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

import static org.apache.james.util.ReactorUtils.DEFAULT_CONCURRENCY;

import java.util.function.Predicate;

import javax.inject.Inject;

import org.apache.james.backends.cassandra.components.CassandraModule;
import org.apache.james.backends.cassandra.components.CassandraTable;
import org.apache.james.backends.cassandra.components.CassandraTable.InitializationStatus;
import org.apache.james.backends.cassandra.utils.CassandraAsyncExecutor;

import com.datastax.driver.core.KeyspaceMetadata;
import com.datastax.driver.core.PagingIterable;
import com.datastax.driver.core.Session;
import com.datastax.driver.core.querybuilder.QueryBuilder;

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.core.scheduler.Schedulers;

public class CassandraTableManager {

    private final Session session;
    private final CassandraModule module;

    @Inject
    public CassandraTableManager(CassandraModule module, Session session) {
        this.session = session;
        this.module = module;
    }

    public InitializationStatus initializeTables() {
        KeyspaceMetadata keyspaceMetadata = session.getCluster()
            .getMetadata()
            .getKeyspace(session.getLoggedKeyspace());

        return module.moduleTables()
                .stream()
                .map(table -> table.initialize(keyspaceMetadata, session))
                .reduce((left, right) -> left.reduce(right))
                .orElse(InitializationStatus.ALREADY_DONE);
    }

    public void clearAllTables() {
        CassandraAsyncExecutor executor = new CassandraAsyncExecutor(session);
        Flux.fromIterable(module.moduleTables())
                .publishOn(Schedulers.elastic())
                .map(CassandraTable::getName)
                .flatMap(name -> truncate(executor, name), DEFAULT_CONCURRENCY)
                .then()
                .block();
    }

    private Mono<Void> truncate(CassandraAsyncExecutor executor, String name) {
        return executor.execute(
                QueryBuilder.select()
                        .from(name)
                        .limit(1)
                        .setFetchSize(1))
                .filter(Predicate.not(PagingIterable::isExhausted))
                .flatMap(ignored -> executor.executeVoid(QueryBuilder.truncate(name)));
    }
}
