res_levis_backend/internal/pkg/logger/logger.go

package logger

import (
	"io"
	"log/slog"
	"os"
)

// CreateLogger creates a logger writing to both stderr and the given file.
// If the file cannot be opened, returns a logger that writes only to stderr and a no-op cleanup.
// Log level is controlled by the LOG_LEVEL env var (debug/info/warn/error); defaults to info.
func CreateLogger(fname string) (*slog.Logger, func()) {
	lvl := &slog.LevelVar{}
	if v := os.Getenv("LOG_LEVEL"); v != "" {
		_ = lvl.UnmarshalText([]byte(v))
	}
	opts := &slog.HandlerOptions{Level: lvl}

	f, err := os.OpenFile(fname, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
	if err != nil {
		return slog.New(slog.NewJSONHandler(os.Stderr, opts)), func() {}
	}
	w := io.MultiWriter(os.Stderr, f)
	logger := slog.New(slog.NewJSONHandler(w, opts))
	cleanup := func() { f.Close() }
	return logger, cleanup
}