package sql;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Collections;
import java.util.Queue;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedQueue;

import models.Configuration;

import org.apache.log4j.Logger;

public class SQL {

	private static final Logger LOGGER = Logger.getLogger(SQL.class);
	/**
	 * Pool of available connections.
	 */
	private static final Queue<MysqlConnection> pool = new ConcurrentLinkedQueue<>();

	/**
	 * Set of connections currently handed out.
	 */
	private static final Set<MysqlConnection> busyConnections = Collections.newSetFromMap(new ConcurrentHashMap<MysqlConnection, Boolean>());

	static {
		try {
			Class.forName("com.mysql.jdbc.Driver").newInstance();
		} catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {
			LOGGER.fatal("Cannot get mysql JDBC driver!", e);
			System.exit(1);
		}
	}

	public static MysqlConnection getConnection() {
		MysqlConnection con;
		for (;;) {
			con = pool.poll();
			if (con == null)
				break;
			if (!con.isValid()) {
				con.release();
				continue;
			}
			if (!busyConnections.add(con))
				throw new RuntimeException("Tried to hand out a busy connection!");
			return con;
		}
		// No pooled connection
		if (busyConnections.size() > 20) {
			LOGGER.warn("Too many open MySQL connections. Possible connection leak!");
			return null;
		}
		try {
			// Create fresh connection
			Connection rawConnection = DriverManager.getConnection(Configuration.getDbUri(),
					Configuration.getDbUsername(), Configuration.getDbPassword());
			// By convention in our program we don't want auto commit
			rawConnection.setAutoCommit(false);
			// Wrap into our proxy
			con = new MysqlConnection(rawConnection);
			// Keep track of busy mysql connection
			if (!busyConnections.add(con))
				throw new RuntimeException("Tried to hand out a busy connection!");
			return con;
		} catch (SQLException e) {
			LOGGER.info("Failed to connect to local mysql server", e);
		}
		return null;
	}

	static void returnConnection(MysqlConnection connection) {
		if (!busyConnections.remove(connection))
			throw new RuntimeException("Tried to return a mysql connection to the pool that was not taken!");
		pool.add(connection);
	}

}// end class