#region File Description
//-----------------------------------------------------------------------------
// BackgroundScreen.cs
//
// Microsoft XNA Community Game Platform
// Copyright (C) Microsoft Corporation. All rights reserved.
//-----------------------------------------------------------------------------
#endregion

#region Using Statements
using System;
using System.Collections.Generic;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.Graphics;
#endregion

namespace NetRumble
{
    /// <summary>
    /// The background screen sits behind all the other menu screens.
    /// It draws a background image that remains fixed in place regardless
    /// of whatever transitions the screens on top of it may be doing.
    /// </summary>
    /// <remarks>
    /// This public class is somewhat similar to one of the same name in the 
    /// GameStateManagement sample.
    /// </remarks>
    public class BackgroundScreen : GameScreen, IDisposable
    {
        #region Constants


        /// <summary>
        /// The period of the parallax motion in the starfield.
        /// </summary>
        const float starsParallaxPeriod = 30f;


        /// <summary>
        /// The amplitude of the parallax motion in the starfield.
        /// </summary>
        const float starsParallaxAmplitude = 2048f;


        #endregion


        #region Graphics Data


        /// <summary>
        /// The star field rendering in the background.
        /// </summary>
        private Starfield starfield;

        /// <summary>
        /// Persistent movement tracker, used to slightly parallax the stars.
        /// </summary>
        private double movement;

        /// <summary>
        /// The application's title texture.
        /// </summary>
        private Texture2D titleTexture;


        #endregion


        #region Initialization Methods


        /// <summary>
        /// Construct a new BackgroundScreen object.
        /// </summary>
        public BackgroundScreen()
        {
            TransitionOnTime = TimeSpan.FromSeconds(1.0);
            TransitionOffTime = TimeSpan.FromSeconds(1.0);
        }


        /// <summary>
        /// Loads graphics content for this screen. The background texture is quite
        /// big, so we use our own local ContentManager to load it. This allows us
        /// to unload before going from the menus into the game itself, wheras if we
        /// used the shared ContentManager provided by the ScreenManager, the content
        /// would remain loaded forever.
        /// </summary>
        public override void LoadContent()
        {
            // load the title texture
            titleTexture = ScreenManager.Content.Load<Texture2D>("Textures/title");
            movement = 0f;

            starfield = new Starfield(
                Vector2.Multiply(new Vector2(
                    (float)Math.Cos(movement / starsParallaxPeriod),
                    (float)Math.Sin(movement / starsParallaxPeriod)),
                    starsParallaxAmplitude), 
                ScreenManager.GraphicsDevice, ScreenManager.Content);
            starfield.LoadContent();

            base.LoadContent();
        }


        /// <summary>
        /// Release graphics data.
        /// </summary>
        public override void UnloadContent()
        {
            if (starfield != null)
            {
                starfield.UnloadContent();
                starfield = null;
            }

            base.UnloadContent();
        }


        #endregion


        #region Updating Methods


        /// <summary>
        /// Updates the background screen. Unlike most screens, this should not
        /// transition off even if it has been covered by another screen: it is
        /// supposed to be covered, after all! This overload forces the
        /// coveredByOtherScreen parameter to false in order to stop the base
        /// Update method wanting to transition off.
        /// </summary>
        public override void Update(GameTime gameTime, bool otherScreenHasFocus,
                                                       bool coveredByOtherScreen)
        {
            base.Update(gameTime, otherScreenHasFocus, false);
        }


        #endregion


        #region Drawing Methods


        /// <summary>
        /// Draws the background screen.
        /// </summary>
        public override void Draw(GameTime gameTime)
        {
            if (starfield != null)
            {
                // update the parallax movement
                movement += gameTime.ElapsedGameTime.TotalSeconds;
                Vector2 position = Vector2.Multiply(new Vector2(
                        (float)Math.Cos(movement / starsParallaxPeriod),
                        (float)Math.Sin(movement / starsParallaxPeriod)),
                        starsParallaxAmplitude);

                // draw the stars
                starfield.Draw(position);
            }

            // draw the title texture
            if (titleTexture != null)
            {
                Vector2 titlePosition = new Vector2(
                    ScreenManager.TitleSafeArea.X +
                       (ScreenManager.TitleSafeArea.Width - titleTexture.Width) / 2f,
                    ScreenManager.TitleSafeArea.Y +
                       ScreenManager.TitleSafeArea.Height * 0.05f);
                titlePosition.Y -= (float)Math.Pow(TransitionPosition, 2) * 
                    titlePosition.Y;
                ScreenManager.SpriteBatch.Begin();
                ScreenManager.SpriteBatch.Draw(titleTexture, titlePosition,
                    new Color(255, 255, 255, TransitionAlpha));
                ScreenManager.SpriteBatch.End();
            }
        }


        #endregion

    
        #region IDisposable Implementation


        /// <summary>
        /// Finalizes the BackgroundScreen object, calls Dispose(false)
        /// </summary>
        ~BackgroundScreen()
        {
            Dispose(false);
        }


        /// <summary>
        /// Disposes the BackgroundScreen object.
        /// </summary>
        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        
        /// <summary>
        /// Disposes this object.
        /// </summary>
        /// <param name="disposing">
        /// True if this method was called as part of the Dispose method.
        /// </param>
        protected virtual void Dispose(bool disposing)
        {
            if (disposing)
            {
                lock (this)
                {
                    if (starfield != null)
                    {
                        starfield.Dispose();
                        starfield = null;
                    }
                }
            }
        }


        #endregion
    }
}