import { NextRequest } from 'next/server';
import { db } from '@/lib/db';
import bcrypt from 'bcryptjs';
import { acceptInvitationTokenForUser, getValidInvitationByToken } from '@/lib/invitations';
import {
  checkRateLimit,
  getClientIp,
  rateLimitHeaders,
  RATE_LIMIT_CONFIGS,
} from '@/lib/rate-limit';
import { apiErrors, successResponse, withCacheControl } from '@/lib/api-response';
import { isInviteCodeRequired } from '@/lib/feature-flags';
import { logError } from '@/lib/logger';
import {
  createVerificationToken,
  isEmailVerificationEnabled,
  sendVerificationEmail,
} from '@/lib/email-verification';
import { isValidEmailAddress, normalizeEmail } from '@/lib/email-validation';
import { recordSignupCompleted } from '@/lib/analytics/signup';
import { readRequestVisitor } from '@/lib/analytics/visitor';

export async function POST(request: NextRequest) {
  try {
    // Rate limiting by IP
    const clientIp = getClientIp(request);
    const rateLimitKey = `register:${clientIp}`;
    const rateLimit = await checkRateLimit(rateLimitKey, 'register');

    if (!rateLimit.allowed) {
      return apiErrors.rateLimited('Too many registration attempts. Please try again later.');
    }

    const body = await request.json();
    const { name, email, password, inviteCode, invitationToken } = body;

    // Validate required fields
    if (!name || typeof name !== 'string' || name.trim().length < 2 || name.trim().length > 100) {
      return apiErrors.badRequest('Name must be between 2 and 100 characters');
    }

    if (!email || typeof email !== 'string') {
      return apiErrors.badRequest('Email is required');
    }
    const normalizedEmail = normalizeEmail(email);

    // Basic email validation
    if (!isValidEmailAddress(normalizedEmail)) {
      return apiErrors.validationError('Invalid email format');
    }

    // Allow registration via a valid invitation token OR global invite code.
    let invitationIsValid = false;
    let validatedInvitationToken: string | null = null;
    if (typeof invitationToken === 'string' && invitationToken.trim()) {
      const normalizedToken = invitationToken.trim();
      const invitation = await getValidInvitationByToken(normalizedToken);
      if (invitation && invitation.email === normalizedEmail) {
        invitationIsValid = true;
        validatedInvitationToken = normalizedToken;
      } else {
        return apiErrors.forbidden('Invalid or expired invitation token');
      }
    }

    if (!invitationIsValid && isInviteCodeRequired()) {
      // Validate invite code using constant-time comparison to prevent timing attacks
      const validInviteCode = process.env.INVITE_CODE;
      if (!validInviteCode || !inviteCode) {
        return apiErrors.forbidden('Invalid invite code');
      }

      // Constant-time comparison
      const { timingSafeEqual } = await import('crypto');
      const validBuffer = Buffer.from(validInviteCode);
      const providedBuffer = Buffer.from(String(inviteCode));

      // Ensure same length for comparison (prevents length-based timing leak)
      const isValidLength = validBuffer.length === providedBuffer.length;
      const compareBuffer = isValidLength ? providedBuffer : validBuffer;
      const isValidCode = isValidLength && timingSafeEqual(validBuffer, compareBuffer);

      if (!isValidCode) {
        return apiErrors.forbidden('Invalid invite code');
      }
    }

    if (!password || typeof password !== 'string' || password.length < 8 || password.length > 128) {
      return apiErrors.badRequest('Password must be between 8 and 128 characters');
    }

    // Check if email already exists
    const existingUser = await db.user.findUnique({
      where: { email: normalizedEmail },
    });

    if (existingUser) {
      return apiErrors.conflict('An account with this email already exists');
    }

    // Hash password
    const hashedPassword = await bcrypt.hash(password, 12);

    // If SMTP is not configured, auto-verify the email so users aren't locked out
    const emailVerificationRequired = isEmailVerificationEnabled();

    // Create user
    const user = await db.user.create({
      data: {
        name: name.trim(),
        email: normalizedEmail,
        password: hashedPassword,
        emailVerified: emailVerificationRequired ? null : new Date(),
      },
      select: {
        id: true,
        name: true,
        email: true,
        createdAt: true,
      },
    });

    if (validatedInvitationToken) {
      const result = await acceptInvitationTokenForUser({
        token: validatedInvitationToken,
        userId: user.id,
        email: normalizedEmail,
      });
      if (result !== 'accepted') {
        await db.user.delete({ where: { id: user.id } });
        return apiErrors.conflict(
          'Invitation could not be accepted. Please request a new invitation.'
        );
      }
    }

    // Ties the account to the first touch stored in this browser's cookie and
    // claims the visitor events that led here. Recorded after the invitation has
    // been accepted, so an account that gets rolled back never leaves a signup.
    await recordSignupCompleted({
      userId: user.id,
      visitor: await readRequestVisitor(request),
    });

    // Send verification email if SMTP is configured
    if (emailVerificationRequired) {
      const verificationToken = await createVerificationToken(normalizedEmail);
      // Invited users are sent back to the invitation after verifying, which forwards them
      // to the workspace/project they joined instead of the generic dashboard.
      await sendVerificationEmail(normalizedEmail, verificationToken, {
        next: validatedInvitationToken
          ? `/invitations/accept?token=${encodeURIComponent(validatedInvitationToken)}`
          : undefined,
      });
    }

    const message = emailVerificationRequired
      ? 'Account created. Please check your email to verify your address before signing in.'
      : 'Account created successfully';

    const response = successResponse({ message, user, emailVerificationRequired }, 201);

    // Add rate limit headers to successful response
    const headers = rateLimitHeaders(rateLimit, RATE_LIMIT_CONFIGS.register.maxRequests);
    Object.entries(headers).forEach(([key, value]) => {
      response.headers.set(key, value);
    });

    return withCacheControl(response, 'private, no-store');
  } catch (error) {
    logError('Registration error:', error);
    return apiErrors.internalError('Failed to create account');
  }
}