Add Regexp checker and tests to v2. (#148)

# Describe Request

Add Regexp checker and tests to v2.

# Change Type

New code.

v2/maker.go

@@ -34,6 +34,7 @@ var makers = map[string]MakeCheckFunc{
 	nameMAC:          makeMAC,
 	nameMaxLen:       makeMaxLen,
 	nameMinLen:       makeMinLen,
+	nameRegexp:       makeRegexp,
 	nameRequired:     makeRequired,
 	nameTitle:        makeTitle,
 	nameTrimLeft:     makeTrimLeft,

v2/regexp.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
+
+import (
+	"reflect"
+	"regexp"
+)
+
+// nameRegexp is the name of the regexp check.
+const nameRegexp = "regexp"
+
+// ErrNotMatch indicates that the given string does not match the regexp pattern.
+var ErrNotMatch = NewCheckError("REGEXP")
+
+// MakeRegexpChecker makes a regexp checker for the given regexp expression with the given invalid result.
+func MakeRegexpChecker(expression string, invalidError error) CheckFunc[reflect.Value] {
+	return func(value reflect.Value) (reflect.Value, error) {
+		if value.Kind() != reflect.String {
+			panic("string expected")
+		}
+
+		matched, err := regexp.MatchString(expression, value.String())
+		if err != nil {
+			return value, err
+		}
+
+		if !matched {
+			return value, invalidError
+		}
+
+		return value, nil
+	}
+}
+
+// makeRegexp makes a checker function for the regexp.
+func makeRegexp(config string) CheckFunc[reflect.Value] {
+	return MakeRegexpChecker(config, ErrNotMatch)
+}
+
+// checkRegexp checks if the given string matches the regexp pattern.
+func checkRegexp(value reflect.Value) (reflect.Value, error) {
+	return makeRegexp(value.String())(value)
+}

v2/regexp_test.go

@@ -0,0 +1,64 @@
+// 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 (
+	"reflect"
+	"testing"
+
+	v2 "github.com/cinar/checker/v2"
+)
+
+func TestCheckRegexpNonString(t *testing.T) {
+	defer FailIfNoPanic(t, "expected panic")
+
+	type User struct {
+		Username int `checkers:"regexp:^[A-Za-z]$"`
+	}
+
+	user := &User{}
+
+	v2.CheckStruct(user)
+}
+
+func TestCheckRegexpInvalid(t *testing.T) {
+	type User struct {
+		Username string `checkers:"regexp:^[A-Za-z]+$"`
+	}
+
+	user := &User{
+		Username: "abcd1234",
+	}
+
+	_, ok := v2.CheckStruct(user)
+	if ok {
+		t.Fatal("expected error")
+	}
+}
+
+func TestCheckRegexpValid(t *testing.T) {
+	type User struct {
+		Username string `checkers:"regexp:^[A-Za-z]+$"`
+	}
+
+	user := &User{
+		Username: "abcd",
+	}
+
+	_, ok := v2.CheckStruct(user)
+	if !ok {
+		t.Fatal("expected valid")
+	}
+}
+
+func TestMakeRegexpChecker(t *testing.T) {
+	checkHex := v2.MakeRegexpChecker("^[A-Fa-f0-9]+$", v2.ErrNotMatch)
+
+	_, err := checkHex(reflect.ValueOf("f0f0f0"))
+	if err != nil {
+		t.Fail()
+	}
+}