/*
    * ====================================================================
    * 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  
  package org.apache.hc.core5.http2.hpack;
  
  import org.apache.hc.core5.http.Header;
  
  final class FifoBuffer {
  
      private HPackHeader[] array;
      private int head;
      private int tail;
  
      FifoBuffer(final int initialCapacity) {
          this.array = new HPackHeader[initialCapacity];
          this.head = 0;
          this.tail = 0;
      }
  
      private void expand() {
  
          int newcapacity = (array.length + 1) << 1;
          if (newcapacity < 0) {
              newcapacity = Integer.MAX_VALUE;
          }
          final Header[] oldArray = array;
          final int len = oldArray.length;
          final HPackHeader/HPackHeader.html#HPackHeader">HPackHeader[] newArray = new HPackHeader[newcapacity];
          System.arraycopy(oldArray, head, newArray, 0, len - head);
          System.arraycopy(oldArray, 0, newArray, len - head, head);
          array = newArray;
          head = len;
          tail = 0;
      }
  
      public void clear() {
          head = 0;
          tail = 0;
      }
  
      public void addFirst(final HPackHeader header) {
          array[head++] = header;
          if (head == array.length) {
              head = 0;
          }
          if (head == tail) {
              expand();
          }
      }
  
      public HPackHeader get(final int index) {
          int i = head - index - 1;
          if (i < 0) {
              i = array.length + i;
          }
          return array[i];
      }
  
      public HPackHeader getFirst() {
          return array[head > 0 ? head - 1 : array.length - 1];
      }
  
      public HPackHeader getLast() {
          return array[tail];
      }
  
      public HPackHeader removeLast() {
          final HPackHeader header = array[tail];
          if (header != null) {
              array[tail++] = null;
              if (tail == array.length) {
                  tail = 0;
              }
          }
          return header;
     }
 
     public int capacity() {
         return array.length;
     }
 
     public int size() {
         int i = head - tail;
         if (i < 0) {
             i = array.length + i;
         }
         return i;
     }
 
 }