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A packaging of the IntelliJ Community Edition core-api library. This is release number 1 of trunk branch 142.
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/*
 * Copyright 2000-2013 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.
 */

/*
 * @author max
 */
package com.intellij.psi.util;

import com.intellij.openapi.util.Key;
import com.intellij.openapi.util.Pair;
import com.intellij.psi.PsiElement;
import com.intellij.reference.SoftReference;
import com.intellij.util.Function;
import org.jetbrains.annotations.NonNls;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

public class PsiCacheKey extends Key>> {
  private final Function myFunction;
  /**
   * One of {@link com.intellij.psi.util.PsiModificationTracker} constants that marks when to flush cache
   */
  @NotNull
  private final Key myModifyCause;

  private PsiCacheKey(@NonNls @NotNull String name, @NotNull Function function, @NotNull Key modifyCause) {
    super(name);
    myFunction = function;
    myModifyCause = modifyCause;
  }

  public final T getValue(@NotNull H h) {
    T result = getCachedValueOrNull(h);
    if (result != null) {
      return result;
    }

    result = myFunction.fun(h);
    final long count = getModificationCount(h.getManager().getModificationTracker());
    h.putUserData(this, new SoftReference>(new Pair(count, result)));
    return result;
  }

  @Nullable
  public final T getCachedValueOrNull(@NotNull H h) {
    SoftReference> ref = h.getUserData(this);
    Pair data = SoftReference.dereference(ref);
    if (data == null || data.getFirst() != getModificationCount(h.getManager().getModificationTracker())) {
      return null;
    }

    return data.getSecond();
  }


  /**
   * Gets modification count from tracker based on {@link #myModifyCause}
   *
   * @param tracker track to get modification count from
   * @return modification count
   * @throws AssertionError if {@link #myModifyCause} is junk
   */
  private long getModificationCount(@NotNull PsiModificationTracker tracker) {
    if (myModifyCause.equals(PsiModificationTracker.JAVA_STRUCTURE_MODIFICATION_COUNT)) {
      return tracker.getJavaStructureModificationCount();
    }
    if (myModifyCause.equals(PsiModificationTracker.OUT_OF_CODE_BLOCK_MODIFICATION_COUNT)) {
      return tracker.getOutOfCodeBlockModificationCount();
    }
    if (myModifyCause.equals(PsiModificationTracker.MODIFICATION_COUNT)) {
      return tracker.getModificationCount();
    }
    throw new AssertionError("No modification tracker found for key " + myModifyCause);
  }

  /**
   * Creates cache key value
   *
   * @param name        key name
   * @param function    function to reproduce new value when old value is stale
   * @param modifyCause one one {@link com.intellij.psi.util.PsiModificationTracker}'s constants that marks when to flush cache
   * @param          value type
   * @param          key type
   * @return instance
   */
  public static  PsiCacheKey create(@NonNls @NotNull String name,
                                                                   @NotNull Function function,
                                                                   @NotNull Key modifyCause) {
    return new PsiCacheKey(name, function, modifyCause);
  }

  /**
   * Creates cache key value using {@link com.intellij.psi.util.PsiModificationTracker#JAVA_STRUCTURE_MODIFICATION_COUNT} as
   * modification count to flush cache
   *
   * @param name     key name
   * @param function function to reproduce new value when old value is stale
   * @param       value type
   * @param       key type
   * @return instance
   */
  public static  PsiCacheKey create(@NonNls @NotNull String name, @NotNull Function function) {
    return create(name, function, PsiModificationTracker.JAVA_STRUCTURE_MODIFICATION_COUNT);
  }
}