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

namespace BouncyCatIsBouncy.Debugging
{
    class LineBrush
    {
        public float Layer { get; set; }
        public Color Color { get; set; }
        public int Thickness { get; set; }
        
        private Texture2D m_lineTexture;
        private Vector2 m_origin;

        public LineBrush()
        {
            Color = Color.Black;
            Thickness = 1;
        }

        public LineBrush(int thickness, Color color)
        {
            Color = color;
            Thickness = thickness;
        }

        public void Load(GraphicsDevice graphics)
        {
            m_lineTexture = DrawingHelper.CreateLineTexture(graphics, Thickness, Color);
            m_origin = new Vector2(0f, Thickness / 2f + 1f);
        }

        public void Draw(SpriteBatch spriteBatch, Vector2 startPoint, Vector2 endPoint)
        {
            Debug.Assert(m_lineTexture != null);

            Vector2 difference = endPoint - startPoint;
            float rotation = CalculateRotation(difference);
            Vector2 scale = CalculateScale(difference);
            spriteBatch.Draw(m_lineTexture, startPoint, null, Color, rotation, m_origin, scale, SpriteEffects.None, Layer);
        }

        private static float CalculateRotation(Vector2 difference)
        {
            difference.Normalize();
            float theta = Vector2.Dot(Vector2.UnitX, difference);

            theta = (float)Math.Acos(theta);
            if (difference.Y < 0)
            {
                theta = -theta;
            }
            return theta;
        }

        private Vector2 CalculateScale(Vector2 difference)
        {
            return new Vector2(difference.Length() / m_lineTexture.Width, 1f);
        }
    }
}