// Package logging builds the application's slog logger. Logs go to stderr
// (readable console in dev, structured JSON otherwise) and, optionally, to a
// file. There is no database sink — see AGENT.md §7.
package logging

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

// Setup returns a configured *slog.Logger and, if a file sink was opened, an
// io.Closer to flush/close it on shutdown (nil when no file sink is used).
func Setup(dev bool, logFile string) (*slog.Logger, io.Closer, error) {
	var w io.Writer = os.Stderr
	var closer io.Closer

	if logFile != "" {
		f, err := os.OpenFile(logFile, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o644)
		if err != nil {
			return nil, nil, err
		}
		w = io.MultiWriter(os.Stderr, f)
		closer = f
	}

	var handler slog.Handler
	if dev {
		handler = slog.NewTextHandler(w, &slog.HandlerOptions{Level: slog.LevelDebug})
	} else {
		handler = slog.NewJSONHandler(w, &slog.HandlerOptions{Level: slog.LevelInfo})
	}

	return slog.New(handler), closer, nil
}