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

namespace XXX
{
    public sealed class Cylinder : MeshPrimitiveBase
    {
        public Cylinder(GraphicsDevice graphicsDevice, Color color)
            : this(graphicsDevice, 1, 1, 32, color)
        {
        }

        public Cylinder(GraphicsDevice graphicsDevice, float height, float diameter, int tessellation, Color color)
            : this(graphicsDevice, height, diameter, diameter, tessellation, color)
        {
        }

        public Cylinder(GraphicsDevice graphicsDevice, float height, float diameterTop, float diameterBottom, int tessellation, Color color)
            : base(graphicsDevice, PrimitiveType.TriangleList)
        {
            Guard.GreaterThan(height, 0, nameof(height));
            Guard.GreaterThan(diameterTop, 0, nameof(diameterTop));
            Guard.GreaterThan(diameterBottom, 0, nameof(diameterBottom));
            Guard.GreaterThan(tessellation, 2, nameof(tessellation));

            CreateMesh(height, diameterTop, diameterBottom, tessellation, color);
        }

        private void CreateMesh(float height, float diameterTop, float diameterBottom, int tessellation, Color color)
        {
            height /= 2;

            var radius1 = diameterTop / 2;
            var radius2 = diameterBottom / 2;

            for (var i = 0; i < tessellation; i++)
            {
                Vector3 normal = GetCircleVector(i, tessellation);

                AddVertex(new VertexPositionColorNormalTexture((normal * radius1) + (Vector3.UnitY * height), color, normal, Vector2.Zero));
                AddVertex(new VertexPositionColorNormalTexture((normal * radius2) - (Vector3.UnitY * height), color, normal, Vector2.Zero));

                AddIndex((i * 2));
                AddIndex(((i * 2) + 1));
                AddIndex(((i * 2) + 2) % (tessellation * 2));

                AddIndex(((i * 2) + 1));
                AddIndex(((i * 2) + 3) % (tessellation * 2));
                AddIndex(((i * 2) + 2) % (tessellation * 2));
            }

            CreateCap(tessellation, height, radius1, color, Vector3.UnitY);
            CreateCap(tessellation, height, radius2, color, -Vector3.UnitY);

            PrepareBuffers();
        }

        private void CreateCap(int tessellation, float height, float radius, Color color, Vector3 normal)
        {
            for (var i = 0; i < tessellation - 2; i++)
            {
                if (normal.Y > 0)
                {
                    AddIndex(VerticesCount);
                    AddIndex(VerticesCount + ((i + 1) % tessellation));
                    AddIndex(VerticesCount + ((i + 2) % tessellation));
                }
                else
                {
                    AddIndex(VerticesCount);
                    AddIndex(VerticesCount + ((i + 2) % tessellation));
                    AddIndex(VerticesCount + ((i + 1) % tessellation));
                }
            }

            for (var i = 0; i < tessellation; i++)
            {
                var position = (GetCircleVector(i, tessellation) * radius) + (normal * height);

                AddVertex(new VertexPositionColorNormalTexture(position, color, normal, Vector2.Zero));
            }
        }

        private static Vector3 GetCircleVector(int i, int tessellation)
        {
            var angle = i * MathHelper.TwoPi / tessellation;

            var dx = (float)Math.Cos(angle);
            var dz = (float)Math.Sin(angle);

            return new Vector3(dx, 0, dz);
        }
    }
}