Implement quiescence search for leaf nodes

src/search/quiescence.rs

@@ -0,0 +1,45 @@
+use crate::{
+    board::{game::Game, history::MoveParameters},
+    evaluation::evaluation::evaluate_position,
+    movegen::r#move::{Move, MoveType},
+};
+
+pub fn quiescence(game: &mut Game, mut alpha: i32, beta: i32) -> (Option<Move>, i32) {
+    let color = game.current_player();
+    let stand_pat = evaluate_position(&game.board);
+
+    if stand_pat >= beta {
+        return (None, beta);
+    }
+
+    if alpha < stand_pat {
+        alpha = stand_pat;
+    }
+
+    let captures = game
+        .board
+        .pseudo_moves_all(color)
+        .into_iter()
+        .filter(|m| !matches!(m.move_type, MoveType::Quiet));
+
+    for mv in captures {
+        let move_parameters = MoveParameters::build(&game.board, &mv);
+        game.board.make_move(&mv);
+
+        if game.board.king_under_check(color) {
+            game.board.unmake_move(move_parameters);
+            continue;
+        }
+
+        let move_score = -quiescence(game, -beta, -alpha).1;
+        game.board.unmake_move(move_parameters);
+
+        if move_score >= beta {
+            return (Some(mv), beta);
+        }
+
+        alpha = alpha.max(move_score);
+    }
+
+    (None, 0)
+}