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/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

package org.elasticsearch.cluster;

import org.elasticsearch.Version;
import org.elasticsearch.common.io.stream.NamedWriteable;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;
import org.elasticsearch.core.Nullable;

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. Comparing to AbstractDiffable, this class also works with NamedWriteables
 */
public abstract class AbstractNamedDiffable> implements Diffable, NamedWriteable {

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

    public static > NamedDiff readDiffFrom(Class tClass, String name, StreamInput in)
        throws IOException {
        return new CompleteNamedDiff<>(tClass, name, in);
    }

    private static class CompleteNamedDiff> implements NamedDiff {

        @Nullable
        private final T part;

        private final String name;

        /**
         * A non-null value is only required for write operation, if the diff was just read from the stream the version
         * is unnecessary.
         */
        @Nullable
        private final Version minimalSupportedVersion;

        /**
         * Creates simple diff with changes
         */
        CompleteNamedDiff(T part) {
            this.part = part;
            this.name = part.getWriteableName();
            this.minimalSupportedVersion = part.getMinimalSupportedVersion();
        }

        /**
         * Creates simple diff without changes
         */
        CompleteNamedDiff(String name, Version minimalSupportedVersion) {
            this.part = null;
            this.name = name;
            this.minimalSupportedVersion = minimalSupportedVersion;
        }

        /**
         * Read simple diff from the stream
         */
        CompleteNamedDiff(Class tClass, String name, StreamInput in) throws IOException {
            if (in.readBoolean()) {
                this.part = in.readNamedWriteable(tClass, name);
                this.minimalSupportedVersion = part.getMinimalSupportedVersion();
            } else {
                this.part = null;
                this.minimalSupportedVersion = null; // We just read this diff, so it's not going to be written
            }
            this.name = name;
        }

        @Override
        public void writeTo(StreamOutput out) throws IOException {
            assert minimalSupportedVersion != null : "shouldn't be called on diff that was de-serialized from the stream";
            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;
            }
        }

        @Override
        public String getWriteableName() {
            return name;
        }

        @Override
        public Version getMinimalSupportedVersion() {
            assert minimalSupportedVersion != null : "shouldn't be called on the diff that was de-serialized from the stream";
            return minimalSupportedVersion;
        }
    }

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

}