/*
    * ====================================================================
    * 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 FifoLinkedList {
  
      private final InternalNode master;
      private int length;
  
      FifoLinkedList() {
          this.master = new InternalNode(null);
          this.master.previous = this.master;
          this.master.next = this.master;
      }
  
      public Header get(final int index) {
          if (index < 0 || index >= length) {
              throw new IndexOutOfBoundsException();
          }
          InternalNode current = master.next;
          int n = 0;
          while (current != master) {
              if (index == n) {
                  return current.header;
              }
              current = current.next;
              n++;
          }
          return null;
      }
  
      public int getIndex(final InternalNode node) {
          final int seqNum = node.seqNum;
          if (seqNum < 1) {
              return -1;
          }
          return length - (seqNum - master.previous.seqNum) - 1;
      }
  
      public Header getFirst() {
          return master.next.header;
      }
  
      public Header getLast() {
          return master.previous.header;
      }
  
      public int size() {
          return length;
      }
  
      public InternalNode addFirst(final HPackHeader header) {
  
          final InternalNode newNode = new InternalNode(header);
          final InternalNode oldNode = master.next;
          master.next = newNode;
          newNode.previous = master;
          newNode.next = oldNode;
          oldNode.previous = newNode;
          newNode.seqNum = oldNode.seqNum + 1;
          length++;
          return newNode;
      }
  
      public InternalNode removeLast() {
  
          final InternalNode last = master.previous;
          if (last.header != null) {
              final InternalNode lastButOne = last.previous;
              master.previous = lastButOne;
              lastButOne.next = master;
              last.previous = null;
             last.next = null;
             last.seqNum = 0;
             length--;
             return last;
         }
         master.seqNum = 0;
         return null;
     }
 
     public void clear() {
 
         master.previous = master;
         master.next = master;
         master.seqNum = 0;
         length = 0;
     }
 
     class InternalNode implements HPackEntry {
 
         private final HPackHeader header;
         private InternalNode previous;
         private InternalNode next;
         private int seqNum;
 
         InternalNode(final HPackHeader header) {
             this.header = header;
         }
 
         @Override
         public HPackHeader getHeader() {
             return header;
         }
 
         @Override
         public int getIndex() {
             return StaticTable.INSTANCE.length() + FifoLinkedList.this.getIndex(this) + 1;
         }
 
         @Override
         public String toString() {
             return "[" +
                     (header != null ? header.toString() : "master") +
                     "; seqNum=" + seqNum +
                     "; previous=" + (previous != null ? previous.header : null) +
                     "; next=" + (next != null ? next.header : null) +
                     ']';
         }
 
     }
 
 }