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A Reactive Streams implementation of the MongoDB Java driver
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/*
 * Copyright 2008-present MongoDB, Inc.
 *
 * 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
 *
 *   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 com.mongodb.reactivestreams.client.internal;

import com.mongodb.ReadConcern;
import com.mongodb.ReadPreference;
import com.mongodb.connection.ClusterType;
import com.mongodb.connection.ServerDescription;
import com.mongodb.internal.async.SingleResultCallback;
import com.mongodb.internal.async.function.AsyncCallbackSupplier;
import com.mongodb.internal.binding.AbstractReferenceCounted;
import com.mongodb.internal.binding.AsyncClusterAwareReadWriteBinding;
import com.mongodb.internal.binding.AsyncConnectionSource;
import com.mongodb.internal.binding.AsyncReadWriteBinding;
import com.mongodb.internal.binding.TransactionContext;
import com.mongodb.internal.connection.AsyncConnection;
import com.mongodb.internal.connection.OperationContext;
import com.mongodb.internal.session.ClientSessionContext;
import com.mongodb.lang.Nullable;
import com.mongodb.reactivestreams.client.ClientSession;
import org.bson.BsonTimestamp;

import static com.mongodb.assertions.Assertions.assertNotNull;
import static com.mongodb.assertions.Assertions.notNull;
import static com.mongodb.connection.ClusterType.LOAD_BALANCED;
import static com.mongodb.connection.ClusterType.SHARDED;

/**
 * This class is not part of the public API and may be removed or changed at any time
 */
public class ClientSessionBinding extends AbstractReferenceCounted implements AsyncReadWriteBinding {
    private final AsyncClusterAwareReadWriteBinding wrapped;
    private final ClientSession session;
    private final boolean ownsSession;
    private final OperationContext operationContext;

    public ClientSessionBinding(final ClientSession session, final boolean ownsSession, final AsyncClusterAwareReadWriteBinding wrapped) {
        this.wrapped = notNull("wrapped", wrapped).retain();
        this.ownsSession = ownsSession;
        this.session = notNull("session", session);
        this.operationContext = wrapped.getOperationContext().withSessionContext(new AsyncClientSessionContext(session));
    }

    @Override
    public ReadPreference getReadPreference() {
        return wrapped.getReadPreference();
    }

    @Override
    public OperationContext getOperationContext() {
        return operationContext;
    }

    @Override
    public void getReadConnectionSource(final SingleResultCallback callback) {
        getConnectionSource(wrapped::getReadConnectionSource, callback);
    }

    @Override
    public void getReadConnectionSource(final int minWireVersion, final ReadPreference fallbackReadPreference,
            final SingleResultCallback callback) {
        getConnectionSource(wrappedConnectionSourceCallback ->
                wrapped.getReadConnectionSource(minWireVersion, fallbackReadPreference, wrappedConnectionSourceCallback),
                callback);
    }

    public void getWriteConnectionSource(final SingleResultCallback callback) {
        getConnectionSource(wrapped::getWriteConnectionSource, callback);
    }

    private void getConnectionSource(final AsyncCallbackSupplier connectionSourceSupplier,
            final SingleResultCallback callback) {
        WrappingCallback wrappingCallback = new WrappingCallback(callback);

        if (!session.hasActiveTransaction()) {
            connectionSourceSupplier.get(wrappingCallback);
            return;
        }
        if (TransactionContext.get(session) == null) {
            connectionSourceSupplier.get((source, t) -> {
                if (t != null) {
                    wrappingCallback.onResult(null, t);
                } else {
                    ClusterType clusterType = assertNotNull(source).getServerDescription().getClusterType();
                    if (clusterType == SHARDED || clusterType == LOAD_BALANCED) {
                        TransactionContext transactionContext = new TransactionContext<>(clusterType);
                        session.setTransactionContext(source.getServerDescription().getAddress(), transactionContext);
                        transactionContext.release();  // The session is responsible for retaining a reference to the context
                    }
                    wrappingCallback.onResult(source, null);
                }
            });
        } else {
            wrapped.getConnectionSource(assertNotNull(session.getPinnedServerAddress()), wrappingCallback);
        }
    }

    @Override
    public AsyncReadWriteBinding retain() {
        super.retain();
        return this;
    }

    @Override
    public int release() {
        int count = super.release();
        if (count == 0) {
            wrapped.release();
            if (ownsSession) {
                session.close();
            }
        }
        return count;
    }

    private class SessionBindingAsyncConnectionSource implements AsyncConnectionSource {
        private AsyncConnectionSource wrapped;

        SessionBindingAsyncConnectionSource(final AsyncConnectionSource wrapped) {
            this.wrapped = wrapped;
            ClientSessionBinding.this.retain();
        }

        @Override
        public ServerDescription getServerDescription() {
            return wrapped.getServerDescription();
        }

        @Override
        public OperationContext getOperationContext() {
            return operationContext;
        }

        @Override
        public ReadPreference getReadPreference() {
            return wrapped.getReadPreference();
        }

        @Override
        public void getConnection(final SingleResultCallback callback) {
            TransactionContext transactionContext = TransactionContext.get(session);
            if (transactionContext != null && transactionContext.isConnectionPinningRequired()) {
                AsyncConnection pinnedConnection = transactionContext.getPinnedConnection();
                if (pinnedConnection == null) {
                    wrapped.getConnection((connection, t) -> {
                        if (t != null) {
                            callback.onResult(null, t);
                        } else {
                            transactionContext.pinConnection(assertNotNull(connection), AsyncConnection::markAsPinned);
                            callback.onResult(connection, null);
                        }
                    });
                } else {
                    callback.onResult(pinnedConnection.retain(), null);
                }
            } else {
                wrapped.getConnection(callback);
            }
        }

        @Override
        public AsyncConnectionSource retain() {
            wrapped = wrapped.retain();
            return this;
        }

        @Override
        public int getCount() {
            return wrapped.getCount();
        }

        @Override
        public int release() {
            int count = wrapped.release();
            if (count == 0) {
                ClientSessionBinding.this.release();
            }
            return count;
        }
    }

    private final class AsyncClientSessionContext extends ClientSessionContext {

        private final ClientSession clientSession;

        AsyncClientSessionContext(final ClientSession clientSession) {
            super(clientSession);
            this.clientSession = clientSession;
        }


        @Override
        public boolean isImplicitSession() {
            return ownsSession;
        }

        @Override
        public boolean notifyMessageSent() {
            return clientSession.notifyMessageSent();
        }

        @Override
        public boolean isSnapshot() {
            Boolean snapshot = clientSession.getOptions().isSnapshot();
            return snapshot != null && snapshot;
        }

        @Override
        public void setSnapshotTimestamp(@Nullable final BsonTimestamp snapshotTimestamp) {
            clientSession.setSnapshotTimestamp(snapshotTimestamp);
        }

        @Override
        @Nullable
        public BsonTimestamp getSnapshotTimestamp() {
            return clientSession.getSnapshotTimestamp();
        }

        @Override
        public boolean hasActiveTransaction() {
            return clientSession.hasActiveTransaction();
        }

        @Override
        public ReadConcern getReadConcern() {
            if (clientSession.hasActiveTransaction()) {
                return assertNotNull(clientSession.getTransactionOptions().getReadConcern());
            } else if (isSnapshot()) {
                return ReadConcern.SNAPSHOT;
            } else {
                return wrapped.getOperationContext().getSessionContext().getReadConcern();
            }
        }
    }

    private class WrappingCallback implements SingleResultCallback {
        private final SingleResultCallback callback;

        WrappingCallback(final SingleResultCallback callback) {
            this.callback = callback;
        }

        @Override
        public void onResult(@Nullable final AsyncConnectionSource result, @Nullable final Throwable t) {
            if (t != null) {
                callback.onResult(null, t);
            } else {
                callback.onResult(new SessionBindingAsyncConnectionSource(assertNotNull(result)), null);
            }
        }
    }
}