log using uber zap and lumberjack (zapcore.AddSync version)

logger.go

// thanks to:
// https://github.com/uber-go/zap/blob/master/FAQ.md#does-zap-support-log-rotation
// https://studygolang.com/articles/17394
// https://stackoverflow.com/questions/54395407/zap-logging-with-1-customized-config-and-2-lumberjack
// Please test and debug it before putting it in production.
package logger

import (
	"fmt"
	"os"

	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
	lumberjack "gopkg.in/natefinch/lumberjack.v2"
)

const (
	// DPanic, Panic and Fatal level can not be set by user
	DebugLevelStr   string = "debug"
	InfoLevelStr    string = "info"
	WarningLevelStr string = "warning"
	ErrorLevelStr   string = "error"
)

var (
	globalLogger *zap.Logger
	devMode      bool = false
)

// call it in defer
func Sync() error {
	return globalLogger.Sync()
}

func Init(logLevel string, logFile string, dev bool) error {
	devMode = dev
	var level zapcore.Level
	switch logLevel {
	case DebugLevelStr:
		level = zap.DebugLevel
	case InfoLevelStr:
		level = zap.InfoLevel
	case WarningLevelStr:
		level = zap.WarnLevel
	case ErrorLevelStr:
		level = zap.ErrorLevel
	default:
		return fmt.Errorf("unknown log level %s", logLevel)
	}

	ws := zapcore.AddSync(&lumberjack.Logger{
		Filename:   logFile,
		MaxSize:    1, //MB
		MaxBackups: 30,
		MaxAge:     90, //days
		Compress:   false,
	})
	core := zapcore.NewCore(
		// use NewConsoleEncoder for human readable output
		zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()),
		// write to stdout as well as log files
		zapcore.NewMultiWriteSyncer(zapcore.AddSync(os.Stdout), ws),
		zap.NewAtomicLevelAt(level),
	)
	var _globalLogger *zap.Logger
	if dev {
		_globalLogger = zap.New(core, zap.AddCaller(), zap.Development())
	} else {
		_globalLogger = zap.New(core)
	}
	zap.ReplaceGlobals(_globalLogger)
	globalLogger = _globalLogger
	return nil
}

func NewSugar(name string) *zap.SugaredLogger {
	return globalLogger.Named(name).Sugar()
}