using System;
using Microsoft.Xna.Framework;

namespace DoubleDebug
{
#if WINDOWS || LINUX
    /// <summary>
    /// The main class.
    /// </summary>
    public static class Program
    {
        private const float EPSILON = 0.001f;

        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            var view = Matrix.CreateLookAt(Vector3.Zero, Vector3.Forward, Vector3.Up);
            var proj = Matrix.CreatePerspectiveFieldOfView(MathHelper.PiOver2, 1.0f, 0.0001f, 100.0f);
            var viewProj = view * proj;


            WriteDelimeter("Setup");
            Console.WriteLine($"View: position: {Vector3.Zero}, forward: {Vector3.Forward}, up: {Vector3.Up}");
            Console.WriteLine($"Projection: near 0.0001f, far: 100.0f, fov: 90 degrees");

            WriteDelimeter("Near and Far plane");

            var point = new Vector3(0, 0, -1);
            var transformed = Transform(point, viewProj);
            Compare($"Point {point}, in front of the camera is transformed to the center of the far plane of the view volume", transformed, new Vector3(0, 0, 1));

            point = new Vector3(0, 0, -99);
            transformed = Transform(point, viewProj);
            Compare($"Point {point}, far away of the camera is transformed to the center of the far plane of the view volume", transformed, new Vector3(0, 0, 1));

            point = new Vector3(0, 0, -101);
            transformed = Transform(point, viewProj);
            Compare($"Point {point}, further away than the camera's far plane is transformed to the center of far plane of the view volume", transformed, new Vector3(0, 0, 1));

            point = new Vector3(0, 0, 1);
            transformed = Transform(point, viewProj);
            Compare($"Point {point}, behind the camera is transformed to the center of far plane of the view volume", transformed, new Vector3(0, 0, 1));

            point = new Vector3(0, 0, 99);
            transformed = Transform(point, viewProj);
            Compare($"Point {point}, far behind the camera is transformed to the center of far plane of the view volume", transformed, new Vector3(0, 0, 1));


            WriteDelimeter("Uncentered");
            point = new Vector3(-1, 0, -2);
            transformed = Transform(point, viewProj);
            Compare($"Point {point}, to the front left of the camera is transformed to the left of the far plane of the view volume", transformed, new Vector3(-0.5f, 0, 1));

            point = new Vector3(-1, 0, 2);
            transformed = Transform(point, viewProj);
            Compare($"Point {point}, to the left and behind of the camera is transformed to the right of the far plane of the view volume", transformed, new Vector3(0.5f, 0, 1));


            WriteDelimeter("Corners");
            var frustum = new BoundingFrustum(viewProj);
            var corners = frustum.GetCorners();

            for (var i = 0; i < corners.Length; i++)
            {
                var corner = corners[i];
                transformed = Transform(corner, viewProj);
                Inside($"Corner {corner} of the frustum is inside the view volume when transformed", transformed, -Vector3.One, Vector3.One);
            }

            Console.Read();
        }


        private static Vector3 Transform(Vector3 point, Matrix matrix)
        {
            var t = Vector4.Transform(new Vector4(point, 1), matrix);
            t /= t.W;

            return new Vector3(t.X, t.Y, t.Z);
        }

        private static void WriteDelimeter(string title)
        {
            Console.ForegroundColor = ConsoleColor.DarkGray;
            Console.WriteLine(new string('*', 20) + $" {title} " + new string('*', 20));
            Console.ResetColor();
        }


        private static void Compare(string explanation, Vector3 a, Vector3 b)
        {
            var equal = Compare(a.X, b.X);
            equal &= Compare(a.Y, b.Y);
            equal &= Compare(a.Z, b.Z);

            Console.Out.WriteLine(explanation);
            if (!equal)
            {
                Fail($"\t{a} is not equal to {b}");
            }

            if (equal)
            {
                Success($"\t{a} is equal to {b}");
            }

            Console.ResetColor();
        }

        private static void Inside(string explanation, Vector3 point, Vector3 min, Vector3 max)
        {
            Console.Out.WriteLine(explanation);

            var box = new BoundingBox(min, max);
            if (box.Contains(point) != ContainmentType.Disjoint)
            {
                Success($"\t{point} is inside {min}, {max}");
            }
            else
            {
                Fail($"\t{point} is not inside {min}, {max}");
            }
        }


        private static void Fail(string s)
        {
            Console.ForegroundColor = ConsoleColor.Red;
            Console.Out.WriteLine(s);
            Console.ResetColor();
        }

        private static void Success(string s)
        {
            Console.ForegroundColor = ConsoleColor.DarkGreen;
            Console.Out.WriteLine(s);
            Console.ResetColor();
        }

        private static bool Compare(float a, float b) => Math.Abs(a - b) < EPSILON;
    }
#endif
}