const User = require("../models/User");
const AuditLog = require("../models/AuditLog");
const { signAccessToken, signRefreshToken, verifyRefreshToken } = require("../utils/jwt");
const logger = require("../utils/logger");

const MAX_FAILED_ATTEMPTS = 5;
const LOCK_DURATION_MS = 15 * 60 * 1000; // 15 minutes
const REFRESH_TOKEN_LIFETIME_MS = 7 * 24 * 60 * 60 * 1000;

// --------------------------------------------------------------------
// Refresh tokens are returned in the JSON response body (and stored by
// the client in localStorage) rather than as an httpOnly cookie.
//
// Why: this API and its frontend are deployed on different domains
// (e.g. a Hugging Face Space + a separate Vercel domain), and some
// hosting proxies in that kind of cross-site setup intercept CORS
// preflight requests before they reach the app and strip the
// Access-Control-Allow-Credentials header — which silently breaks any
// flow that depends on browsers sending a cross-site cookie. Avoiding
// `credentials: include` entirely sidesteps that class of problem.
//
// The trade-off: an httpOnly cookie can never be read by JavaScript,
// even from an XSS payload; a token sitting in localStorage can be.
// We narrow that risk with what's still in our control — access
// tokens stay short-lived (15 min) and refresh tokens rotate on every
// use with reuse detection (see `refresh` below) — but this is
// genuinely a lower security bar than the cookie-based approach, and
// worth knowing if you migrate this API to a same-site deployment
// later (at which point switching back to an httpOnly cookie is
// recommended).
// --------------------------------------------------------------------

async function audit(action, req, extra = {}) {
  try {
    await AuditLog.create({
      actor: req.user ? req.user._id : null,
      actorEmail: req.user ? req.user.email : extra.email || null,
      action,
      ip: req.ip,
      userAgent: req.headers["user-agent"],
      metadata: extra.metadata || {},
    });
  } catch (err) {
    logger.error("Failed to write audit log", { action, error: err.message });
  }
}

function issueSession(user, req) {
  const accessToken = signAccessToken(user);
  const { token: refreshToken, jti } = signRefreshToken(user);
  user.activeRefreshTokens = (user.activeRefreshTokens || [])
    .filter((rt) => rt.expiresAt > new Date()) // prune expired sessions as we go
    .concat({
      jti,
      expiresAt: new Date(Date.now() + REFRESH_TOKEN_LIFETIME_MS),
      userAgent: req.headers["user-agent"],
      ip: req.ip,
    });
  return { accessToken, refreshToken };
}

async function signup(req, res, next) {
  try {
    const { name, email, password } = req.body;

    const existing = await User.findOne({ email: email.toLowerCase() });
    if (existing) {
      // Do not reveal which part of the credential pair is wrong to
      // avoid account enumeration.
      return res.status(409).json({ error: "Unable to create account with the details provided." });
    }

    const user = new User({ name, email: email.toLowerCase() });
    await user.setPassword(password);
    await user.save();

    await audit("user.signup", req, { email: user.email });

    const { accessToken, refreshToken } = issueSession(user, req);
    await user.save();

    res.status(201).json({ user: user.toSafeJSON(), accessToken, refreshToken });
  } catch (err) {
    next(err);
  }
}

async function login(req, res, next) {
  try {
    const { email, password } = req.body;

    const user = await User.findOne({ email: email.toLowerCase() }).select(
      "+passwordHash +failedLoginAttempts +lockUntil +activeRefreshTokens"
    );

    // Constant-shaped response whether the user exists or not.
    const genericError = () => res.status(401).json({ error: "Invalid email or password." });

    if (!user || !user.isActive) return genericError();

    if (user.isLocked()) {
      return res.status(423).json({
        error: "Account temporarily locked due to repeated failed attempts. Try again later.",
      });
    }

    const valid = await user.comparePassword(password);
    if (!valid) {
      user.failedLoginAttempts = (user.failedLoginAttempts || 0) + 1;
      if (user.failedLoginAttempts >= MAX_FAILED_ATTEMPTS) {
        user.lockUntil = new Date(Date.now() + LOCK_DURATION_MS);
        user.failedLoginAttempts = 0;
        await audit("user.login.locked", req, { email: user.email });
      }
      await user.save();
      return genericError();
    }

    user.failedLoginAttempts = 0;
    user.lockUntil = null;

    const { accessToken, refreshToken } = issueSession(user, req);
    await user.save();

    await audit("user.login", req, { email: user.email });

    res.json({ user: user.toSafeJSON(), accessToken, refreshToken });
  } catch (err) {
    next(err);
  }
}

async function refresh(req, res, next) {
  try {
    const { refreshToken: token } = req.body;
    if (!token) return res.status(401).json({ error: "No refresh token provided." });

    let payload;
    try {
      payload = verifyRefreshToken(token);
    } catch {
      return res.status(401).json({ error: "Invalid or expired session, please log in again." });
    }

    const user = await User.findById(payload.sub).select("+activeRefreshTokens");
    if (!user || !user.isActive || user.tokenVersion !== payload.tokenVersion) {
      return res.status(401).json({ error: "Session no longer valid, please log in again." });
    }

    const stillActive = (user.activeRefreshTokens || []).some((rt) => rt.jti === payload.jti);
    if (!stillActive) {
      // Possible reuse of an already-rotated (or logged-out) refresh
      // token — deny it. As a precaution, also revoke every other
      // active session for this account, since a replayed token is a
      // signal the original may have leaked.
      user.activeRefreshTokens = [];
      await user.save();
      return res.status(401).json({ error: "Session no longer valid, please log in again." });
    }

    // Rotate: remove old jti, issue a new refresh token.
    user.activeRefreshTokens = user.activeRefreshTokens.filter((rt) => rt.jti !== payload.jti);
    const { accessToken, refreshToken: newRefreshToken } = issueSession(user, req);
    await user.save();

    res.json({ accessToken, refreshToken: newRefreshToken, user: user.toSafeJSON() });
  } catch (err) {
    next(err);
  }
}

async function logout(req, res, next) {
  try {
    const { refreshToken: token } = req.body;
    if (token) {
      try {
        const payload = verifyRefreshToken(token);
        await User.findByIdAndUpdate(payload.sub, { $pull: { activeRefreshTokens: { jti: payload.jti } } });
      } catch {
        // token already invalid — nothing to revoke
      }
    }
    res.json({ success: true });
  } catch (err) {
    next(err);
  }
}

async function me(req, res) {
  res.json({ user: req.user.toSafeJSON() });
}

module.exports = { signup, login, refresh, logout, me };