using X86Disassembler.X86.Operands;

namespace X86Disassembler.X86.Handlers.Shift;

/// <summary>
/// Handler for SHR r/m32, imm8 instruction (0xC1 /5)
/// </summary>
public class ShrRm32ByImmHandler : InstructionHandler
{
    /// <summary>
    /// Initializes a new instance of the ShrRm32ByImmHandler class
    /// </summary>
    /// <param name="decoder">The instruction decoder that owns this handler</param>
    public ShrRm32ByImmHandler(InstructionDecoder decoder)
        : base(decoder)
    {
    }

    /// <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)
    {
        // SHR r/m32, imm8 is encoded as 0xC1 /5
        if (opcode != 0xC1)
            return false;

        // Check if we can read the ModR/M byte
        if (!Decoder.CanReadByte())
            return false;

        // Check if the reg field of the ModR/M byte is 5 (SHR)
        var reg = ModRMDecoder.PeakModRMReg();
        return reg == 5; // 5 = SHR
    }

    /// <summary>
    /// Decodes a SHR r/m32, imm8 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 instruction type
        instruction.Type = InstructionType.Shr;

        // Read the ModR/M byte
        var (_, _, _, operand) = ModRMDecoder.ReadModRM();

        // Check if we can read the immediate byte
        if (!Decoder.CanReadByte())
            return false;

        // Read the immediate byte (shift count)
        byte imm8 = Decoder.ReadByte();

        // Create an immediate operand for the shift count
        var immOperand = OperandFactory.CreateImmediateOperand(imm8);

        // Set the structured operands
        instruction.StructuredOperands = 
        [
            operand,
            immOperand
        ];

        return true;
    }
}