/*
    * 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.lang3.math;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertInstanceOf;
  import static org.junit.jupiter.api.Assertions.assertThrows;
  
  import java.io.ByteArrayInputStream;
  import java.io.InvalidObjectException;
  import java.io.ObjectInputStream;
  import java.util.HashMap;
  import java.util.Map;
  import java.util.Objects;
  
  import org.apache.commons.lang3.SerializationException;
  import org.apache.commons.lang3.SerializationUtils;
  import org.apache.commons.lang3.SerializationUtilsTest;
  import org.apache.commons.lang3.reflect.FieldUtils;
  import org.junit.jupiter.api.Test;
  
  /**
   * Tests that a serialized {@link Fraction} can't store a bad cached hashCode.
   */
  public class FractionReadObjectTest {
  
      private static Object deserialize(final byte[] bytes) throws Exception {
          try (ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(bytes))) {
              return ois.readObject();
          }
      }
  
      private static void setInt(final Object target, final String name, final int value) throws Exception {
          FieldUtils.writeDeclaredField(target, name, value, true);
      }
  
      @Test
      public void testBadHashCodeStreamIsRejected() throws Exception {
          final Fraction fraction = Fraction.getFraction(3, 7);
          final byte[] bytes = SerializationUtils.serialize(fraction);
          final int hashCode = (Integer) FieldUtils.readDeclaredField(fraction, "hashCode", true);
          final byte[] edited = SerializationUtilsTest.replaceLastInt(bytes, hashCode, 0xCAFEBABE);
          final SerializationException ex = assertThrows(SerializationException.class, () -> SerializationUtils.deserialize(edited),
                  "Bad hashCode in stream must be rejected with InvalidObjectException");
          assertInstanceOf(InvalidObjectException.class, ex.getCause());
          assertEquals("java.io.InvalidObjectException: Fraction hashCode does not match numerator/denominator.", ex.getMessage());
      }
  
      /**
       * Forged stream: numerator=0, denominator=0, hashCode=hash(0,0). The public factory refuses denominator 0 (negative control); readObject does not, so the
       * forged Fraction(0,0) deserializes and divides by zero on {@code intValue()}.
       */
      @Test
      void testForgedZeroDenominatorDividesByZero() throws Exception {
          // Negative control: no public factory can build a zero-denominator Fraction.
          assertThrows(ArithmeticException.class, () -> Fraction.getFraction(0, 0));
          final Fraction seed = Fraction.getFraction(1, 2);
          setInt(seed, "numerator", 0);
          setInt(seed, "denominator", 0);
          setInt(seed, "hashCode", Objects.hash(Integer.valueOf(0), Integer.valueOf(0)));
          assertThrows(ArithmeticException.class, () -> deserialize(SerializationUtils.serialize(seed)));
          assertThrows(ArithmeticException.class, () -> SerializationUtils.roundtrip(seed));
      }
  
      @Test
      public void testHashMapLookupAfterRoundTrip() throws Exception {
          final Fraction fraction = Fraction.getFraction(1, 4);
          final byte[] bytes = SerializationUtils.serialize(fraction);
          final Fraction deserialized = SerializationUtils.deserialize(bytes);
          final Map<Fraction, String> map = new HashMap<>();
          map.put(fraction, "quarter");
          assertEquals("quarter", map.get(deserialized), "HashMap lookup must work after deserialization");
      }
  
      @Test
      public void testRoundTripPreservesHashCode() throws Exception {
          final Fraction fraction = Fraction.getFraction(1, 4);
          final Fraction roundtrip = SerializationUtils.roundtrip(fraction);
          assertEquals(fraction.hashCode(), roundtrip.hashCode(), "Round-trip serialization must preserve the correct hashCode");
          assertEquals(fraction, roundtrip);
      }
  }