1 files changed, 68 insertions, 0 deletions
diff --git a/watch.go b/watch.go
new file mode 100644
index 0000000..864557b
--- /dev/null
+++ b/watch.go
@@ -0,0 +1,68 @@
+package flyscrape
+
+import (
+	"errors"
+	"fmt"
+	"os"
+
+	"github.com/fsnotify/fsnotify"
+)
+
+var StopWatch = errors.New("stop watch")
+
+func Watch(path string, fn func(string) error) error {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return fmt.Errorf("creating file watcher: %w", err)
+	}
+	defer watcher.Close()
+
+	if err := watcher.Add(path); err != nil {
+		return fmt.Errorf("watching file %q: %w", path, err)
+	}
+
+	update := func() error {
+		data, err := os.ReadFile(path)
+		if err != nil {
+			return err
+		}
+		return fn(string(data))
+	}
+
+	if err := update(); err != nil {
+		if errors.Is(err, StopWatch) {
+			return nil
+		}
+		return err
+	}
+
+	for {
+		select {
+		case event, ok := <-watcher.Events:
+			if !ok {
+				return nil
+			}
+			if event.Has(fsnotify.Remove) {
+				return nil
+			}
+			if event.Has(fsnotify.Chmod) {
+				continue
+			}
+			watcher.Remove(path)
+			watcher.Add(path)
+			if err := update(); err != nil {
+				if errors.Is(err, StopWatch) {
+					return nil
+				}
+				return err
+			}
+		case err, ok := <-watcher.Errors:
+			if !ok {
+				return nil
+			}
+			if err != nil {
+				return err
+			}
+		}
+	}
+}