/*
    * 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.commons.imaging.formats.tiff.itu_t4;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  
  import org.apache.commons.imaging.ImagingException;
  
  /**
   * A Huffman tree implemented as 1 array for high locality of reference.
   */
  final class HuffmanTree<T> {
      private static final class Node<T> {
          boolean empty = true;
          T value;
      }
  
      private final List<Node<T>> nodes = new ArrayList<>();
  
      public T decode(final BitInputStreamFlexible bitStream) throws ImagingException {
          int position = 0;
          Node<T> node = nodes.get(0);
          while (node.value == null) {
              int nextBit;
              try {
                  nextBit = bitStream.readBits(1);
              } catch (final IOException ioEx) {
                  throw new ImagingException("Error reading stream for huffman tree", ioEx);
              }
              if (nextBit == 0) {
                  position = (position << 1) + 1;
              } else {
                  position = position + 1 << 1;
              }
              if (position >= nodes.size()) {
                  throw new ImagingException("Invalid bit pattern");
              }
              node = nodes.get(position);
              if (node.empty) {
                  throw new ImagingException("Invalid bit pattern");
              }
          }
          return node.value;
      }
  
      private Node<T> growAndGetNode(final int position) {
          while (position >= nodes.size()) {
              nodes.add(new Node<>());
          }
          final Node<T> node = nodes.get(position);
          node.empty = false;
          return node;
      }
  
      public void insert(final String pattern, final T value) throws ImagingException {
          int position = 0;
          Node<T> node = growAndGetNode(position);
          if (node.value != null) {
              throw new ImagingException("Can't add child to a leaf");
          }
          for (int patternPosition = 0; patternPosition < pattern.length(); patternPosition++) {
              final char nextChar = pattern.charAt(patternPosition);
              if (nextChar == '0') {
                  position = (position << 1) + 1;
              } else {
                  position = position + 1 << 1;
              }
              node = growAndGetNode(position);
              if (node.value != null) {
                  throw new ImagingException("Can't add child to a leaf");
              }
          }
          node.value = value;
      }
  }