namespace X86Disassembler.X86.Handlers.Sub;

/// <summary>
/// Handler for SUB r16, r/m16 instruction (0x2B with 0x66 prefix)
/// </summary>
public class SubR16Rm16Handler : InstructionHandler
{
    /// <summary>
    /// Initializes a new instance of the SubR16Rm16Handler class
    /// </summary>
    /// <param name="codeBuffer">The buffer containing the code to decode</param>
    /// <param name="decoder">The instruction decoder that owns this handler</param>
    /// <param name="length">The length of the buffer</param>
    public SubR16Rm16Handler(byte[] codeBuffer, InstructionDecoder decoder, int length)
        : base(codeBuffer, decoder, length)
    {
    }

    /// <summary>
    /// Checks if this handler can decode the given opcode
    /// </summary>
    /// <param name="opcode">The opcode to check</param>
    /// <returns>True if this handler can decode the opcode</returns>
    public override bool CanHandle(byte opcode)
    {
        // Check if the opcode is 0x2B and we have a 0x66 prefix
        return opcode == 0x2B && Decoder.HasOperandSizeOverridePrefix();
    }

    /// <summary>
    /// Decodes a SUB r16, r/m16 instruction
    /// </summary>
    /// <param name="opcode">The opcode of the instruction</param>
    /// <param name="instruction">The instruction object to populate</param>
    /// <returns>True if the instruction was successfully decoded</returns>
    public override bool Decode(byte opcode, Instruction instruction)
    {
        // Set the mnemonic
        instruction.Mnemonic = "sub";
        
        int position = Decoder.GetPosition();
        
        if (position >= Length)
        {
            return false;
        }
        
        // Read the ModR/M byte
        byte modRM = CodeBuffer[position++];
        Decoder.SetPosition(position);
        
        // Extract the fields from the ModR/M byte
        byte mod = (byte)((modRM & 0xC0) >> 6);
        byte reg = (byte)((modRM & 0x38) >> 3);
        byte rm = (byte)(modRM & 0x07);
        
        // Get register name (16-bit)
        string regName = ModRMDecoder.GetRegisterName(reg, 16);
        
        // For mod == 3, both operands are registers
        if (mod == 3)
        {
            string rmRegName = ModRMDecoder.GetRegisterName(rm, 16);
            instruction.Operands = $"{regName}, {rmRegName}";
        }
        else // Memory operand
        {
            // Get the memory operand string (use false for is64Bit)
            string memOperand = ModRMDecoder.DecodeModRM(mod, rm, false);
            
            // Replace "dword" with "word" in the memory operand
            memOperand = memOperand.Replace("dword", "word");
            
            instruction.Operands = $"{regName}, {memOperand}";
        }
        
        return true;
    }
}