// ------------------------------------------------------
// Using Directives
// ------------------------------------------------------

using System.Collections.Generic;
using System.Windows.Forms;
using System.Drawing;
using System;

// ------------------------------------------------------
// Ball
// ------------------------------------------------------

public class Ball
{
   // ------------------------------------------------------
   // Ball - Create a Ball object using 'size' and 'fill'.
   // The drawing area's 'width' and 'height' are also used
   // ------------------------------------------------------

   public Ball(int size, Brush fill, int width, int height)
   {
      // 'mHeight' and 'mWidth' are used in 'GetX' and 'GetY'
      // so ensure those variables are initialized right away

      mSize   = size;
      mFill   = fill;
      mWidth  = width;
      mHeight = height;

      mBallX      = GetX();
      mBallY      = GetY();
      mBallXSpeed = GetSpeed();
      mBallYSpeed = GetSpeed();
   }

   // ------------------------------------------------------
   // Update - Update the ball's x and y location, also
   //          handle colliding with a wall
   // ------------------------------------------------------

   public void Update()
   {
       mBallX += mBallXSpeed;

       if (mBallX < 0 || mBallX + mSize > mWidth)
           mBallXSpeed = -mBallXSpeed;

       mBallY += mBallYSpeed;

       if (mBallY < 0 || mBallY + mSize > mHeight)
           mBallYSpeed = -mBallYSpeed;
   }

   // ------------------------------------------------------
   // Render - Draw the ball at its current location
   // ------------------------------------------------------

   public void Render(Graphics g)
   {
      g.FillEllipse(mFill, mBallX, mBallY, mSize, mSize);
      g.DrawEllipse(Pens.Black, mBallX, mBallY, mSize, mSize);
   }

   // ------------------------------------------------------
   // Get a random 'speed', 'x' or 'y' location
   // ------------------------------------------------------

   private int GetSpeed()
   {
      return(mRandom.Next(MIN_SPEED, MAX_SPEED));
   }

   private int GetX()
   {
      return(mRandom.Next(0, mWidth - mSize));
   }

   private int GetY()
   {
      return(mRandom.Next(0, mHeight - mSize));
   }

   // ------------------------------------------------------
   // The min/max speed of the ball, MIN_SPEED should be >= 1
   // otherwise the ball will not move
   // ------------------------------------------------------

   private const int MIN_SPEED = 1;
   private const int MAX_SPEED = 5;

   private int    mSize;
   private Brush  mFill;
   private int    mBallX;
   private int    mBallY;
   private int    mBallXSpeed;
   private int    mBallYSpeed;
   private int    mWidth;
   private int    mHeight;

   private static Random mRandom = new Random();
}

// ------------------------------------------------------
// BallInfo - A Ball's 'size' and 'fill' values
// ------------------------------------------------------

public class BallInfo
{
   public BallInfo(int size, Brush fill)
   {
      Size = size;
      Fill = fill;
   }

   public int   Size { get; private set; }
   public Brush Fill { get; private set; }
}

// ------------------------------------------------------
// BallsForm
// ------------------------------------------------------

public class BallsForm : Form
{
   public BallsForm()
   {
      // ------------------------------------------------------
      // Size our form
      // ------------------------------------------------------

      Size = new Size(FORM_WIDTH, FORM_HEIGHT);

      // ------------------------------------------------------
      // Create our balls
      // ------------------------------------------------------

      var info = new BallInfo[]
      {
         new BallInfo(40, Brushes.Blue),
         new BallInfo(20, Brushes.Red),
         new BallInfo(30, Brushes.Green),
         new BallInfo(35, Brushes.Cyan),
         new BallInfo(15, Brushes.Magenta),
         new BallInfo(25, Brushes.Yellow)
      };

      foreach(var entry in info)
      {
         mList.Add(
            new Ball(
               entry.Size, entry.Fill, ClientSize.Width, ClientSize.Height
            )
         );
      }

      // ------------------------------------------------------
      // Set up our timer and our form
      // ------------------------------------------------------

      mMoveBallsTimer.Enabled  = true;
      mMoveBallsTimer.Interval = 10;
      mMoveBallsTimer.Tick    += new System.EventHandler(MoveBallsTick);

      // ------------------------------------------------------
      // Use double buffering to reduce flicker
      // ------------------------------------------------------

      FormBorderStyle = FormBorderStyle.Fixed3D;
      Text            = "Bouncing Balls";
      Paint          += new PaintEventHandler(RenderBalls);

      SetStyle(
         ControlStyles.AllPaintingInWmPaint |
         ControlStyles.UserPaint |
         ControlStyles.DoubleBuffer,
         true
      );

      UpdateStyles();
   }

   // ------------------------------------------------------
   // MoveBallsTick - Update the location of each ball
   // ------------------------------------------------------

   private void MoveBallsTick(object sender, EventArgs e)
   {
      mList.ForEach(delegate(Ball b) { b.Update(); });
      Refresh();
   }

   // ------------------------------------------------------
   // RenderBalls - Draw each ball at its current location
   // ------------------------------------------------------

   private void RenderBalls(object sender, PaintEventArgs e)
   {
      e.Graphics.Clear(BackColor);
      mList.ForEach(delegate(Ball b) { b.Render(e.Graphics); });
   }

   // ------------------------------------------------------
   // Settings
   // ------------------------------------------------------

   private const int FORM_WIDTH  = 500;
   private const int FORM_HEIGHT = 500;

   // ------------------------------------------------------
   // Member variables
   // ------------------------------------------------------

   private Timer mMoveBallsTimer = new System.Windows.Forms.Timer();
   private List<Ball> mList      = new List<Ball>();

   // ------------------------------------------------------
   // Main
   // ------------------------------------------------------

   [STAThread]

   static void Main()
   {
      Application.Run(new BallsForm());
   }
}