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Extended functionality for the Java driver.

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/*
 * Copyright DataStax, Inc.
 *
 * 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 com.datastax.driver.extras.codecs.guava;

import com.datastax.driver.core.TypeCodec;
import com.datastax.driver.extras.codecs.MappingCodec;
import com.google.common.base.Optional;
import com.google.common.base.Predicate;
import com.google.common.reflect.TypeParameter;
import com.google.common.reflect.TypeToken;
import java.util.Collection;
import java.util.Map;

/**
 * A codec that wraps other codecs around Guava's {@link Optional} API.
 *
 * @param  The wrapped Java type
 */
public class OptionalCodec extends MappingCodec, T> {

  private final Predicate isAbsent;

  public OptionalCodec(TypeCodec codec) {
    this(
        codec,
        new Predicate() {
          @Override
          public boolean apply(T input) {
            return input == null
                || input instanceof Collection && ((Collection) input).isEmpty()
                || input instanceof Map && ((Map) input).isEmpty();
          }
        });
  }

  public OptionalCodec(TypeCodec codec, Predicate isAbsent) {
    // @formatter:off
    super(
        codec,
        new TypeToken>() {}.where(new TypeParameter() {}, codec.getJavaType()));
    // @formatter:on
    this.isAbsent = isAbsent;
  }

  @Override
  protected Optional deserialize(T value) {
    return isAbsent(value) ? Optional.absent() : Optional.fromNullable(value);
  }

  @Override
  protected T serialize(Optional value) {
    return value.isPresent() ? value.get() : absentValue();
  }

  protected T absentValue() {
    return null;
  }

  protected boolean isAbsent(T value) {
    return isAbsent.apply(value);
  }
}