content: /*
   * Copyright (C) 2016 The Android Open Source Project
   *
   * 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.android.server.wifi.util;
  
  import java.util.ArrayList;
  
  /**
   * A ring buffer where each element of the ring is itself a byte array.
   */
  public class ByteArrayRingBuffer {
      private ArrayList<byte[]> mArrayList;
      private int mMaxBytes;
      private int mBytesUsed;
  
      /**
       * Creates a ring buffer that holds at most |maxBytes| of data. The overhead for each element
       * is not included in this limit.
       * @param maxBytes upper bound on the amount of data to hold
       */
      public ByteArrayRingBuffer(int maxBytes) {
          if (maxBytes < 1) {
              throw new IllegalArgumentException();
          }
          mArrayList = new ArrayList<byte[]>();
          mMaxBytes = maxBytes;
          mBytesUsed = 0;
      }
  
      /**
       * Adds |newData| to the ring buffer. Removes existing entries to make room, if necessary.
       * Existing entries are removed in FIFO order.
       * <p><b>Note:</b> will fail if |newData| itself exceeds the size limit for this buffer.
       * Will first remove all existing entries in this case. (This guarantees that the ring buffer
       * always represents a contiguous sequence of data.)
       * @param newData data to be added to the ring
       * @return true if the data was added
       */
      public boolean appendBuffer(byte[] newData) {
          pruneToSize(mMaxBytes - newData.length);
          if (mBytesUsed + newData.length > mMaxBytes) {
              return false;
          }
  
          mArrayList.add(newData);
          mBytesUsed += newData.length;
          return true;
      }
  
      /**
       * Returns the |i|-th element of the ring. The element retains its position in the ring.
       * @param i
       * @return the requested element
       */
      public byte[] getBuffer(int i) {
          return mArrayList.get(i);
      }
  
      /**
       * Returns the number of elements present in the ring.
       * @return the number of elements present
       */
      public int getNumBuffers() {
          return mArrayList.size();
      }
  
      /**
       * Resize the buffer, removing existing data if necessary.
       * @param maxBytes upper bound on the amount of data to hold
       */
      public void resize(int maxBytes) {
          pruneToSize(maxBytes);
          mMaxBytes = maxBytes;
      }
  
      private void pruneToSize(int sizeBytes) {
          int newBytesUsed = mBytesUsed;
          int i = 0;
          while (i < mArrayList.size() && newBytesUsed > sizeBytes) {
              newBytesUsed -= mArrayList.get(i).length;
              i++;
          }
          mArrayList.subList(0, i).clear();
          mBytesUsed = newBytesUsed;
      }
  }
  