#include "CPU.h"

#include <stdexcept>
#include <iostream>
#include <iomanip>
#include <stdlib.h>
#include <array>

CPU::CPU(std::shared_ptr<Bus> bus) : m_Bus(bus), m_Context({m_Instruction, m_InstructionPointer, m_Flags, m_Registers, m_Bus}){
  m_InstructionPointer = 0x00008000;

  for(int i = 0; i < 16; i++)
  {
    m_Registers[i] = 0;
  }
}

void CPU::Step(){
  FetchDecode();
  Execute();
}

void CPU::FetchDecode(){
  std::cout << "Fetching instruction: " << std::hex << m_InstructionPointer << std::endl;
  m_InstructionRaw = m_Bus->AccessX<uint64_t>(m_InstructionPointer); // Slice of 8 bytes.

  std::cout << "Context window fetched: " << std::hex <<  m_InstructionRaw << std::endl; // Start Decode Instruction
  uint64_t first_byte = m_InstructionRaw & 0xFF;
  std::cout << "Decoded first byte: " << std::hex << first_byte << std::endl;
  Opcode opcode = static_cast<Opcode>(first_byte);

  if(first_byte >= 0xB8 && first_byte <= 0xBF)
  {
    m_Instruction.m_Operand1 = first_byte - 0xB8;
    opcode = Opcode::MOV_R_IMM32;
  }
    
  switch(opcode){
  case Opcode::NOP:    m_Instruction.m_Length = 1;    break;
  case Opcode::HLT:    m_Instruction.m_Length = 1;    break;
  case Opcode::MOV_R_IMM32:
    m_Instruction.m_Operand2 = m_Bus->AccessX<uint32_t>(m_InstructionPointer + 1);
    m_Instruction.m_Length = 5;
    break;
  case Opcode::ADD_RM32_R32:
    m_Instruction.m_Operand1 = m_Bus->AccessX<uint8_t>(m_InstructionPointer + 1);
    m_Instruction.m_Operand2 = m_Bus->AccessX<uint32_t>(m_InstructionPointer + 2);
    m_Instruction.m_Length = 6;
    break;
  default:
    std::runtime_error("Decode encountered unexpected opcode.");
    break;
  }

  m_Instruction.m_Opcode = opcode;
  m_InstructionPointer += m_Instruction.m_Length;
}

void CPU::Execute(){
  std::cout << "Executing... \n";
  uint8_t opcode_value = static_cast<uint8_t>(m_Instruction.m_Opcode);
  auto& exec_table = GetExecutorTable();
  if(exec_table[opcode_value])
  {
    exec_table[opcode_value](m_Context);
    return;
  }
  throw std::runtime_error("Opcode not found!");
}