cetkaik_full_state_transition 0.2.2

#![warn(clippy::pedantic)]
#![allow(clippy::too_many_lines, clippy::missing_errors_doc)]

#[macro_use]
extern crate enum_primitive;

use serde::{Deserialize, Serialize};

/// Represents the season. Currently, only four-season games are supported.
/// ／季節を表現する。今のところ4季制のことしか考えていない。
#[derive(Clone, Debug, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum Season {
    ///春, Spring
    Iei2,
    ///夏, Summer
    Xo1,
    ///秋, Autumn
    Kat2,
    ///冬, Winter
    Iat1,
}

/// Describes the inputs from the players.
/// ／プレイヤーからの入力を表現する。
pub mod message;

/// Describes the probability distribution of states. Exactly which state is reached depends on the server-side result of casting sticks.
/// ／状態の確率分布を表現する。サーバー側で投げ棒を乱択することで、どの状態に至るかが決まる。
pub mod probabilistic;

impl Season {
    #[must_use]
    pub fn next(self) -> Option<Self> {
        match self {
            Season::Iei2 => Some(Season::Xo1),
            Season::Xo1 => Some(Season::Kat2),
            Season::Kat2 => Some(Season::Iat1),
            Season::Iat1 => None,
        }
    }

    #[must_use]
    pub fn to_index(self) -> usize {
        match self {
            Season::Iei2 => 0,
            Season::Xo1 => 1,
            Season::Kat2 => 2,
            Season::Iat1 => 3,
        }
    }
}

use cetkaik_core::absolute;

/// Describes the state that the game is in.
/// ／ゲームの状態を表現する型。状態遷移図は複雑なので、詳しくはプレゼン
/// <https://docs.google.com/presentation/d/1IL8lelkw3oZif3QUQaKzGCPCLiBguM2kXjgOx9Cgetw/edit#slide=id.g788f78d7d6_0_0> または画像 <https://pbs.twimg.com/media/EqCkMhXUcAIynsd?format=png&name=900x900> を参照すること。
pub mod state;

impl state::C {
    #[must_use]
    pub fn piece_at_flying_piece_src(&self) -> absolute::Piece {
        *self
            .c
            .f
            .board
            .get(&self.c.flying_piece_src)
            .expect("Invalid `state::C`: at `flying_piece_src` there is no piece")
    }

    #[must_use]
    pub fn piece_at_flying_piece_step(&self) -> absolute::Piece {
        *self
            .c
            .f
            .board
            .get(&self.c.flying_piece_step)
            .expect("Invalid `state::C`: at `flying_piece_step` there is no piece")
    }
}

/// Theoretically speaking, it is necessary to distinguish x32 and x64
/// because it is possible to score 1 point (3+3-5).
/// Not that it will ever be of use in any real situation.
/// ／3点役2つと-5点役一つを同時成立させることにより1点の得点を得ることが可能である。したがって、二人の得点の総和が40点である以上、32倍レートと64倍レートを区別する必要がある（32点を獲得することは必ずしも勝利を意味しないが、64点を獲得することは必ず勝利を意味するので）。
///
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash, Serialize, Deserialize)]
pub enum Rate {
    X1,
    X2,
    X4,
    X8,
    X16,
    X32,
    X64,
}

use probabilistic::Probabilistic;

impl Rate {
    #[must_use]
    pub fn next(self) -> Self {
        match self {
            Rate::X1 => Rate::X2,
            Rate::X2 => Rate::X4,
            Rate::X4 => Rate::X8,
            Rate::X8 => Rate::X16,
            Rate::X16 => Rate::X32,
            Rate::X32 | Rate::X64 => Rate::X64,
        }
    }

    #[must_use]
    pub fn num(self) -> i32 {
        match self {
            Rate::X1 => 1,
            Rate::X2 => 2,
            Rate::X4 => 4,
            Rate::X8 => 8,
            Rate::X16 => 16,
            Rate::X32 => 32,
            Rate::X64 => 64,
        }
    }
}

fn apply_tam_move(
    old_state: &state::A,
    src: absolute::Coord,
    first_dest: absolute::Coord,
    second_dest: absolute::Coord,
    step: Option<absolute::Coord>,
    config: Config,
) -> Result<Probabilistic<state::HandNotResolved>, &'static str> {
    let (penalty1, is_a_hand1) = if old_state.tam_has_moved_previously {
        match config.moving_tam_immediately_after_tam_has_moved {
                Consequence::Allowed => (0, false),
                Consequence::Penalized{penalty, is_a_hand} => (penalty, is_a_hand),
                Consequence::Forbidden => return Err(
                    "By config, it is prohibited for tam2 to move immediately after the previous player has moved the tam2."
                )
            }
    } else {
        (0, false)
    };

    let (penalty2, is_a_hand2) =
        if src == second_dest {
            match config.tam_mun_mok {
                Consequence::Forbidden => return Err(
                    "By config, it is prohibited for tam2 to start and end at the same position.",
                ),
                Consequence::Allowed => (0, false),
                Consequence::Penalized { penalty, is_a_hand } => (penalty, is_a_hand),
            }
        } else {
            (0, false)
        };
    let mut new_field = old_state.f.clone();
    let expect_tam = new_field
        .board
        .remove(&src)
        .ok_or("expected tam2 but found an empty square")?;
    if !expect_tam.is_tam2() {
        return Err("expected tam2 but found a non-tam2 piece");
    }

    if new_field.board.contains_key(&first_dest) {
        return Err("the first destination is already occupied");
    }

    if let Some(st) = step {
        if !new_field.board.contains_key(&st) {
            return Err("the stepping square is empty");
        }
    }

    if new_field.board.contains_key(&second_dest) {
        return Err("the second destination is already occupied");
    }

    new_field.board.insert(second_dest, absolute::Piece::Tam2);

    Ok(Probabilistic::Pure(state::HandNotResolved {
        previous_a_side_hop1zuo1: old_state.f.a_side_hop1zuo1.clone(),
        previous_ia_side_hop1zuo1: old_state.f.ia_side_hop1zuo1.clone(),

        // When Tam2 moves, Tam2 is never stepped on (this assumption fails with the two-tam rule, which is not yet supported.)
        // 皇の動きで撃皇が発生することはない（二皇の場合は修正が必要）
        kut2tam2_happened: false,
        tam2tysak2_raw_penalty: penalty1 + penalty2,
        tam2tysak2_will_trigger_taxottymok: is_a_hand1 || is_a_hand2,
        rate: old_state.rate,
        i_have_moved_tam_in_this_turn: true,
        season: old_state.season,
        scores: old_state.scores,
        whose_turn: old_state.whose_turn,
        f: new_field,
    }))
}

fn apply_nontam_move(
    old_state: &state::A,
    src: absolute::Coord,
    dest: absolute::Coord,
    step: Option<absolute::Coord>,
    config: Config,
) -> Result<Probabilistic<state::HandNotResolved>, &'static str> {
    let nothing_happened = state::HandNotResolved {
        previous_a_side_hop1zuo1: old_state.f.a_side_hop1zuo1.clone(),
        previous_ia_side_hop1zuo1: old_state.f.ia_side_hop1zuo1.clone(),
        kut2tam2_happened: !config.failure_to_complete_the_move_means_exempt_from_kut2_tam2
            && match step {
                None => false,
                Some(step) => matches!(old_state.f.board.get(&step), Some(absolute::Piece::Tam2)),
            },
        rate: old_state.rate,
        i_have_moved_tam_in_this_turn: false,
        season: old_state.season,
        scores: old_state.scores,
        whose_turn: old_state.whose_turn,
        f: old_state.f.clone(),

        tam2tysak2_will_trigger_taxottymok: false,
        tam2tysak2_raw_penalty: 0,
    };

    if let Some(st) = step {
        if !old_state.f.board.contains_key(&st) {
            return Err("expected a stepping square but found an empty square");
        }
    }

    let src_piece = old_state
        .f
        .board
        .get(&src)
        .ok_or("src does not contain a piece")?;

    let (new_board, maybe_captured_piece) =
        move_nontam_piece_from_src_to_dest_while_taking_opponent_piece_if_needed(
            &old_state.f.board,
            src,
            dest,
            old_state.whose_turn,
        )?;
    let mut new_field = absolute::Field {
        board: new_board,
        a_side_hop1zuo1: old_state.f.a_side_hop1zuo1.clone(),
        ia_side_hop1zuo1: old_state.f.ia_side_hop1zuo1.clone(),
    };

    if let Some(absolute::NonTam2Piece { color, prof }) = maybe_captured_piece {
        new_field.insert_nontam_piece_into_hop1zuo1(color, prof, old_state.whose_turn);
    }

    let success = state::HandNotResolved {
        previous_a_side_hop1zuo1: old_state.f.a_side_hop1zuo1.clone(),
        previous_ia_side_hop1zuo1: old_state.f.ia_side_hop1zuo1.clone(),
        kut2tam2_happened: match step {
            None => false,
            Some(step) => matches!(old_state.f.board.get(&step), Some(absolute::Piece::Tam2)),
        },
        rate: old_state.rate,
        i_have_moved_tam_in_this_turn: false,
        season: old_state.season,
        scores: old_state.scores,
        whose_turn: old_state.whose_turn,
        f: new_field,

        tam2tysak2_will_trigger_taxottymok: false,
        tam2tysak2_raw_penalty: 0,
    };

    // 入水判定
    // water-entry cast
    if !absolute::is_water(src)
        && !src_piece.has_prof(cetkaik_core::Profession::Nuak1)
        && absolute::is_water(dest)
    {
        return Ok(Probabilistic::Water {
            failure: nothing_happened,
            success,
        });
    }
    Ok(Probabilistic::Pure(success))
}

/// When completely stuck, call this function to end the game.
/// ／完全に手詰まりのときは、この関数を呼び出すことで即時決着がつく。
pub fn no_move_possible_at_all(
    old_state: &state::A,
    config: Config,
) -> Result<state::HandResolved, &'static str> {
    let (hop1zuo1_candidates, candidates) = old_state.get_candidates(config);
    if hop1zuo1_candidates.is_empty() && candidates.is_empty() {
        Ok(state::HandResolved::GameEndsWithoutTymokTaxot(
            old_state.scores.which_side_is_winning(),
        ))
    } else {
        Err("At least one valid move exists")
    }
}

/// `NormalMove` sends `A` to `Probabilistic<HandNotResolved>`
pub fn apply_normal_move(
    old_state: &state::A,
    msg: message::NormalMove,
    config: Config,
) -> Result<Probabilistic<state::HandNotResolved>, &'static str> {
    let (hop1zuo1_candidates, candidates) = old_state.get_candidates(config);
    match msg {
        message::NormalMove::NonTamMoveFromHopZuo { color, prof, dest } => {
            let mut new_field = old_state
                .f
                .find_and_remove_piece_from_hop1zuo1(color, prof, old_state.whose_turn)
                .ok_or("Cannot find the specified piece in the hop1zuo1")?;

            if new_field.board.contains_key(&dest) {
                return Err("The destination is already occupied and hence cannot place a piece from hop1 zuo1");
            }

            new_field.board.insert(
                dest,
                absolute::Piece::NonTam2Piece {
                    color,
                    prof,
                    side: old_state.whose_turn,
                },
            );

            // For the sake of consistency, `cetkaik_yhuap_move_candidates` is called,
            // but since all illegal moves from hop1zuo1 are those that are trivially illegal
            // (that is, "you can't place onto a non-empty square" and "you can't place what you don't have"),
            // `cetkaik_yhuap_move_candidates` should never report a failure.
            // that is why it is not `return Err` but is `unreachable`.
            // 念のため `cetkaik_yhuap_move_candidates` を呼び出しておくが、
            // 持ち駒から打つ際の違法手というのが実は自明なものを除いて不存在なので、
            // ここで弾かれるとしたらコードがバグっているということになる。
            // したがって、 return Err ではなく unreachable としてある。

            if !hop1zuo1_candidates.contains(&message::PureMove::NormalMove(msg)) {
                unreachable!("inconsistencies found between cetkaik_yhuap_move_candidates::PureMove::NonTamMoveFromHopZuo and cetkaik_full_state_transition::apply_nontam_move")
            }

            Ok(Probabilistic::Pure(state::HandNotResolved {
                previous_a_side_hop1zuo1: old_state.f.a_side_hop1zuo1.clone(),
                previous_ia_side_hop1zuo1: old_state.f.ia_side_hop1zuo1.clone(),

                // The stepping of Tam2 never occurs if you are playing from hop1zuo1
                // 持ち駒から打つ際には撃皇は決して起こらない
                kut2tam2_happened: false,
                rate: old_state.rate,
                i_have_moved_tam_in_this_turn: false,
                season: old_state.season,
                scores: old_state.scores,
                whose_turn: old_state.whose_turn,
                f: new_field,
                tam2tysak2_will_trigger_taxottymok: false,
                tam2tysak2_raw_penalty: 0,
            }))
        }
        message::NormalMove::TamMoveNoStep {
            src,
            first_dest,
            second_dest,
        } => {
            if candidates.contains(&message::PureMove::NormalMove(msg)) {
                apply_tam_move(old_state, src, first_dest, second_dest, None, config)
            } else {
                Err("The provided TamMoveNoStep was rejected by the crate `cetkaik_yhuap_move_candidates`.")
            }
        }
        message::NormalMove::TamMoveStepsDuringFormer {
            src,
            first_dest,
            second_dest,
            step,
        } => {
            if candidates.contains(&message::PureMove::NormalMove(msg)) {
                apply_tam_move(old_state, src, first_dest, second_dest, Some(step), config)
            } else {
                Err("The provided TamMoveStepsDuringFormer was rejected by the crate `cetkaik_yhuap_move_candidates`.")
            }
        }
        message::NormalMove::TamMoveStepsDuringLatter {
            src,
            first_dest,
            second_dest,
            step,
        } => {
            if candidates.contains(&message::PureMove::NormalMove(msg)) {
                apply_tam_move(old_state, src, first_dest, second_dest, Some(step), config)
            } else {
                Err("The provided TamMoveStepsDuringLatter was rejected by the crate `cetkaik_yhuap_move_candidates`.")
            }
        }

        message::NormalMove::NonTamMoveSrcDst { src, dest } => {
            if candidates.contains(&message::PureMove::NormalMove(msg)) {
                apply_nontam_move(old_state, src, dest, None, config)
            } else {
                Err("The provided NonTamMoveSrcDst was rejected by the crate `cetkaik_yhuap_move_candidates`.")
            }
        }
        message::NormalMove::NonTamMoveSrcStepDstFinite { src, step, dest } => {
            if candidates.contains(&message::PureMove::NormalMove(msg)) {
                apply_nontam_move(old_state, src, dest, Some(step), config)
            } else {
                Err("The provided NonTamMoveSrcStepDstFinite was rejected by the crate `cetkaik_yhuap_move_candidates`.")
            }
        }
    }
}

/// `InfAfterStep` sends `A` to `Probabilistic<C>`
pub fn apply_inf_after_step(
    old_state: &state::A,
    msg: message::InfAfterStep,
    config: Config,
) -> Result<Probabilistic<state::C>, &'static str> {
    if !old_state.f.board.contains_key(&msg.src) {
        return Err("In InfAfterStep, `src` is not occupied; illegal");
    }

    if !old_state.f.board.contains_key(&msg.step) {
        return Err("In InfAfterStep, `step` is not occupied; illegal");
    }

    let (hop1zuo1_candidates, candidates) = old_state.get_candidates(config);
    assert!(hop1zuo1_candidates.is_empty());

    if !candidates
        .into_iter()
        .filter(|cand| match cand {
            message::PureMove::InfAfterStep(message::InfAfterStep {
                src,
                step,
                planned_direction: _,
            }) => *src == msg.src && *step == msg.step,
            _ => false,
        })
        .count()
        > 0
    {
        return Err(
            "The provided InfAfterStep was rejected by the crate `cetkaik_yhuap_move_candidates`.",
        );
    }

    let c = state::CWithoutCiurl {
        f: old_state.f.clone(),
        whose_turn: old_state.whose_turn,
        flying_piece_src: msg.src,
        flying_piece_step: msg.step,
        season: old_state.season,
        scores: old_state.scores,
        rate: old_state.rate,
    };

    Ok(Probabilistic::Sticks {
        s0: state::C {
            c: c.clone(),
            ciurl: 0,
        },
        s1: state::C {
            c: c.clone(),
            ciurl: 1,
        },
        s2: state::C {
            c: c.clone(),
            ciurl: 2,
        },
        s3: state::C {
            c: c.clone(),
            ciurl: 3,
        },
        s4: state::C {
            c: c.clone(),
            ciurl: 4,
        },
        s5: state::C { c, ciurl: 5 },
    })
}

mod score;

pub use score::Scores;

fn move_nontam_piece_from_src_to_dest_while_taking_opponent_piece_if_needed(
    board: &absolute::Board,
    src: absolute::Coord,
    dest: absolute::Coord,
    whose_turn: absolute::Side,
) -> Result<(absolute::Board, Option<absolute::NonTam2Piece>), &'static str> {
    let mut new_board = board.clone();

    let src_piece = new_board
        .remove(&src)
        .ok_or("src does not contain a piece")?;
    if src_piece.is_tam2() {
        return Err("Expected a NonTam2Piece to be present at the src, but found a Tam2");
    }

    if !src_piece.has_side(whose_turn) {
        return Err("Found the opponent piece at the src");
    }

    let maybe_captured_piece = new_board.remove(&dest);
    new_board.insert(dest, src_piece);

    if let Some(captured_piece) = maybe_captured_piece {
        match captured_piece {
            absolute::Piece::Tam2 => return Err("Tried to capture a Tam2"),
            absolute::Piece::NonTam2Piece {
                color: captured_piece_color,
                prof: captured_piece_prof,
                side: captured_piece_side,
            } => {
                if captured_piece_side == whose_turn {
                    return Err("Tried to capture an ally");
                }
                return Ok((
                    new_board,
                    Some(absolute::NonTam2Piece {
                        color: captured_piece_color,
                        prof: captured_piece_prof,
                    }),
                ));
            }
        }
    }
    Ok((new_board, None))
}

/// `AfterHalfAcceptance` sends `C` to `Probabilistic<HandNotResolved>`
pub fn apply_after_half_acceptance(
    old_state: &state::C,
    msg: message::AfterHalfAcceptance,
    config: Config,
) -> Result<Probabilistic<state::HandNotResolved>, &'static str> {
    let nothing_happened = state::HandNotResolved {
        previous_a_side_hop1zuo1: old_state.c.f.a_side_hop1zuo1.clone(),
        previous_ia_side_hop1zuo1: old_state.c.f.ia_side_hop1zuo1.clone(),
        kut2tam2_happened: !config.failure_to_complete_the_move_means_exempt_from_kut2_tam2
            && old_state.piece_at_flying_piece_step().is_tam2(),
        rate: old_state.c.rate,
        i_have_moved_tam_in_this_turn: false,
        season: old_state.c.season,
        scores: old_state.c.scores,
        whose_turn: old_state.c.whose_turn,
        f: old_state.c.f.clone(),
        tam2tysak2_will_trigger_taxottymok: false,
        tam2tysak2_raw_penalty: 0,
    };

    let candidates = old_state.get_candidates(config);

    if !candidates.contains(&msg) {
        return Err(
                    "The provided InfAfterStep was rejected either by the crate `cetkaik_yhuap_move_candidates`, or because the ciurl limit was exceeded.",
                );
    }

    if let Some(dest) = msg.dest {
        let piece = old_state.piece_at_flying_piece_src();

        let (new_board, maybe_captured_piece) =
            move_nontam_piece_from_src_to_dest_while_taking_opponent_piece_if_needed(
                &old_state.c.f.board,
                old_state.c.flying_piece_src,
                dest,
                old_state.c.whose_turn,
            )?;

        let mut new_field = absolute::Field {
            board: new_board,
            ia_side_hop1zuo1: old_state.c.f.ia_side_hop1zuo1.clone(),
            a_side_hop1zuo1: old_state.c.f.a_side_hop1zuo1.clone(),
        };

        if let Some(absolute::NonTam2Piece { color, prof }) = maybe_captured_piece {
            new_field.insert_nontam_piece_into_hop1zuo1(color, prof, old_state.c.whose_turn);
        };

        let success = state::HandNotResolved {
            previous_a_side_hop1zuo1: old_state.c.f.a_side_hop1zuo1.clone(),
            previous_ia_side_hop1zuo1: old_state.c.f.ia_side_hop1zuo1.clone(),
            kut2tam2_happened: old_state.piece_at_flying_piece_step().is_tam2(),
            rate: old_state.c.rate,
            i_have_moved_tam_in_this_turn: false,
            season: old_state.c.season,
            scores: old_state.c.scores,
            whose_turn: old_state.c.whose_turn,
            f: new_field,

            tam2tysak2_will_trigger_taxottymok: false,
            tam2tysak2_raw_penalty: 0,
        };

        // Trying to enter the water without any exemptions (neither the piece started from within water, nor the piece is a Vessel).
        // Hence sticks must be cast.
        // 入水判定が免除される特例（出発地点が皇水であるか、移動している駒が船である）なしで水に入ろうとしているので、判定が必要。
        if !absolute::is_water(old_state.c.flying_piece_src)
            && !piece.has_prof(cetkaik_core::Profession::Nuak1)
            && absolute::is_water(dest)
        {
            Ok(Probabilistic::Water {
                success,
                failure: nothing_happened,
            })
        } else {
            // 入水判定が絶対にないので確率は1
            // succeeds with probability 1
            Ok(Probabilistic::Pure(success))
        }
    } else {
        // the only possible side effect is that Stepping Tam might
        // modify the score (this side effect is to be handled by `resolve`). Water entry cannot fail,
        // since the piece has not actually moved.
        // 唯一ありえる副作用は、撃皇で点が減っている可能性があるということ（それは `resolve` で処理される）。
        // パスが発生した以上、駒の動きは実際には発生していないので、
        // 入水判定は発生していない。

        Ok(Probabilistic::Pure(nothing_happened))
    }
}

pub use score::Victor;

/// An auxiliary type that represents whether we should terminate the game or proceed to the next season if the player chose to end the current season.
/// ／もし終季が選ばれた際、次の季節に進むのか、それともゲームが終了するのかを保持するための補助的な型。
#[derive(Clone, Debug)]
pub enum IfTaxot {
    NextSeason(Probabilistic<state::A>),

    VictoriousSide(Victor),
}

/// Describes the minor differences between the numerous rule variants.
/// ／細かなルール差を吸収するための型。
#[readonly::make]
#[derive(Clone, Debug, Copy, PartialEq, Eq, Hash)]
pub struct Config {
    /// Describes whether the Stepping of Tam2 is considered a hand. If `false`, the Stepping of Tam2 results in the immediate subtraction of 5 points and does not trigger the taxot / tymok unless another hand is simultaneously created.
    /// ／撃皇が役であるかどうかのフラグ。`false`である場合、撃皇は即時5点減点であり、同時に他の役が成立していない限り終季・再行の判定を発生させない。
    pub step_tam_is_a_hand: bool,

    /// Described whether the square that Tam2 itself is in is considered as a tam2 hue. This matters only when you are stepping a Tam2.
    /// ／皇のあるマス自身が皇処になるかどうかのフラグ。撃皇をするときにのみ関係のあるフラグ。
    pub tam_itself_is_tam_hue: bool,

    /// hsjoihs 2020/02/18
    /// 「@SY 皇をもとの位置に戻す皇再来と、相手が動かした後の皇動かしによる皇再来を言い分けたいときってどうするんだろう（cerke_onlineは後者のみを禁じており、前者に関しては無罰則）」
    /// SY 2020/02/18 - 2020/02/19
    /// 「前者は皇無行とかっぽそう。後者が狭義の皇再来なのかもしれん。ただややこしい」
    pub moving_tam_immediately_after_tam_has_moved: Consequence,

    /// hsjoihs 2020/02/18
    /// 「@SY 皇をもとの位置に戻す皇再来と、相手が動かした後の皇動かしによる皇再来を言い分けたいときってどうするんだろう（cerke_onlineは後者のみを禁じており、前者に関しては無罰則）」
    /// SY 2020/02/18 - 2020/02/19
    /// 「前者は皇無行とかっぽそう。後者が狭義の皇再来なのかもしれん。ただややこしい」
    pub tam_mun_mok: Consequence,

    /// 入水判定や踏越え判定に失敗したときに、撃皇が免除されるかどうか
    pub failure_to_complete_the_move_means_exempt_from_kut2_tam2: bool,
}

/// Describes whether an action is forbidden, penalized, or allowed without any penalty.
/// 行為が禁止されるか、罰則付きであるか、それとも許容されるかを表現する型。
#[derive(Clone, Debug, Copy, PartialEq, Eq, Hash)]
pub enum Consequence {
    Allowed,
    Penalized { penalty: i32, is_a_hand: bool },
    Forbidden,
}

impl Config {
    /// Cerke Online α版での config 設定。
    #[must_use]
    pub fn cerke_online_alpha() -> Config {
        Config {
            step_tam_is_a_hand: false,
            tam_itself_is_tam_hue: true,
            moving_tam_immediately_after_tam_has_moved: Consequence::Forbidden,
            tam_mun_mok: Consequence::Allowed,
            failure_to_complete_the_move_means_exempt_from_kut2_tam2: false,
        }
    }

    /// 厳密官定での config 設定。
    #[must_use]
    pub fn strict_y1_huap1() -> Config {
        Config {
            step_tam_is_a_hand: true,
            tam_itself_is_tam_hue: false,
            moving_tam_immediately_after_tam_has_moved: Consequence::Penalized {
                penalty: -3,
                is_a_hand: true,
            },
            tam_mun_mok: Consequence::Penalized {
                penalty: -3,
                is_a_hand: true,
            },
            failure_to_complete_the_move_means_exempt_from_kut2_tam2: false,
        }
    }
}

/// Sends `HandNotResolved` to `HandResolved`.
#[must_use]
pub fn resolve(state: &state::HandNotResolved, config: Config) -> state::HandResolved {
    use cetkaik_calculate_hand::{calculate_hands_and_score_from_pieces, ScoreAndHands};
    let tymoxtaxot_because_of_kut2tam2 = state.kut2tam2_happened && config.step_tam_is_a_hand;

    let tymoxtaxot_because_of_newly_acquired: Option<i32> = match state.whose_turn {
        absolute::Side::ASide => {
            if state.previous_a_side_hop1zuo1 == state.f.a_side_hop1zuo1 {
                None
            } else {
                let ScoreAndHands {
                    score: _,
                    hands: old_hands,
                } = calculate_hands_and_score_from_pieces(&state.previous_a_side_hop1zuo1).unwrap();
                let ScoreAndHands {
                    score: new_score,
                    hands: new_hands,
                } = calculate_hands_and_score_from_pieces(&state.f.a_side_hop1zuo1).unwrap();

                // whether newly-acquired hand exists
                if new_hands.difference(&old_hands).count() > 0 {
                    Some(new_score)
                } else {
                    None
                }
            }
        }
        absolute::Side::IASide => {
            if state.previous_ia_side_hop1zuo1 == state.f.ia_side_hop1zuo1 {
                None
            } else {
                let ScoreAndHands {
                    score: _,
                    hands: old_hands,
                } = calculate_hands_and_score_from_pieces(&state.previous_ia_side_hop1zuo1)
                    .unwrap();
                let ScoreAndHands {
                    score: new_score,
                    hands: new_hands,
                } = calculate_hands_and_score_from_pieces(&state.f.ia_side_hop1zuo1).unwrap();

                // whether newly-acquired hand exists
                if new_hands.difference(&old_hands).count() > 0 {
                    Some(new_score)
                } else {
                    None
                }
            }
        }
    };

    if !tymoxtaxot_because_of_kut2tam2
        && tymoxtaxot_because_of_newly_acquired.is_none()
        && !state.tam2tysak2_will_trigger_taxottymok
    {
        // nothing happened; hand the turn to the next person
        // 役ができていないので、次の人に手番を渡す
        // 減点分×レートは引く。
        match state.scores.edit(
            state.tam2tysak2_raw_penalty,
            state.whose_turn,
            state.rate,
        ) {
            Ok(new_scores) => {
                return state::HandResolved::NeitherTymokNorTaxot(state::A {
                    f: state.f.clone(),
                    whose_turn: !state.whose_turn, /* hand the turn to the next person */
                    season: state.season,
                    scores: new_scores,
                    rate: state.rate,
                    tam_has_moved_previously: state.i_have_moved_tam_in_this_turn,
                });
            }

            Err(victor) => return state::HandResolved::GameEndsWithoutTymokTaxot(victor),
        }
    }

    // In all the other cases, a hand exists due to some reason; hence tymok/taxot
    // それ以外の場合、なんらかの理由で役が存在するので、終季・再行を行わねばならない
    let raw_score = state.tam2tysak2_raw_penalty
        + if tymoxtaxot_because_of_kut2tam2 {
            -5
        } else {
            0
        }
        + tymoxtaxot_because_of_newly_acquired.unwrap_or(0);

    let if_taxot = match state.scores.edit(raw_score, state.whose_turn, state.rate) {
        Err(victor) => IfTaxot::VictoriousSide(victor),
        Ok(new_scores) => {
            state.season.next().map_or(
                /* All seasons have ended */
                IfTaxot::VictoriousSide(new_scores.which_side_is_winning()),
                /* The next season exists */
                |next_season| IfTaxot::NextSeason(beginning_of_season(next_season, new_scores)),
            )
        }
    };

    state::HandResolved::HandExists {
        if_tymok: state::A {
            f: state.f.clone(),
            whose_turn: !state.whose_turn, /* hand the turn to the next person */
            season: state.season,
            scores: state.scores,
            rate: state.rate.next(), /* double the stake */
            tam_has_moved_previously: state.i_have_moved_tam_in_this_turn,
        },

        if_taxot,
    }
}

/// Start of the game, with the season in spring and each player holding 20 points
/// ／ゲーム開始、季節は春で所持点は20
#[must_use]
pub fn initial_state() -> Probabilistic<state::A> {
    beginning_of_season(Season::Iei2, Scores::new())
}

fn beginning_of_season(season: Season, scores: Scores) -> Probabilistic<state::A> {
    let ia_first = state::A {
        whose_turn: absolute::Side::IASide,
        scores,
        rate: Rate::X1,
        season,
        tam_has_moved_previously: false,
        f: absolute::Field {
            a_side_hop1zuo1: vec![],
            ia_side_hop1zuo1: vec![],
            board: cetkaik_core::absolute::yhuap_initial_board(),
        },
    };
    Probabilistic::WhoGoesFirst {
        a_first: state::A {
            whose_turn: absolute::Side::ASide,
            ..ia_first.clone()
        },
        ia_first,
    }
}