add app config and logging interface

internal/logger/log.go

@@ -0,0 +1,11 @@
+package logger
+
+var Log Logger
+
+func init() {
+	SetLogger(&nopLogger{})
+}
+
+func SetLogger(logger Logger) {
+	Log = logger
+}

internal/logger/logger.go

@@ -0,0 +1,34 @@
+package logger
+
+type Logger interface {
+	Errorf(format string, args ...interface{})
+	Infof(format string, args ...interface{})
+	Info(args ...interface{})
+	Debugf(format string, args ...interface{})
+	Debug(args ...interface{})
+	// WithFields(map[string]interface{}) Logger
+}
+
+func Errorf(format string, args ...interface{}) {
+	Log.Errorf(format, args...)
+}
+
+func Infof(format string, args ...interface{}) {
+	Log.Infof(format, args...)
+}
+
+func Info(args ...interface{}) {
+	Log.Info(args...)
+}
+
+func Debugf(format string, args ...interface{}) {
+	Log.Debugf(format, args...)
+}
+
+func Debug(args ...interface{}) {
+	Log.Debug(args...)
+}
+
+// func WithFields(fields map[string]interface{}) Logger {
+// 	return Log.WithFields(fields)
+// }

internal/logger/nop_logger.go

@@ -0,0 +1,11 @@
+package logger
+
+type nopLogger struct{}
+
+func (l *nopLogger) Errorf(format string, args ...interface{}) {}
+func (l *nopLogger) Infof(format string, args ...interface{})  {}
+func (l *nopLogger) Info(args ...interface{})                  {}
+func (l *nopLogger) Debugf(format string, args ...interface{}) {}
+func (l *nopLogger) Debug(args ...interface{})                 {}
+
+// func (l *nopLogger) WithFields(fields map[string]interface{}) Logger { return &nopLogger{} }