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Used to provide data for different clients from different sources according to the requirement
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/*
 * Copyright (c) 2017, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
 *
 * WSO2 Inc. licenses this file to you 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 org.wso2.carbon.data.provider;

import com.google.gson.Gson;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.wso2.carbon.data.provider.bean.DataModel;
import org.wso2.carbon.data.provider.bean.DataSetMetadata;
import org.wso2.carbon.data.provider.endpoint.DataProviderEndPoint;
import org.wso2.carbon.data.provider.exception.DataProviderException;

import java.io.IOException;
import java.util.ArrayList;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

/**
 * Abstract data provider class.
 */
public abstract class AbstractDataProvider implements DataProvider {
    private static final Logger LOGGER = LoggerFactory.getLogger(AbstractDataProvider.class);
    private String topic;
    private String sessionId;
    private ScheduledExecutorService dataPublishingExecutorService = Executors.newSingleThreadScheduledExecutor();
    private ScheduledExecutorService dataPurgingExecutorService = Executors.newSingleThreadScheduledExecutor();
    private long publishingInterval;
    private long purgingInterval;
    private boolean isPurgingEnable;
    private boolean isPaginationEnabled;

    public DataProvider init(String topic, String sessionId, ProviderConfig providerConfig)
            throws DataProviderException {
        if (this.configValidator(providerConfig)) {
            this.topic = topic;
            this.sessionId = sessionId;
            this.publishingInterval = providerConfig.getPublishingInterval();
            this.purgingInterval = providerConfig.getPurgingInterval();
            this.isPurgingEnable = providerConfig.isPurgingEnable();
            this.isPaginationEnabled = providerConfig.isPaginationEnabled();
            this.setProviderConfig(providerConfig);
            return this;
        } else {
            throw new DataProviderException("Invalid configuration provided. Unable to complete initialization " +
                    "of data provider.");
        }
    }

    @Override
    public void stop() {
        dataPublishingExecutorService.shutdown();
        dataPurgingExecutorService.shutdown();
    }

    @Override
    public void start() {
        if (!this.isPaginationEnabled) {
            this.dataPublishingExecutorService.scheduleAtFixedRate(() -> {
                this.publish(this.topic, this.sessionId);
            }, 0L, this.publishingInterval, TimeUnit.SECONDS);
        }
        if (isPurgingEnable) {
            dataPublishingExecutorService.scheduleAtFixedRate(() -> {
                purging();
            }, 0, purgingInterval, TimeUnit.SECONDS);
        }
    }

    public void publishToEndPoint(ArrayList data, String sessionId, String topic) {
        DataModel dataModel = new DataModel(getMetadata(), data.toArray(new Object[0][0]), -1, topic);
        try {
            DataProviderEndPoint.sendText(sessionId, new Gson().toJson(dataModel));
        } catch (IOException e) {
            LOGGER.error("Failed to deliver message to client " + e.getMessage(), e);
        }
    }

    @Override
    public abstract boolean configValidator(ProviderConfig providerConfig) throws DataProviderException;

    public abstract void publish(String topic, String sessionId);

    public abstract void purging();

    /**
     * Set the provider configuration, child class will be maintained
     * its own provider configuration bean object.
     *
     * @param providerConfig client provided configuration.
     */
    public abstract void setProviderConfig(ProviderConfig providerConfig);

    /**
     * Get the meta data of the RDBMS provider.
     *
     * @return rdbms meta data object.
     */
    public abstract DataSetMetadata getMetadata();
}