using System.Collections.Generic;
using System.Windows.Forms;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using ButtonState = Microsoft.Xna.Framework.Input.ButtonState;
using Keys = Microsoft.Xna.Framework.Input.Keys;

namespace ParticleSystem
{
    /// <summary>
    /// This is the main type for your game.
    /// </summary>
    public class Game1 : Game
    {
        private readonly GraphicsDeviceManager graphics;
        private SpriteBatch spriteBatch;

        private const int particleCount = 10000;
        private const float particleSpeed = 1f;

        private Texture2D particleTexture;
        private readonly List<Particle> particles = new List<Particle>();

        public Game1()
        {
            graphics = new GraphicsDeviceManager( this )
            {
                IsFullScreen = true,
                PreferredBackBufferWidth = Screen.PrimaryScreen.Bounds.Width,
                PreferredBackBufferHeight = Screen.PrimaryScreen.Bounds.Height
            };
            graphics.ApplyChanges();
            Content.RootDirectory = "Content";
        }

        /// <summary>
        /// Allows the game to perform any initialization it needs to before starting to run.
        /// This is where it can query for any required services and load any non-graphic
        /// related content.  Calling base.Initialize will enumerate through any components
        /// and initialize them as well.
        /// </summary>
        protected override void Initialize()
        {
            // TODO: Add your initialization logic here
            IsMouseVisible = true;

            base.Initialize();
        }

        /// <summary>
        /// LoadContent will be called once per game and is the place to load
        /// all of your content.
        /// </summary>
        protected override void LoadContent()
        {
            // Create a new SpriteBatch, which can be used to draw textures.
            spriteBatch = new SpriteBatch( GraphicsDevice );

            // TODO: use this.Content to load your game content here
            particleTexture = Content.Load<Texture2D>( "Particle" );

            for ( int i = 0; i < particleCount; i++ )
            {
                particles.Add( new Particle( graphics.GraphicsDevice.Viewport.Width, graphics.GraphicsDevice.Viewport.Height,
                                             particleTexture, Color.White ) );
            }
        }

        /// <summary>
        /// UnloadContent will be called once per game and is the place to unload
        /// game-specific content.
        /// </summary>
        protected override void UnloadContent()
        {
            // TODO: Unload any non ContentManager content here
        }

        /// <summary>
        /// Allows the game to run logic such as updating the world,
        /// checking for collisions, gathering input, and playing audio.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        protected override void Update( GameTime gameTime )
        {
            if ( GamePad.GetState( PlayerIndex.One ).Buttons.Back == ButtonState.Pressed || Keyboard.GetState().IsKeyDown( Keys.Escape ) )
            {
                Exit();
            }

            // TODO: Add your update logic here
            if ( Mouse.GetState().LeftButton == ButtonState.Pressed )
            {
                UpdateParticlesPosition( gameTime, Mouse.GetState().Position.ToVector2() );
            }

            base.Update( gameTime );
        }

        /// <summary>
        /// This is called when the game should draw itself.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        protected override void Draw( GameTime gameTime )
        {
            GraphicsDevice.Clear( Color.CornflowerBlue );

            // TODO: Add your drawing code here
            spriteBatch.Begin();

            DrawParticles();

            spriteBatch.End();

            base.Draw( gameTime );
        }

        private void DrawParticles()
        {
            for ( int i = 0; i < particleCount; i++ )
            {
                Particle particle = particles[ i ];

                spriteBatch.Draw( particle.Texture, particle.Position, scale: particle.Scale, color: particle.Color );
            }
        }

        private void UpdateParticlesPosition( GameTime gameTime, Vector2 target )
        {
            for ( int i = 0; i < particleCount; i++ )
            {
                Particle particle = particles[ i ];

                Vector2 direction = target - particle.Position;
                Vector2 normalizedDirection = new Vector2( direction.X, direction.Y );
                normalizedDirection.Normalize();
                Vector2 movement = Vector2.Multiply( normalizedDirection, particleSpeed * ( float ) gameTime.ElapsedGameTime.TotalMilliseconds );

                if ( movement.Length() > direction.Length() )
                {
                    particle.Position = target;
                }
                else
                {
                    particle.Position += movement;
                }
            }
        }
    }
}