/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch 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.elasticsearch.cluster;

import org.elasticsearch.common.Nullable;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;

import java.io.IOException;

/**
 * Abstract diffable object with simple diffs implementation that sends the entire object if object has changed or
 * nothing is object remained the same.
 */
public abstract class AbstractDiffable<T extends Diffable<T>> implements Diffable<T> {

    @Override
    public Diff<T> diff(T previousState) {
        if (this.get().equals(previousState)) {
            return new CompleteDiff<>();
        } else {
            return new CompleteDiff<>(get());
        }
    }

    public static <T extends Diffable<T>> Diff<T> readDiffFrom(Reader<T> reader, StreamInput in) throws IOException {
        return new CompleteDiff<T>(reader, in);
    }

    private static class CompleteDiff<T extends Diffable<T>> implements Diff<T> {

        @Nullable
        private final T part;

        /**
         * Creates simple diff with changes
         */
        CompleteDiff(T part) {
            this.part = part;
        }

        /**
         * Creates simple diff without changes
         */
        CompleteDiff() {
            this.part = null;
        }

        /**
         * Read simple diff from the stream
         */
        CompleteDiff(Reader<T> reader, StreamInput in) throws IOException {
            if (in.readBoolean()) {
                this.part = reader.read(in);
            } else {
                this.part = null;
            }
        }

        @Override
        public void writeTo(StreamOutput out) throws IOException {
            if (part != null) {
                out.writeBoolean(true);
                part.writeTo(out);
            } else {
                out.writeBoolean(false);
            }
        }

        @Override
        public T apply(T part) {
            if (this.part != null) {
                return this.part;
            } else {
                return part;
            }
        }
    }

    @SuppressWarnings("unchecked")
    public T get() {
        return (T) this;
    }
}