using StgSharp;
using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;

namespace StgSharp.Graphics
{
    public partial class Form
    {
        /// <summary>
        /// Create an instance of <see cref="Shader"/> program
        /// </summary>
        /// <returns>New instance of <see cref="Shader"/> instance. </returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        protected ShaderProgram CreateShaderProgram(ShaderType shaderType)
        {
            return new ShaderProgram(GL, 1);
        }
    }

    public class Shader
    {
        internal readonly glHandle handle;
        public readonly ShaderType type;
        private readonly IglFunc GL;



        internal Shader(IglFunc gl, glHandle handle)
        {
            this.handle = handle;
            GL = gl;
        }

        /// <summary>
        /// Compile the vertex shader to be attached to this shader.
        /// </summary>
        /// <param name="shaderCode">GLSL code of vertex shader.</param>
        public unsafe void Compile(string shaderCode, ShaderType usage, int index)
        {
            handle.handle[index] = GL.CompileShader(shaderCode, type).handle;
        }

        //TODO:写链接着色器的文档注释
        /// <summary>
        /// 
        /// </summary>
        /// <param name="target"></param>
        /// <param name="usage"></param>
        public void AttachTo(ShaderProgram target, ShaderType usage)
        {
            switch (usage)
            {
                case ShaderType.Fragment:

                    break;
                case ShaderType.Vertex:
                    GL.AttachShader(target.handle,)
                    break;
                default:
                    throw new ArgumentException();
            }
        }

    }

    public class ShaderProgram
    {
        internal readonly glHandle handle;
        private readonly IglFunc GL;

        /// <summary>
        /// Inti a shader with no program attached.
        /// </summary>
        internal unsafe ShaderProgram(IglFunc gl, int count)
        {
            GL = gl;
            handle = GL.CreateProgram();
        }

        /// <summary>
        /// Link the shader to current context.
        /// </summary>
        public void Link()
        {
            if (InternalIO.InternalLinkShaderProgram(handle[0]) == 0)
            {
                IntPtr logPtr = InternalIO.InternalReadLog();
                try
                {
                    byte[] logByte = new byte[512];
                    Marshal.Copy(logPtr, logByte, 0, 512);
                    string log = Encoding.UTF8.GetString(logByte);
                    log = log.Replace("\0", "");
                    InternalIO.InternalWriteLog(log, LogType.Error);
                }
                catch (Exception ex)
                {
                    InternalIO.InternalWriteLog(ex.Message, LogType.Error);
                }
            }
        }

        /// <summary>
        /// Get a uniform form current shader, 
        /// the value type of the uniform should be provided. 
        /// </summary>
        /// <param name="name">Name of the Uniform in shader code</param>
        /// <returns></returns>
        public unsafe Uniform<T> GetUniform<T>(string name) where T : struct
        {
            byte[] bytes = Encoding.ASCII.GetBytes(name);
            int uniform;
            fixed (byte* ptr = bytes)
            {
                uniform = GL.GetUniformLocation(handle[0], ptr);
            }
            if (uniform != -1)
            {
                return new Uniform<T>(uniform);
            }
            else
            {
                throw new Exception($"Cannot find the uniform {name} in shader {handle[0]}");
            }
        }
        /// <summary>
        /// Get a uniform form current shader, 
        /// the value type of the uniform should be provided. 
        /// </summary>
        /// <param name="name">Name of the Uniform in shader code</param>
        /// <returns></returns>
        public unsafe Uniform<T, U> GetUniform<T, U>(string name)
            where T : struct
            where U : struct
        {
            byte[] bytes = Encoding.ASCII.GetBytes(name);
            int uniform;
            fixed (byte* ptr = bytes)
            {
                uniform = GL.GetUniformLocation(handle[0], ptr);
            }
            if (uniform != -1)
            {
                return new Uniform<T, U>(uniform);
            }
            else
            {
                throw new Exception($"Cannot find the uniform {name} in shader {handle[0]}");
            }
        }
        /// <summary>
        /// Get a uniform form current shader, 
        /// the value type of the uniform should be provided. 
        /// </summary>
        /// <param name="name">Name of the Uniform in shader code</param>
        /// <returns></returns>
        public unsafe Uniform<T, U, V> GetUniform<T, U, V>(int index, string name)
            where T : struct
            where U : struct
            where V : struct
        {
            byte[] bytes = Encoding.ASCII.GetBytes(name);
            int uniform;
            fixed (byte* ptr = bytes)
            {
                uniform = GL.GetUniformLocation(handle[index], ptr);
            }
            if (uniform != -1)
            {
                return new Uniform<T, U, V>(uniform);
            }
            else
            {
                throw new Exception($"Cannot find the uniform {name} in shader {handle[index]}");
            }
        }

        /// <summary>
        /// Let the current context use this shader.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public unsafe void Use(int index)
        {
            GL.UseProgram(handle[index]);
        }

    }
}