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/**
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 *
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 */
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package in.shop2020.metamodel.util;
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import in.shop2020.util.DBUtils;
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import in.shop2020.util.Utils;
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import java.io.File;
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import java.io.Serializable;
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import java.util.Arrays;
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/**
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 * Utility class to generate unique numbers
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 *
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 * @author naveen
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 *
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 *
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 */
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public class SequenceGenerator implements Serializable {
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	/**
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	 *
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	 */
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	private static final long serialVersionUID = 1L;
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	/**
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	 * Entity object's starting sequence number
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	 */
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	public static final int ENTITY = 0;
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	/**
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	 * Singleton instance that is de-serialized from file on the disk
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	 *
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	 * @return 	SequenceGenerator 	instance of SequenceGenerator
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	 * @throws Exception
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	 */
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	public static final SequenceGenerator getInstance() throws Exception {
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		// De-serialize
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		String dbFile = Utils.CONTENT_DB_PATH + "entities" + File.separator + "sequence.ser";
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		SequenceGenerator sequenceGenerator =
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			(SequenceGenerator) DBUtils.read(dbFile);
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		if(sequenceGenerator == null) {
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			sequenceGenerator = new SequenceGenerator();
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		}
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		return sequenceGenerator;
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	}
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	/**
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	 * Instance member that records all current counts
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	 */
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	private long[] currentCounts = null;
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	/**
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	 * A private Constructor prevents any other class from instantiating. All
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	 * objects that need dynamic sequence generation need to provide starting
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	 * number here.
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	 */
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	private SequenceGenerator() {
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		this.currentCounts = new long[1];
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		// Set initial values
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		this.currentCounts[ENTITY] = 1000000;
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	}
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	/**
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	 * Client of the class call this method to get new sequence number.
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	 * Once a sequence number if fetched it cannot be undone.
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	 *
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	 * @param index
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	 * @return currentCount
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	 * @throws Exception
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	 */
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	public long getNextSequence(int index) throws Exception {
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		// Increment
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		this.currentCounts[index]++;
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		// Store back
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		String dbFile = Utils.CONTENT_DB_PATH + "entities" + File.separator + "sequence.ser";
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		DBUtils.store(this, dbFile);
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		return this.currentCounts[index];
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	}
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	/* (non-Javadoc)
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	 * @see java.lang.Object#toString()
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	 */
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	@Override
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	public String toString() {
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		return "SequenceGenerator [currentCounts="
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				+ Arrays.toString(currentCounts) + "]";
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	}
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}