cassandra-trunk/src/java/org/apache/cassandra/schema/SchemaTransformation.java
/*
 * 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.cassandra.schema;

import java.util.Optional;

public interface SchemaTransformation
{
    /**
     * Apply a statement transformation to a schema snapshot.
     * <p>
     * Implementing methods should be side-effect free (outside of throwing exceptions if the transformation cannot
     * be successfully applied to the provided schema).
     *
     * @param schema Keyspaces to base the transformation on
     * @return Keyspaces transformed by the statement
     */
    Keyspaces apply(Keyspaces schema);

    /**
     * If the transformation should be applied with a certain timestamp, this method should be overriden. This is used
     * by {@link SchemaTransformations#updateSystemKeyspace(KeyspaceMetadata, long)} when we need to set the fixed
     * timestamp in order to preserve user settings.
     */
    default Optional<Long> fixedTimestampMicros()
    {
        return Optional.empty();
    }

    /**
     * The result of applying (on this node) a given schema transformation.
     */
    class SchemaTransformationResult
    {
        public final DistributedSchema before;
        public final DistributedSchema after;
        public final Keyspaces.KeyspacesDiff diff;

        public SchemaTransformationResult(DistributedSchema before, DistributedSchema after, Keyspaces.KeyspacesDiff diff)
        {
            this.before = before;
            this.after = after;
            this.diff = diff;
        }

        @Override
        public String toString()
        {
            return String.format("SchemaTransformationResult{%s --> %s, diff=%s}", before.getVersion(), after.getVersion(), diff);
        }
    }
}
