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package prerna.util;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Enumeration;
import java.util.Hashtable;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

import prerna.engine.impl.rdbms.RDBMSNativeEngine;
import prerna.util.sql.AbstractSqlQueryUtil;

public class PersistentHash {

	private static final Logger classLogger = LogManager.getLogger(PersistentHash.class);

	// simple hash table that saves and gets values from the database
	private static final String TABLE_NAME = "KVSTORE";

	private RDBMSNativeEngine engine = null;

	public Hashtable thisHash = new Hashtable();
	boolean dirty = false;

	public PersistentHash() {

	}

	public void setEngine(RDBMSNativeEngine engine) {
		this.engine = engine;
	}

	public void load() {
		if (engine == null) {
			return;
		}
		
		// this is only for local master!!!
		Connection conn = null;
		try {
			conn = engine.getConnection();
			try (Statement stmt = conn.createStatement()) {
				ResultSet rs = stmt.executeQuery("SELECT K, V from " + TABLE_NAME);
				while(rs.next()) {
					this.thisHash.put(rs.getString(1),rs.getString(2));
				}	
			}
		} catch (SQLException e) {
			classLogger.error(Constants.STACKTRACE, e);
		} finally {
			try {
				if (engine.isConnectionPooling() && conn != null) {
					conn.close();
				}
			} catch (SQLException e) {
				classLogger.error(Constants.STACKTRACE, e);
			}
		}
	}

	public void put(String key, String value) {
		this.thisHash.put(key, value);
		dirty = true;
	}

	public boolean containsKey(String key) {
		return this.thisHash.containsKey(key);
	}

	public String get(String key) {
		return this.thisHash.get(key);
	}

	public void persistBack() {
		if(engine != null && this.dirty) {
			Connection conn = null;
			Statement stmt = null;
			PreparedStatement ps = null;
			try {
				conn = engine.getConnection();
				stmt = conn.createStatement();
				stmt.execute("DELETE FROM " + TABLE_NAME);
				Enumeration  keys = thisHash.keys();
				ps = conn.prepareStatement("INSERT KVSTORE(K, V) VALUES(?, ?)");
				while(keys.hasMoreElements()) {
					String key = keys.nextElement();
					String value = thisHash.get(key);
					int parameterIndex = 1;
					ps.setString(parameterIndex++, key);
					ps.setString(parameterIndex++, value);
					ps.addBatch();
				}
				ps.executeBatch();
				if(!ps.getConnection().getAutoCommit()) {
					ps.getConnection().commit();
				}
				this.dirty = false;
			} catch(Exception e) {
				classLogger.error(Constants.STACKTRACE, e);
			} finally {
				ConnectionUtils.closeStatement(stmt);
				ConnectionUtils.closeAllConnectionsIfPooling(engine, ps);
			}
		}
	}

	/**
	 * See if we can init the persistent hash
	 * @param engine
	 * @return
	 */
	public static boolean canInit(RDBMSNativeEngine engine, Connection conn) {
		try {
			if(engine == null) {
				return false;
			}
			
			AbstractSqlQueryUtil queryUtil = engine.getQueryUtil();
			if(queryUtil == null) {
				return false;
			}
			// make sure the KVSTORE table exists
			return queryUtil.tableExists(conn, TABLE_NAME, engine.getDatabase(), engine.getSchema());
		} catch (Exception e) {
			classLogger.error(Constants.STACKTRACE, e);
		} finally {
			try {
				if(engine.isConnectionPooling() && conn != null) {
					conn.close();
				}
			} catch (SQLException e) {
				classLogger.error(Constants.STACKTRACE, e);
			}
		}
		return false;
	}
}