Lua-CSharp/src/Lua/Runtime/LuaVirtualMachine.cs

using System.Buffers;
using System.Runtime.CompilerServices;
using Lua.Internal;

namespace Lua.Runtime;

public static partial class LuaVirtualMachine
{
    internal async static ValueTask<int> ExecuteClosureAsync(LuaState state, Closure closure, CallStackFrame frame, Memory<LuaValue> buffer, CancellationToken cancellationToken)
    {
        var stack = state.Stack;
        var chunk = closure.Proto;

        for (var pc = 0; pc < chunk.Instructions.Length; pc++)
        {
            var instruction = chunk.Instructions[pc];

            var RA = instruction.A + frame.Base;
            var RB = instruction.B + frame.Base;

            switch (instruction.OpCode)
            {
                case OpCode.Move:
                    stack.EnsureCapacity(RA + 1);
                    stack.UnsafeGet(RA) = stack.UnsafeGet(RB);
                    stack.NotifyTop(RA + 1);
                    break;
                case OpCode.LoadK:
                    stack.EnsureCapacity(RA + 1);
                    stack.UnsafeGet(RA) = chunk.Constants[instruction.Bx];
                    stack.NotifyTop(RA + 1);
                    break;
                case OpCode.LoadKX:
                    throw new NotImplementedException();
                case OpCode.LoadBool:
                    stack.EnsureCapacity(RA + 1);
                    stack.UnsafeGet(RA) = instruction.B != 0;
                    stack.NotifyTop(RA + 1);
                    if (instruction.C != 0) pc++;
                    break;
                case OpCode.LoadNil:
                    stack.EnsureCapacity(RA + instruction.B + 1);
                    stack.GetBuffer().Slice(RA, instruction.B + 1).Clear();
                    stack.NotifyTop(RA + instruction.B + 1);
                    break;
                case OpCode.GetUpVal:
                    {
                        stack.EnsureCapacity(RA + 1);
                        var upValue = closure.UpValues[instruction.B];
                        stack.UnsafeGet(RA) = upValue.GetValue();
                        stack.NotifyTop(RA + 1);
                        break;
                    }
                case OpCode.GetTabUp:
                    {
                        stack.EnsureCapacity(RA + 1);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);
                        var upValue = closure.UpValues[instruction.B];
                        var table = upValue.GetValue();
                        var value = await GetTableValue(state, chunk, pc, table, vc, cancellationToken);
                        stack.UnsafeGet(RA) = value;
                        stack.NotifyTop(RA + 1);
                        break;
                    }
                case OpCode.GetTable:
                    {
                        stack.EnsureCapacity(RA + 1);
                        var table = stack.UnsafeGet(RB);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);
                        var value = await GetTableValue(state, chunk, pc, table, vc, cancellationToken);
                        stack.UnsafeGet(RA) = value;
                        stack.NotifyTop(RA + 1);
                    }
                    break;
                case OpCode.SetTabUp:
                    {
                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);

                        var upValue = closure.UpValues[instruction.A];
                        var table = upValue.GetValue();
                        await SetTableValue(state, chunk, pc, table, vb, vc, cancellationToken);
                        break;
                    }
                case OpCode.SetUpVal:
                    {
                        var upValue = closure.UpValues[instruction.B];
                        upValue.SetValue(stack.UnsafeGet(RA));
                        break;
                    }
                case OpCode.SetTable:
                    {
                        var table = stack.UnsafeGet(RA);
                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);
                        await SetTableValue(state, chunk, pc, table, vb, vc, cancellationToken);
                    }
                    break;
                case OpCode.NewTable:
                    stack.EnsureCapacity(RA + 1);
                    stack.UnsafeGet(RA) = new LuaTable(instruction.B, instruction.C);
                    stack.NotifyTop(RA + 1);
                    break;
                case OpCode.Self:
                    {
                        stack.EnsureCapacity(RA + 2);
                        var table = stack.UnsafeGet(RB).Read<LuaTable>();
                        var vc = RK(stack, chunk, instruction.C, frame.Base);
                        stack.UnsafeGet(RA + 1) = table;
                        stack.UnsafeGet(RA) = table[vc];
                        stack.NotifyTop(RA + 2);
                    }
                    break;
                case OpCode.Add:
                    {
                        stack.EnsureCapacity(RA + 1);

                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);

                        if (vb.TryRead<double>(out var valueB) && vc.TryRead<double>(out var valueC))
                        {
                            stack.UnsafeGet(RA) = valueB + valueC;
                        }
                        else if (vb.TryGetMetamethod(Metamethods.Add, out var metamethod) || vc.TryGetMetamethod(Metamethods.Add, out metamethod))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);
                            stack.Push(vc);

                            using var methodBuffer = new PooledArray<LuaValue>(1024);
                            await func.InvokeAsync(new()
                            {
                                State = state,
                                ArgumentCount = 2,
                                SourcePosition = chunk.SourcePositions[pc],
                            }, methodBuffer.AsMemory(), cancellationToken);

                            stack.UnsafeGet(RA) = methodBuffer[0];
                        }
                        else
                        {
                            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "add", vb, vc);
                        }

                        stack.NotifyTop(RA + 1);
                    }
                    break;
                case OpCode.Sub:
                    {
                        stack.EnsureCapacity(RA + 1);

                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);

                        if (vb.TryRead<double>(out var valueB) && vc.TryRead<double>(out var valueC))
                        {
                            stack.UnsafeGet(RA) = valueB - valueC;
                        }
                        else if (vb.TryGetMetamethod(Metamethods.Sub, out var metamethod) || vc.TryGetMetamethod(Metamethods.Sub, out metamethod))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);
                            stack.Push(vc);

                            using var methodBuffer = new PooledArray<LuaValue>(1024);
                            await func.InvokeAsync(new()
                            {
                                State = state,
                                ArgumentCount = 2,
                                SourcePosition = chunk.SourcePositions[pc],
                            }, methodBuffer.AsMemory(), cancellationToken);

                            stack.UnsafeGet(RA) = methodBuffer[0];
                        }
                        else
                        {
                            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "sub", vb, vc);
                        }

                        stack.NotifyTop(RA + 1);
                    }
                    break;
                case OpCode.Mul:
                    {
                        stack.EnsureCapacity(RA + 1);

                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);

                        if (vb.TryRead<double>(out var valueB) && vc.TryRead<double>(out var valueC))
                        {
                            stack.UnsafeGet(RA) = valueB * valueC;
                        }
                        else if (vb.TryGetMetamethod(Metamethods.Mul, out var metamethod) || vc.TryGetMetamethod(Metamethods.Mul, out metamethod))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);
                            stack.Push(vc);

                            using var methodBuffer = new PooledArray<LuaValue>(1024);
                            await func.InvokeAsync(new()
                            {
                                State = state,
                                ArgumentCount = 2,
                                SourcePosition = chunk.SourcePositions[pc],
                            }, methodBuffer.AsMemory(), cancellationToken);

                            stack.UnsafeGet(RA) = methodBuffer[0];
                        }
                        else
                        {
                            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "mul", vb, vc);
                        }

                        stack.NotifyTop(RA + 1);
                    }
                    break;
                case OpCode.Div:
                    {
                        stack.EnsureCapacity(RA + 1);

                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);

                        if (vb.TryRead<double>(out var valueB) && vc.TryRead<double>(out var valueC))
                        {
                            stack.UnsafeGet(RA) = valueB / valueC;
                        }
                        else if (vb.TryGetMetamethod(Metamethods.Div, out var metamethod) || vc.TryGetMetamethod(Metamethods.Div, out metamethod))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);
                            stack.Push(vc);

                            using var methodBuffer = new PooledArray<LuaValue>(1024);
                            await func.InvokeAsync(new()
                            {
                                State = state,
                                ArgumentCount = 2,
                                SourcePosition = chunk.SourcePositions[pc],
                            }, methodBuffer.AsMemory(), cancellationToken);

                            stack.UnsafeGet(RA) = methodBuffer[0];
                        }
                        else
                        {
                            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "div", vb, vc);
                        }

                        stack.NotifyTop(RA + 1);
                    }
                    break;
                case OpCode.Mod:
                    {
                        stack.EnsureCapacity(RA + 1);

                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);

                        if (vb.TryRead<double>(out var valueB) && vc.TryRead<double>(out var valueC))
                        {
                            stack.UnsafeGet(RA) = valueB % valueC;
                        }
                        else if (vb.TryGetMetamethod(Metamethods.Mod, out var metamethod)  || vc.TryGetMetamethod(Metamethods.Mod, out metamethod))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);
                            stack.Push(vc);

                            using var methodBuffer = new PooledArray<LuaValue>(1024);
                            await func.InvokeAsync(new()
                            {
                                State = state,
                                ArgumentCount = 2,
                                SourcePosition = chunk.SourcePositions[pc],
                            }, methodBuffer.AsMemory(), cancellationToken);

                            stack.UnsafeGet(RA) = methodBuffer[0];
                        }
                        else
                        {
                            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "mod", vb, vc);
                        }

                        stack.NotifyTop(RA + 1);
                    }
                    break;
                case OpCode.Pow:
                    {
                        stack.EnsureCapacity(RA + 1);

                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);

                        if (vb.TryRead<double>(out var valueB) && vc.TryRead<double>(out var valueC))
                        {
                            stack.UnsafeGet(RA) = Math.Pow(valueB, valueC);
                        }
                        else if (vb.TryGetMetamethod(Metamethods.Pow, out var metamethod) || vc.TryGetMetamethod(Metamethods.Pow, out metamethod))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);
                            stack.Push(vc);

                            using var methodBuffer = new PooledArray<LuaValue>(1024);
                            await func.InvokeAsync(new()
                            {
                                State = state,
                                ArgumentCount = 2,
                                SourcePosition = chunk.SourcePositions[pc],
                            }, methodBuffer.AsMemory(), cancellationToken);

                            stack.UnsafeGet(RA) = methodBuffer[0];
                        }
                        else
                        {
                            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "pow", vb, vc);
                        }

                        stack.NotifyTop(RA + 1);
                    }
                    break;
                case OpCode.Unm:
                    {
                        stack.EnsureCapacity(RA + 1);

                        var vb = stack.UnsafeGet(RB);

                        if (vb.TryRead<double>(out var valueB))
                        {
                            stack.UnsafeGet(RA) = -valueB;
                        }
                        else if (vb.TryGetMetamethod(Metamethods.Unm, out var metamethod))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);

                            using var methodBuffer = new PooledArray<LuaValue>(1024);
                            await func.InvokeAsync(new()
                            {
                                State = state,
                                ArgumentCount = 1,
                                SourcePosition = chunk.SourcePositions[pc],
                            }, methodBuffer.AsMemory(), cancellationToken);

                            stack.UnsafeGet(RA) = methodBuffer[0];
                        }
                        else
                        {
                            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "unm", vb);
                        }

                        stack.NotifyTop(RA + 1);
                    }
                    break;
                case OpCode.Not:
                    {
                        stack.EnsureCapacity(RA + 1);

                        var rb = stack.UnsafeGet(RB);

                        if (rb.TryRead<bool>(out var valueB))
                        {
                            stack.UnsafeGet(RA) = !valueB;
                        }
                        else
                        {
                            stack.UnsafeGet(RA) = false;
                        }

                        stack.NotifyTop(RA + 1);
                    }
                    break;
                case OpCode.Len:
                    {
                        stack.EnsureCapacity(RA + 1);

                        var vb = stack.UnsafeGet(RB);

                        if (vb.TryRead<string>(out var str))
                        {
                            stack.UnsafeGet(RA) = str.Length;
                        }
                        else if (vb.TryGetMetamethod(Metamethods.Len, out var metamethod))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);

                            using var methodBuffer = new PooledArray<LuaValue>(1024);
                            await func.InvokeAsync(new()
                            {
                                State = state,
                                ArgumentCount = 1,
                                SourcePosition = chunk.SourcePositions[pc],
                            }, methodBuffer.AsMemory(), cancellationToken);

                            stack.UnsafeGet(RA) = methodBuffer[0];
                        }
                        else if (vb.TryRead<LuaTable>(out var table))
                        {
                            stack.UnsafeGet(RA) = table.ArrayLength;
                        }
                        else
                        {
                            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "get length of", vb);
                        }

                        stack.NotifyTop(RA + 1);
                    }
                    break;
                case OpCode.Concat:
                    {
                        stack.EnsureCapacity(RA + 1);

                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);

                        var bIsValid = vb.TryRead<string>(out var strB);
                        var cIsValid = vc.TryRead<string>(out var strC);

                        if (!bIsValid && vb.TryRead<double>(out var numB))
                        {
                            strB = numB.ToString();
                            bIsValid = true;
                        }
                        if (!cIsValid && vc.TryRead<double>(out var numC))
                        {
                            strC = numC.ToString();
                            cIsValid = true;
                        }

                        if (bIsValid && cIsValid)
                        {
                            stack.UnsafeGet(RA) = strB + strC;
                        }
                        else if (vb.TryGetMetamethod(Metamethods.Concat, out var metamethod) || vc.TryGetMetamethod(Metamethods.Concat, out metamethod))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);
                            stack.Push(vc);

                            using var methodBuffer = new PooledArray<LuaValue>(1024);
                            await func.InvokeAsync(new()
                            {
                                State = state,
                                ArgumentCount = 2,
                                SourcePosition = chunk.SourcePositions[pc],
                            }, methodBuffer.AsMemory(), cancellationToken);

                            stack.UnsafeGet(RA) = methodBuffer[0];
                        }
                        else
                        {
                            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "concat", vb, vc);
                        }

                        stack.NotifyTop(RA + 1);
                    }
                    break;
                case OpCode.Jmp:
                    pc += instruction.SBx;
                    if (instruction.A != 0)
                    {
                        state.CloseUpValues(instruction.A);
                    }
                    break;
                case OpCode.Eq:
                    {
                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);
                        var compareResult = vb == vc;

                        if (!compareResult && (vb.TryGetMetamethod(Metamethods.Eq, out var metamethod) || vc.TryGetMetamethod(Metamethods.Eq, out metamethod)))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);
                            stack.Push(vc);

                            var methodBuffer = ArrayPool<LuaValue>.Shared.Rent(1);
                            methodBuffer.AsSpan().Clear();
                            try
                            {
                                await func.InvokeAsync(new()
                                {
                                    State = state,
                                    ArgumentCount = 2,
                                    SourcePosition = chunk.SourcePositions[pc],
                                }, methodBuffer, cancellationToken);

                                compareResult = methodBuffer[0].ToBoolean();
                            }
                            finally
                            {
                                ArrayPool<LuaValue>.Shared.Return(methodBuffer);
                            }
                        }

                        if (compareResult != (instruction.A == 1))
                        {
                            pc++;
                        }
                    }
                    break;
                case OpCode.Lt:
                    {
                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);
                        var compareResult = false;
                        
                        if (vb.TryRead<double>(out var valueB) && vc.TryRead<double>(out var valueC))
                        {
                            compareResult = valueB < valueC;
                        }
                        else if (vb.TryGetMetamethod(Metamethods.Lt, out var metamethod) || vc.TryGetMetamethod(Metamethods.Lt, out metamethod))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);
                            stack.Push(vc);

                            var methodBuffer = ArrayPool<LuaValue>.Shared.Rent(1);
                            methodBuffer.AsSpan().Clear();
                            try
                            {
                                await func.InvokeAsync(new()
                                {
                                    State = state,
                                    ArgumentCount = 2,
                                    SourcePosition = chunk.SourcePositions[pc],
                                }, methodBuffer, cancellationToken);

                                compareResult = methodBuffer[0].ToBoolean();
                            }
                            finally
                            {
                                ArrayPool<LuaValue>.Shared.Return(methodBuffer);
                            }
                        }
                        else
                        {
                            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "less than", vb, vc);
                        }

                        if (compareResult != (instruction.A == 1))
                        {
                            pc++;
                        }
                    }
                    break;
                case OpCode.Le:
                    {
                        var vb = RK(stack, chunk, instruction.B, frame.Base);
                        var vc = RK(stack, chunk, instruction.C, frame.Base);
                        var compareResult = false;

                        if (vb.TryRead<double>(out var valueB) && vc.TryRead<double>(out var valueC))
                        {
                            compareResult = valueB <= valueC;
                        }
                        else if (vb.TryGetMetamethod(Metamethods.Le, out var metamethod) || vc.TryGetMetamethod(Metamethods.Le, out metamethod))
                        {
                            if (!metamethod.TryRead<LuaFunction>(out var func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }

                            stack.Push(vb);
                            stack.Push(vc);

                            var methodBuffer = ArrayPool<LuaValue>.Shared.Rent(1);
                            methodBuffer.AsSpan().Clear();
                            try
                            {
                                await func.InvokeAsync(new()
                                {
                                    State = state,
                                    ArgumentCount = 2,
                                    SourcePosition = chunk.SourcePositions[pc],
                                }, methodBuffer, cancellationToken);

                                compareResult = methodBuffer[0].ToBoolean();
                            }
                            finally
                            {
                                ArrayPool<LuaValue>.Shared.Return(methodBuffer);
                            }
                        }
                        else
                        {
                            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "less than or equals", vb, vc);
                        }

                        if (compareResult != (instruction.A == 1))
                        {
                            pc++;
                        }
                    }
                    break;
                case OpCode.Test:
                    {
                        if (stack.UnsafeGet(RA).ToBoolean() != (instruction.C == 1))
                        {
                            pc++;
                        }
                    }
                    break;
                case OpCode.TestSet:
                    {
                        if (stack.UnsafeGet(RB).ToBoolean() != (instruction.C == 1))
                        {
                            pc++;
                        }
                        else
                        {
                            stack.UnsafeGet(RA) = stack.UnsafeGet(RB);
                            stack.NotifyTop(RA + 1);
                        }
                    }
                    break;
                case OpCode.Call:
                    {
                        var va = stack.UnsafeGet(RA);
                        if (!va.TryRead<LuaFunction>(out var func))
                        {
                            if (va.TryGetMetamethod(Metamethods.Call, out var metamethod) && metamethod.TryRead<LuaFunction>(out func))
                            {   
                            }
                            else
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }
                        }

                        (var newBase, var argumentCount) = PrepareForFunctionCall(state, func, instruction, RA, false);

                        var resultBuffer = ArrayPool<LuaValue>.Shared.Rent(1024);
                        resultBuffer.AsSpan().Clear();
                        try
                        {
                            var resultCount = await func.InvokeAsync(new()
                            {
                                State = state,
                                ArgumentCount = argumentCount,
                                StackPosition = newBase,
                                SourcePosition = chunk.SourcePositions[pc],
                                ChunkName = chunk.Name,
                                RootChunkName = chunk.GetRoot().Name,
                            }, resultBuffer.AsMemory(), cancellationToken);

                            if (instruction.C != 0)
                            {
                                resultCount = instruction.C - 1;
                            }

                            stack.EnsureCapacity(RA + resultCount);
                            for (int i = 0; i < resultCount; i++)
                            {
                                stack.UnsafeGet(RA + i) = resultBuffer[i];
                            }
                            stack.NotifyTop(RA + resultCount);
                        }
                        finally
                        {
                            ArrayPool<LuaValue>.Shared.Return(resultBuffer);
                        }
                    }
                    break;
                case OpCode.TailCall:
                    {
                        state.CloseUpValues(frame.Base);

                        var va = stack.UnsafeGet(RA);
                        if (!va.TryRead<LuaFunction>(out var func))
                        {
                            if (!va.TryGetMetamethod(Metamethods.Call, out var metamethod) && !metamethod.TryRead<LuaFunction>(out func))
                            {
                                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
                            }
                        }

                        (var newBase, var argumentCount) = PrepareForFunctionCall(state, func, instruction, RA, true);

                        return await func.InvokeAsync(new()
                        {
                            State = state,
                            ArgumentCount = argumentCount,
                            StackPosition = newBase,
                            SourcePosition = chunk.SourcePositions[pc],
                            ChunkName = chunk.Name,
                            RootChunkName = chunk.GetRoot().Name,
                        }, buffer, cancellationToken);
                    }
                case OpCode.Return:
                    {
                        state.CloseUpValues(frame.Base);

                        var retCount = instruction.B - 1;

                        if (retCount == -1)
                        {
                            retCount = stack.Count - RA;
                        }

                        for (int i = 0; i < retCount; i++)
                        {
                            buffer.Span[i] = stack.UnsafeGet(RA + i);
                        }

                        return retCount;
                    }
                case OpCode.ForLoop:
                    {
                        stack.EnsureCapacity(RA + 4);

                        // TODO: add error message
                        var variable = stack.UnsafeGet(RA).Read<double>();
                        var limit = stack.UnsafeGet(RA + 1).Read<double>();
                        var step = stack.UnsafeGet(RA + 2).Read<double>();

                        var va = variable + step;
                        stack.UnsafeGet(RA) = va;

                        if (step >= 0 ? va <= limit : va >= limit)
                        {
                            pc += instruction.SBx;
                            stack.UnsafeGet(RA + 3) = va;
                            stack.NotifyTop(RA + 4);
                        }
                        else
                        {
                            stack.NotifyTop(RA + 1);
                        }
                    }
                    break;
                case OpCode.ForPrep:
                    {
                        // TODO: add error message
                        stack.UnsafeGet(RA) = stack.UnsafeGet(RA).Read<double>() - stack.UnsafeGet(RA + 2).Read<double>();
                        stack.NotifyTop(RA + 1);
                        pc += instruction.SBx;
                    }
                    break;
                case OpCode.TForCall:
                    {
                        var iterator = stack.UnsafeGet(RA).Read<LuaFunction>();

                        var nextBase = RA + 3 + instruction.C;
                        
                        var resultBuffer = ArrayPool<LuaValue>.Shared.Rent(1024);
                        resultBuffer.AsSpan().Clear();
                        try
                        {
                            await iterator.InvokeAsync(new()
                            {
                                State = state,
                                ArgumentCount = 2,
                                StackPosition = nextBase,
                                SourcePosition = chunk.SourcePositions[pc],
                                ChunkName = chunk.Name,
                                RootChunkName = chunk.GetRoot().Name,
                            }, resultBuffer.AsMemory(), cancellationToken);

                            stack.EnsureCapacity(RA + instruction.C + 3);
                            for (int i = 1; i <= instruction.C; i++)
                            {
                                stack.UnsafeGet(RA + 2 + i) = resultBuffer[i - 1];
                            }
                            stack.NotifyTop(RA + instruction.C + 3);
                        }
                        finally
                        {
                            ArrayPool<LuaValue>.Shared.Return(resultBuffer);
                        }
                    }
                    break;
                case OpCode.TForLoop:
                    {
                        var forState = stack.UnsafeGet(RA + 1);
                        if (forState.Type is not LuaValueType.Nil)
                        {
                            stack.UnsafeGet(RA) = forState;
                            pc += instruction.SBx;
                        }
                    }
                    break;
                case OpCode.SetList:
                    {
                        var table = stack.UnsafeGet(RA).Read<LuaTable>();

                        var count = instruction.B == 0
                            ? stack.Count - (RA + 1)
                            : instruction.B;

                        table.EnsureArrayCapacity((instruction.C - 1) * 50 + count);
                        stack.AsSpan().Slice(RA + 1, count)
                            .CopyTo(table.GetArraySpan()[((instruction.C - 1) * 50)..]);
                    }
                    break;
                case OpCode.Closure:
                    stack.EnsureCapacity(RA + 1);
                    stack.UnsafeGet(RA) = new Closure(state, chunk.Functions[instruction.SBx]);
                    stack.NotifyTop(RA + 1);
                    break;
                case OpCode.VarArg:
                    {
                        var count = instruction.B == 0
                            ? frame.VariableArgumentCount
                            : instruction.B - 1;

                        stack.EnsureCapacity(RA + count);
                        for (int i = 0; i < count; i++)
                        {
                            stack.UnsafeGet(RA + i) = stack.UnsafeGet(frame.Base - (count - i));
                        }
                        stack.NotifyTop(RA + count);
                    }
                    break;
                case OpCode.ExtraArg:
                    throw new NotImplementedException();
                default:
                    break;
            }
        }

        return 0;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    static LuaValue RK(LuaStack stack, Chunk chunk, ushort index, int frameBase)
    {
        return index >= 256 ? chunk.Constants[index - 256] : stack.UnsafeGet(index + frameBase);
    }

#if NET6_0_OR_GREATER
    [AsyncMethodBuilder(typeof(PoolingAsyncValueTaskMethodBuilder<>))]
#endif
    static async ValueTask<LuaValue> GetTableValue(LuaState state, Chunk chunk, int pc, LuaValue table, LuaValue key, CancellationToken cancellationToken)
    {
        var stack = state.Stack;
        var isTable = table.TryRead<LuaTable>(out var t);

        if (isTable && t.TryGetValue(key, out var result))
        {
            return result;
        }
        else if (table.TryGetMetamethod(Metamethods.Index, out var metamethod))
        {
            if (!metamethod.TryRead<LuaFunction>(out var indexTable))
            {
                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
            }

            stack.Push(table);
            stack.Push(key);

            var methodBuffer = ArrayPool<LuaValue>.Shared.Rent(1024);
            methodBuffer.AsSpan().Clear();
            try
            {
                await indexTable.InvokeAsync(new()
                {
                    State = state,
                    ArgumentCount = 2,
                    SourcePosition = chunk.SourcePositions[pc],
                }, methodBuffer, cancellationToken);

                return methodBuffer[0];
            }
            finally
            {
                ArrayPool<LuaValue>.Shared.Return(methodBuffer);
            }
        }
        else if (isTable)
        {
            return LuaValue.Nil;
        }
        else
        {
            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "index", table);
            return default; // dummy
        }
    }

#if NET6_0_OR_GREATER
    [AsyncMethodBuilder(typeof(PoolingAsyncValueTaskMethodBuilder))]
#endif
    static async ValueTask SetTableValue(LuaState state, Chunk chunk, int pc, LuaValue table, LuaValue key, LuaValue value, CancellationToken cancellationToken)
    {
        var stack = state.Stack;
        var isTable = table.TryRead<LuaTable>(out var t);

        if (isTable && t.ContainsKey(key))
        {
            t[key] = value;
        }
        else if (table.TryGetMetamethod(Metamethods.NewIndex, out var metamethod))
        {
            if (!metamethod.TryRead<LuaFunction>(out var indexTable))
            {
                LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "call", metamethod);
            }

            stack.Push(table);
            stack.Push(key);
            stack.Push(value);

            var methodBuffer = ArrayPool<LuaValue>.Shared.Rent(1024);
            methodBuffer.AsSpan().Clear();
            try
            {
                await indexTable.InvokeAsync(new()
                {
                    State = state,
                    ArgumentCount = 3,
                    SourcePosition = chunk.SourcePositions[pc],
                }, methodBuffer, cancellationToken);
            }
            finally
            {
                ArrayPool<LuaValue>.Shared.Return(methodBuffer);
            }
        }
        else if (isTable)
        {
            t[key] = value;
        }
        else
        {
            LuaRuntimeException.AttemptInvalidOperation(GetTracebacks(state, chunk, pc), "index", table);
        }
    }

    static (int FrameBase, int ArgumentCount) PrepareForFunctionCall(LuaState state, LuaFunction function, Instruction instruction, int RA, bool isTailCall)
    {
        var stack = state.Stack;

        var argumentCount = instruction.B - 1;
        if (instruction.B == 0)
        {
            argumentCount = (ushort)(stack.Count - (RA + 1));
        }

        var newBase = RA + 1;

        // In the case of tailcall, the local variables of the caller are immediately discarded, so there is no need to retain them.
        // Therefore, a call can be made without allocating new registers.
        if (isTailCall)
        {
            var currentBase = state.GetCurrentFrame().Base;
            var stackBuffer = stack.GetBuffer();
            stackBuffer.Slice(newBase, argumentCount).CopyTo(stackBuffer.Slice(currentBase, argumentCount));
            newBase = currentBase;
        }

        var variableArgumentCount = function is Closure luaClosure && luaClosure.Proto.HasVariableArgments
            ? argumentCount - luaClosure.Proto.ParameterCount
            : 0;

        // If there are variable arguments, the base of the stack is moved by that number and the values ​​of the variable arguments are placed in front of it.
        // see: https://wubingzheng.github.io/build-lua-in-rust/en/ch08-02.arguments.html
        if (variableArgumentCount > 0)
        {
            var temp = newBase;
            newBase += variableArgumentCount;

            var buffer = ArrayPool<LuaValue>.Shared.Rent(argumentCount);
            try
            {
                stack.EnsureCapacity(newBase + argumentCount);
                stack.NotifyTop(newBase + argumentCount);

                var stackBuffer = stack.GetBuffer();
                stackBuffer.Slice(temp, argumentCount).CopyTo(buffer);
                buffer.AsSpan(0, argumentCount).CopyTo(stackBuffer[newBase..]);

                buffer.AsSpan(argumentCount - variableArgumentCount, variableArgumentCount).CopyTo(stackBuffer[temp..]);
            }
            finally
            {
                ArrayPool<LuaValue>.Shared.Return(buffer);
            }
        }

        return (newBase, argumentCount);
    }

    static Tracebacks GetTracebacks(LuaState state, Chunk chunk, int pc)
    {
        var frame = state.GetCurrentFrame();
        state.PushCallStackFrame(frame with
        {
            CallPosition = chunk.SourcePositions[pc],
            ChunkName = chunk.Name,
            RootChunkName = chunk.GetRoot().Name,
        });
        var tracebacks = state.GetTracebacks();
        state.PopCallStackFrame();

        return tracebacks;
    }
}