refactor: refactor logging system with conditional builds

- Remove logging implementation from `logger.go`
- Create `logger_default.go` with the previous logging implementation from `logger.go`
- Create `logger_slog.go` with a new logging implementation using `slog` for the `Infof` method
- Add build tags to differentiate between `logger_default.go` and `logger_slog.go` based on Go version

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

logger.go

@@ -1,11 +1,5 @@
 package graceful
 
-import (
-	"fmt"
-	"log"
-	"os"
-)
-
 // Logger interface is used throughout gorush
 type Logger interface {
 	Infof(format string, args ...interface{})
@@ -16,45 +10,6 @@ type Logger interface {
 	Fatal(args ...interface{})
 }
 
-// NewLogger for simple logger.
-func NewLogger() Logger {
-	return defaultLogger{
-		infoLogger:  log.New(os.Stdout, "INFO: ", log.Ldate|log.Ltime|log.Lshortfile),
-		errorLogger: log.New(os.Stderr, "ERROR: ", log.Ldate|log.Ltime|log.Lshortfile),
-		fatalLogger: log.New(os.Stderr, "FATAL: ", log.Ldate|log.Ltime|log.Lshortfile),
-	}
-}
-
-type defaultLogger struct {
-	infoLogger  *log.Logger
-	errorLogger *log.Logger
-	fatalLogger *log.Logger
-}
-
-func (l defaultLogger) Infof(format string, args ...interface{}) {
-	l.infoLogger.Printf(format, args...)
-}
-
-func (l defaultLogger) Errorf(format string, args ...interface{}) {
-	l.errorLogger.Printf(format, args...)
-}
-
-func (l defaultLogger) Fatalf(format string, args ...interface{}) {
-	l.fatalLogger.Fatalf(format, args...)
-}
-
-func (l defaultLogger) Info(args ...interface{}) {
-	l.infoLogger.Println(fmt.Sprint(args...))
-}
-
-func (l defaultLogger) Error(args ...interface{}) {
-	l.errorLogger.Println(fmt.Sprint(args...))
-}
-
-func (l defaultLogger) Fatal(args ...interface{}) {
-	l.fatalLogger.Println(fmt.Sprint(args...))
-}
-
 // NewEmptyLogger for simple logger.
 func NewEmptyLogger() Logger {
 	return emptyLogger{}
@@ -63,6 +18,8 @@ func NewEmptyLogger() Logger {
 // EmptyLogger no meesgae logger
 type emptyLogger struct{}
 
+// Infof logs an informational message with a formatted string and optional arguments.
+// It does not perform any logging in the emptyLogger implementation.
 func (l emptyLogger) Infof(format string, args ...interface{})  {}
 func (l emptyLogger) Errorf(format string, args ...interface{}) {}
 func (l emptyLogger) Fatalf(format string, args ...interface{}) {}

logger_default.go

@@ -0,0 +1,48 @@
+//go:build !go1.21
+
+package graceful
+
+import (
+	"fmt"
+	"log"
+	"os"
+)
+
+// NewLogger for simple logger.
+func NewLogger() Logger {
+	return defaultLogger{
+		infoLogger:  log.New(os.Stdout, "INFO: ", log.Ldate|log.Ltime|log.Lshortfile),
+		errorLogger: log.New(os.Stderr, "ERROR: ", log.Ldate|log.Ltime|log.Lshortfile),
+		fatalLogger: log.New(os.Stderr, "FATAL: ", log.Ldate|log.Ltime|log.Lshortfile),
+	}
+}
+
+type defaultLogger struct {
+	infoLogger  *log.Logger
+	errorLogger *log.Logger
+	fatalLogger *log.Logger
+}
+
+func (l defaultLogger) Infof(format string, args ...interface{}) {
+	l.infoLogger.Printf(format, args...)
+}
+
+func (l defaultLogger) Errorf(format string, args ...interface{}) {
+	l.errorLogger.Printf(format, args...)
+}
+
+func (l defaultLogger) Fatalf(format string, args ...interface{}) {
+	l.fatalLogger.Fatalf(format, args...)
+}
+
+func (l defaultLogger) Info(args ...interface{}) {
+	l.infoLogger.Println(fmt.Sprint(args...))
+}
+
+func (l defaultLogger) Error(args ...interface{}) {
+	l.errorLogger.Println(fmt.Sprint(args...))
+}
+
+func (l defaultLogger) Fatal(args ...interface{}) {
+	l.fatalLogger.Println(fmt.Sprint(args...))
+}

logger_slog.go

@@ -0,0 +1,49 @@
+//go:build go1.21
+
+package graceful
+
+import (
+	"fmt"
+	"log"
+	"log/slog"
+	"os"
+)
+
+// NewLogger for simple logger.
+func NewLogger() Logger {
+	return defaultLogger{
+		infoLogger:  log.New(os.Stdout, "INFO: ", log.Ldate|log.Ltime|log.Lshortfile),
+		errorLogger: log.New(os.Stderr, "ERROR: ", log.Ldate|log.Ltime|log.Lshortfile),
+		fatalLogger: log.New(os.Stderr, "FATAL: ", log.Ldate|log.Ltime|log.Lshortfile),
+	}
+}
+
+type defaultLogger struct {
+	infoLogger  *log.Logger
+	errorLogger *log.Logger
+	fatalLogger *log.Logger
+}
+
+func (l defaultLogger) Infof(format string, args ...interface{}) {
+	slog.Info(format, args...)
+}
+
+func (l defaultLogger) Errorf(format string, args ...interface{}) {
+	l.errorLogger.Printf(format, args...)
+}
+
+func (l defaultLogger) Fatalf(format string, args ...interface{}) {
+	l.fatalLogger.Fatalf(format, args...)
+}
+
+func (l defaultLogger) Info(args ...interface{}) {
+	l.infoLogger.Println(fmt.Sprint(args...))
+}
+
+func (l defaultLogger) Error(args ...interface{}) {
+	l.errorLogger.Println(fmt.Sprint(args...))
+}
+
+func (l defaultLogger) Fatal(args ...interface{}) {
+	l.fatalLogger.Println(fmt.Sprint(args...))
+}