feat(core): AI 棋形评分模块 — 连五/活四/冲四/活三等棋形打分

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

core/src/ai/evaluate.rs

@@ -0,0 +1,122 @@
+use crate::board::Board;
+use crate::types::{CellState, Color, Position};
+
+/// 棋形分数
+const FIVE: f64 = 100000.0;
+const OPEN_FOUR: f64 = 10000.0;
+const RUSH_FOUR: f64 = 5000.0;
+const OPEN_THREE: f64 = 1000.0;
+const SLEEP_THREE: f64 = 500.0;
+const OPEN_TWO: f64 = 100.0;
+const SLEEP_TWO: f64 = 50.0;
+const OPEN_ONE: f64 = 10.0;
+
+/// 评估整个棋盘对 player 的得分 (player得分 - 对手得分)
+pub fn evaluate_board(board: &Board, player: Color) -> f64 {
+    let player_score = evaluate_player(board, player);
+    let opponent_score = evaluate_player(board, player.opponent());
+    player_score - opponent_score
+}
+
+fn evaluate_player(board: &Board, color: Color) -> f64 {
+    let directions: [(isize, isize); 4] = [(0, 1), (1, 0), (1, 1), (1, -1)];
+    let mut total = 0.0f64;
+    let size = board.size;
+
+    for x in 0..size {
+        for y in 0..size {
+            if board.get(Position::new(x, y)) != CellState::Occupied(color) {
+                continue;
+            }
+            for &(dx, dy) in &directions {
+                let (count, start_open, end_open) =
+                    scan_pattern(board, Position::new(x, y), color, dx, dy);
+                total += score_pattern(count, start_open, end_open);
+            }
+        }
+    }
+    total
+}
+
+/// 从 pos 向 (dx,dy) 方向扫描, 只计数起点
+fn scan_pattern(
+    board: &Board,
+    pos: Position,
+    color: Color,
+    dx: isize,
+    dy: isize,
+) -> (u32, bool, bool) {
+    let mut count = 1u32;
+
+    // 正方向
+    let mut nx = pos.x as isize + dx;
+    let mut ny = pos.y as isize + dy;
+    while in_bounds(board, nx, ny)
+        && board.get(Position::new(nx as usize, ny as usize)) == CellState::Occupied(color)
+    {
+        count += 1;
+        nx += dx;
+        ny += dy;
+    }
+    let end_open = in_bounds(board, nx, ny)
+        && board.get(Position::new(nx as usize, ny as usize)) == CellState::Empty;
+
+    // 反方向 (检查是否是起点)
+    let sx = pos.x as isize - dx;
+    let sy = pos.y as isize - dy;
+    let start_open = in_bounds(board, sx, sy)
+        && board.get(Position::new(sx as usize, sy as usize)) == CellState::Empty;
+
+    // 如果不是连续段的起点, 不计分 (避免重复)
+    if in_bounds(board, sx, sy)
+        && board.get(Position::new(sx as usize, sy as usize)) == CellState::Occupied(color)
+    {
+        return (0, false, false);
+    }
+
+    (count, start_open, end_open)
+}
+
+fn score_pattern(count: u32, start_open: bool, end_open: bool) -> f64 {
+    let open_count = start_open as u32 + end_open as u32;
+    match (count, open_count) {
+        (5, _) => FIVE,
+        (4, 2) => OPEN_FOUR,
+        (4, 1) => RUSH_FOUR,
+        (3, 2) => OPEN_THREE,
+        (3, 1) => SLEEP_THREE,
+        (2, 2) => OPEN_TWO,
+        (2, 1) => SLEEP_TWO,
+        (1, 2) => OPEN_ONE,
+        _ => 0.0,
+    }
+}
+
+fn in_bounds(board: &Board, x: isize, y: isize) -> bool {
+    x >= 0 && y >= 0 && (x as usize) < board.size && (y as usize) < board.size
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::board::Board;
+    use crate::types::{Color, Position};
+
+    #[test]
+    fn test_evaluate_empty_board() {
+        let board = Board::new(15);
+        let score = evaluate_board(&board, Color::Black);
+        assert_eq!(score, 0.0);
+    }
+
+    #[test]
+    fn test_five_in_a_row_high_score() {
+        let board = Board::new(15);
+        let mut board = board;
+        for y in 5..10 {
+            board = board.place(Position::new(7, y), Color::Black).unwrap();
+        }
+        let score = evaluate_board(&board, Color::Black);
+        assert!(score > 10000.0);
+    }
+}

core/src/ai/mod.rs

@@ -0,0 +1,11 @@
+use crate::board::Board;
+use crate::types::{Color, Position};
+
+/// AI 引擎统一接口
+pub trait AiEngine: Send + Sync {
+    /// 返回 AI 的最佳落子位置, 无位置返回 None
+    fn best_move(&self, board: &Board, color: Color) -> Option<Position>;
+}
+
+pub mod evaluate;
+pub mod search;

core/src/ai/search.rs

@@ -0,0 +1,2 @@
+//! AI 搜索模块 — 占位符, 待实现 Alpha-Beta 搜索
+//! TODO: 在 Task 6 中实现完整搜索逻辑

core/src/lib.rs

@@ -1,5 +1,6 @@
 // Gobang core library — 纯游戏逻辑，零 GUI 依赖
 
+pub mod ai;
 pub mod board;
 pub mod rules;
 pub mod types;