dnswatcher/internal/logger/logger.go

// Package logger provides structured logging with slog.
package logger

import (
	"log/slog"
	"os"

	"go.uber.org/fx"

	"sneak.berlin/go/dnswatcher/internal/globals"
)

// Params contains dependencies for Logger.
type Params struct {
	fx.In

	Globals *globals.Globals
}

// Logger wraps slog.Logger with level control.
type Logger struct {
	log    *slog.Logger
	level  *slog.LevelVar
	params Params
}

// New creates a new Logger with TTY detection for output format.
func New(_ fx.Lifecycle, params Params) (*Logger, error) {
	loggerInstance := &Logger{
		level:  new(slog.LevelVar),
		params: params,
	}
	loggerInstance.level.Set(slog.LevelInfo)

	isTTY := detectTTY()

	var handler slog.Handler

	if isTTY {
		handler = slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{
			Level:     loggerInstance.level,
			AddSource: true,
		})
	} else {
		handler = slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
			Level:     loggerInstance.level,
			AddSource: true,
		})
	}

	loggerInstance.log = slog.New(handler)

	return loggerInstance, nil
}

func detectTTY() bool {
	fileInfo, err := os.Stdout.Stat()
	if err != nil {
		return false
	}

	return (fileInfo.Mode() & os.ModeCharDevice) != 0
}

// Get returns the underlying slog.Logger.
func (l *Logger) Get() *slog.Logger {
	return l.log
}

// EnableDebugLogging sets the log level to debug.
func (l *Logger) EnableDebugLogging() {
	l.level.Set(slog.LevelDebug)
	l.log.Debug("debug logging enabled", "debug", true)
}

// Identify logs application startup information.
func (l *Logger) Identify() {
	l.log.Info("starting",
		"appname", l.params.Globals.Appname,
		"version", l.params.Globals.Version,
	)
}