#ifndef INTCODE_HPP_
#define INTCODE_HPP_

#include <cstddef>
#include <cstdint>
#include <istream>
#include <unordered_map>
#include <variant>
#include <vector>

template <class... Ts> struct overloaded : Ts... { using Ts::operator()...; };
template <class... Ts> overloaded(Ts...) -> overloaded<Ts...>;

namespace intcode {

  using value_type = std::int64_t;

  struct Input {
    value_type &pos;
  };

  struct Output {
    value_type val;
  };

  struct Halt {};

class Machine {
  std::vector<value_type> rom_;
  std::unordered_map<std::size_t, value_type> ram_;
  std::size_t pc_;
  std::size_t base_;

  auto ref(value_type instruction, value_type p, std::size_t offset)
      -> value_type &;

public:
  Machine();
  explicit Machine(std::vector<value_type> ram);
  auto step() -> std::variant<Input, Output, Halt>;
  auto at(std::size_t) -> value_type &;

};

struct BadInstruction : public std::exception {
  std::size_t pc;
  value_type instruction;
  explicit BadInstruction(std::size_t pc, value_type instruction);
  const char *what() const noexcept override;
};

auto parse_stream(std::istream &in) -> std::vector<value_type>;

}

#endif // INTCODE_HPP_