/*
 * 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.beam.sdk.io.kinesis;

import java.util.NoSuchElementException;
import java.util.Objects;

/**
 * Similar to Guava {@code Optional}, but throws {@link NoSuchElementException} for missing element.
 */
abstract class CustomOptional<T> {
    @SuppressWarnings("unchecked")
    public static <T> CustomOptional<T> absent() {
        return (Absent<T>) Absent.INSTANCE;
    }

    public static <T> CustomOptional<T> of(T v) {
        return new Present<>(v);
    }

    public abstract boolean isPresent();

    public abstract T get();

    private static class Present<T> extends CustomOptional<T> {
        private final T value;

        private Present(T value) {
            this.value = value;
        }

        @Override
        public boolean isPresent() {
            return true;
        }

        @Override
        public T get() {
            return value;
        }

        @Override
        public boolean equals(Object o) {
            if (!(o instanceof Present)) {
                return false;
            }

            Present<?> present = (Present<?>) o;
            return Objects.equals(value, present.value);
        }

        @Override
        public int hashCode() {
            return Objects.hash(value);
        }
    }

    private static class Absent<T> extends CustomOptional<T> {
        private static final Absent<Object> INSTANCE = new Absent<>();

        private Absent() {
        }

        @Override
        public boolean isPresent() {
            return false;
        }

        @Override
        public T get() {
            throw new NoSuchElementException();
        }

        @Override
        public boolean equals(Object o) {
            return o instanceof Absent;
        }

        @Override
        public int hashCode() {
            return 0;
        }
    }
}