/*

  * #%L

  * CursorStreamingCallback.java - mongodb-async-driver - Allanbank Consulting, Inc.

  * %%

  * Copyright (C) 2011 - 2014 Allanbank Consulting, 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.

  * #L%

  */

 package com.allanbank.mongodb.client.callback;

 import java.util.List;

 import com.allanbank.mongodb.MongoCursorControl;

 import com.allanbank.mongodb.MongoDbException;

 import com.allanbank.mongodb.ReadPreference;

 import com.allanbank.mongodb.StreamCallback;

 import com.allanbank.mongodb.bson.Document;

 import com.allanbank.mongodb.bson.NumericElement;

 import com.allanbank.mongodb.bson.builder.BuilderFactory;

 import com.allanbank.mongodb.bson.builder.DocumentBuilder;

 import com.allanbank.mongodb.bson.element.StringElement;

 import com.allanbank.mongodb.client.Client;

 import com.allanbank.mongodb.client.MongoIteratorImpl;

 import com.allanbank.mongodb.client.message.CursorableMessage;

 import com.allanbank.mongodb.client.message.GetMore;

 import com.allanbank.mongodb.client.message.KillCursors;

 import com.allanbank.mongodb.client.message.Query;

 import com.allanbank.mongodb.client.message.Reply;

 import com.allanbank.mongodb.error.ReplyException;

 /**

  * Callback to convert a {@link CursorableMessage} {@link Reply} into a series

  * of callback for each document received.

  * 

  * @api.no This class is <b>NOT</b> part of the drivers API. This class may be

  *         mutated in incompatible ways between any two releases of the driver.

  * @copyright 2012-2014, Allanbank Consulting, Inc., All Rights Reserved

  */

 public final class CursorStreamingCallback extends

         AbstractValidatingReplyCallback implements MongoCursorControl,

         AddressAware {

     /** The server the original request was sent to. */

     private volatile String myAddress;

     /** The requested batch size. */

     private int myBatchSize;

     /** The original query. */

     private final Client myClient;

     /**

      * Flag to indictate that the stream has been closed.

      */

     private volatile boolean myClosed = false;

     /** The name of the collection the query was originally created on. */

     private final String myCollectionName;

     /** If true then the callback should expect a command formated cursor reply. */

     private boolean myCommand;

     /** The original query. */

     private long myCursorId = 0;

     /** The name of the database the query was originally created on. */

     private final String myDatabaseName;

     /** The callback to forward the returned documents to. */

     private final StreamCallback<Document> myForwardCallback;

     /**

      * The maximum number of document to return from the cursor. Zero or

      * negative means all.

      */

     private int myLimit = 0;

     /** The original message that started the cursor, if known. */

     private final CursorableMessage myMessage;

     /** The last reply. */

     private volatile Reply myReply;

     /**

      * Flag to shutdown this iterator gracefully without closing the cursor on

      * the server.

      */

     private boolean myShutdown = false;

     /**

      * Create a new CursorCallback.

      * 

      * @param client

      *            The client interface to the server.

      * @param originalMessage

      *            The original message.

      * @param command

      *            If true then the callback should expect a command formated

      *            cursor reply.

      * @param results

      *            The callback to update with each document.

      */

     public CursorStreamingCallback(final Client client,

             final CursorableMessage originalMessage, final boolean command,

             final StreamCallback<Document> results) {

         myClient = client;

         myDatabaseName = originalMessage.getDatabaseName();

         myCollectionName = originalMessage.getCollectionName();

         myBatchSize = originalMessage.getBatchSize();

         myMessage = originalMessage;

         myCommand = command;

         myForwardCallback = results;

         myLimit = originalMessage.getLimit();

     }

     /**

      * Create a new CursorCallback from a cursor document.

      * 

      * @param client

      *            The client interface to the server.

      * @param cursorDocument

      *            The original query.

      * @param results

      *            The callback to update with each document.

      * 

      * @see MongoIteratorImpl#asDocument()

      */

     public CursorStreamingCallback(final Client client,

             final Document cursorDocument,

             final StreamCallback<Document> results) {

         final String ns = cursorDocument.get(StringElement.class,

                 NAME_SPACE_FIELD).getValue();

         String db = ns;

         String collection = ns;

         final int index = ns.indexOf('.');

         if (0 < index) {

             db = ns.substring(0, index);

             collection = ns.substring(index + 1);

         }

         myMessage = null;

         myCommand = false;

         myClient = client;

         myDatabaseName = db;

         myCollectionName = collection;

         myForwardCallback = results;

         myCursorId = cursorDocument.get(NumericElement.class, CURSOR_ID_FIELD)

                 .getLongValue();

         myLimit = cursorDocument.get(NumericElement.class, LIMIT_FIELD)

                 .getIntValue();

         myBatchSize = cursorDocument

                 .get(NumericElement.class, BATCH_SIZE_FIELD).getIntValue();

         myAddress = cursorDocument.get(StringElement.class, SERVER_FIELD)

                 .getValue();

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to return the current state of the stream as a document.

      * </p>

      */

     @Override

     public Document asDocument() {

         final long cursorId = myCursorId;

         if (cursorId != 0) {

             final DocumentBuilder b = BuilderFactory.start();

             b.add(NAME_SPACE_FIELD, myDatabaseName + "." + myCollectionName);

             b.add(CURSOR_ID_FIELD, cursorId);

             b.add(SERVER_FIELD, myAddress);

             b.add(LIMIT_FIELD, myLimit);

             b.add(BATCH_SIZE_FIELD, myBatchSize);

             return b.build();

         }

         return null;

     }

     /**

      * Overridden to close the iterator and send a {@link KillCursors} for the

      * open cursor, if any.

      */

     @Override

     public void close() {

         synchronized (myForwardCallback) {

             myClosed = true;

             sendKill();

         }

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to forward the error the the user.

      * </p>

      */

     @Override

     public void exception(final Throwable thrown) {

         try {

             synchronized (myForwardCallback) {

                 myForwardCallback.exception(thrown);

             }

         }

         finally {

             close();

         }

     }

     /**

      * Returns the server the original request was sent to.

      * 

      * @return The server the original request was sent to.

      */

     public String getAddress() {

         return myAddress;

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to set the batch size.

      * </p>

      */

     @Override

     public int getBatchSize() {

         return myBatchSize;

     }

     /**

      * Returns the client value.

      * 

      * @return The client value.

      */

     public Client getClient() {

         return myClient;

     }

     /**

      * Returns the collection name.

      * 

      * @return The collection name.

      */

     public String getCollectionName() {

         return myCollectionName;

     }

     /**

      * Returns the cursor Id value.

      * 

      * @return The cursor Id value.

      */

     public long getCursorId() {

         return myCursorId;

     }

     /**

      * Returns the database name value.

      * 

      * @return The database name value.

      */

     public String getDatabaseName() {

         return myDatabaseName;

     }

     /**

      * Returns the limit value.

      * 

      * @return The limit value.

      */

     public int getLimit() {

         return myLimit;

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to return false.

      * </p>

      */

     @Override

     public boolean isLightWeight() {

         return false;

     }

     /**

      * Restarts the stream by sending a request for the next batch of documents.

      * 

      * @throws MongoDbException

      *             On a failure to send the request for more document.

      */

     public void restart() {

         sendRequest();

     }

     /**

      * Sets the value of the server the original request was sent to.

      * 

      * @param address

      *            The new value for the server the original request was sent to.

      */

     @Override

     public void setAddress(final String address) {

         myAddress = address;

         // For races make sure that the push has the server name.

         if (myReply != null) {

             final Reply reply = myReply;

             myReply = null;

             push(reply);

         }

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to get the batch size.

      * </p>

      */

     @Override

     public void setBatchSize(final int batchSize) {

         myBatchSize = batchSize;

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to stop requesting more batches of documents.

      * </p>

      */

     @Override

     public void stop() {

         myShutdown = true;

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to add the {@link Query} to the exception.

      * </p>

      * 

      * @see AbstractReplyCallback#asError(Reply, int, int, String)

      */

     @Override

     protected MongoDbException asError(final Reply reply, final int okValue,

             final int errorNumber, final String errorMessage) {

         return new ReplyException(okValue, errorNumber, errorMessage,

                 myMessage, reply);

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to push the documents to the application's callback.

      * </p>

      * 

      * @see AbstractReplyCallback#convert(Reply)

      */

     @Override

     protected void handle(final Reply reply) throws MongoDbException {

         // Handle the first reply being from a command.

         Reply result = reply;

         if (isCommand()) {

             result = CommandCursorTranslator.translate(reply);

             // But only the first reply...

             myCommand = false;

         }

         myReply = result;

         if (myAddress != null) {

             push(result);

         }

     }

     /**

      * Returns true if the callback should expect a command formated cursor

      * reply.

      * 

      * @return True if the callback should expect a command formated cursor

      *         reply.

      */

     protected boolean isCommand() {

         return myCommand;

     }

     /**

      * Loads more documents. This issues a get_more command as soon as the

      * previous results start to be used.

      * 

      * @param reply

      *            The last reply received.

      * @return The list of loaded documents.

      * 

      * @throws RuntimeException

      *             On a failure to load documents.

      */

     protected List<Document> loadDocuments(final Reply reply)

             throws RuntimeException {

         myCursorId = reply.getCursorId();

         // Setup the documents and adjust the limit for the documents we have.

         // Do this before the fetch again so the nextBatchSize() has the updated

         // limit.

         List<Document> docs = reply.getResults();

         if (0 < myLimit) {

             // Check if we have too many docs.

             if (myLimit <= docs.size()) {

                 docs = docs.subList(0, myLimit);

                 close();

             }

             myLimit -= docs.size();

         }

         // Pre-fetch the next set of documents while we iterate over the

         // documents we just got.

         if ((myCursorId != 0) && !myShutdown) {

             sendRequest();

         }

         // Exhausted the cursor - no more results.

         // Don't need to kill the cursor since we exhausted it.

         return docs;

     }

     /**

      * Computes the size for the next batch of documents to get.

      * 

      * @return The returnNex

      */

     protected int nextBatchSize() {

         if ((0 < myLimit) && (myLimit <= myBatchSize)) {

             return myLimit;

         }

         return myBatchSize;

     }

     /**

      * Sends a {@link KillCursors} message if there is an active cursor.

      * 

      * @throws MongoDbException

      *             On a failure to send the {@link KillCursors} message.

      */

     protected void sendKill() throws MongoDbException {

         final long cursorId = myCursorId;

         if ((cursorId != 0) && !myShutdown) {

             myCursorId = 0;

             myClient.send(new KillCursors(new long[] { cursorId },

                     ReadPreference.server(myAddress)), null);

         }

     }

     /**

      * Sends a request to start the next match of documents.

      * 

      * @throws MongoDbException

      *             On a failure to send the request.

      */

     protected void sendRequest() throws MongoDbException {

         final GetMore getMore = new GetMore(myDatabaseName, myCollectionName,

                 myCursorId, nextBatchSize(), ReadPreference.server(myAddress));

         myClient.send(getMore, this);

     }

     /**

      * Pushes the results from the reply to the application's callback.

      * 

      * @param reply

      *            The reply containing the results to push to the application's

      *            callback.

      */

     private void push(final Reply reply) {

         // Request the load in the synchronized block so there is only 1

         // outstanding request.

         synchronized (myForwardCallback) {

             if (myClosed) {

                 myCursorId = reply.getCursorId();

                 sendKill();

             }

             else {

                 try {

                     for (final Document document : loadDocuments(reply)) {

                         myForwardCallback.callback(document);

                     }

                     if (myCursorId == 0) {

                         // Signal the end of the results.

                         myForwardCallback.done();

                     }

                 }

                 catch (final RuntimeException re) {

                     exception(re);

                     close();

                 }

             }

         }

     }

 }