From 7523af09f0b799c2b5cf4ee6fe7f0855fe880978 Mon Sep 17 00:00:00 2001
From: DD <liudi08@gmail.com>
Date: Thu, 5 Oct 2017 18:12:28 -0400
Subject: [PATCH] add missing file

---
 src/helper/undo.js | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 src/helper/undo.js

diff --git a/src/helper/undo.js b/src/helper/undo.js
new file mode 100644
index 00000000..449aa834
--- /dev/null
+++ b/src/helper/undo.js
@@ -0,0 +1,45 @@
+// undo functionality
+// modifed from https://github.com/memononen/stylii
+import paper from 'paper';
+
+const performSnapshot = function (dispatchPerformSnapshot) {
+    dispatchPerformSnapshot({
+        json: paper.project.exportJSON({asString: false})
+    });
+
+    // @todo enable/disable buttons
+    // updateButtonVisibility();
+};
+
+const _restore = function (entry) {
+    paper.project.clear();
+    paper.project.importJSON(entry.json);
+    paper.view.update();
+};
+
+const performUndo = function (undoState, dispatchPerformUndo) {
+    if (undoState.pointer > 0) {
+        _restore(undoState.stack[undoState.pointer - 1]);
+        dispatchPerformUndo();
+
+        // @todo enable/disable buttons
+        // updateButtonVisibility();
+    }
+};
+
+
+const performRedo = function (undoState, dispatchPerformRedo) {
+    if (undoState.pointer >= 0 && undoState.pointer < undoState.stack.length - 1) {
+        _restore(undoState.stack[undoState.pointer + 1]);
+        dispatchPerformRedo();
+        
+        // @todo enable/disable buttons
+        // updateButtonVisibility();
+    }
+};
+
+export {
+    performSnapshot,
+    performUndo,
+    performRedo
+};