fix: ensure user inputs are normalized (#724)

Co-authored-by: Elias Schneider <login@eliasschneider.com>

backend/internal/utils/sqlite/sqlite_util.go

@@ -0,0 +1,51 @@
+package sqlite
+
+import (
+	"database/sql/driver"
+	"errors"
+	"fmt"
+	"strings"
+
+	sqlitelib "github.com/glebarez/go-sqlite"
+	"golang.org/x/text/unicode/norm"
+)
+
+func RegisterSqliteFunctions() {
+	// Register the `normalize(text, form)` function, which performs Unicode normalization on the text
+	// This is currently only used in migration functions
+	sqlitelib.MustRegisterDeterministicScalarFunction("normalize", 2, func(ctx *sqlitelib.FunctionContext, args []driver.Value) (driver.Value, error) {
+		if len(args) != 2 {
+			return nil, errors.New("normalize requires 2 arguments")
+		}
+
+		arg0, ok := args[0].(string)
+		if !ok {
+			return nil, fmt.Errorf("first argument for normalize is not a string: %T", args[0])
+		}
+
+		arg1, ok := args[1].(string)
+		if !ok {
+			return nil, fmt.Errorf("second argument for normalize is not a string: %T", args[1])
+		}
+
+		var form norm.Form
+		switch strings.ToLower(arg1) {
+		case "nfc":
+			form = norm.NFC
+		case "nfd":
+			form = norm.NFD
+		case "nfkc":
+			form = norm.NFKC
+		case "nfkd":
+			form = norm.NFKD
+		default:
+			return nil, fmt.Errorf("unsupported form: %s", arg1)
+		}
+
+		if len(arg0) == 0 {
+			return arg0, nil
+		}
+
+		return form.String(arg0), nil
+	})
+}