refactor code to fewer files; remove unused code

core/test_helper.go

@@ -0,0 +1,20 @@
+package core
+
+import (
+	"errors"
+	"fmt"
+	"go-nkode/util"
+)
+
+func SelectKeyByAttrIdx(interfaceUser []int, passcodeIdxs []int, keypadSize KeypadDimension) ([]int, error) {
+	selectedKeys := make([]int, len(passcodeIdxs))
+	for idx := range passcodeIdxs {
+		attrIdx := util.IndexOf[int](interfaceUser, passcodeIdxs[idx])
+		keyNumb := attrIdx / keypadSize.AttrsPerKey
+		if keyNumb < 0 || keyNumb >= keypadSize.NumbOfKeys {
+			return nil, errors.New(fmt.Sprintf("index key number: %d out of range 0-%d", keyNumb, keypadSize.NumbOfKeys-1))
+		}
+		selectedKeys[idx] = keyNumb
+	}
+	return selectedKeys, nil
+}