using System.Diagnostics.Contracts;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using OpenTK.Graphics.OpenGL;
using OpenTK.Mathematics;
using Vector2 = System.Numerics.Vector2;
using Vector3 = System.Numerics.Vector3;

namespace Dashboard.Drawing.OpenGL
{
    public class DrawCallRecorder : IGLDisposable, IInitializer
    {
        private int _vao = 0;
        private int _vbo = 0;
        private readonly List<DrawVertex> _vertices = new List<DrawVertex>();
        private readonly List<DrawCall> _calls = new List<DrawCall>();

        private int _start = 0;
        private int _count = 0;
        private int _primitives = 0;
        private Vector3 _charCoords;
        private int _cmdIndex;
        private int _texture0, _texture1, _texture2, _texture3;
        private TextureTarget _target0, _target1, _target2, _target3;
        private Matrix4 _transforms = Matrix4.Identity;

        public int CommandModulus = 64;
        public int CommandBuffer = 0;
        public int CommandSize = 64;

        private int CommandByteSize => CommandModulus * CommandSize;

        public int TransformsLocation { get; set; }

        public void Transforms(in Matrix4 transforms)
        {
            _transforms = transforms;
        }

        public void Begin(PrimitiveType type)
        {
            if (_primitives != 0)
                throw new InvalidOperationException("Attempt to begin new draw call before finishing previous one.");

            _primitives = (int)type;
            _start = _vertices.Count;
            _count = 0;
        }

        public void TexCoords2(Vector2 texCoords)
        {
            _charCoords = new Vector3(texCoords, 0);
        }

        public void CharCoords(Vector3 charCoords)
        {
            _charCoords = charCoords;
        }

        public void CommandIndex(int index)
        {
            _cmdIndex = index;
        }

        public void Vertex3(Vector3 vertex)
        {
            _vertices.Add(new DrawVertex()
            {
                Position = vertex,
                CharCoords = _charCoords,
                CmdIndex = _cmdIndex % CommandModulus,
            });
            _count++;
        }

        public void End()
        {
            if (_primitives == 0)
                throw new InvalidOperationException("Attempt to end draw call before starting one.");

            _calls.Add(
                new DrawCall()
                {
                    Type = (PrimitiveType)_primitives,
                    Start = _start,
                    Count = _count,
                    CmdIndex = _cmdIndex,
                    Target0 = _target0,
                    Target1 = _target1,
                    Target2 = _target2,
                    Target3 = _target3,
                    Texture0 = _texture0,
                    Texture1 = _texture1,
                    Texture2 = _texture2,
                    Texture3 = _texture3,
                    Transforms = _transforms,
                });

            _primitives = 0;
        }

        public void BindTexture(TextureTarget target, int texture) => BindTexture(target, 0, texture);

        public void BindTexture(TextureTarget target, int unit, int texture)
        {
            switch (unit)
            {
                case 0:
                    _texture0 = 0;
                    _target0 = target;
                    break;
                case 1:
                    _texture1 = 0;
                    _target1 = target;
                    break;
                case 2:
                    _texture2 = 0;
                    _target2 = target;
                    break;
                case 3:
                    _texture3 = 0;
                    _target3 = target;
                    break;
                default:
                    throw new ArgumentOutOfRangeException(nameof(unit), "I did not write support for more than 4 textures.");
            }
        }

        public void DrawArrays(PrimitiveType type, int first, int count)
        {
            throw new NotImplementedException();
        }

        public void Execute()
        {
            GL.BindVertexArray(_vao);
            GL.BindBuffer(BufferTarget.ArrayBuffer, _vbo);

            ReadOnlySpan<DrawVertex> vertices = CollectionsMarshal.AsSpan(_vertices);
            GL.BufferData(BufferTarget.ArrayBuffer, _vertices.Count * Unsafe.SizeOf<DrawVertex>(), vertices, BufferUsage.DynamicDraw);

            foreach (DrawCall call in _calls)
            {
                GL.BindBufferRange(BufferTarget.UniformBuffer, 0, CommandBuffer, call.CmdIndex / CommandModulus * CommandByteSize, CommandByteSize);
                GL.ActiveTexture(TextureUnit.Texture0);
                GL.BindTexture(call.Target0, call.Texture0);
                GL.ActiveTexture(TextureUnit.Texture1);
                GL.BindTexture(call.Target1, call.Texture1);
                GL.ActiveTexture(TextureUnit.Texture2);
                GL.BindTexture(call.Target2, call.Texture2);
                GL.ActiveTexture(TextureUnit.Texture3);
                GL.BindTexture(call.Target3, call.Texture3);

                Matrix4 transforms = call.Transforms;
                GL.UniformMatrix4f(TransformsLocation, 1, true, ref transforms);
                GL.DrawArrays(call.Type, call.Start, call.Count);
            }
        }

        public void Clear()
        {
            _vertices.Clear();
            _calls.Clear();
        }

        public void Dispose()
        {
            throw new NotImplementedException();
        }

        public void Dispose(bool safeExit)
        {
            throw new NotImplementedException();
        }

        public bool IsInitialized { get; private set; }
        public void Initialize()
        {
            if (IsInitialized)
                return;
            IsInitialized = true;

            _vao = GL.CreateVertexArray();
            _vbo = GL.CreateBuffer();

            GL.BindVertexArray(_vao);
            GL.BindBuffer(BufferTarget.ArrayBuffer, _vbo);

            GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 32, 0);
            GL.VertexAttribPointer(1, 3, VertexAttribPointerType.Float, false, 32, 16);
            GL.VertexAttribIPointer(2, 1, VertexAttribIType.Int, 32, 28);
            GL.EnableVertexAttribArray(0);
            GL.EnableVertexAttribArray(1);
            GL.EnableVertexAttribArray(2);
        }

        private struct DrawCall
        {
            public PrimitiveType Type;
            public int Start;
            public int Count;
            public int CmdIndex;

            public int Texture0;
            public int Texture1;
            public int Texture2;
            public int Texture3;

            public TextureTarget Target0;
            public TextureTarget Target1;
            public TextureTarget Target2;
            public TextureTarget Target3;

            public Matrix4 Transforms;
        }

        [StructLayout(LayoutKind.Explicit, Size = 32)]
        private struct DrawVertex
        {
            [FieldOffset(0)]
            public Vector3 Position;
            [FieldOffset(16)]
            public Vector3 CharCoords;
            [FieldOffset(28)]
            public int CmdIndex;
        }
    }

    /// <summary>
    /// A customizable immediate mode draw call queue, for the modern OpenGL user.
    /// </summary>
    /// <typeparam name="TCall">The call info type.</typeparam>
    /// <typeparam name="TVertex">The vertex structure.</typeparam>
    public abstract class DrawCallRecorder<TCall, TVertex> : IGLDisposable, IInitializer
        where TVertex : unmanaged
    {
        /// <summary>
        /// The vertex array for this queue.
        /// </summary>
        public int Vao { get; private set; }

        /// <summary>
        /// The vertex buffer for this queue.
        /// </summary>
        public int Vbo { get; private set; }

        /// <summary>
        /// Number of calls recorded in this queue.
        /// </summary>
        public int CallCount => Calls.Count;

        /// <summary>
        /// The number of total vertices recorded.
        /// </summary>
        public int TotalVertices => Vertices.Count;

        /// <summary>
        /// The latest draw call info.
        /// </summary>
        public ref TCall CurrentCall => ref _currentCall;

        /// <summary>
        /// The latest vertex emitted.
        /// </summary>
        public ref TVertex CurrentVertex => ref _currentVertex;

        /// <summary>
        /// True if currently recording a draw call.
        /// </summary>
        public bool InCall => _primitiveMode != 0;

        /// <summary>
        /// Size of one vertex.
        /// </summary>
        protected int VertexSize => Unsafe.SizeOf<TVertex>();

        /// <summary>
        /// The list of draw calls.
        /// </summary>
        protected List<DrawCall> Calls { get; } = new List<DrawCall>();

        /// <summary>
        /// The list of all vertices.
        /// </summary>
        protected List<TVertex> Vertices { get; } = new List<TVertex>();

        /// <summary>
        /// The value to write for the draw call info at the start of a call.
        /// </summary>
        [Pure] protected virtual TCall DefaultCall => default(TCall);

        /// <summary>
        /// The value to write for last vertex at the start of a call.
        /// </summary>
        [Pure] protected virtual TVertex DefaultVertex => default;

        private int _start = 0;
        private int _count = 0;
        private int _primitiveMode = 0;
        private TCall _currentCall;
        private TVertex _currentVertex;

        protected DrawCallRecorder()
        {
            _currentCall = DefaultCall;
            _currentVertex = DefaultVertex;
        }

        /// <summary>
        /// Record a draw call directly.
        /// </summary>
        /// <param name="type">The primitive type to use.</param>
        /// <param name="callInfo">The call info structure to use</param>
        /// <param name="vertices">The list of vertices to use.</param>
        /// <exception cref="InvalidOperationException">You attempted to use this function during another draw call.</exception>
        public void DrawArrays(PrimitiveType type, in TCall callInfo, ReadOnlySpan<TVertex> vertices)
        {
            if (InCall)
                throw new InvalidOperationException("Cannot use draw arrays in the middle of an ongoing immediate-mode call.");

            DrawCall call = new DrawCall()
            {
                Type = type,
                Start = Vertices.Count,
                Count = vertices.Length,
                CallInfo = callInfo,
            };

            Vertices.AddRange(vertices);
            Calls.Add(call);
        }

        /// <summary>
        /// Start a draw call.
        /// </summary>
        /// <param name="type">The primitive type for the call.</param>
        public void Begin(PrimitiveType type) => Begin(type, DefaultCall);

        /// <summary>
        /// Start a draw call.
        /// </summary>
        /// <param name="type">The primitive type for the call.</param>
        /// <param name="callInfo">The call info.</param>
        /// <exception cref="InvalidOperationException">You attempted to create a draw call within a draw call.</exception>
        public void Begin(PrimitiveType type, TCall callInfo)
        {
            if (InCall)
                throw new InvalidOperationException("Attempt to begin new draw call before finishing previous one.");

            _primitiveMode = (int)type;
            _start = Vertices.Count;
            _count = 0;
            CurrentCall = callInfo;
            CurrentVertex = DefaultVertex;
        }

        /// <summary>
        /// Emit the latest or modified vertex.
        /// </summary>
        public void Vertex()
        {
            Vertex(CurrentVertex);
        }

        /// <summary>
        /// Emit a vertex.
        /// </summary>
        /// <param name="vertex">The vertex to emit.</param>
        public void Vertex(in TVertex vertex)
        {
            Vertices.Add(CurrentVertex = vertex);
            _count++;
        }

        /// <summary>
        /// End the current call.
        /// </summary>
        /// <exception cref="InvalidOperationException">You tried to end a call that you didn't begin recording.</exception>
        public void End()
        {
            if (!InCall)
                throw new InvalidOperationException("Attempt to end draw call before starting one.");

            Calls.Add(new DrawCall()
            {
                Start = _start,
                Count = _count,
                Type = (PrimitiveType)_primitiveMode,
                CallInfo = CurrentCall,
            });

            _primitiveMode = 0;
        }

        /// <summary>
        /// Called by the execution engine before a draw call is executed.
        /// </summary>
        /// <param name="call">The call to prepare.</param>
        protected abstract void PrepareCall(in TCall call);

        /// <summary>
        /// Set the vertex format for the <see cref="Vao"/> and <see cref="Vbo"/> created by the recorder.
        /// </summary>
        protected abstract void SetVertexFormat();

        /// <summary>
        /// Execute all the recorded draw calls.
        /// </summary>
        public void Execute()
        {
            GL.BindVertexArray(Vao);
            GL.BindBuffer(BufferTarget.ArrayBuffer, Vbo);

            ReadOnlySpan<TVertex> vertices = CollectionsMarshal.AsSpan(Vertices);
            GL.BufferData(BufferTarget.ArrayBuffer, Vertices.Count * VertexSize, vertices, BufferUsage.DynamicDraw);

            foreach (DrawCall call in Calls)
            {
                PrepareCall(call.CallInfo);
                GL.DrawArrays(call.Type, call.Start, call.Count);
            }
        }

        /// <summary>
        /// Clear the draw call queue.
        /// </summary>
        public void Clear()
        {
            Vertices.Clear();
            Calls.Clear();
        }

        public void Dispose()
        {
            throw new NotImplementedException();
        }

        public void Dispose(bool safeExit)
        {
            throw new NotImplementedException();
        }

        public bool IsInitialized { get; private set; }
        public void Initialize()
        {
            if (IsInitialized)
                return;
            IsInitialized = true;

            Vao = GL.CreateVertexArray();
            Vbo = GL.CreateBuffer();

            GL.BindVertexArray(Vao);
            GL.BindBuffer(BufferTarget.ArrayBuffer, Vbo);

            SetVertexFormat();
        }

        protected struct DrawCall
        {
            public PrimitiveType Type;
            public int Start;
            public int Count;
            public TCall CallInfo;
        }
    }
}