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 Shader CreateShader()
        {
            return new Shader(GL);
        }

        public class Shader
        {
            /// <summary>
            /// A <see cref="uint"/> value represent this shader.
            /// </summary>
            public readonly uint programID;
            internal uint vertexShaderID;
            internal uint fragmentShaderID;
            private IglFunc GL;

            /// <summary>
            /// Inti a shader with no program attached.
            /// </summary>
            internal unsafe Shader(IglFunc glFunc)
            {
                GL = glFunc;
                programID = GL.CreateProgram();
            }

            /// <summary>
            /// Compile the vertex shader to be attached to this shader.
            /// </summary>
            /// <param name="shaderCode">GLSL code of vertex shader.</param>
            public unsafe void CompileVertexShader(string shaderCode)
            {
                vertexShaderID = GL.CompileShader(shaderCode, ShaderType.VERTEX);
                GL.AttachShader(programID, vertexShaderID);
            }

            /// <summary>
            /// Compile the fragment shader to be attached to this shader.
            /// </summary>
            /// <param name="shaderCode">GLSL code of fragment shader.</param>
            public unsafe void CompileFragmentShader(string shaderCode)
            {
                fragmentShaderID = GL.CompileShader(shaderCode, ShaderType.FRAGMENT);
                GL.AttachShader(programID, fragmentShaderID);
            }

            /// <summary>
            /// Link the shader to current context.
            /// </summary>
            public void Link()
            {
                if (InternalIO.InternalLinkShaderProgram(programID) == 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"></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(programID, ptr);
                }
                if (uniform != -1)
                {
                    return new Uniform<T>(uniform);
                }
                else
                {
                    throw new Exception($"Cannot find the uniform {name} in shader {programID}");
                }
            }

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

        }
    }
}