integration of legal moves into the upper generate legal moves function (#87)

Author: Hardcode3

include/bitbishop/movegen/legal_moves.hpp

@@ -0,0 +1,65 @@
+#pragma once
+
+#include <bitbishop/attacks/generate_attacks.hpp>
+#include <bitbishop/bitboard.hpp>
+#include <bitbishop/board.hpp>
+#include <bitbishop/color.hpp>
+#include <bitbishop/lookups/attackers.hpp>
+#include <bitbishop/move.hpp>
+#include <bitbishop/movegen/bishop_moves.hpp>
+#include <bitbishop/movegen/castling_moves.hpp>
+#include <bitbishop/movegen/check_mask.hpp>
+#include <bitbishop/movegen/king_moves.hpp>
+#include <bitbishop/movegen/knight_moves.hpp>
+#include <bitbishop/movegen/pawn_moves.hpp>
+#include <bitbishop/movegen/pins.hpp>
+#include <bitbishop/movegen/queen_moves.hpp>
+#include <bitbishop/movegen/rook_moves.hpp>
+#include <vector>
+
+/**
+ * @brief Generates all legal moves for the given side in the current position.
+ *
+ * This function computes the full set of legal moves for @p us, taking into
+ * account checks, pins, enemy attacks, and special rules such as castling
+ * and en passant. Move legality is enforced during generation rather than
+ * by post-filtering.
+ *
+ * The generation pipeline is:
+ *  - Detect checkers and compute the check resolution mask
+ *  - Compute pinned pieces and their allowed movement rays
+ *  - Generate legal king moves (always allowed)
+ *  - Generate legal castling moves (only when not in check)
+ *  - If in double check, stop after king moves
+ *  - Otherwise, generate legal moves for all remaining pieces
+ *
+ * @param moves Vector to append generated legal moves to
+ * @param board Current board position
+ * @param us Color of the side to generate moves for
+ *
+ * @note The move list is appended to; it is not cleared by this function.
+ * @note Assumes the board position is internally consistent and legal.
+ */
+void generate_legal_moves(std::vector<Move> moves, const Board& board, Color us) {
+  Square king_sq = board.king_square(us).value();
+  Color them = ColorUtil::opposite(us);
+
+  Bitboard checkers = attackers_to(king_sq, them);
+  Bitboard check_mask = compute_check_mask(king_sq, checkers, board);
+  PinResult pins = compute_pins(king_sq, board, us);
+  Bitboard enemy_attacks = generate_attacks(board, them);
+
+  generate_legal_king_moves(moves, board, us, king_sq, enemy_attacks, check_mask);
+
+  generate_castling_moves(moves, board, us, checkers, enemy_attacks);
+
+  if (checkers.count() > 1) {
+    return;
+  }
+
+  generate_knight_legal_moves(moves, board, us, check_mask, pins);
+  generate_bishop_legal_moves(moves, board, us, check_mask, pins);
+  generate_rook_legal_moves(moves, board, us, check_mask, pins);
+  generate_queen_legal_moves(moves, board, us, check_mask, pins);
+  generate_pawn_legal_moves(moves, board, us, king_sq, check_mask, pins);
+}