package config

import (
	"log/slog"
	"time"

	"github.com/fsnotify/fsnotify"
)

// Watch watches the config file and calls onReload with the new config on change.
// Debounces Write/Create events by 500ms to avoid multiple triggers on a single save.
func Watch(path string, provider *Provider, onReload func(*Config)) error {
	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		return err
	}
	if err := watcher.Add(path); err != nil {
		watcher.Close()
		return err
	}

	go func() {
		defer watcher.Close()
		var debounce *time.Timer
		for {
			select {
			case event, ok := <-watcher.Events:
				if !ok {
					return
				}
				if event.Has(fsnotify.Write) || event.Has(fsnotify.Create) {
					if debounce != nil {
						debounce.Stop()
					}
					debounce = time.AfterFunc(500*time.Millisecond, func() {
						cfg, err := Load(path)
						if err != nil {
							slog.Error("hot reload: invalid config, keeping old", "err", err)
							return
						}
						provider.Swap(cfg)
						slog.Info("config reloaded")
						if onReload != nil {
							onReload(cfg)
						}
					})
				}
			case err, ok := <-watcher.Errors:
				if !ok {
					return
				}
				slog.Error("config watcher error", "err", err)
			}
		}
	}()
	return nil
}