstrap ------------------------------ */

loadAuth(); // make sure auth.json exists with default credentials on first run

fs.writeFileSync(PID_FILE, String(process.pid), 'utf8');
process.on('exit', () => {
  try { fs.unlinkSync(PID_FILE); } catch (e) {}
});
process.on('SIGINT', () => process.exit(0));
process.on('SIGTERM', () => process.exit(0));

const server = app.listen(PORT, HOST, () => {
  console.log(`[customer-crm] running at http://${HOST}:${PORT}`);
});

server.on('error', (e) => {
  if (e.code === 'EADDRINUSE') {
    console.log('[customer-crm] another instance is already running on this port, exiting.');
    try { fs.unlinkSync(PID_FILE); } catch (err) {}
    process.exit(0);
  }
  throw e;
});