Endgame-Analyzer/game_state.hpp

#include <cassert>
#include <algorithm>
#include <iterator>

namespace Hanabi {

    Card &Card::operator++() {
        rank++;
        return *this;
    }

    Card Card::successor() const { return {suit, static_cast<rank_t>(rank + 1)}; }

    const Card Card::operator++(int) {
        Card ret = *this;
        rank++;
        return ret;
    }

    template<std::size_t num_suits>
    std::ostream &operator<<(std::ostream &os, const Stacks<num_suits> &stacks) {
        for (size_t i = 0; i < stacks.size() - 1; i++) {
            os << starting_card_rank - stacks[i] << ", ";
        }
        os << starting_card_rank - stacks.back();
        return os;
    }

    template<std::size_t num_suits, typename T, bool respect_card_duplicity>
    CardArray<num_suits, T, respect_card_duplicity>::CardArray(T default_val) {
        for(size_t suit = 0; suit < num_suits; suit++) {
            for (rank_t rank = 0; rank < starting_card_rank; rank++) {
                if constexpr (respect_card_duplicity) {
                    std::ranges::fill(_vals.array[suit][rank], default_val);
                } else {
                    _vals.array[suit][rank] = default_val;
                }
            }
        }
    }

    template<std::size_t num_suits, typename T, bool respect_card_duplicity>
    const T& CardArray<num_suits, T, respect_card_duplicity>::operator[](const Card &card) const {
        if constexpr (respect_card_duplicity) {
            return _vals.array[card.suit][card.rank][card.copy];
        } else {
            return _vals.array[card.suit][card.rank];
        }
    };

    template<std::size_t num_suits, typename T, bool respect_card_duplicity>
    T& CardArray<num_suits, T, respect_card_duplicity>::operator[](const Card &card) {
        if constexpr (respect_card_duplicity) {
            return _vals.array[card.suit][card.rank][card.copy];
        } else {
            return _vals.array[card.suit][card.rank];
        }
    };

    template<size_t num_suits, player_t num_players, size_t hand_size>
    HanabiState<num_suits, num_players, hand_size>::HanabiState(const std::vector<Card> &deck):
    _turn(0),
    _num_clues(max_num_clues),
    _weighted_draw_pile_size(deck.size()),
    _stacks(),
    _hands(),
    _card_positions(draw_pile),
    _draw_pile(),
    _pace(deck.size() - 5 * num_suits - num_players * (hand_size - 1)),
    _score(0) {
        std::ranges::fill(_stacks, starting_card_rank);
        for(const Card& card: deck) {
            _draw_pile.push_back({card, 1});
        }
        for(player_t player = 0; player < num_players; player++) {
            for(std::uint8_t index = 0; index < hand_size; index++) {
                draw(index);
            }
            incr_turn();
        }
        assert(_turn == 0);
    }

    template<size_t num_suits, player_t num_players, size_t hand_size>
    BacktrackAction HanabiState<num_suits, num_players, hand_size>::clue() {
        assert(_num_clues > 0);
        --_num_clues;

        incr_turn();

        return BacktrackAction{ActionType::clue, {}, {}};
    }

    template<size_t num_suits, player_t num_players, size_t hand_size>
    void HanabiState<num_suits, num_players, hand_size>::incr_turn() {
        _turn = (_turn + 1) % num_players;
        if(endgame_turns_left != -1) {
            endgame_turns_left--;
        }
    }

    template<size_t num_suits, player_t num_players, size_t hand_size>
    void HanabiState<num_suits, num_players, hand_size>::decr_turn() {
        _turn = (_turn + num_players - 1) % num_players;
        if (endgame_turns_left != -1) {
            endgame_turns_left++;
        }
    }

    template<size_t num_suits, player_t num_players, size_t hand_size>
    bool HanabiState<num_suits, num_players, hand_size>::is_playable(const Hanabi::Card &card) const {
        return card.rank == _stacks[card.suit] - 1;
    }

    template<size_t num_suits, player_t num_players, size_t hand_size>
    bool HanabiState<num_suits, num_players, hand_size>::is_trash(const Hanabi::Card &card) const {
        return card.rank >= _stacks[card.suit];
    }

    template<std::size_t num_suits, player_t num_players, std::size_t hand_size>
    BacktrackAction HanabiState<num_suits, num_players, hand_size>::play(
            std::uint8_t index) {
        assert(index < _hands[_turn].size());
        const Card card = _hands[_turn][index];
        assert(card.rank == _stacks[card.suit] - 1);

        --_stacks[card.suit];
        _score++;

        BacktrackAction ret{ActionType::play, _hands[_turn][index], index, 0};

        if (card.rank == 0) {
            // update clues if we played the last card of a stack
            _num_clues++;
        }

        ret.multiplicity = draw(index);
        incr_turn();

        return ret;
    }

    template<std::size_t num_suits, player_t num_players, std::size_t hand_size>
    BacktrackAction HanabiState<num_suits, num_players, hand_size>::discard(std::uint8_t index) {
        assert(index < _hands[_turn].size());
        assert(_num_clues != max_num_clues);

        _num_clues++;
        _pace--;

        BacktrackAction ret{ActionType::discard, _hands[_turn][index], index};

        ret.multiplicity = draw(index);
        incr_turn();

        return ret;
    }

    template<std::size_t num_suits, player_t num_players, std::size_t hand_size>
    std::uint8_t HanabiState<num_suits, num_players, hand_size>::find_card_in_hand(
            const Hanabi::Card &card) const {
       for(std::uint8_t i = 0; i < hand_size; i++) {
           if(_hands[_turn][i].rank == card.rank && _hands[_turn][i].suit == card.suit) {
               return i;
           }
       }
       return -1;
    }

    template<std::size_t num_suits, player_t num_players, std::size_t hand_size>
    std::ostream &operator<<(std::ostream &os, const HanabiState<num_suits, num_players, hand_size> hanabi_state) {
        os << "Stacks: " << hanabi_state._stacks << " (score " << +hanabi_state._score << ")";
        os << ", clues: " << +hanabi_state._num_clues << std::endl;
        os << "Draw pile: ";
        for (const auto &[card, mul]: hanabi_state._draw_pile) {
            os << card;
            if (mul > 1) {
                os << " (" << +mul << ")";
            }
            os << ", ";
        }
        os << "(size " << +hanabi_state._weighted_draw_pile_size << ")" << std::endl;
        os << "Hands: ";
        for (const auto &hand: hanabi_state._hands) {
            for (const auto &card: hand) {
                os << card << ", ";
            }
            os << " | ";
        }
        return os;
    }

    template<std::size_t num_suits, player_t num_players, std::size_t hand_size>
    std::uint8_t HanabiState<num_suits, num_players, hand_size>::draw(uint8_t index) {
        assert(index < _hands[_turn].size());

        const Card& discarded = _hands[_turn][index];
        if (_stacks[discarded.suit] > discarded.rank) {
            _card_positions[_hands[_turn][index]] = trash_or_play_stack;
        }

        // draw a new card if the draw pile is not empty
        if (!_draw_pile.empty()) {
            --_weighted_draw_pile_size;

            const CardMultiplicity draw = _draw_pile.front();
            _draw_pile.pop_front();
            assert(draw.multiplicity > 0);

            if (draw.multiplicity > 1) {
                _draw_pile.push_back(draw);
                _draw_pile.back().multiplicity--;
            }

            Card& card_in_hand = _hands[_turn][index];
            card_in_hand = draw.card;
            card_in_hand.copy = draw.multiplicity - 1;

            if (_stacks[draw.card.suit] > draw.card.rank) {
                _card_positions[card_in_hand] = _turn;
            }

            if(_draw_pile.empty()) {
                endgame_turns_left = num_players;
            }
            return draw.multiplicity;
        }
        return 0;
    }

    template<std::size_t num_suits, player_t num_players, std::size_t hand_size>
    void HanabiState<num_suits, num_players, hand_size>::revert_draw(std::uint8_t index, Card card) {
        endgame_turns_left = -1;
        assert(index < _hands[_turn].size());
        const Card& discarded = _hands[_turn][index];
        if (_stacks[discarded.suit] > discarded.rank) {
            _card_positions[discarded] = draw_pile;
        }

        // put card back into draw pile (at the back)
        if (!_draw_pile.empty() and _draw_pile.back().card.suit == _hands[_turn][index].suit and _draw_pile.back().card.rank == _hands[_turn][index].rank) {
            _draw_pile.back().multiplicity++;
        } else {
            _draw_pile.push_back({_hands[_turn][index], 1});
        }

        _hands[_turn][index] = card;
        if (_stacks[card.suit] > card.rank) {
            _card_positions[card] = _turn;
        }
        _weighted_draw_pile_size++;
    }

    template<std::size_t num_suits, player_t num_players, std::size_t hand_size>
    void HanabiState<num_suits, num_players, hand_size>::normalize_draw_and_positions() {
        const Card trash = [this]() -> Card {
            for(suit_t suit = 0; suit < num_suits; suit++) {
                if(_stacks[suit] < starting_card_rank) {
                    return {suit, starting_card_rank - 1, 0};
                }
            }
            return {0,0,0};
        }();

        CardArray<num_suits, std::uint8_t, false> nums_in_draw_pile;
        std::uint8_t num_trash_in_draw_pile = 0;
        for(const auto [card, multiplicity] : _draw_pile) {
            if (_stacks[card.suit] > card.rank) {
                nums_in_draw_pile[card] += multiplicity;
            } else {
                num_trash_in_draw_pile++;
            }
        }

        _draw_pile.clear();
        for(suit_t suit = 0; suit < num_suits; suit++) {
            for(rank_t rank = 0; rank < starting_card_rank; rank++) {
                Card card {suit, rank, 0};
                if (nums_in_draw_pile[card] > 0) {
                    _draw_pile.push_back({card, nums_in_draw_pile[card]});
                    for (std::uint8_t copy = 0; copy < nums_in_draw_pile[card]; copy++) {
                        card.copy = copy;
                        _card_positions[card] = draw_pile;
                    }
                }
            }
        }
        _draw_pile.push_back({trash, num_trash_in_draw_pile});

        for(player_t player = 0; player < num_players; player++) {
            for(Card& card : _hands[player]) {
                if (_stacks[card.suit] > card.rank) {
                    card.copy = nums_in_draw_pile[card];
                    nums_in_draw_pile[card]++;
                }
            }
        }
    }

    template<std::size_t num_suits, player_t num_players, std::size_t hand_size>
    void HanabiState<num_suits, num_players, hand_size>::revert(
            const BacktrackAction &action) {
        decr_turn();
        switch (action.type) {
            case ActionType::clue:
                assert(_num_clues < max_num_clues);
                _num_clues++;
                break;
            case ActionType::discard:
                assert(_num_clues > 0);
                _num_clues--;
                _pace++;
                revert_draw(action.index, action.discarded);
                break;
            case ActionType::play:
                if (action.discarded.rank == 0) {
                    _num_clues--;
                }
                revert_draw(action.index, action.discarded);
                _stacks[action.discarded.suit]++;
                _score--;
            default:
                break;
        }
    }

    #define UPDATE_PROBABILITY(new_probability) \
        best_probability = std::max(best_probability, new_probability); \
        if (best_probability == 1) { \
            return best_probability; \
        }

    template<std::size_t num_suits, player_t num_players, std::size_t hand_size>
    double HanabiState<num_suits, num_players, hand_size>::backtrack() {
        std::cout << *this << std::endl;
        if (_score == 5 * num_suits) {
            return 1;
        }
        if(_pace < 0 || endgame_turns_left == 0) {
            return 0;
        }

        // TODO: Have some endgame analysis here?

        // First, check if we have any playable cards
        double best_probability = 0;
        const std::array<Card, hand_size> hand = _hands[_turn];

        // First, check for playables
        for(std::uint8_t index = 0; index < hand_size; index++) {
            if(is_playable(hand[index])) {
                double sum_of_probabilities = 0;
                uint8_t sum_of_mults = 0;
                for(size_t i = 0; i < _draw_pile.size(); i++) {
                    BacktrackAction action = play(index);
                    sum_of_probabilities += backtrack() * action.multiplicity;
                    sum_of_mults += action.multiplicity;
                    revert(action);
                    assert(sum_of_mults <= _weighted_draw_pile_size);
                }
                assert(sum_of_mults == _weighted_draw_pile_size);
                const double probability_for_this_play = sum_of_probabilities / _weighted_draw_pile_size;
                UPDATE_PROBABILITY(probability_for_this_play);
            }
        }

        // Check for discards now
        if(_pace > 0) {
            for(std::uint8_t index = 0; index < hand_size; index++) {
                if (is_trash(hand[index])) {
                    double sum_of_probabilities = 0;
                    for(size_t i = 0; i < _draw_pile.size(); i++) {
                        BacktrackAction action = discard(index);
                        sum_of_probabilities += backtrack() * action.multiplicity;
                        revert(action);
                    }
                    const double probability_discard = sum_of_probabilities / _weighted_draw_pile_size;
                    UPDATE_PROBABILITY(probability_discard);

                    // All discards are equivalent, do not continue searching for different trash
                    break;
                }
            }
        }

        // Last option is to stall
        if(_num_clues > 0) {
            BacktrackAction action = clue();
            const double probability_stall = backtrack();
            revert(action);
            UPDATE_PROBABILITY(probability_stall);
        }

        return best_probability;
    }

} // namespace Hanabi