platform/vcs-impl/src/com/intellij/openapi/vcs/changes/actions/DiffRequestPresentableProxy.java

/*
 * Copyright 2000-2010 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.intellij.openapi.vcs.changes.actions;

import com.intellij.openapi.actionSystem.AnAction;
import com.intellij.openapi.vcs.VcsException;
import org.jetbrains.annotations.NotNull;

import java.util.Collections;
import java.util.List;

public abstract class DiffRequestPresentableProxy implements DiffRequestPresentable {
  private DiffRequestPresentable myDelegate;
  private List<? extends AnAction> myCachedActions;
  private MyResult myStepResult;

  @NotNull
  protected abstract DiffRequestPresentable init() throws VcsException;

  @NotNull
  private DiffRequestPresentable initRequest() throws VcsException {
    if (myDelegate == null) {
      myDelegate = init();
    }
    return myDelegate;
  }

  public List<? extends AnAction> createActions(DiffExtendUIFactory uiFactory) {
    if (myCachedActions == null) {
      try {
        myCachedActions = initRequest().createActions(uiFactory);
      }
      catch (VcsException e) {
        //should not occur
        return Collections.emptyList();
      }
    }
    return myCachedActions;
  }

  public MyResult step(DiffChainContext context) {
    final DiffRequestPresentable request;
    try {
      request = initRequest();
      myStepResult = request.step(context);
    }
    catch (VcsException e) {
      myStepResult = new MyResult(null, DiffPresentationReturnValue.quit, e.getMessage());
    }
    return myStepResult;
  }

  public void haveStuff() throws VcsException {
    final DiffRequestPresentable request = initRequest();
    request.haveStuff();
  }
}