handle those failed test cases

Signed-off-by: Kenneth Obsequio <k80308392@gmail.com>

controllers/auth.controller.js

@@ -120,12 +120,56 @@ exports.register = async (req, res) => {
   const transaction = await sequelize.transaction();
  
   try {
-    const { email, password, personal_info, group_code } = req.body;
- 
+    const { email, password, personal_info, group_code, confirm_resume } = req.body;
+
     // ── Duplicate check ───────────────────────────────────────────────────────
+    // A verified account owns the email outright — hard block. An unverified
+    // one is just an abandoned attempt (e.g. dropped connection before the OTP
+    // step completed, or the client retried after a failed send) — the same
+    // person retrying should be able to resume it rather than dead-end here.
+    // The client must explicitly confirm_resume (after the user accepts a
+    // confirmation dialog) before we overwrite that abandoned attempt's data.
     const existing = await mdl_Users.findOne({ where: { email } });
-    if (existing) return R.error(res, 'Email is already registered.', 409);
- 
+    if (existing) {
+      if (existing.is_verified) {
+        await transaction.rollback();
+        return R.error(res, 'Email is already registered.', 409);
+      }
+      if (existing.reg_type !== 'system') {
+        await transaction.rollback();
+        return R.error(res, 'This email is linked to a Google account. Please sign in with Google instead.', 409, { google: true });
+      }
+
+      if (!confirm_resume) {
+        await transaction.rollback();
+        return R.error(
+          res,
+          'An account with this email already has a pending verification. Resend the code and continue?',
+          409,
+          { pendingVerification: true },
+        );
+      }
+
+      const hashed = await bcrypt.hash(password, 12);
+      const otp    = generateOTP();
+
+      await existing.update({
+        password:       hashed,
+        personal_info:  personal_info ?? existing.personal_info,
+        otp_code:       otp,
+        otp_expires_at: getOTPExpiry(),
+      }, { transaction });
+
+      await transaction.commit();
+
+      sendEmail({ to: email, type: 'OTP', data: { otp } })
+        .catch(err => console.error('[AUTH] Failed to send OTP email:', err));
+
+      return R.success(res, 'Registration successful. Please check your email for the OTP.', {
+        email: existing.email,
+      }, 201);
+    }
+
     // ── Validate group_code if provided ───────────────────────────────────────
     let group = null;
     if (group_code) {