Refactor Package structure

This commit cleans up the package structure, to make two new top-level
packages `internal` (for internal-use packages) and `pkg` (for general
shared utility code).

pkg/fsx/touch.go

@@ -0,0 +1,29 @@
+package fsx
+
+import (
+	"os"
+	"time"
+)
+
+// Touch touches a file.
+// It is similar to the unix 'touch' command.
+//
+// If the file does not exist exists, it is created using [os.Create].
+// If the file does exist, it's access and modification times are updated to the current time.
+func Touch(path string) error {
+	_, err := os.Stat(path)
+	switch {
+	case os.IsNotExist(err):
+		f, err := os.Create(path)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+		return nil
+	case err != nil:
+		return err
+	default:
+		now := time.Now().Local()
+		return os.Chtimes(path, now, now)
+	}
+}