using System.Text;
using Dashboard.Drawing;
using OpenTK.Graphics.OpenGL;

namespace Dashboard.OpenGL.Drawing
{
    public static class KhronosShaderHelper
    {
        public static int CompileStage(ShaderType type, string source, out string? log)
        {
            log = null;
            int shader = GL.CreateShader(type);

            GL.ShaderSource(shader, source);
            GL.CompileShader(shader);

            GL.GetShaderi(shader, ShaderParameterName.CompileStatus, out int flag);

            if (flag != 0)
                return shader;

            GL.GetShaderInfoLog(shader, out log);
            GL.DeleteShader(shader);
            return 0;
        }

        public static int LinkStages(ReadOnlySpan<int> stages, out string? log)
        {
            log = null;
            int program = GL.CreateProgram();

            foreach (int stage in stages)
            {
                GL.AttachShader(program, stage);
            }

            GL.LinkProgram(program);
            GL.GetProgrami(program, ProgramProperty.LinkStatus, out int flag);

            if (flag != 0)
                return program;

            GL.GetProgramInfoLog(program, out log);
            GL.DeleteProgram(program);
            return 0;
        }

        public static int CreateProgram(this GlslShaderCreateInfo glsl)
        {
            Span<int> stages = stackalloc int[5];
            int failed = 0;
            StringBuilder builder = new StringBuilder();

            int count = 0;

            Compile(ShaderType.VertexShader, glsl.VertexShader, "Vertex", stages);
            Compile(ShaderType.FragmentShader, glsl.FragmentShader, "Fragment", stages);
            Compile(ShaderType.GeometryShader, glsl.GeometryShader, "Geometry", stages);
            Compile(ShaderType.TessControlShader, glsl.TesselationControl, "Tesselation Control", stages);
            Compile(ShaderType.TessEvaluationShader, glsl.TesselationEvaluation, "Tesselation Evaluation", stages);

            if (failed > 0)
            {
                throw new Exception($"{failed} shader stage(s) failed to compile. See the exception data for details.")
                {
                    Data =
                    {
                        ["Log"] = builder.ToString(),
                    },
                };
            }

            int program = KhronosShaderHelper.LinkStages(stages[..count], out string? log);
            if (program == 0)
            {
                throw new Exception($"Shader program failed to link. See the exception data for details.")
                {
                    Data =
                    {
                        ["Log"] = log,
                    },
                };
            }

            return program;

            void Compile(ShaderType type, string? source, string name, Span<int> stages)
            {
                if (source == null)
                    return;

                int stage = CompileStage(type, source, out string? log);
                if (stage == 0)
                {
                    failed++;
                    builder.Append($"=== {name} Shader Compile Log Begin ===\n{log}\n=== {name} Shader Compile Log End ===\n\n");
                }
                else
                {
                    stages[count++] = stage;
                }
            }
        }

        public static int CreateProgram(this GlslComputeShaderCreateInfo glsl)
        {
            int compute = CompileStage(ShaderType.ComputeShader, glsl.Source, out string? log);
            if (compute == 0)
            {
                throw new Exception("Failed to compile compute shader. See the exception data for details.")
                {
                    Data =
                    {
                        ["Log"] = log,
                    },
                };
            }

            int program = KhronosShaderHelper.LinkStages([compute], out log);

            if (program != 0)
                return program;

            throw new Exception("Failed to link compute shader. See the exception data for details.")
            {
                Data =
                {
                    ["Log"] = log,
                },
            };
        }

        public static int CreateProgram(this SpirvShaderCreateInfo spirv)
        {
            int program = GL.CreateProgram();
            GL.ProgramBinary(program, (All)spirv.Format, spirv.Binary, spirv.Binary.Length);

            GL.GetProgrami(program, ProgramProperty.LinkStatus, out int flag);
            if (flag == 0)
                return program;

            GL.GetProgramInfoLog(program, out string? log);
            GL.DeleteProgram(program);

            throw new Exception("Failed to load program binary. See the exception data for details.")
            {
                Data =
                {
                    ["Log"] = log,
                },
            };
        }
    }


}