new endpoint to return product list

app/utils/query/find/found_rows_callback.go

@@ -0,0 +1,46 @@
+package find
+
+import (
+	"errors"
+
+	"gorm.io/gorm"
+)
+
+const (
+	// Key under which result of `SELECT FOUND_ROWS()` should be stored in the
+	// driver context.
+	FOUND_ROWS_CTX_KEY = "maal:found_rows"
+	// Suggested name under which [find.FoundRowsCallback] can be registered.
+	FOUND_ROWS_CALLBACK = "maal:found_rows"
+)
+
+// Searches query clauses for presence of `SQL_CALC_FOUND_ROWS` and runs `SELECT
+// FOUND_ROWS();` right after the query containing such clause. The result is
+// put in the driver context under key [find.FOUND_ROWS_CTX_KEY]. For the
+// callback to work correctly it must be registered and executed before the
+// `gorm:preload` callback.
+func FoundRowsCallback(d *gorm.DB) {
+	if _, ok := d.Statement.Clauses["SELECT"].AfterNameExpression.(sqlCalcFound); ok {
+		var count uint64
+		sqlDB, err := d.DB()
+		if err != nil {
+			_ = d.AddError(err)
+			return
+		}
+		res := sqlDB.QueryRowContext(d.Statement.Context, "SELECT FOUND_ROWS();")
+		if res == nil {
+			_ = d.AddError(errors.New(`fialed to issue SELECT FOUND_ROWS() query`))
+			return
+		}
+		if res.Err() != nil {
+			_ = d.AddError(res.Err())
+			return
+		}
+		err = res.Scan(&count)
+		if err != nil {
+			_ = d.AddError(err)
+			return
+		}
+		d.Set(FOUND_ROWS_CTX_KEY, count)
+	}
+}