@@ -0,0 +1,137 @@
+package update
+
+import (
+	"io/fs"
+	"os"
+	"path"
+	"path/filepath"
+	"slices"
+	"time"
+
+	"go.alanpearce.eu/x/log"
+
+	"github.com/fsnotify/fsnotify"
+	"gitlab.com/tozd/go/errors"
+)
+
+var (
+	ignores = []string{
+		"*.templ",
+		"*.go",
+	}
+	checkSettleInterval = 200 * time.Millisecond
+)
+
+type FileWatcher struct {
+	log *log.Logger
+	*fsnotify.Watcher
+}
+
+func NewFileWatcher(logger *log.Logger, dirs ...string) (*FileWatcher, error) {
+	fsn, err := fsnotify.NewWatcher()
+	if err != nil {
+		return nil, errors.WithMessage(err, "could not create file watcher")
+	}
+
+	for _, dir := range dirs {
+		err = fsn.Add(dir)
+		if err != nil {
+			return nil, errors.WithMessagef(err, "could not add directory %s to file watcher", dir)
+		}
+	}
+
+	return &FileWatcher{
+		Watcher: fsn,
+		log:     logger,
+	}, nil
+}
+
+func (fw *FileWatcher) matches(name string) func(string) bool {
+	return func(pattern string) bool {
+		matched, err := path.Match(pattern, name)
+		if err != nil {
+			fw.log.Warn("error checking watcher ignores", "error", err)
+		}
+
+		return matched
+	}
+}
+
+func (fw *FileWatcher) ignored(pathname string) bool {
+	return slices.ContainsFunc(ignores, fw.matches(path.Base(pathname)))
+}
+
+func (fw *FileWatcher) AddRecursive(from string) error {
+	fw.log.Debug("walking directory tree", "root", from)
+	err := filepath.WalkDir(from, func(path string, entry fs.DirEntry, err error) error {
+		if err != nil {
+			return errors.WithMessagef(err, "could not walk directory %s", path)
+		}
+		if entry.IsDir() {
+			if entry.Name() == ".git" {
+				fw.log.Debug("skipping directory", "entry", entry.Name())
+
+				return fs.SkipDir
+			}
+			fw.log.Debug("adding directory to watcher", "path", path)
+			if err = fw.Add(path); err != nil {
+				return errors.WithMessagef(err, "could not add directory %s to watcher", path)
+			}
+		}
+
+		return nil
+	})
+
+	return errors.WithMessage(err, "error walking directory tree")
+}
+
+func (fw *FileWatcher) Wait(events chan<- Event, errs chan<- error) error {
+	var timer *time.Timer
+
+	go func() {
+		var fileEvents []fsnotify.Event
+		for {
+			select {
+			case baseEvent := <-fw.Watcher.Events:
+				if !fw.ignored(baseEvent.Name) {
+					fw.log.Debug(
+						"watcher event",
+						"name",
+						baseEvent.Name,
+						"op",
+						baseEvent.Op.String(),
+					)
+					if baseEvent.Has(fsnotify.Create) || baseEvent.Has(fsnotify.Rename) {
+						f, err := os.Stat(baseEvent.Name)
+						if err != nil {
+							errs <- errors.WithMessagef(err, "error handling event %s", baseEvent.Op.String())
+						} else if f.IsDir() {
+							err = fw.Add(baseEvent.Name)
+							if err != nil {
+								errs <- errors.WithMessage(err, "error adding new folder to watcher")
+							}
+						}
+					}
+					if baseEvent.Has(fsnotify.Rename) || baseEvent.Has(fsnotify.Write) ||
+						baseEvent.Has(fsnotify.Create) || baseEvent.Has(fsnotify.Chmod) {
+						fileEvents = append(fileEvents, baseEvent)
+						if timer == nil {
+							timer = time.AfterFunc(checkSettleInterval, func() {
+								events <- Event{
+									FileEvents: fileEvents,
+									Revision:   "",
+								}
+								fileEvents = []fsnotify.Event{}
+							})
+						}
+						timer.Reset(checkSettleInterval)
+					}
+				}
+			case err := <-fw.Watcher.Errors:
+				errs <- errors.WithMessage(err, "error in watcher")
+			}
+		}
+	}()
+
+	return nil
+}