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
    {
        internal readonly glHandle Handle;
        public readonly ShaderType type;
        private IglFunc GL;

        /// <summary>
        /// Inti a shader with no program attached.
        /// </summary>
        internal unsafe Shader(IglFunc gl, ShaderType t, int count)
        {
            GL = gl;
            type = t;
            if (type == ShaderType.Program)
            {
                Handle = GL.CreateProgram();
            }
        }

        internal void ChangeEnvironment(IglFunc gl)
        {
            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 CompileShader(string shaderCode)
        {
            vertexHandle = GL.CompileShader(shaderCode, type);
            GL.AttachShader(programHandle, vertexHandle);
        }

        /// <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)
        {
            fragmentHandle = GL.CompileShader(shaderCode, ShaderType.FRAGMENT);
            GL.AttachShader(programHandle, fragmentHandle);
        }

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

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

    }
}