package com.atypon.registration.helper;

import java.sql.Connection;
import java.sql.DriverManager;
import java.util.ArrayList;

/**
 * This class will help us to reuse connections rather than create new one each time a connection is requested
 *
 * @author Ibrahim Al-Bzour
 * @version 1.0
 */

public class ConnectionPool {

    // make ConnectionPool class as singleton because we need only one object of type ConnectionPool
    private static ConnectionPool instance = new ConnectionPool();
    private final int MAX_POOL_SIZE = 20;
    private String driverName, url, username, password;
    private ArrayList<Connection> connectionPool = new ArrayList<>();
    private boolean isWaiting = false;

    private ConnectionPool() {
        this.url = Constants.DB_URL;
        this.username = Constants.DB_USERNAME;
        this.password = Constants.DB_PASSWORD;
        this.driverName = Constants.DB_DRIVER;

        while (!checkIfConnectionPoolIsFull()) {
            //Adding new connection instance until the pool is full
            Connection connection = createNewConnectionForPool();
            if (connection != null)
                connectionPool.add(createNewConnectionForPool());
            else
                break;
        }
    }

    public static ConnectionPool getInstance() {
        return instance;
    }

    private boolean checkIfConnectionPoolIsFull() {
        // Check if the pool is full
        return connectionPool.size() > MAX_POOL_SIZE;
    }

    // Creating a connection
    private Connection createNewConnectionForPool() {
        Connection connection;
        try {
            Class.forName(driverName);
            connection = DriverManager.getConnection(url, username, password);
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
        return connection;
    }

    public Connection getConnectionFromPool() throws InterruptedException {
        Connection connection = null;
        synchronized (this) {
            if (connectionPool.isEmpty()) {
                isWaiting = true;
                wait();
            }
            connection = connectionPool.get(0);
            connectionPool.remove(0);

        }
        //Giving away the connection from the connection pool
        return connection;
    }

    public void returnConnectionToPool(Connection connection) {
        //Adding the connection from the client back to the connection pool
        synchronized (this) {
            connectionPool.add(connection);
            if (isWaiting) {
                notify();
                isWaiting = false;
            }
        }
    }
}