From 695856b2056a075ee2c225dbbcc76a6a38dcc310 Mon Sep 17 00:00:00 2001
From: Victor Vrantchan <vrancean+github@gmail.com>
Date: Sat, 20 Feb 2021 18:24:39 -0500
Subject: [PATCH] Handle unique constraint for user registration.

Returns an error if the same username or email already exists.
---
 internal/data/user/user.go        | 17 ++++++++++++-----
 internal/data/user/user_sqlite.go |  5 +++++
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/internal/data/user/user.go b/internal/data/user/user.go
index 8cee2150..bbc9f9e6 100644
--- a/internal/data/user/user.go
+++ b/internal/data/user/user.go
@@ -183,8 +183,15 @@ func (err Error) Error() string {
 	}
 }
 
-var constraints = map[string]map[string]string{
-	"chk_email_not_empty":    map[string]string{"email": "You must provide an email address."},
-	"chk_username_not_empty": map[string]string{"username": "You must provide a username."},
-	"chk_password_not_empty": map[string]string{"password": "You must provide a password."},
-}
+var (
+	constraints = map[string]map[string]string{
+		"chk_email_not_empty":    map[string]string{"email": "You must provide an email address."},
+		"chk_username_not_empty": map[string]string{"username": "You must provide a username."},
+		"chk_password_not_empty": map[string]string{"password": "You must provide a password."},
+	}
+
+	constraintsUnique = map[string]map[string]string{
+		"users.username": map[string]string{"username": "This username already exists."},
+		"users.email":    map[string]string{"email": "This email already exists."},
+	}
+)
diff --git a/internal/data/user/user_sqlite.go b/internal/data/user/user_sqlite.go
index 6bd20adb..37784a63 100644
--- a/internal/data/user/user_sqlite.go
+++ b/internal/data/user/user_sqlite.go
@@ -151,6 +151,11 @@ func checkSqlite(err error) error {
 	}
 
 	switch sErr.Code {
+	case sqlite.SQLITE_CONSTRAINT_UNIQUE:
+		c := strings.Split(sErr.Msg, ": ")
+		if kv, ok := constraintsUnique[c[len(c)-1]]; ok {
+			return Error{invalid: kv}
+		}
 	case sqlite.SQLITE_CONSTRAINT_CHECK:
 		c := strings.Split(sErr.Msg, ": ")
 		if kv, ok := constraints[c[len(c)-1]]; ok {