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package org.apache.james.backends.cassandra.versions;

import static com.datastax.driver.core.querybuilder.QueryBuilder.bindMarker;
import static com.datastax.driver.core.querybuilder.QueryBuilder.insertInto;
import static com.datastax.driver.core.querybuilder.QueryBuilder.select;
import static com.datastax.driver.core.querybuilder.QueryBuilder.truncate;
import static org.apache.james.backends.cassandra.versions.table.CassandraSchemaVersionTable.KEY;
import static org.apache.james.backends.cassandra.versions.table.CassandraSchemaVersionTable.TABLE_NAME;
import static org.apache.james.backends.cassandra.versions.table.CassandraSchemaVersionTable.VALUE;

import java.util.Optional;

import javax.inject.Inject;

import org.apache.james.backends.cassandra.utils.CassandraAsyncExecutor;
import org.apache.james.backends.cassandra.versions.table.CassandraSchemaVersionTable;

import com.datastax.driver.core.PreparedStatement;
import com.datastax.driver.core.Session;
import com.datastax.driver.core.utils.UUIDs;
import com.google.common.annotations.VisibleForTesting;

import reactor.core.publisher.Mono;

public class CassandraSchemaVersionDAO {
    private final PreparedStatement readVersionStatement;
    private final PreparedStatement writeVersionStatement;
    private final CassandraAsyncExecutor cassandraAsyncExecutor;

    @Inject
    public CassandraSchemaVersionDAO(Session session) {
        cassandraAsyncExecutor = new CassandraAsyncExecutor(session);
        readVersionStatement = prepareReadVersionStatement(session);
        writeVersionStatement = prepareWriteVersionStatement(session);
    }

    private PreparedStatement prepareReadVersionStatement(Session session) {
        return session.prepare(
            select(VALUE)
                .from(TABLE_NAME));
    }

    private PreparedStatement prepareWriteVersionStatement(Session session) {
        return session.prepare(
            insertInto(CassandraSchemaVersionTable.TABLE_NAME)
                .value(KEY, bindMarker(KEY))
                .value(VALUE, bindMarker(VALUE)));
    }

    public Mono<Optional<SchemaVersion>> getCurrentSchemaVersion() {
        return cassandraAsyncExecutor.executeRows(readVersionStatement.bind())
            .map(row -> row.getInt(VALUE))
            .reduce(Math::max)
            .map(SchemaVersion::new)
            .map(Optional::of)
            .defaultIfEmpty(Optional.empty());
    }

    public Mono<Void> updateVersion(SchemaVersion newVersion) {
        return cassandraAsyncExecutor.executeVoid(
            writeVersionStatement.bind()
                .setUUID(KEY, UUIDs.timeBased())
                .setInt(VALUE, newVersion.getValue()));
    }

    @VisibleForTesting
    public Mono<Void> truncateVersion() {
        return cassandraAsyncExecutor.executeVoid(truncate(TABLE_NAME));
    }
}

