using System;
using System.Diagnostics;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

namespace BouncyCatIsBouncy.Debugging
{
    static class OBBRenderer
    {
        static LineBrush s_brush;
        static bool s_initialized;

        static private void Init(GraphicsDevice graphics)
        {
            s_brush = new LineBrush(2, Color.Red);
            s_brush.Load(graphics);
            s_initialized = true;
        }

        [Conditional("DEBUG")]
        static public void Draw(SpriteBatch spriteBatch, OBB boundingBox)
        {
            Debug.Assert(spriteBatch != null);
            if (!s_initialized)
                Init(spriteBatch.GraphicsDevice);

            DrawCenter(spriteBatch, ref boundingBox);
            DrawSides(spriteBatch, ref boundingBox);
        }

        static private Vector2 PolarToXY(float rotation)
        {
            var sin = (float)Math.Sin(rotation);
            var cos = (float)Math.Cos(rotation);

            return new Vector2(sin, cos);
        }

        static private void DrawCenter(SpriteBatch spriteBatch, ref OBB boundingBox)
        {
            const float LENGTH = 10.0f;

            var xAxis = PolarToXY(boundingBox.Rotation) * LENGTH;
            var yAxis = PolarToXY(boundingBox.Rotation + (float)Math.PI / 2.0f) * LENGTH;


            s_brush.Draw(spriteBatch, boundingBox.Center + xAxis, boundingBox.Center - xAxis);
            s_brush.Draw(spriteBatch, boundingBox.Center + yAxis, boundingBox.Center - yAxis);
        }

        static private Vector2 RotateVector(Vector2 position, float radians)
        {
            var sin = (float)Math.Sin(-radians);
            var cos = (float)Math.Cos(-radians);

            return new Vector2(position.X * cos + position.Y * -sin , 
                position.X * sin + position.Y * cos);
        }

        static private void DrawSides(SpriteBatch spriteBatch, ref OBB boundingBox)
        {
            var halfWidth = boundingBox.Width / 2.0f;
            var halfHeight = boundingBox.Height / 2.0f;
            var rot = boundingBox.Rotation;

            var upperRight = RotateVector(new Vector2(halfWidth, -halfHeight), rot);
            var upperLeft = RotateVector(new Vector2(-halfWidth, -halfHeight), rot);
            var lowerLeft = RotateVector(new Vector2(-halfWidth, halfHeight), rot);
            var lowerRight = RotateVector(new Vector2(halfWidth, halfHeight), rot);


            s_brush.Draw(spriteBatch, boundingBox.Center + upperRight, boundingBox.Center + upperLeft);
            s_brush.Draw(spriteBatch, boundingBox.Center + upperLeft, boundingBox.Center + lowerLeft);
            s_brush.Draw(spriteBatch, boundingBox.Center + lowerLeft, boundingBox.Center + lowerRight);
            s_brush.Draw(spriteBatch, boundingBox.Center + lowerRight, boundingBox.Center + upperRight);
        }
    }
}