const crypto = require('crypto');
const bcrypt = require('bcryptjs');
const { getDb } = require('../db/database');
const { buildDeviceFingerprint } = require('./loginFingerprint');
const { encryptSecret, decryptSecret } = require('./encryptionService');

// Store SHA-256(token) in the DB; the raw token stays only in the cookie.
function hashSession(token) {
  return crypto.createHash('sha256').update(token).digest('hex');
}

const COOKIE_NAME = 'bt_session';
const SINGLE_COOKIE_NAME = 'bt_single_session';
const SESSION_DAYS = 7;

// Pre-computed hash used to equalize login timing when the account is unknown,
// inactive, or OIDC-only. Without it those paths skip bcrypt.compare and
// respond measurably faster, letting an attacker enumerate valid usernames.
// Cost factor 12 matches real password hashes. Computed once at module load.
const TIMING_EQUALIZATION_HASH = bcrypt.hashSync(crypto.randomBytes(32).toString('hex'), 12);

function envFlag(name) {
  const value = process.env[name];
  if (value === undefined) return null;
  return ['1', 'true', 'yes', 'on'].includes(String(value).toLowerCase());
}

function requestLooksHttps(req) {
  if (!req) return false;
  if (req.secure) return true;
  const proto = req.get?.('x-forwarded-proto') || req.headers?.['x-forwarded-proto'];
  return String(proto || '').split(',').map(s => s.trim()).includes('https');
}

/**
 * Build session-cookie options.
 *
 * COOKIE_SECURE=true/false is explicit. HTTPS=true keeps the old deployment knob.
 * Otherwise, mark cookies Secure only when the current request appears to be HTTPS.
 */
function cookieOpts(req) {
  const cookieSecure = envFlag('COOKIE_SECURE');
  const httpsSecure  = envFlag('HTTPS');
  const secure = cookieSecure !== null
    ? cookieSecure
    : httpsSecure !== null
    ? httpsSecure
    : requestLooksHttps(req);

  return {
    httpOnly: true,
    sameSite: 'strict',
    secure,
    maxAge: SESSION_DAYS * 86400 * 1000,
    path: '/',
  };
}

async function login(username, password) {
  const db = getDb();
  const user = db.prepare('SELECT * FROM users WHERE username = ?').get(username);

  // Unknown, inactive, or OIDC-only account: still burn a bcrypt comparison so
  // the response time is indistinguishable from a wrong password (no timing
  // oracle for username enumeration).
  if (!user || user.active === 0 || (user.auth_provider && user.auth_provider !== 'local')) {
    await bcrypt.compare(password, TIMING_EQUALIZATION_HASH);
    return null;
  }

  const valid = await bcrypt.compare(password, user.password_hash);
  // Return userId so the route can log the failed attempt against the known account.
  // The external response is identical either way — no user enumeration.
  if (!valid) return { error: 'bad_password', userId: user.id };

  // TOTP is enabled — don't create a session yet; issue a short-lived challenge instead
  if (user.totp_enabled) {
    const { createChallenge } = require('./totpService');
    const challengeToken = createChallenge(getDb(), user.id);
    return { requires_totp: true, challenge_token: challengeToken };
  }

  // WebAuthn is enabled — issue a WebAuthn authentication challenge instead
  if (user.webauthn_enabled) {
    const { createAuthenticationChallenge, createLoginChallenge } = require('./webauthnService');
    const { options, challengeId } = await createAuthenticationChallenge(getDb(), user.id);
    const loginToken = createLoginChallenge(getDb(), user.id, challengeId);
    return { requires_webauthn: true, challenge_token: loginToken, webauthn_options: options };
  }

  // Clean up expired sessions for this user before creating new session
  try {
    db.prepare("DELETE FROM sessions WHERE user_id = ? AND expires_at < datetime('now')").run(user.id);
  } catch (err) {
    console.error('[cleanup-error] Failed to cleanup user expired sessions:', err.message);
  }

  const sessionId = crypto.randomUUID();
  const expiresAt = new Date(Date.now() + SESSION_DAYS * 86400000)
    .toISOString().slice(0, 19).replace('T', ' ');

  db.prepare('INSERT INTO sessions (id, user_id, expires_at) VALUES (?, ?, ?)')
    .run(hashSession(sessionId), user.id, expiresAt);

  // Update last_login_at if column exists (added in v0.17 migration)
  try {
    db.prepare("UPDATE users SET last_login_at = datetime('now') WHERE id = ?").run(user.id);
  } catch { /* column may not exist on older schemas */ }

  return { sessionId, user: publicUser(user) };
}

async function createSession(userId) {
  const db = getDb();
  const user = db.prepare('SELECT * FROM users WHERE id = ?').get(userId);
  if (!user) return null;
  if (user.active === 0) return null;

  // Clean up expired sessions for this user before creating new session
  try {
    db.prepare("DELETE FROM sessions WHERE user_id = ? AND expires_at < datetime('now')").run(userId);
  } catch (err) {
    console.error('[cleanup-error] Failed to cleanup user expired sessions:', err.message);
  }

  const sessionId = crypto.randomUUID();
  const expiresAt = new Date(Date.now() + SESSION_DAYS * 86400000)
    .toISOString().slice(0, 19).replace('T', ' ');

  db.prepare('INSERT INTO sessions (id, user_id, expires_at) VALUES (?, ?, ?)')
    .run(hashSession(sessionId), user.id, expiresAt);

  return { sessionId, user: publicUser(user) };
}

function logout(sessionId) {
  if (!sessionId) return;
  getDb().prepare('DELETE FROM sessions WHERE id = ?').run(hashSession(sessionId));
}

/**
 * Regenerate session ID for security (e.g., on privilege escalation).
 * This invalidates the old session and creates a new one with the same user.
 */
function rotateSessionId(oldSessionId, userId) {
  if (!oldSessionId || !userId) return null;
  
  const db = getDb();
  
  // Verify the old session belongs to the user and is valid
  const existingSession = db.prepare('SELECT user_id FROM sessions WHERE id = ? AND expires_at > datetime(\'now\')').get(hashSession(oldSessionId));
  if (!existingSession || existingSession.user_id !== userId) {
    return null;
  }

  // Generate new session ID
  const newSessionId = crypto.randomUUID();
  const expiresAt = new Date(Date.now() + SESSION_DAYS * 86400000)
    .toISOString().slice(0, 19).replace('T', ' ');

  // Delete old session and create new one atomically
  try {
    db.transaction(() => {
      db.prepare('DELETE FROM sessions WHERE id = ?').run(hashSession(oldSessionId));
      db.prepare('INSERT INTO sessions (id, user_id, expires_at) VALUES (?, ?, ?)')
        .run(hashSession(newSessionId), userId, expiresAt);
    })();
  } catch {
    return null;
  }

  return newSessionId;
}

function getSessionUser(sessionId) {
  if (!sessionId) return null;
  const row = getDb().prepare(`
    SELECT u.id, u.username, u.display_name, u.role, u.must_change_password, u.first_login,
           u.active, u.is_default_admin, u.last_seen_version
    FROM sessions s
    JOIN users u ON u.id = s.user_id
    WHERE s.id = ? AND s.expires_at > datetime('now') AND u.active = 1
  `).get(hashSession(sessionId));
  return row || null;
}

async function hashPassword(password) {
  return bcrypt.hash(password, 12);
}

function publicUser(u) {
  const displayName = u.display_name || null;
  return {
    id: u.id,
    username: u.username,
    display_name: displayName,
    displayName,
    name: displayName || u.username,
    role: u.role,
    active: u.active !== 0,
    is_default_admin: !!u.is_default_admin,
    must_change_password: !!u.must_change_password,
    first_login: !!u.first_login,
    last_seen_version: u.last_seen_version || null,
    webauthn_enabled: !!u.webauthn_enabled,
  };
}

/**
 * Records a successful login with encrypted IP/UA and prunes older entries
 * so each user keeps at most 10 login history rows.
 * Session fingerprint is stored for current-session detection.
 * New device alerts and geolocation are resolved asynchronously.
 */
function recordLogin(userId, ipAddress, userAgent, sessionId) {
  const db = getDb();
  const device = buildDeviceFingerprint({ userAgent, ipAddress });

  const encIp = ipAddress ? encryptSecret(ipAddress) : null;
  const encUa = userAgent ? encryptSecret(userAgent.slice(0, 500)) : null;
  const sessionFingerprint = sessionId
    ? crypto.createHash('sha256').update(sessionId).digest('hex').slice(0, 32)
    : null;

  // Collect prior fingerprints before insert to detect new devices
  let priorFingerprints;
  try {
    priorFingerprints = db.prepare(`
      SELECT device_fingerprint FROM user_login_history
      WHERE user_id = ? AND success = 1
      ORDER BY logged_in_at DESC, id DESC LIMIT 10
    `).all(userId).map(r => r.device_fingerprint);
  } catch {
    priorFingerprints = [];
  }

  let insertedId;
  db.transaction(() => {
    const result = db.prepare(`
      INSERT INTO user_login_history (
        user_id, logged_in_at, ip_address, user_agent,
        browser, os, device_type, device_fingerprint, session_fingerprint, success
      )
      VALUES (?, datetime('now'), ?, ?, ?, ?, ?, ?, ?, 1)
    `).run(
      userId,
      encIp,
      encUa,
      device.browser,
      device.os,
      device.device_type,
      device.device_fingerprint,
      sessionFingerprint,
    );
    insertedId = result.lastInsertRowid;

    // Keep only the 10 most recent rows for this user
    db.prepare(`
      DELETE FROM user_login_history
      WHERE user_id = ? AND id NOT IN (
        SELECT id FROM user_login_history
        WHERE user_id = ?
        ORDER BY logged_in_at DESC, id DESC
        LIMIT 10
      )
    `).run(userId, userId);
  })();

  // Background tasks: geolocation + new device push alert
  if (insertedId) {
    setImmediate(() => {
      // Geolocation — only when the user has opted in, and skip private/loopback IPs
      const loginUser = getDb().prepare('SELECT geolocation_enabled FROM users WHERE id = ?').get(userId);
      if (ipAddress && loginUser?.geolocation_enabled) {
        const isPrivate = /^(10\.|172\.(1[6-9]|2\d|3[01])\.|192\.168\.|127\.|::1|localhost)/i.test(ipAddress);
        if (!isPrivate) {
          fetch(`http://ip-api.com/json/${ipAddress}?fields=status,city,country,regionName,isp`, { signal: AbortSignal.timeout(5000) })
            .then(r => r.json())
            .then(data => {
              if (data.status !== 'success') return;
              const updDb = getDb();
              updDb.prepare(`
                UPDATE user_login_history
                SET location_city=?, location_country=?, location_region=?, location_isp=?
                WHERE id=?
              `).run(
                encryptSecret(data.city || ''),
                encryptSecret(data.country || ''),
                encryptSecret(data.regionName || ''),
                encryptSecret(data.isp || ''),
                insertedId,
              );
            })
            .catch(() => {});
        }
      }

      // New device alert via push notification
      const isNewDevice = device.device_fingerprint &&
        !priorFingerprints.includes(device.device_fingerprint);
      if (isNewDevice) {
        try {
          const { sendPushToUser } = require('./notificationService')._push;
          const alertUser = getDb().prepare('SELECT * FROM users WHERE id = ?').get(userId);
          if (alertUser?.notify_push_enabled && alertUser?.push_channel) {
            const deviceDesc = [device.browser, device.os, device.device_type !== 'desktop' ? device.device_type : null]
              .filter(Boolean).join(' / ');
            const ipDesc = ipAddress || 'unknown IP';
            sendPushToUser(
              alertUser,
              'New device sign-in — Bill Tracker',
              `A sign-in was detected from a new device: ${deviceDesc} (${ipDesc}).`,
              'today',
            ).catch(() => {});
          }
        } catch { /* push is best-effort */ }
      }
    });
  }
}

/**
 * Records a failed login attempt (wrong password for a known account).
 * Stored with success=0 so it shows in login history but doesn't count as
 * a real session. Only called when the username maps to a real user —
 * unknown usernames are not tracked to prevent user-enumeration side-channels.
 */
function recordFailedLogin(userId, ipAddress, userAgent) {
  if (!userId) return;
  try {
    const db = getDb();
    const device = buildDeviceFingerprint({ userAgent, ipAddress });
    const encIp = ipAddress ? encryptSecret(ipAddress) : null;
    const encUa = userAgent ? encryptSecret(userAgent.slice(0, 500)) : null;

    db.transaction(() => {
      db.prepare(`
        INSERT INTO user_login_history (
          user_id, logged_in_at, ip_address, user_agent,
          browser, os, device_type, device_fingerprint, success
        )
        VALUES (?, datetime('now'), ?, ?, ?, ?, ?, ?, 0)
      `).run(
        userId, encIp, encUa,
        device.browser, device.os, device.device_type, device.device_fingerprint,
      );

      // Prune: keep 10 most recent (success or fail) per user
      db.prepare(`
        DELETE FROM user_login_history
        WHERE user_id = ? AND id NOT IN (
          SELECT id FROM user_login_history
          WHERE user_id = ?
          ORDER BY logged_in_at DESC, id DESC
          LIMIT 10
        )
      `).run(userId, userId);
    })();
  } catch { /* never fail a request because of history logging */ }
}

// Prune expired sessions — called by daily worker
function pruneExpiredSessions() {
  const result = getDb().prepare("DELETE FROM sessions WHERE expires_at <= datetime('now')").run();
  console.log(`[cleanup] Purged ${result.changes} expired sessions`);
  return result;
}

/**
 * Invalidate all sessions for a user except for a specific session ID
 * @param {number} userId - User ID
 * @param {string} keepSessionId - Session ID to keep (typically the current session)
 * @returns {Object} Result object with changes count
 */
function invalidateOtherSessions(userId, keepSessionId) {
  if (!userId) return { changes: 0 };
  
  const db = getDb();
  let result;
  
  if (keepSessionId) {
    result = db.prepare(
      "DELETE FROM sessions WHERE user_id = ? AND id != ?"
    ).run(userId, hashSession(keepSessionId));
  } else {
    result = db.prepare(
      "DELETE FROM sessions WHERE user_id = ?"
    ).run(userId);
  }
  
  return result;
}

module.exports = { login, logout, createSession, getSessionUser, hashPassword, publicUser, pruneExpiredSessions, cookieOpts, COOKIE_NAME, SINGLE_COOKIE_NAME, SESSION_DAYS, rotateSessionId, invalidateOtherSessions, recordLogin, recordFailedLogin };
