using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Content;

namespace Tadv01
{
    class ScrollingBackground
    {
        //Sprites that make up scrolling images
        List<Sprite> mBackgroundSprites;

        //The Spright at right end of chain
        Sprite mRightMostSprite;
        //Left End
        Sprite mLeftMostSprite;

        //Viewing are for drawing images within
        Viewport mViewport;

        //Direction to scroll images
        public enum HorizontalScrollDirection
        {
            Left,
            Right
        }

        public ScrollingBackground(Viewport theViewport)
        {
            mBackgroundSprites = new List<Sprite>();
            mRightMostSprite = null;
            mLeftMostSprite = null;
            mViewport = theViewport;
        }

        public void LoadContent(ContentManager theContentManager)
        {
            //clear currently stored sprites
            mRightMostSprite = null;
            mLeftMostSprite = null;

            //total width of all sprites
            float aWidth = 0;

            CycleSprites();

            FillWidth(2);
        }

        //If width of all sprites does not fill twice the Viewport width then cycle
        //through images until enough background images are added to fill twice the width
        public void FillWidth(int widthMultiplier)
        {
            int aIndex = 0;
            if (mBackgroundSprites.Count > 0 && aWidth < mViewport.Width * widthMultiplier)
            {
                do
                {
                    //add another image to the chain
                    Sprite aBackgroundSprite = new Sprite();
                    aBackgroundSprite.AssetName = mBackgroundSprites[aIndex].AssetName;
                    aBackgroundSprite.LoadContent(theContentManager, aBackgroundSprite.AssetName);
                    aBackgroundSprite.Scale = mViewport.Height / aBackgroundSprite.Size.Height;
                    aBackgroundSprite.Position = new Vector2(mRightMostSprite.Position.X
                            + mRightMostSprite.Size.Width, mViewport.Y);
                    mBackgroundSprites.Add(aBackgroundSprite);
                    mRightMostSprite = aBackgroundSprite;

                    //Add new image's width to total chain width
                    aWidth += aBackgroundSprite.Size.Width;

                    //Move to next image
                    //If at end of indexes, start over
                    // might want to double check this - don't have a c# compiler to hand to check I've got it right ;]
                    aIndex = ++aIndex > mBackgroundSprites.Count -1 ? aIndex++ : aIndex = 0;

                } while (aWidth < mViewport.Width * widthMultiplier);
            }
        }

        //adds background sprite to scroll through screen
        public void AddBackground(string theAssetName)
        {
            Sprite aBackgroundSprite = new Sprite();
            aBackgroundSprite.AssetName = theAssetName;

            mBackgroundSprites.Add(aBackgroundSprite);
        }

        public bool GoingLeft(HorizontalScrollDirection direction)
        {
            return theDirection == HorizontalScrollDirection.Left;
        }

        //Check to see if any of the sprites have moved off screen. If the have
        //move them to right of background chain
        public void CheckSpriteMovement()
        {
            if(GoingLeft(theDirection))
            {
                foreach (Sprite aBackgroundSprite in mBackgroundSprites)
                {
                    if (aBackgroundSprite.Position.X < mViewport.X - aBackgroundSprite.Size.Width)
                    {
                        aBackgroundSprite.Position = new Vector2(mRightMostSprite.Position.X
                                + mRightMostSprite.Size.Width, mViewport.Y);
                        mRightMostSprite = aBackgroundSprite;
                    }
                }
            }
            else // aint going left, must be going right
            {
                //Repeat process for placing at left of chain
                foreach (Sprite aBackgroundSprite in mBackgroundSprites)
                {
                    if (aBackgroundSprite.Position.X > mViewport.X + mViewport.Width)
                    {
                        aBackgroundSprite.Position = new Vector2(mLeftMostSprite.Position.X
                                - mLeftMostSprite.Size.Width, mViewport.Y);
                        mLeftMostSprite = aBackgroundSprite;
                    }
                }
            }
        }

        //update position of background images
        public void Update(GameTime theGameTime, int theSpeed, HorizontalScrollDirection theDirection)
        {
            CheckSpriteMovement();
            //set direction based on movent passed in
            Vector2 aDirection = Vector2.Zero;

            aDirection.X = GoingLeft() ? -1 : 1;
            UpdateSpriteDirection(aDirection);
        }

        //update positions of each background sprite
        public void UpdateSpriteDirection(HorizontalScrollDirection direction)
        {
            foreach (Sprite aBackgroundSprite in mBackgroundSprites)
            {
                aBackgroundSprite.Update(theGameTime, new Vector2(theSpeed, 0), aDirection);
            }
        }

        //Cycle through background sprites, load and position them
        public void CycleSprites()
        {
            foreach (Sprite aBackgroundSprite in mBackgroundSprites)
            {
                //Load content and apply scale. scale is calculated by figuring out how far
                //the sprite needs to strecth to fill viewport height
                aBackgroundSprite.LoadContent(theContentManager, aBackgroundSprite.AssetName);
                aBackgroundSprite.Scale = mViewport.Height / aBackgroundSprite.Size.Height;

                //if background sprite is first in line, then mRightMostSprite will be null
                if (mRightMostSprite == null)
                {
                    aBackgroundSprite.Position = new Vector2(mViewport.X, mViewport.Y);
                    mLeftMostSprite = aBackgroundSprite;
                }
                else
                {
                    //Position sprite after last in line
                    aBackgroundSprite.Position = new Vector2(mRightMostSprite.Position.X
                            + mRightMostSprite.Size.Width, mViewport.Y);
                }

                //set sprite as last in line
                mRightMostSprite = aBackgroundSprite;
                aWidth += aBackgroundSprite.Size.Width;
            }
        }

        //Draw background on screen
        public void Draw(SpriteBatch theSpriteBatch)
        {
            foreach (Sprite aBackgroundSprite in mBackgroundSprites)
            {
                aBackgroundSprite.Draw(theSpriteBatch);
            }
        }
    }
}