platform/lang-impl/src/com/intellij/find/findUsages/UsageHistory.java

/*
 * Copyright 2000-2014 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.find.findUsages;

import com.intellij.openapi.util.Condition;
import com.intellij.usages.ConfigurableUsageTarget;
import com.intellij.util.containers.ContainerUtil;
import org.jetbrains.annotations.NotNull;

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

public class UsageHistory {
  // the last element is the most recent
  private final List<ConfigurableUsageTarget> myHistory = ContainerUtil.createLockFreeCopyOnWriteList();

  public void add(@NotNull ConfigurableUsageTarget usageTarget) {
    final String descriptiveName = usageTarget.getLongDescriptiveName();
    ContainerUtil.retainAll(myHistory, new Condition<ConfigurableUsageTarget>() {
      @Override
      public boolean value(ConfigurableUsageTarget existing) {
        return !existing.getLongDescriptiveName().equals(descriptiveName);
      }
    });
    myHistory.add(usageTarget);

    // todo configure history depth limit
    if (myHistory.size() > 15) {
      myHistory.remove(0);
    }
  }

  @NotNull
  public List<ConfigurableUsageTarget> getAll() {
    removeInvalidElementsFromHistory();
    return Collections.unmodifiableList(myHistory);
  }

  private void removeInvalidElementsFromHistory() {
    for (ConfigurableUsageTarget target : myHistory) {
      if (!target.isValid()) myHistory.remove(target);
    }
  }

}