start implementing expression balancer

src/main/java/parser/ast/ExpressionBalancer.java

@@ -0,0 +1,88 @@
+package parser.ast;
+
+public final class ExpressionBalancer {
+
+    private ExpressionBalancer() {}
+
+    // Spiegelt den Baum, da meine Müll-Grammatik die EXPRs rückwärts parst
+    public static void flip(AST tree) {
+        flip(tree.getRoot());
+    }
+
+    private static void flip(Node root) {
+        for (Node child : root.getChildren()) {
+            flip(child);
+        }
+
+        if (root.getChildren().size() == 2) {
+            Node left = root.getChildren().get(0);
+            Node right = root.getChildren().get(1);
+
+            root.setChildren(right, left);
+        }
+    }
+
+    // Führt Linksrotationen durch
+    // Es werden EXPR-Nodes (2 Childs, 1 davon EXPR, Kein Wert) solange wie möglich linksrotiert
+    public static void leftPrecedence(AST tree) {
+        boolean change;
+
+        do {
+            change = leftPrecedence(tree.getRoot());
+        } while (change);
+    }
+
+    private static boolean leftPrecedence(Node root) {
+        for (Node child : root.getChildren()) {
+            leftPrecedence(child);
+        }
+
+        Node expr = getExpr(root);
+
+        if (expr == null || root.getChildren().size() != 2 || !root.getValue().isEmpty()) {
+            return false;
+        }
+
+        leftRotate(root);
+
+        return true;
+    }
+
+    private static void leftRotate(Node root) {
+        Node left = root.getChildren().get(0);
+        Node right = root.getChildren().get(1);
+
+        // Verhindert Wurzel mit nur einem EXPR-Child
+        if (endOfExpr(right)) {
+            root.setName(right.getName());
+            root.setValue(right.getValue());
+            root.setChildren(left, right.getChildren().get(0));
+            return;
+        }
+
+        Node insertLeft = new Node(root.getName());
+        insertLeft.setValue(right.getValue());
+        insertLeft.setChildren(left, right.getChildren().get(0));
+
+        root.setName(right.getName());
+        root.setChildren(insertLeft, right.getChildren().get(1));
+    }
+
+    private static Node getExpr(Node root) {
+        for (Node child : root.getChildren()) {
+            if (child.getName().equals("EXPR")) {
+                return child;
+            }
+        }
+
+        return null;
+    }
+
+    private static boolean endOfExpr(Node root) {
+        return root.getChildren().size() == 1;
+    }
+
+    public static void operatorPrecedence(AST tree) {
+
+    }
+}