MetaPolicy.java

/*
Copyright 2016 McDowell

Licensed 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 uk.kludje;

import java.util.*;
import java.util.function.BiPredicate;
import java.util.function.Function;
import java.util.function.ToIntFunction;

final class MetaPolicy {

  private static final Map<Class<?>, BiPredicate<Object, Object>> PRIMITIVE_ARRAY_EQUALS_CHECKS = new IdentityHashMap<>();
  static {
    PRIMITIVE_ARRAY_EQUALS_CHECKS.put(boolean[].class, MetaPolicy.<boolean[]>primitiveEqualsCheck(Arrays::equals));
    PRIMITIVE_ARRAY_EQUALS_CHECKS.put(char[].class, MetaPolicy.<char[]>primitiveEqualsCheck(Arrays::equals));
    PRIMITIVE_ARRAY_EQUALS_CHECKS.put(byte[].class, MetaPolicy.<byte[]>primitiveEqualsCheck(Arrays::equals));
    PRIMITIVE_ARRAY_EQUALS_CHECKS.put(short[].class, MetaPolicy.<short[]>primitiveEqualsCheck(Arrays::equals));
    PRIMITIVE_ARRAY_EQUALS_CHECKS.put(int[].class, MetaPolicy.<int[]>primitiveEqualsCheck(Arrays::equals));
    PRIMITIVE_ARRAY_EQUALS_CHECKS.put(long[].class, MetaPolicy.<long[]>primitiveEqualsCheck(Arrays::equals));
    PRIMITIVE_ARRAY_EQUALS_CHECKS.put(float[].class, MetaPolicy.<float[]>primitiveEqualsCheck(Arrays::equals));
    PRIMITIVE_ARRAY_EQUALS_CHECKS.put(double[].class, MetaPolicy.<double[]>primitiveEqualsCheck(Arrays::equals));
  }

  private static final Map<Class<?>, ToIntFunction<Object>> PRIMITIVE_ARRAY_HASHERS = new  IdentityHashMap<>();
  static {
    PRIMITIVE_ARRAY_HASHERS.put(boolean[].class, MetaPolicy.<boolean[]>primitiveHashcode(Arrays::hashCode));
    PRIMITIVE_ARRAY_HASHERS.put(char[].class, MetaPolicy.<char[]>primitiveHashcode(Arrays::hashCode));
    PRIMITIVE_ARRAY_HASHERS.put(byte[].class, MetaPolicy.<byte[]>primitiveHashcode(Arrays::hashCode));
    PRIMITIVE_ARRAY_HASHERS.put(short[].class, MetaPolicy.<short[]>primitiveHashcode(Arrays::hashCode));
    PRIMITIVE_ARRAY_HASHERS.put(int[].class, MetaPolicy.<int[]>primitiveHashcode(Arrays::hashCode));
    PRIMITIVE_ARRAY_HASHERS.put(long[].class, MetaPolicy.<long[]>primitiveHashcode(Arrays::hashCode));
    PRIMITIVE_ARRAY_HASHERS.put(float[].class, MetaPolicy.<float[]>primitiveHashcode(Arrays::hashCode));
    PRIMITIVE_ARRAY_HASHERS.put(double[].class, MetaPolicy.<double[]>primitiveHashcode(Arrays::hashCode));
  }

  private static final Map<Class<?>, Function<Object, String>> PRIMITIVE_ARRAY_STRINGIFIERS = new  IdentityHashMap<>();
  static {
    PRIMITIVE_ARRAY_STRINGIFIERS.put(boolean[].class, MetaPolicy.<boolean[]>toStringFunction(Arrays::toString));
    PRIMITIVE_ARRAY_STRINGIFIERS.put(char[].class, MetaPolicy.<char[]>toStringFunction(Arrays::toString));
    PRIMITIVE_ARRAY_STRINGIFIERS.put(byte[].class, MetaPolicy.<byte[]>toStringFunction(Arrays::toString));
    PRIMITIVE_ARRAY_STRINGIFIERS.put(short[].class, MetaPolicy.<short[]>toStringFunction(Arrays::toString));
    PRIMITIVE_ARRAY_STRINGIFIERS.put(int[].class, MetaPolicy.<int[]>toStringFunction(Arrays::toString));
    PRIMITIVE_ARRAY_STRINGIFIERS.put(long[].class, MetaPolicy.<long[]>toStringFunction(Arrays::toString));
    PRIMITIVE_ARRAY_STRINGIFIERS.put(float[].class, MetaPolicy.<float[]>toStringFunction(Arrays::toString));
    PRIMITIVE_ARRAY_STRINGIFIERS.put(double[].class, MetaPolicy.<double[]>toStringFunction(Arrays::toString));
  }

  private MetaPolicy() { /* never instantiated */ }

  public static boolean isSameClassInstance(Class<?> declaredType, Object thatInstance) {
    return declaredType == thatInstance.getClass();
  }

  public static boolean isInstanceOfClass(Class<?> thisType, Object thatInstance) {
    return thisType.isInstance(thatInstance);
  }

  public static boolean areEqualWithShallowArrayCheck(Object o1, Object o2) {
    if (o1 == o2) {
      return true;
    }
    if (o1 == null || o2 == null) {
      return false;
    }

    if (o1 instanceof Object[] && o2 instanceof Object[]) {
      // object array
      Object[] a1 = (Object[]) o1;
      Object[] a2 = (Object[]) o2;
      return Arrays.equals(a1, a2);
    } else if (o1.getClass().isArray() && o2.getClass().isArray() && o1.getClass() == o2.getClass()) {
      // primitive array
      return PRIMITIVE_ARRAY_EQUALS_CHECKS.get(o1.getClass())
        .test(o1, o2);
    }

    return Objects.equals(o1, o2);
  }

  @SuppressWarnings("unchecked")
  private static <T> BiPredicate<Object, Object> primitiveEqualsCheck(BiPredicate<T, T> predicate) {
    return (BiPredicate<Object, Object>) predicate;
  }

  public static int toHashcodeWithShallowArrayHandling(Object o) {
    if (o == null) {
      return 0;
    }

    if (o instanceof Object[]) {
      return Arrays.hashCode((Object[]) o);
    } else if (o.getClass().isArray()) {
      return PRIMITIVE_ARRAY_HASHERS.get(o.getClass())
        .applyAsInt(o);
    }

    return o.hashCode();
  }

  @SuppressWarnings("unchecked")
  private static <T> ToIntFunction<Object> primitiveHashcode(ToIntFunction<T> fn) {
    return (ToIntFunction<Object>) fn;
  }

  public static String toStringWithShallowArrayHandling(Object o) {
    if (o == null) {
      return "null";
    }

    if (o.getClass().isArray()) {
      if (o instanceof Object[]) {
        return Arrays.toString((Object[]) o);
      }
      return PRIMITIVE_ARRAY_STRINGIFIERS.get(o.getClass())
        .apply(o);
    }

    return o.toString();
  }

  @SuppressWarnings("unchecked")
  private static <T> Function<Object, String> toStringFunction(Function<T, String> fn) {
    return (Function<Object, String>) fn;
  }
}