/*
    * 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
    *
    *      https://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.collections4.trie.analyzer;
  
  import org.apache.commons.collections4.trie.KeyAnalyzer;
  
  /**
   * An {@link KeyAnalyzer} for {@link String}s.
   * <p>
   * This class is stateless.
   * </p>
   *
   * @since 4.0
   */
  public class StringKeyAnalyzer extends KeyAnalyzer<String> {
  
      private static final long serialVersionUID = -7032449491269434877L;
  
      /** A singleton instance of {@link StringKeyAnalyzer}. */
      public static final StringKeyAnalyzer INSTANCE = new StringKeyAnalyzer();
  
      /** The number of bits per {@link Character} plus a presence bit. */
      public static final int LENGTH = Character.SIZE + 1;
  
      /** A bit mask where the first bit is 1 and the others are zero. */
      private static final int MSB = 0x8000;
  
      /** Returns a bit mask where the given bit is set. */
      private static int mask(final int bit) {
          return MSB >>> bit;
      }
  
      /**
       * Constructs a new instance.
       *
       * @deprecated Use {@link #INSTANCE}.
       */
      @Deprecated
      public StringKeyAnalyzer() {
          // empty
      }
  
      @Override
      public int bitIndex(final String key, final int offsetInBits, final int lengthInBits,
                          final String other, final int otherOffsetInBits, final int otherLengthInBits) {
  
          if (offsetInBits % LENGTH != 0 || otherOffsetInBits % LENGTH != 0
                  || lengthInBits % LENGTH != 0 || otherLengthInBits % LENGTH != 0) {
              throw new IllegalArgumentException("The offsets and lengths must be at Character boundaries");
          }
  
          final int beginIndex1 = offsetInBits / LENGTH;
          final int beginIndex2 = otherOffsetInBits / LENGTH;
  
          final int endIndex1 = beginIndex1 + lengthInBits / LENGTH;
          final int endIndex2 = other == null ? beginIndex2 : beginIndex2 + otherLengthInBits / LENGTH;
  
          final int length = Math.max(endIndex1, endIndex2);
  
          for (int i = 0; i < length; i++) {
              final int index1 = beginIndex1 + i;
              final int index2 = beginIndex2 + i;
  
              if (index1 < endIndex1 && other != null && index2 < endIndex2) {
                  final char k = key.charAt(index1);
                  final char f = other.charAt(index2);
  
                  if (k != f) {
                      final int x = k ^ f;
                      return i * LENGTH + 1 + Integer.numberOfLeadingZeros(x) - (LENGTH - 1);
                  }
              } else {
                  // One has ended, the other has not. They differ at the presence bit of this block.
                  return i * LENGTH;
              }
          }
  
          if (lengthInBits == 0 && (other == null || otherLengthInBits == 0)) {
              return NULL_BIT_KEY;
          }
  
          // Both keys are equal
          return EQUAL_BIT_KEY;
      }
  
     @Override
     public int bitsPerElement() {
         return LENGTH;
     }
 
     @Override
     public boolean isBitSet(final String key, final int bitIndex, final int lengthInBits) {
         if (key == null || bitIndex >= lengthInBits) {
             return false;
         }
 
         final int index = bitIndex / LENGTH;
         final int bit = bitIndex % LENGTH;
 
         if (bit == 0) {
             return true;
         }
         return (key.charAt(index) & mask(bit - 1)) != 0;
     }
 
     @Override
     public boolean isPrefix(final String prefix, final int offsetInBits,
                             final int lengthInBits, final String key) {
         if (offsetInBits % LENGTH != 0 || lengthInBits % LENGTH != 0) {
             throw new IllegalArgumentException(
                     "Cannot determine prefix outside of Character boundaries");
         }
 
         final String s1 = prefix.substring(offsetInBits / LENGTH, lengthInBits / LENGTH);
         return key.startsWith(s1);
     }
 
     @Override
     public int lengthInBits(final String key) {
         return key != null ? key.length() * LENGTH : 0;
     }
 }