fixed various quirks and removed dirty hacks on quickslot bar/pie

src/net/torvald/terrarum/debuggerapp/TraversingCircularArray.java

@@ -1,7 +1,60 @@
 package net.torvald.terrarum.debuggerapp;
 
 /**
+ * To be used as undo/redo buffer. Which means, current position can go backward and rewrite objects ahead.
+ *
+ * The most recent item will be same as the current edit.
+ *
  * Created by minjaesong on 2019-01-09.
  */
-public class TraversingCircularArray {
+public class TraversingCircularArray<T> {
+
+    private T[] buf;
+    private int size;
+
+    public TraversingCircularArray(int size) {
+        buf = (T[]) new Object[size]; // create array of nulls
+        this.size = size;
+    }
+
+    public int getSize() {
+        return size;
+    }
+
+    private int tail = 0;
+    private int head = -1;
+
+    private int unreliableAddCount = 0;
+
+    /**
+     * Adds new item.
+     * @param item
+     */
+    public void undoNew(T item) {
+        if (unreliableAddCount <= size) unreliableAddCount += 1;
+
+        head = (head + 1) % size;
+        if (unreliableAddCount > size) {
+            tail = (tail + 1) % size;
+        }
+
+        buf[head] = item; // overwrites oldest item when eligible
+    }
+
+    /**
+     * Pops existing item. This function is analogous to rewinding the tape. Existing data will be untouched.
+     * @return
+     */
+    public T redo() {
+        tail -= 1;
+        return buf[tail];
+    }
+
+    /**
+     * Undo the redo. This function is analogous to fast-forwarding the tape, without touching already recorded data.
+     * If head of the tape reached, will do nothing.
+     */
+    public T undoAgain() {
+        return null;
+    }
 }