othello/src/logic/move.rs

use std::cmp::Ordering;

use super::board_value::BoardValueMap;
use crate::repr::{Board, CoordPair, Piece, Winner};
use allocative::Allocative;

pub type MoveCoord = Option<CoordPair>;

#[derive(Clone, Copy, PartialEq, Eq, Allocative, Debug, PartialOrd, Ord)]
pub enum MVSGameState {
    Win = 1,
    Loss = 0,
    Tie = -1,
}

#[derive(Clone, Copy, Debug, Allocative, PartialEq, Eq, Default)]
pub struct MoveValueStats {
    state: Option<MVSGameState>,
    wins: u16,
    losses: u16,
    pub value: i32,
}

impl MoveValueStats {
    fn chance_win(&self) -> Option<f32> {
        let sum = self.losses + self.wins;
        if sum == 0 {
            return None;
        }
        Some(self.wins as f32 / sum as f32)
    }

    pub fn populate_self_from_children(&mut self, others: &[Self]) {
        let wins = others.iter().map(|x| x.wins).sum::<u16>()
            + others
                .iter()
                .filter(|x| x.state == Some(MVSGameState::Win))
                .count() as u16;
        let losses = others.iter().map(|x| x.losses).sum::<u16>()
            + others
                .iter()
                .filter(|x| x.state == Some(MVSGameState::Loss))
                .count() as u16;

        self.wins = wins;
        self.losses = losses;
    }
}

impl PartialOrd for MoveValueStats {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for MoveValueStats {
    fn cmp(&self, other: &Self) -> Ordering {
        if self.state.is_some() && other.state.is_some() {
            return self.state.cmp(&other.state);
        }

        let s_cw = self.chance_win();
        let o_cw = other.chance_win();
        if s_cw.is_some() && o_cw.is_some() {
            if s_cw > o_cw {
                return Ordering::Greater;
            } else if o_cw > s_cw {
                return Ordering::Less;
            }
        }

        self.value.cmp(&other.value)
    }
}

#[derive(Clone, Debug, Allocative)]
pub struct Move {
    /// Coordinates (i, j) of the move (if it exists)
    pub coord: MoveCoord,

    /// Current winner of the match
    pub winner: Winner,

    /// Index of this move's parent
    pub parent: Option<usize>,

    /// Indices of this Move's Children
    // PERF! this accounts for ~40% of memory usage
    // I'm thinking maybe switching to this actually being `Vec<Box<Move>>`
    // and ditching the entire `Arena` idea, that would have
    // cascading effects though, something to think about
    pub children: Vec<usize>,

    /// Value of this move (including children)
    pub value: MoveValueStats,

    /// What is the inherit value of this move (not including children)
    pub self_value: i16,

    /// Which color made a move on this move?
    pub color: Piece,

    /// Was this move's children previously trimmed?
    pub is_trimmed: bool,
}

pub struct MoveValueConfig {
    pub self_value_raw: bool,
}

impl Move {
    pub fn new(
        coord: MoveCoord,
        board: Board,
        color: Piece,
        agent_color: Piece,
        mvc: MoveValueConfig,
    ) -> Self {
        let mut m = Move {
            coord,
            winner: board.game_winner(),
            parent: None,
            children: Vec::new(),
            value: Default::default(),
            color,
            is_trimmed: false,
            self_value: 0,
        };

        // set wins/losses values appropriately
        match m.winner {
            Winner::Player(piece) => {
                if piece == agent_color {
                    m.value.wins += 1;
                    m.value.state = Some(MVSGameState::Win);
                } else {
                    m.value.losses += 1;
                    m.value.state = Some(MVSGameState::Loss);
                }
            }
            Winner::Tie => {
                m.value.state = Some(MVSGameState::Tie);
            }
            Winner::None => {}
        }

        if !mvc.self_value_raw {
            m.self_value = m.compute_self_value(agent_color, &board, mvc);
        } else {
            m.self_value = const { BoardValueMap::weighted() }.board_value(&board, agent_color);
        }
        m
    }

    fn compute_self_value(&self, agent_color: Piece, board: &Board, _mvc: MoveValueConfig) -> i16 {
        if self.winner == Winner::Player(!agent_color) {
            // if this board results in the opponent winning, MAJORLY negatively weigh this move
            // NOTE! this branch isn't completely deleted because if so, the bot wouldn't make a move.
            // We shouldn't prune branches because we still need to always react to the opponent's moves
            return i16::MIN + 1;
        } else if self.winner == Winner::Player(agent_color) {
            // results in a win for the agent
            return i16::MAX - 1;
        }

        // I guess ignore Ties here, don't give them an explicit value,
        const { BoardValueMap::weighted() }.board_value(board, agent_color)
    }

    /// Sort children of the [`Move`] by their self_value in `arena`
    pub fn sort_children(&mut self, arena: &[Move]) {
        self.children.sort_by(|&a, &b| {
            arena[b].value.cmp(&arena[a].value) // Descending order for agent's max nodes
        });
    }
}