#include "intcode.hpp"
#include <iostream>

namespace intcode {

BadInstruction::BadInstruction(std::size_t pc, value_type instruction)
    : pc{pc}, instruction{instruction} {}

char const *BadInstruction::what() const noexcept { return "bad instruction"; }

Machine::Machine() : rom_{}, ram_{}, pc_{0}, base_{0} {}

Machine::Machine(std::vector<value_type> ram)
    : rom_{ram}, ram_{}, pc_{0}, base_{0} {}

auto Machine::ref(value_type instruction, value_type p, std::size_t offset)
    -> value_type & {
  auto &i = at(pc_ + offset);
  switch (instruction / p % 10) {
  case 0:
    return at(i);
  case 1:
    return i;
  case 2:
    return at(base_ + i);
  default:
    throw BadInstruction{pc_, instruction};
  }
}

auto Machine::at(std::size_t i) -> value_type & {
  return i < rom_.size() ? rom_[i] : ram_[i];
}

auto Machine::step() -> std::variant<Input, Output, Halt> {
  for (;;) {
    auto instruction = at(pc_);
    auto a = [=]() -> auto & { return ref(instruction, 100, 1); };
    auto b = [=]() -> auto & { return ref(instruction, 1000, 2); };
    auto c = [=]() -> auto & { return ref(instruction, 10000, 3); };

    switch (instruction % 100) {
    case 1:
      c() = a() + b();
      pc_ += 4;
      break;

    case 2:
      c() = a() * b();
      pc_ += 4;
      break;

    case 3: {
      auto &pos = a();
      pc_ += 2;
      return Input{pos};
    }

    case 4: {
      auto val = a();
      pc_ += 2;
      return Output{val};
    }

    case 5:
      pc_ = a() ? b() : pc_ + 3;
      break;

    case 6:
      pc_ = a() ? pc_ + 3 : b();
      break;

    case 7:
      c() = a() < b();
      pc_ += 4;
      break;

    case 8:
      c() = a() == b();
      pc_ += 4;
      break;

    case 9:
      base_ += a();
      pc_ += 2;
      break;

    case 99:
      return Halt{};

    default:
      throw BadInstruction{pc_, instruction};
    }
  }
}

auto parse_stream(std::istream &in) -> std::vector<value_type> {
  value_type x;
  std::string str;
  std::vector<value_type> result;
  while (std::getline(in, str, ',')) {
    result.push_back(std::stoi(str));
  }
  return result;
}

}