platform/util/src/com/intellij/util/containers/Queue.java

/*
 * 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.
 */
package com.intellij.util.containers;

import com.intellij.util.ArrayUtil;
import com.intellij.util.Processor;
import org.jetbrains.annotations.NotNull;

import java.util.Arrays;
import java.util.List;

public class Queue<T> {
  private Object[] myArray;
  private int myFirst;
  private int myLast;
  // if true, elements are located at myFirst..myArray.length and 0..myLast
  // otherwise, they are at myFirst..myLast
  private boolean isWrapped;

  public Queue(int initialCapacity) {
    myArray = initialCapacity > 0 ? new Object[initialCapacity] : ArrayUtil.EMPTY_OBJECT_ARRAY;
  }

  public void addLast(T object) {
    int currentSize = size();
    if (currentSize == myArray.length) {
      myArray = normalize(Math.max(currentSize * 2, 5));
      myFirst = 0;
      myLast = currentSize;
      isWrapped = false;
    }
    myArray[myLast] = object;
    myLast++;
    if (myLast == myArray.length) {
      isWrapped = !isWrapped;
      myLast = 0;
    }
  }

  public T removeLast() {
    if (myLast == 0) {
      isWrapped = !isWrapped;
      myLast = myArray.length;
    }
    myLast--;
    @SuppressWarnings("unchecked") T result = (T)myArray[myLast];
    myArray[myLast] = null;
    return result;
  }


  public boolean isEmpty() {
    return size() == 0;
  }

  public int size() {
    return isWrapped ? myArray.length - myFirst + myLast : myLast - myFirst;
  }

  public List<T> toList() {
    return Arrays.asList(normalize(size()));
  }

  public Object[] toArray() {
    return normalize(size());
  }

  public T pullFirst() {
    T result = peekFirst();
    myArray[myFirst] = null;
    myFirst++;
    if (myFirst == myArray.length) {
      myFirst = 0;
      isWrapped = !isWrapped;
    }
    return result;
  }

  public T peekFirst() {
    if (isEmpty()) {
      throw new IndexOutOfBoundsException("queue is empty");
    }
    @SuppressWarnings("unchecked") T t = (T)myArray[myFirst];
    return t;
  }

  private int copyFromTo(int first, int last, Object[] result, int destinationPos) {
    int length = last - first;
    System.arraycopy(myArray, first, result, destinationPos, length);
    return length;
  }

  private T[] normalize(int capacity) {
    @SuppressWarnings("unchecked") T[] result = (T[])new Object[capacity];
    if (isWrapped) {
      int tailLength = copyFromTo(myFirst, myArray.length, result, 0);
      copyFromTo(0, myLast, result, tailLength);
    }
    else {
      copyFromTo(myFirst, myLast, result, 0);
    }
    return result;
  }

  public void clear() {
    Arrays.fill(myArray, null);
    myFirst = myLast = 0;
    isWrapped = false;
  }

  public T set(int index, T value) {
    int arrayIndex;
    if (isWrapped) {
      if (myFirst + index >= myArray.length) {
        arrayIndex = index - myArray.length + myFirst;
      }
      else {
        arrayIndex = myFirst + index;
      }
    }
    else {
      arrayIndex = myFirst + index;
    }
    final Object old = myArray[arrayIndex];
    myArray[arrayIndex] = value;
    @SuppressWarnings("unchecked") T t = (T)old;
    return t;
  }

  public boolean process(@NotNull Processor<T> processor) {
    if (isWrapped) {
      for (int i = myFirst; i < myArray.length; i++) {
        @SuppressWarnings("unchecked") T t = (T)myArray[i];
        if (!processor.process(t)) return false;
      }
      for (int i = 0; i < myLast; i++) {
        @SuppressWarnings("unchecked") T t = (T)myArray[i];
        if (!processor.process(t)) return false;
      }
    }
    else {
      for (int i = myFirst; i < myLast; i++) {
        @SuppressWarnings("unchecked") T t = (T)myArray[i];
        if (!processor.process(t)) return false;
      }
    }
    return true;
  }

  @Override
  public String toString() {
    if (isEmpty()) return "<empty>";
    List<Object> list = Arrays.asList(myArray);
    if (isWrapped) {
      return "[[[ " + list.subList(0, myLast) + " ||| ... " +
             list.subList(myLast, myFirst) + " ... ||| " +
             list.subList(myFirst, myArray.length) + " ]]]";
    }
    else {
      return "[[[ ... " + list.subList(0, myFirst) + " ... ||| " +
                 list.subList(myFirst, myLast) + " ||| ... " +
                 list.subList(myFirst, myArray.length) + " ... ]]]";
    }
  }
}