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package org.normandra.cassandra;

import com.datastax.driver.core.*;
import com.datastax.driver.core.querybuilder.Delete;
import com.datastax.driver.core.querybuilder.QueryBuilder;
import com.datastax.driver.core.querybuilder.Select;
import org.apache.commons.lang.NullArgumentException;
import org.normandra.AbstractTransactional;
import org.normandra.DatabaseQuery;
import org.normandra.DatabaseSession;
import org.normandra.NormandraException;
import org.normandra.cache.EntityCache;
import org.normandra.data.ColumnAccessor;
import org.normandra.meta.ColumnMeta;
import org.normandra.meta.EntityMeta;
import org.normandra.util.EntityPersistence;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.Serializable;
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.stream.Collectors;

/**
 * a cassandra database session
 * <p>
 * <p>
 * Date: 2/1/14
 */
public class CassandraDatabaseSession extends AbstractTransactional implements DatabaseSession {
    private static final Logger logger = LoggerFactory.getLogger(CassandraDatabaseSession.class);

    private final String keyspaceName;

    private final Session session;

    private final EntityCache cache;

    private final List<RegularStatement> statements = new CopyOnWriteArrayList<>();

    private final Map<String, CassandraPreparedStatement> preparedStatements;

    private final AtomicBoolean closed = new AtomicBoolean(false);

    private final AtomicBoolean activeUnitOfWork = new AtomicBoolean(false);

    private final Executor executor;

    public CassandraDatabaseSession(final String keyspace, final Session session,
            final Map<String, CassandraPreparedStatement> map, final EntityCache cache, final Executor executor) {
        if (null == keyspace || keyspace.isEmpty()) {
            throw new IllegalArgumentException("Keyspace cannot be null/empty.");
        }
        if (null == session) {
            throw new NullArgumentException("session");
        }
        if (null == cache) {
            throw new NullArgumentException("cache");
        }
        if (null == executor) {
            throw new NullArgumentException("executor");
        }
        this.keyspaceName = keyspace;
        this.session = session;
        this.cache = cache;
        this.executor = executor;
        this.preparedStatements = new LinkedHashMap<>(map);
    }

    @Override
    public void close() {
        // do nothing - session is thread safe and can be shared
        this.closed.getAndSet(true);
        this.cache.clear();
    }

    public boolean isClosed() {
        return this.closed.get();
    }

    public String getKeyspace() {
        return this.keyspaceName;
    }

    public Session getSession() {
        return this.session;
    }

    public Cluster getCluster() {
        return this.session.getCluster();
    }

    protected ResultSet executeSync(final Statement statement) {
        final CassandraDatabaseActivity activity = new CassandraDatabaseActivity(statement, this.session);
        return activity.execute();
    }

    protected Future<ResultSet> executeAsync(final Statement statement) {
        final CassandraDatabaseActivity activity = new CassandraDatabaseActivity(statement, this.session);
        final Callable<ResultSet> callable = () -> activity.execute();
        final FutureTask<ResultSet> task = new FutureTask<>(callable);
        this.executor.execute(task);
        return task;
    }

    @Override
    public void clear() {
        this.cache.clear();
    }

    @Override
    public boolean pendingWork() {
        return this.activeUnitOfWork.get();
    }

    @Override
    public void beginWork() throws NormandraException {
        if (this.activeUnitOfWork.get()) {
            throw new IllegalStateException("Unit of work already active.");
        }
        this.activeUnitOfWork.getAndSet(true);
    }

    @Override
    public void commitWork() throws NormandraException {
        if (!this.activeUnitOfWork.get()) {
            throw new IllegalStateException("No active transaction.");
        }
        if (this.statements.isEmpty()) {
            return;
        }
        try {
            for (final RegularStatement statement : this.statements) {
                this.executeSync(statement);
            }
            this.statements.clear();
            this.activeUnitOfWork.getAndSet(false);
        } catch (final Exception e) {
            throw new NormandraException("Unable to commit batch unit of work.", e);
        }
    }

    @Override
    public void rollbackWork() throws NormandraException {
        if (!this.activeUnitOfWork.get()) {
            throw new IllegalStateException("No active transaction.");
        }
        this.statements.clear();
        this.activeUnitOfWork.getAndSet(false);
    }

    @Override
    public boolean exists(final EntityMeta meta, final Object key) throws NormandraException {
        if (this.isClosed()) {
            throw new IllegalStateException("Session is closed.");
        }
        if (null == meta || null == key) {
            return false;
        }

        try {
            final Map<ColumnMeta, Object> columns = meta.getId().fromKey(key);
            final List<String> namelist = columns.keySet().stream().map(ColumnMeta::getName)
                    .collect(Collectors.toList());
            final String[] names = namelist.toArray(new String[namelist.size()]);
            final Select statement = QueryBuilder.select(names).from(this.keyspaceName, meta.getTable()).limit(1);
            boolean hasWhere = false;
            for (final Map.Entry<ColumnMeta, Object> entry : columns.entrySet()) {
                final ColumnMeta property = entry.getKey();
                final Object value = entry.getValue();
                statement.where(QueryBuilder.eq(property.getName(), value));
                hasWhere = true;
            }
            if (!hasWhere) {
                logger.warn("Unable to #exists value without key - empty where statement for type [" + meta + "].");
                return false;
            }

            final ResultSet results = this.executeSync(statement);
            if (null == results) {
                return false;
            }
            final Row row = results.one();
            if (null == row) {
                return false;
            }

            final ColumnDefinitions definitions = row.getColumnDefinitions();
            return definitions != null && definitions.size() > 0;
        } catch (final Exception e) {
            throw new NormandraException("Unable to query entity [" + meta + "] by key [" + key + "].", e);
        }
    }

    @Override
    public Object get(final EntityMeta meta, final Object key) throws NormandraException {
        if (this.isClosed()) {
            throw new IllegalStateException("Session is closed.");
        }
        final CassandraEntityQuery query = new CassandraEntityQuery(this, this.cache);
        return query.query(meta, key);
    }

    @Override
    public List<Object> get(final EntityMeta meta, final Object... keys) throws NormandraException {
        if (this.isClosed()) {
            throw new IllegalStateException("Session is closed.");
        }
        final CassandraEntityQuery query = new CassandraEntityQuery(this, this.cache);
        return query.query(meta, keys);
    }

    @Override
    public void delete(final EntityMeta meta, final Object element) throws NormandraException {
        if (null == element) {
            throw new NullArgumentException("entity");
        }
        if (this.isClosed()) {
            throw new IllegalStateException("Session is closed.");
        }

        try {
            final List<Delete> deletes = new ArrayList<>();
            boolean hasValue = false;
            final Delete statement = QueryBuilder.delete().all().from(this.keyspaceName, meta.getTable());
            for (final ColumnMeta column : meta.getPrimaryKeys()) {
                final String name = column.getName();
                final ColumnAccessor accessor = meta.getAccessor(column);
                final Object value = accessor != null ? accessor.getValue(element, this) : null;
                if (value != null) {
                    hasValue = true;
                    statement.where(QueryBuilder.eq(name, value));
                }
            }
            if (hasValue) {
                deletes.add(statement);
            }
            if (deletes.isEmpty()) {
                throw new NormandraException("No column values found - cannot delete entity.");
            }

            final RegularStatement batch;
            if (deletes.size() == 1) {
                batch = deletes.get(0);
            } else {
                final RegularStatement[] list = deletes.toArray(new RegularStatement[deletes.size()]);
                batch = QueryBuilder.batch(list);
            }

            final Object key = meta.getId().fromEntity(element);
            if (key instanceof Serializable) {
                this.cache.remove(meta, key);
            }

            if (this.activeUnitOfWork.get()) {
                this.statements.add(batch);
            } else {
                this.executeSync(batch);
            }
        } catch (final Exception e) {
            throw new NormandraException("Unable to delete entity [" + element + "] of type [" + meta + "].", e);
        }
    }

    @Override
    public DatabaseQuery query(final EntityMeta meta, final String query, final Map<String, Object> parameters)
            throws NormandraException {
        final CassandraPreparedStatement prepared = this.preparedStatements.get(query);
        if (null == prepared) {
            return new CassandraQueryParser(meta, this).parse(query, parameters);
        } else {
            return new CassandraDatabaseQuery<>(meta, prepared.bind(parameters), this);
        }
    }

    public Object scalarQuery(final String queryOrName) throws NormandraException {
        final CassandraDatabaseQuery query;
        final CassandraPreparedStatement prepared = this.preparedStatements.get(queryOrName);
        if (null == prepared) {
            query = new CassandraQueryParser(null, this).parse(queryOrName, Collections.EMPTY_MAP);
        } else {
            query = new CassandraDatabaseQuery<>(null, null, this);
        }

        final Row row = query.firstRow();
        if (null == row) {
            return null;
        }

        return row.getObject(0);
    }

    @Override
    public void save(final EntityMeta meta, final Object element) throws NormandraException {
        if (this.isClosed()) {
            throw new IllegalStateException("Session is closed.");
        }
        if (null == meta) {
            throw new NullArgumentException("entity metadata");
        }
        if (null == element) {
            throw new NullArgumentException("element");
        }

        try {
            // generate insert/updateInstance statements
            final CassandraDataHandler helper = new CassandraDataHandler(this);
            new EntityPersistence(this).save(meta, element, helper);
            final List<RegularStatement> operations = helper.getOperations();
            if (operations.isEmpty()) {
                throw new IllegalStateException(
                        "No operations or columns identify for update - cannot save empty entity.");
            }
            final RegularStatement batch;
            if (operations.size() == 1) {
                batch = operations.get(0);
            } else {
                final RegularStatement[] list = operations.toArray(new RegularStatement[operations.size()]);
                batch = QueryBuilder.batch(list);
            }
            if (this.activeUnitOfWork.get()) {
                this.statements.add(batch);
            } else {
                this.executeSync(batch);
            }

            final Object key = meta.getId().fromEntity(element);
            this.cache.put(meta, key, element);
        } catch (final Exception e) {
            throw new NormandraException("Unable to save entity [" + meta + "] instance [" + element + "].", e);
        }
    }
}