Add title normalizer and tests to v2. (#147)

# Describe Request

Add title normalizer and tests to v2.

# Change Type

New code.

v2/maker.go

@@ -35,6 +35,7 @@ var makers = map[string]MakeCheckFunc{
 	nameMaxLen:       makeMaxLen,
 	nameMinLen:       makeMinLen,
 	nameRequired:     makeRequired,
+	nameTitle:        makeTitle,
 	nameTrimLeft:     makeTrimLeft,
 	nameTrimRight:    makeTrimRight,
 	nameTrimSpace:    makeTrimSpace,

v2/title.go

@@ -0,0 +1,51 @@
+// Copyright (c) 2023-2024 Onur Cinar.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+// https://github.com/cinar/checker
+
+package v2
+
+import (
+	"reflect"
+	"strings"
+	"unicode"
+)
+
+const (
+	// nameTitle is the name of the title normalizer.
+	nameTitle = "title"
+)
+
+// Title returns the value of the string with the first letter of each word in upper case.
+func Title(value string) (string, error) {
+	var sb strings.Builder
+	begin := true
+
+	for _, c := range value {
+		if unicode.IsLetter(c) {
+			if begin {
+				c = unicode.ToUpper(c)
+				begin = false
+			} else {
+				c = unicode.ToLower(c)
+			}
+		} else {
+			begin = true
+		}
+
+		sb.WriteRune(c)
+	}
+
+	return sb.String(), nil
+}
+
+// reflectTitle returns the value of the string with the first letter of each word in upper case.
+func reflectTitle(value reflect.Value) (reflect.Value, error) {
+	newValue, err := Title(value.Interface().(string))
+	return reflect.ValueOf(newValue), err
+}
+
+// makeTitle returns the title normalizer function.
+func makeTitle(_ string) CheckFunc[reflect.Value] {
+	return reflectTitle
+}

v2/title_test.go

@@ -0,0 +1,47 @@
+// Copyright (c) 2023-2024 Onur Cinar.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+// https://github.com/cinar/checker
+
+package v2_test
+
+import (
+	"testing"
+
+	v2 "github.com/cinar/checker/v2"
+)
+
+func TestTitle(t *testing.T) {
+	input := "the checker"
+	expected := "The Checker"
+
+	actual, err := v2.Title(input)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if actual != expected {
+		t.Fatalf("actual %s expected %s", actual, expected)
+	}
+}
+
+func TestReflectTitle(t *testing.T) {
+	type Book struct {
+		Chapter string `checkers:"title"`
+	}
+
+	book := &Book{
+		Chapter: "the checker",
+	}
+
+	expected := "The Checker"
+
+	errs, ok := v2.CheckStruct(book)
+	if !ok {
+		t.Fatalf("got unexpected errors %v", errs)
+	}
+
+	if book.Chapter != expected {
+		t.Fatalf("actual %s expected %s", book.Chapter, expected)
+	}
+}