Tennis Game

<html>

<canvas id="gameCanvas" width="1350" height="640"></canvas>

<script>
var canvas;
var canvasContext;
var ballX = 50;
var ballY = 50;
var ballSpeedX = 10;
var ballSpeedY = 5;

var player1Score = 0
var player2Score = 0
const WINNING_SCORE = 3;

var showingWinScreen = false;

var paddle1Y = 250;
var paddle2Y = 250;
const PADDLE_THICKNESS = 10;
const PADDLE_HEIGHT = 100;

function calculateMousePos(evt) {
                var rect = canvas.getBoundingClientRect();
                var root = document.documentElement;
                var mouseX = evt.clientX - rect.left  - root.scrollLeft;
                var mouseY = evt.clientY - rect.top  - root.scrollTop;
                return  {
                              x:mouseX,
                              y:mouseY
                };
}

function handleMouseClick(evt) {
                if(showingWinScreen) {
                              player1Score = 0;
                              player2Score = 0;
                              showingWinScreen = false;
                }
}

window.onload = function() {
                console.log("Hello World!");
                canvas = document.getElementById('gameCanvas');
                canvasContext = canvas.getContext('2d');

                var framesPerSecond = 30
                setInterval(function() {
                            moveEverything();
                            drawEverything();
                }, 1000/framesPerSecond);


                canvas.addEventListener('mousedown',handleMouseClick);

                canvas.addEventListener('mousemove',
                               function(evt) {
                                             var mousePos = calculateMousePos(evt);
                                             paddle1Y = mousePos.y-(PADDLE_HEIGHT/2);
                })
}

function ballReset() {
             if(player1Score >= WINNING_SCORE ||
                 player2Score >= WINNING_SCORE) {
                          showingWinScreen = true
             }
             ballSpeedX = -ballSpeedX;
             ballX = canvas.width/2;
             ballY = canvas.height/2;
}

function computerMovement() {
             var paddle2YCenter = paddle2Y + (PADDLE_HEIGHT/2);
             if(paddle2YCenter < ballY-35) {
                         paddle2Y += 6;
             } else  if(paddle2YCenter > ballY+35) {
                         paddle2Y -= 6;
             }
}

function moveEverything() {
             if(showingWinScreen) {
                           return;
}
             computerMovement();
             ballX += ballSpeedX;
             ballY += ballSpeedY;

             if(ballX < 0) {
                                  if(ballY > paddle1Y &&
                                      ballY < paddle1Y+PADDLE_HEIGHT) {
                                              ballSpeedX = -ballSpeedX;

                                              var deltaY = ballY - (paddle1Y+PADDLE_HEIGHT/2);
                                              ballSpeedY = deltaY * 0.35;
                                  } else {
                                  player2Score += 1;
                                  ballReset();
                                  }
             }
             if(ballX > canvas.width) {
                                  if(ballY > paddle2Y &&
                                      ballY < paddle2Y+PADDLE_HEIGHT) {
                                              ballSpeedX = -ballSpeedX;

                                              var deltaY = ballY - (paddle2Y+PADDLE_HEIGHT/2);
                                              ballSpeedY = deltaY * 0.35;
                                  } else {
                                  player1Score++;
                                  ballReset();
                                  }
             }
             if(ballY < 0) {
                                  ballSpeedY = -ballSpeedY;
             }
             if(ballY > canvas.height) {
                                  ballSpeedY = -ballSpeedY;
             }
}

function drawNet() {
            for(var i=0;i<canvas.height; i+=40) {
                           colorRect(canvas.width/2-1,i,2,20, 'white');
            }
}

function drawEverything() {
            // background
            colorRect(0,0,canvas.width,canvas.height,'black');

            if(showingWinScreen) {
                           canvasContext.fillStyle = 'white';

                           if(player1Score >= WINNING_SCORE) {
                           canvasContext.fillText("Player Won", 650,200);
                           } else if(player2Score >= WINNING_SCORE) {
                           canvasContext.fillText("Computer Won", 650,200);
                           }
                           canvasContext.fillText("Click to continue", 637,480);
                           return;
}

            // net
            drawNet();

            // left player paddle
            colorRect(0,paddle1Y,PADDLE_THICKNESS,PADDLE_HEIGHT,'white');

            // right computer paddle
            colorRect(canvas.width-PADDLE_THICKNESS,paddle2Y,PADDLE_THICKNESS,PADDLE_HEIGHT,'white');

            // ball
            colorCircle(ballX, ballY, 10, 'white');

            canvasContext.fillText(player1Score, 100,100);
            canvasContext.fillText(player2Score, canvas.width - 100,100);
}

function colorCircle(centerX, centerY, radius, drawColor) {
            canvasContext.fillStyle = drawColor;
            canvasContext.beginPath();
            canvasContext.arc(centerX, centerY, radius, 0,Math.PI*2, true);
            canvasContext.fill();
}

function colorRect(leftX,topY, width,height, drawColor) {
            canvasContext.fillStyle = drawColor;
            canvasContext.fillRect(leftX,topY, width,height);
}

</script>

</html>