using System;
using CPUx86 = Cosmos.Assembler.x86;
using Cosmos.Assembler;
using Cosmos.IL2CPU.Plugs.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 };
      }

      // pop the array
      new CPUx86.Pop { DestinationReg = CPUx86.Registers.EDX };
      // convert to real memory address
      new CPUx86.Mov { DestinationReg = CPUx86.Registers.EDX, SourceReg = CPUx86.RegistersEnum.EDX, SourceIsIndirect = true };

      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);
    }
  }
}