using System;
using CPUx86 = Cosmos.Assembler.x86;
using Cosmos.Assembler;
using Cosmos.IL2CPU.IL.CustomImplementations.System;

namespace Cosmos.IL2CPU.X86.IL
{
    [Cosmos.IL2CPU.OpCode(ILOpCode.Code.Ldelem_Ref)]
    public class Ldelem_Ref: ILOp
    {
        public Ldelem_Ref(Cosmos.Assembler.Assembler aAsmblr)
            : base(aAsmblr)
        {
        }

        public static void Assemble(Cosmos.Assembler.Assembler aAssembler, uint aElementSize, bool isSigned, bool debugEnabled)
        {
            DoNullReferenceCheck(aAssembler, debugEnabled, 4);
            //if (aElementSize <= 0 || aElementSize > 8 || (aElementSize > 4 && aElementSize < 8))
            //{
            //    throw new Exception("Unsupported size for Ldelem_Ref: " + aElementSize);
            //}

            new CPUx86.Pop {DestinationReg = CPUx86.Registers.EAX};
            new CPUx86.Mov {DestinationReg = CPUx86.Registers.EDX, SourceValue = aElementSize};
            new CPUx86.Multiply {DestinationReg = CPUx86.Registers.EDX};

            new CPUx86.Add {DestinationReg = CPUx86.Registers.EAX, SourceValue = (ObjectImpl.FieldDataOffset + 4)};

            if (aElementSize > 4)
            {
                // we start copying the last bytes
                new CPUx86.Add {DestinationReg = CPUx86.Registers.EAX, SourceValue = aElementSize - 4};
            }

            new CPUx86.Pop {DestinationReg = CPUx86.Registers.EDX};
            new CPUx86.Add {DestinationReg = CPUx86.Registers.EDX, SourceReg = CPUx86.Registers.EAX};

            var xSizeLeft = aElementSize;
            while (xSizeLeft > 0)
            {
                var xCurrentStep = Math.Min(xSizeLeft, 4);
                if (xSizeLeft % 4 != 0)
                {
                    xCurrentStep = xSizeLeft % 4;
                }
                xSizeLeft = xSizeLeft - xCurrentStep;
                switch (xCurrentStep)
                {
                    case 1:
                        if (isSigned)
                        {
                            new CPUx86.MoveSignExtend {DestinationReg = CPUx86.Registers.ECX, Size = 8, SourceReg = CPUx86.Registers.EDX, SourceIsIndirect = true};
                        }
                        else
                        {
                            new CPUx86.MoveZeroExtend {DestinationReg = CPUx86.Registers.ECX, Size = 8, SourceReg = CPUx86.Registers.EDX, SourceIsIndirect = true};
                        }
                        new CPUx86.Push {DestinationReg = CPUx86.Registers.ECX};
                        break;
                    case 2:
                        if (isSigned)
                        {
                            new CPUx86.MoveSignExtend {DestinationReg = CPUx86.Registers.ECX, Size = 16, SourceReg = CPUx86.Registers.EDX, SourceIsIndirect = true};
                        }
                        else
                        {
                            new CPUx86.MoveZeroExtend {DestinationReg = CPUx86.Registers.ECX, Size = 16, SourceReg = CPUx86.Registers.EDX, SourceIsIndirect = true};
                        }
                        new CPUx86.Push {DestinationReg = CPUx86.Registers.ECX};
                        break;
                    case 4:
                        // copy a full dword
                        new CPUx86.Push {DestinationReg = CPUx86.Registers.EDX, DestinationIsIndirect = true};
                        new CPUx86.Sub {DestinationReg = CPUx86.RegistersEnum.EDX, SourceValue = 4}; // move to previous 4 bytes
                        break;
                    //case 8:
                    //    new CPUx86.Push {DestinationReg = CPUx86.Registers.EDX, DestinationDisplacement = 4, DestinationIsIndirect = true};
                    //    new CPUx86.Push {DestinationReg = CPUx86.Registers.EDX, DestinationIsIndirect = true};
                    //    break;
                }
            }
        }

        public override void Execute(MethodInfo aMethod, ILOpCode aOpCode)
        {
            Assemble( Assembler, 4, false, DebugEnabled);
        }
    }
}