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Apache Solr (module: core)
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.solr.logging;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * FIFO Circular List.
 *
 * Once the size is reached, it will overwrite previous entries
 */
public class CircularList implements Iterable {
  private T[] data;
  private int head = 0;
  private int tail = 0;
  private int size = 0;

  @SuppressWarnings("unchecked")
  public CircularList(int size) {
    data = (T[]) new Object[size];
  }

  @SuppressWarnings("unchecked")
  public synchronized void resize(int newsize) {
    if (newsize == this.size) return;

    T[] vals = (T[]) new Object[newsize];
    int i = 0;
    if (newsize > size) {
      for (i = 0; i < size; i++) {
        vals[i] = data[convert(i)];
      }
    } else {
      int off = size - newsize;
      for (i = 0; i < newsize; i++) {
        vals[i] = data[convert(i + off)];
      }
    }
    data = vals;
    head = 0;
    tail = i;
  }

  private int convert(int index) {
    return (index + head) % data.length;
  }

  public boolean isEmpty() {
    return head == tail; // or size == 0
  }

  public int size() {
    return size;
  }

  public int getBufferSize() {
    return data.length;
  }

  private void checkIndex(int index) {
    if (index >= size || index < 0)
      throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
  }

  public T get(int index) {
    checkIndex(index);
    return data[convert(index)];
  }

  public synchronized void add(T o) {
    data[tail] = o;
    tail = (tail + 1) % data.length;
    if (size == data.length) {
      head = (head + 1) % data.length;
    }
    size++;
    if (size > data.length) {
      size = data.length;
    }
  }

  public synchronized void clear() {
    for (int i = 0; i < data.length; i++) {
      data[i] = null; // for GC
    }
    head = tail = size = 0;
  }

  public List toList() {
    ArrayList list = new ArrayList<>(size);
    for (int i = 0; i < size; i++) {
      list.add(data[convert(i)]);
    }
    return list;
  }

  @Override
  public String toString() {
    StringBuilder str = new StringBuilder();
    str.append("[");
    for (int i = 0; i < size; i++) {
      if (i > 0) {
        str.append(",");
      }
      str.append(data[convert(i)]);
    }
    str.append("]");
    return str.toString();
  }

  @Override
  public Iterator iterator() {
    return new Iterator<>() {
      int idx = 0;

      @Override
      public boolean hasNext() {
        return idx < size;
      }

      @Override
      public T next() {
        return get(idx++);
      }

      @Override
      public void remove() {
        throw new UnsupportedOperationException();
      }
    };
  }
}