Added DelegateOperation to proxy Operations.

src/main/java/com/sk89q/worldedit/function/operation/DelegateOperation.java

@@ -0,0 +1,60 @@
+/*
+ * WorldEdit, a Minecraft world manipulation toolkit
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldEdit team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldedit.function.operation;
+
+import com.sk89q.worldedit.WorldEditException;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * Executes a delegete operation, but returns to another operation upon
+ * completing the delegate.
+ */
+public class DelegateOperation implements Operation {
+
+    private final Operation original;
+    private Operation delegate;
+
+    /**
+     * Create a new operation delegate.
+     *
+     * @param original the operation to return to
+     * @param delegate the delegate operation to complete before returning
+     */
+    public DelegateOperation(Operation original, Operation delegate) {
+        checkNotNull(original);
+        checkNotNull(delegate);
+        this.original = original;
+        this.delegate = delegate;
+    }
+
+    @Override
+    public Operation resume() throws WorldEditException {
+        delegate = delegate.resume();
+        return delegate != null ? this : original;
+    }
+
+    @Override
+    public void cancel() {
+        delegate.cancel();
+        original.cancel();
+    }
+
+}