kportal/internal/config/watcher.go

package config

import (
	"fmt"
	"log"
	"path/filepath"
	"sync"

	"github.com/fsnotify/fsnotify"
	"github.com/nvm/kportal/internal/logger"
)

// ReloadCallback is called when the configuration file changes.
// It receives the new configuration and should return an error if the reload fails.
type ReloadCallback func(*Config) error

// Watcher watches a configuration file for changes and triggers hot-reload.
type Watcher struct {
	configPath string
	callback   ReloadCallback
	watcher    *fsnotify.Watcher
	done       chan struct{}
	verbose    bool
	wg         sync.WaitGroup // Ensures watch goroutine exits before Stop returns
	stopOnce   sync.Once      // Ensures Stop is safe to call multiple times
}

// NewWatcher creates a new file watcher for the given config file.
func NewWatcher(configPath string, callback ReloadCallback, verbose bool) (*Watcher, error) {
	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		return nil, fmt.Errorf("failed to create file watcher: %w", err)
	}

	absPath, err := filepath.Abs(configPath)
	if err != nil {
		_ = watcher.Close()
		return nil, fmt.Errorf("failed to resolve absolute path: %w", err)
	}

	// Watch the directory instead of the file to handle atomic writes
	// (many editors delete and recreate files on save)
	dir := filepath.Dir(absPath)
	if err := watcher.Add(dir); err != nil {
		_ = watcher.Close()
		return nil, fmt.Errorf("failed to watch directory %s: %w", dir, err)
	}

	return &Watcher{
		configPath: absPath,
		callback:   callback,
		watcher:    watcher,
		done:       make(chan struct{}),
		verbose:    verbose,
	}, nil
}

// Start begins watching the configuration file for changes.
func (w *Watcher) Start() {
	w.wg.Add(1)
	go w.watch()
}

// Stop stops watching the configuration file and waits for the watch goroutine to exit.
// Safe to call multiple times.
func (w *Watcher) Stop() {
	w.stopOnce.Do(func() {
		close(w.done)
		_ = w.watcher.Close()
	})
	w.wg.Wait() // Wait for watch goroutine to exit
}

// watch runs the file watching loop.
func (w *Watcher) watch() {
	defer w.wg.Done()

	if w.verbose {
		log.Printf("Watching configuration file: %s", w.configPath)
	}

	for {
		select {
		case event, ok := <-w.watcher.Events:
			if !ok {
				return
			}

			// Only process events for our config file
			eventPath, err := filepath.Abs(event.Name)
			if err != nil {
				if w.verbose {
					log.Printf("Failed to resolve event path: %v", err)
				}
				continue
			}

			if eventPath != w.configPath {
				continue
			}

			// Handle write and create events (create happens on atomic writes)
			if event.Op&fsnotify.Write == fsnotify.Write || event.Op&fsnotify.Create == fsnotify.Create {
				if w.verbose {
					log.Printf("Configuration file changed, reloading...")
				}
				w.handleReload()
			}

		case err, ok := <-w.watcher.Errors:
			if !ok {
				return
			}
			log.Printf("File watcher error: %v", err)

		case <-w.done:
			return
		}
	}
}

// handleReload loads and validates the new configuration, then calls the callback.
func (w *Watcher) handleReload() {
	// Load new configuration
	newCfg, err := LoadConfig(w.configPath)
	if err != nil {
		logger.Error("Failed to load configuration during hot-reload", map[string]interface{}{
			"config_path": w.configPath,
			"error":       err.Error(),
		})
		logger.Info("Keeping previous configuration active", nil)
		return
	}

	// Validate new configuration
	validator := NewValidator()
	if errs := validator.ValidateConfig(newCfg); len(errs) > 0 {
		logger.Error("Configuration validation failed during hot-reload", map[string]interface{}{
			"config_path":       w.configPath,
			"validation_errors": len(errs),
		})
		logger.Info("Keeping previous configuration active", nil)
		return
	}

	// Call reload callback
	if err := w.callback(newCfg); err != nil {
		logger.Error("Failed to apply new configuration", map[string]interface{}{
			"config_path": w.configPath,
			"error":       err.Error(),
		})
		logger.Info("Keeping previous configuration active", nil)
		return
	}

	logger.Info("Configuration reloaded successfully", map[string]interface{}{
		"config_path":    w.configPath,
		"forwards_count": len(newCfg.GetAllForwards()),
	})
}