Go Logger

log.go

package log

import (
	"context"
	"log/slog"
	"os"

	"github.com/covalenthq/lumberjack"
	slogmulti "github.com/samber/slog-multi"
	"go.opentelemetry.io/otel/trace"
)

type logWithContext func(ctx context.Context, message string, attributes ...attribute)

var (
	Debug logWithContext
	Info  logWithContext
	Warn  logWithContext
	Error func(ctx context.Context, err error, attributes ...attribute)
)

type attribute struct {
	Key   string
	Value any
}

func NewAttribute(key string, value any) attribute {
	return attribute{Key: key, Value: value}
}

func InitLogger(serviceName string, version string, environment string, logLevel string) {
	logFile := &lumberjack.Logger{
		Filename: "logs/log.log",
		MaxAge:   7,
	}
	var slogLevel slog.Level
	err := slogLevel.UnmarshalText([]byte(logLevel))
	if err != nil {
		panic(err)
	}
	var consoleHandler slog.Handler
	if environment == "test" {
		consoleHandler = slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: slogLevel})
	} else {
		consoleHandler = slog.NewJSONHandler(os.Stderr, &slog.HandlerOptions{Level: slog.LevelError})
	}
	hostname, err := os.Hostname()
	if err != nil {
		panic(err)
	}
	fanoutHandler := slogmulti.Fanout(
		slog.NewJSONHandler(logFile, &slog.HandlerOptions{Level: slogLevel}),
		consoleHandler,
	)
	slogger := *slog.New(
		fanoutHandler,
	).With("service.name", serviceName).With("service.version", version).With("environment", environment).With("host.name", hostname)

	writeLog := func(ctx context.Context, logF func(ctx context.Context, msg string, args ...any), message string, attributes ...attribute) {
		slogAttrs := make([]any, 0)
		for _, attribute := range attributes {
			slogAttrs = append(slogAttrs, slog.Any(attribute.Key, attribute.Value))
		}
		spanContext := trace.SpanFromContext(ctx).SpanContext()
		if spanContext.IsValid() {
			attr := slog.String("trace_id", spanContext.TraceID().String())
			slogAttrs = append(slogAttrs, attr)
		}
		logF(ctx, message, slogAttrs...)
	}

	Debug = func(ctx context.Context, message string, attributes ...attribute) {
		writeLog(ctx, slogger.DebugContext, message, attributes...)
	}
	Info = func(ctx context.Context, message string, attributes ...attribute) {
		writeLog(ctx, slogger.InfoContext, message, attributes...)
	}
	Warn = func(ctx context.Context, message string, attributes ...attribute) {
		writeLog(ctx, slogger.WarnContext, message, attributes...)
	}
	Error = func(ctx context.Context, err error, attributes ...attribute) {
		writeLog(ctx, slogger.ErrorContext, err.Error(), attributes...)
	}
}