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()
        {
            return new ShaderProgram(GL);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        protected Shader CreateShader(ShaderType type, int count)
        {
            return new Shader(this.gl, gl.CreateShaderSet(count, type), type);
        }
    }

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

        internal Shader(IglFunc gl, glHandleSet handle, ShaderType usage)
        {
            this.handle = handle;
            GL = gl;
            type = usage;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public unsafe void Compile(int index, string code)
        {
            if (code == null)
            {
                throw new ArgumentNullException("Must provide enough code");
            }
            GL.LoadShaderSource(handle[index], code + '\0');
            GL.CompileShader(handle[index]);
        }

        //TODO:写链接着色器的文档注释
        /// <summary>
        ///
        /// </summary>
        /// <param name="target"></param>
        /// <param name="index"></param>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AttachTo(int index, ShaderProgram target)
        {
            GL.AttachShader(target.handle, handle[index]);
        }

        public override string ToString()
        {
            return $"This is a {type} shader, its shader handles are {handle.ToString()}.";
        }
    }

    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)
        {
            GL = gl;
            handle = GL.CreateProgram();
        }

        /// <summary>
        /// Link the shader to current context.
        /// </summary>
        public unsafe void Link()
        {
            if (InternalIO.InternalLinkShaderProgram(GL.Context, handle.Value) == 0)
            {
                IntPtr logPtr = InternalIO.InternalReadSSCLog();
                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>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public unsafe Uniform<T> GetUniform<T>(string name) where T : struct
        {
            return new Uniform<T>(this, name, GL);
        }

        /// <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
        {
            return new Uniform<T, U>(this, name, GL);
        }

        /// <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
        {
            return new Uniform<T, U, V>(this, name, GL);
        }

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