CompositeMigrationResolver.java

/**
 * Copyright 2010-2015 Axel Fontaine
 * <p/>
 * 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
 * <p/>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p/>
 * 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.contrastsecurity.cassandra.migration.resolver;

import com.contrastsecurity.cassandra.migration.CassandraMigrationException;
import com.contrastsecurity.cassandra.migration.config.ScriptsLocation;
import com.contrastsecurity.cassandra.migration.config.ScriptsLocations;
import com.contrastsecurity.cassandra.migration.info.ResolvedMigration;
import com.contrastsecurity.cassandra.migration.resolver.cql.CqlMigrationResolver;
import com.contrastsecurity.cassandra.migration.resolver.java.JavaMigrationResolver;

import java.util.*;

/**
 * Facility for retrieving and sorting the available migrations from the classpath through the various migration
 * resolvers.
 */
public class CompositeMigrationResolver implements MigrationResolver {
    /**
     * The migration resolvers to use internally.
     */
    private Collection<MigrationResolver> migrationResolvers = new ArrayList<MigrationResolver>();

    /**
     * The available migrations, sorted by version, newest first. An empty list is returned when no migrations can be
     * found.
     */
    private List<ResolvedMigration> availableMigrations;

    /**
     * Creates a new CompositeMigrationResolver.
     *
     * @param classLoader              The ClassLoader for loading migrations on the classpath.
     * @param locations                The locations where migrations are located.
     * @param encoding                 The encoding of Cql migrations.
     * @param customMigrationResolvers Custom Migration Resolvers.
     */
    public CompositeMigrationResolver(ClassLoader classLoader, ScriptsLocations locations,
                                      String encoding,
                                      MigrationResolver... customMigrationResolvers) {
        for (ScriptsLocation location : locations.getLocations()) {
            migrationResolvers.add(new CqlMigrationResolver(classLoader, location, encoding));
            migrationResolvers.add(new JavaMigrationResolver(classLoader, location));
        }

        migrationResolvers.addAll(Arrays.asList(customMigrationResolvers));
    }

    /**
     * Finds all available migrations using all migration resolvers (cql, java, ...).
     *
     * @return The available migrations, sorted by version, oldest first. An empty list is returned when no migrations
     * can be found.
     * @throws CassandraMigrationException when the available migrations have overlapping versions.
     */
    public List<ResolvedMigration> resolveMigrations() {
        if (availableMigrations == null) {
            availableMigrations = doFindAvailableMigrations();
        }

        return availableMigrations;
    }

    /**
     * Finds all available migrations using all migration resolvers (cql, java, ...).
     *
     * @return The available migrations, sorted by version, oldest first. An empty list is returned when no migrations
     * can be found.
     * @throws CassandraMigrationException when the available migrations have overlapping versions.
     */
    private List<ResolvedMigration> doFindAvailableMigrations() throws CassandraMigrationException {
        List<ResolvedMigration> migrations = new ArrayList<ResolvedMigration>(collectMigrations(migrationResolvers));
        Collections.sort(migrations, new ResolvedMigrationComparator());

        checkForIncompatibilities(migrations);

        return migrations;
    }

    /**
     * Collects all the migrations for all migration resolvers.
     *
     * @param migrationResolvers The migration resolvers to check.
     * @return All migrations.
     */
    /* private -> for testing */
    static Collection<ResolvedMigration> collectMigrations(Collection<MigrationResolver> migrationResolvers) {
        Set<ResolvedMigration> migrations = new HashSet<ResolvedMigration>();
        for (MigrationResolver migrationResolver : migrationResolvers) {
            migrations.addAll(migrationResolver.resolveMigrations());
        }
        return migrations;
    }

    /**
     * Checks for incompatible migrations.
     *
     * @param migrations The migrations to check.
     * @throws CassandraMigrationException when two different migration with the same version number are found.
     */
    /* private -> for testing */
    static void checkForIncompatibilities(List<ResolvedMigration> migrations) {
        // check for more than one migration with same version
        for (int i = 0; i < migrations.size() - 1; i++) {
            ResolvedMigration current = migrations.get(i);
            ResolvedMigration next = migrations.get(i + 1);
            if (current.getVersion().compareTo(next.getVersion()) == 0) {
                throw new CassandraMigrationException(String.format("Found more than one migration with version %s\nOffenders:\n-> %s (%s)\n-> %s (%s)",
                        current.getVersion(),
                        current.getPhysicalLocation(),
                        current.getType(),
                        next.getPhysicalLocation(),
                        next.getType()));
            }
        }
    }

}