log

type Config interface {
	// Level returns the configured log level.
	Level() string

	// File returns the configured log file.
	File() string

	// Format returns the configured log format.
	Format() string
}

type Logger interface {
	WithField(key string, value interface{}) Logger
	WithFields(fields map[string]interface{}) Logger
	WithError(err error) Logger

	Debug(args ...interface{})
	Debugln(args ...interface{})
	Debugf(format string, args ...interface{})

	Info(args ...interface{})
	Infoln(args ...interface{})
	Infof(format string, args ...interface{})

	Print(args ...interface{})
	Println(args ...interface{})
	Printf(format string, args ...interface{})

	Warning(args ...interface{})
	Warningln(args ...interface{})
	Warningf(format string, args ...interface{})

	Error(args ...interface{})
	Errorln(args ...interface{})
	Errorf(format string, args ...interface{})

	Fatal(args ...interface{})
	Fatalln(args ...interface{})
	Fatalf(format string, args ...interface{})

	V(l int) bool
}

type NullLogger struct{}