add log formatting system

pkg/etcdmtr/log.go

@@ -3,6 +3,7 @@ package etcdmtr
 import (
 	"fmt"
 	"os"
+	"strings"
 )
 
 type LogLevel int64
@@ -21,13 +22,67 @@ type ELog struct {
 	name         string
 	Level        LogLevel
 	DefaultLevel LogLevel
+	Format       *LogFormat
+}
+
+type LogFormatToken int64
+
+const (
+	LOGFORMAT_TIMESTAMP LogFormatToken = iota
+	LOGFORMAT_NAME
+	LOGFORMAT_MESSAGE
+)
+
+type LogFormat struct {
+	Next  *LogFormat
+	Token LogFormatToken
+}
+
+func NewFormat(firstToken LogFormatToken) *LogFormat {
+	return &LogFormat{
+		Token: firstToken,
+	}
+}
+
+// Append appends the token/node to the end of the chain, and returns the node Append was called on.
+func (f *LogFormat) Append(token LogFormatToken) *LogFormat {
+	tail := f
+	for tail.Next != nil {
+		tail = tail.Next
+	}
+	tail.Next = &LogFormat{
+		Token: token,
+	}
+	return f
+}
+
+func NewRootLogger() *ELog {
+	logger := &ELog{
+		Format: NewFormat(LOGFORMAT_TIMESTAMP).Append(LOGFORMAT_NAME).Append(LOGFORMAT_MESSAGE),
+	}
+	return logger
 }
 
 func (e *ELog) _Log(level LogLevel, message string, a ...any) (n int, err error) {
-	if level >= e.Level {
-		return fmt.Printf(message+"\n", a...)
+	if level < e.Level {
+		return 0, nil
 	}
-	return 0, nil
+	log := strings.Builder{}
+	tail := e.Format
+	for tail != nil {
+		switch token := tail.Token; token {
+		case LOGFORMAT_TIMESTAMP:
+			log.WriteString("TS")
+		case LOGFORMAT_NAME:
+			log.WriteString("main")
+		case LOGFORMAT_MESSAGE:
+			log.WriteString(fmt.Sprintf(message, a...))
+		default:
+			panic(fmt.Sprintf("bad log format token: %s", token))
+		}
+		tail = tail.Next
+	}
+	return fmt.Println(log.String())
 }
 
 func (e *ELog) Log(message string, a ...any) (n int, err error) {
@@ -59,8 +114,3 @@ func (e *ELog) Fatal(message string, a ...any) (n int, err error) {
 	os.Exit(1)
 	return 0, nil
 }
-
-func NewRootLogger() *ELog {
-	logger := &ELog{}
-	return logger
-}