// -----------------------------------------------------------------------------
// file="Shader"
// Project: StgSharp
// Copyright (c) Nitload.
// SPDX-License-Identifier: MIT
// -----------------------------------------------------------------------------

using StgSharp;
using StgSharp.Graphics;
using StgSharp.Internal;

using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.IO;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;
using System.Xml.Linq;

namespace StgSharp.Graphics.OpenGL
{
    public abstract partial class glRender : RenderStream
    {

        /// <summary>
        ///   Create an instance of <see cref="Shader" /> program
        /// </summary>
        /// <returns>
        ///   New instance of <see cref="Shader" /> instance.
        /// </returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        protected sealed override ShaderProgram CreateShaderProgram()
        {
            return new ShaderProgram(this);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        protected sealed override Shader CreateShaderSegment(
                                         ShaderType type,
                                         int count
        )
        {
            return new Shader(GL.CreateShaderSet(count, type), type, this);
        }

    }

    public class Shader
    {

        private readonly OpenGLFunction GL;
        internal readonly GlHandle[] handle;
        public readonly ShaderType type;

        internal unsafe Shader(
                        GlHandle[] handle,
                        ShaderType usage,
                        glRender stream
        )
        {
            this.handle = handle;
            GL = stream.GL;
            type = usage;
        }

        /// <summary>
        ///   Attach one shader code to a shader program.
        /// </summary>
        /// <param _label="target">
        ///   Shader program to attach
        /// </param>
        /// <param _label="index">
        ///   Index of shader code in current shader code set.
        /// </param>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AttachTo(
                    int index,
                    [NotNull]ShaderProgram target
        )
        {
            GL.AttachShader(target.handle, handle[index]);
        }

        public void CheckStatus(
                    int index,
                    ShaderStatus status
        )
        {
            string log = GL.GetShaderStatus(this, index, (int)status);
            if (!string.IsNullOrEmpty(log)) {
                throw new InvalidOperationException($"{$"Shader Error \t{status}\n"}{log}");
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public unsafe void Compile(
                           int index,
                           ReadOnlySpan<byte> codeU8Stream
        )
        {
            GL.LoadShaderSource(handle[index], codeU8Stream);
            GL.CompileShader(handle[index]);
            CheckStatus(index, ShaderStatus.CompileStatus);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public unsafe void Compile(
                           int index,
                           byte[] codeStream
        )
        {
            ArgumentNullException.ThrowIfNull(codeStream);
            GL.LoadShaderSource(handle[index], codeStream);
            GL.CompileShader(handle[index]);
            CheckStatus(index, ShaderStatus.CompileStatus);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public unsafe void Compile(
                           int index,
                           string codeStream
        )
        {
            ArgumentNullException.ThrowIfNull(codeStream);
            GL.LoadShaderSource(handle[index], codeStream.AsSpan());
            GL.CompileShader(handle[index]);
            CheckStatus(index, ShaderStatus.CompileStatus);
        }

        public void FromBytes(
                    byte[] stream
        )
        {
            throw new NotImplementedException();
        }

        public static byte[] FromCodeFile(
                             string fileRoute
        )
        {
            string str = File.ReadAllText(fileRoute);
            if (string.IsNullOrEmpty(str)) {
                throw new InvalidOperationException($"Cannot load and GLSL code from {fileRoute}");
            }
            return Encoding.UTF8.GetBytes(str);
        }

        public byte[] GetBytes()
        {
            return Array.Empty<byte>();
        }

        public byte[] GetBytes(
                      out int length
        )
        {
            throw new NotImplementedException();
        }

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

    }

    public enum ShaderStatus : int
    {

        CompileStatus = glConst.COMPILE_STATUS,

    }

    public class ShaderProgram
    {

        private readonly OpenGLFunction GL;
        internal readonly GlHandle handle;

        /// <summary>
        ///   CustomizeInit a program with no shader attached.
        /// </summary>
        internal unsafe ShaderProgram(
                        glRender binding
        )
        {
            GL = binding.GL;
            handle = GL.CreateProgram();
        }

        /// <summary>
        ///   Get a uniform form current shader, the value type of the uniform should be provided.
        /// </summary>
        /// <param _label="name">
        ///   ContextName of the Uniform in shader code
        /// </param>
        /// <returns>
        ///
        /// </returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public unsafe Uniform<T> GetUniform<T>(
                                 string name
        ) where T : unmanaged
        {
            return new Uniform<T>(GL.GetUniformLocation(this.handle, name));
        }

        /// <summary>
        ///   Get a uniform form current shader, the value type of the uniform should be provided.
        /// </summary>
        /// <param _label="name">
        ///   ContextName of the Uniform in shader code
        /// </param>
        /// <returns>
        ///
        /// </returns>
        public unsafe Uniform<T, U> GetUniform<T, U>(
                                    string name
        ) where T : unmanaged where U : struct
        {
            return new Uniform<T, U>(GL.GetUniformLocation(this.handle, name));
        }

        /// <summary>
        ///   Get a uniform form current shader, the value type of the uniform should be provided.
        /// </summary>
        /// <param _label="name">
        ///   ContextName of the Uniform in shader code
        /// </param>
        /// <returns>
        ///
        /// </returns>
        public unsafe Uniform<T, U, V> GetUniform<T, U, V>(
                                       string name
        ) where T : unmanaged where U : struct where V : struct
        {
            return new Uniform<T, U, V>(GL.GetUniformLocation(this.handle, name));
        }

        /// <summary>
        ///   Get a uniform form current shader, the value type of the uniform should be provided.
        /// </summary>
        /// <param _label="name">
        ///   ContextName of the Uniform in shader code
        /// </param>
        /// <returns>
        ///
        /// </returns>
        public unsafe Uniform<T, U, V, W> GetUniform<T, U, V, W>(
                                          string name
        ) where T : unmanaged where U : struct where V : struct where W : struct
        {
            return new Uniform<T, U, V, W>(GL.GetUniformLocation(this.handle, name));
        }

        /// <summary>
        ///   Link the shader to current viewPortDisplay.
        /// </summary>
        public unsafe void Link()
        {
            if (GraphicFramework.InternalLinkShaderProgram(
                (OpenglContext*)this.GL.ContextHandle, handle.Value) == 0)
            {
                IntPtr logPtr = GraphicFramework.InternalReadSSCLog();
                try
                {
                    byte[] logByte = new byte[512];
                    Marshal.Copy(logPtr, logByte, 0, 512);
                    string log = Encoding.UTF8.GetString(logByte);
                    log = log.Replace("\0", string.Empty);
                    DefaultLog.InternalWriteLog(log, LogType.Error);
                }
                catch (Exception ex)
                {
                    DefaultLog.InternalWriteLog(ex.Message, LogType.Error);
                }
            }
        }

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

        ~ShaderProgram()
        {
            // handle.Dispose();
        }

    }
}