From a2b8b9013cea10ef122bfa469aa3ce51fbe9b950 Mon Sep 17 00:00:00 2001
From: Peter Karpov <PeterKarpov@inversed.ru>
Date: Thu, 4 Jul 2024 15:26:55 +0300
Subject: [PATCH] Initial implementation of priority drops

---
 src/parser.cpp   | 12 ++++++++++++
 src/position.cpp |  2 ++
 src/position.h   |  3 +++
 src/variant.h    |  1 +
 src/variants.ini |  1 +
 5 files changed, 19 insertions(+)

diff --git a/src/parser.cpp b/src/parser.cpp
index 3ebf1b16f..f7f6d87ac 100644
--- a/src/parser.cpp
+++ b/src/parser.cpp
@@ -410,6 +410,18 @@ Variant* VariantParser<DoCheck>::parse(Variant* v) {
         if (DoCheck && (idx == std::string::npos || idx2 == std::string::npos))
             std::cerr << "promotedPieceType - Invalid piece type: " << token << std::endl;
     }
+    // priority drops
+    const auto& it_pr_drop = config.find("priorityDropTypes");
+    if (it_pr_drop != config.end())
+    {
+        char token;
+        size_t idx = 0;
+        std::stringstream ss(it_pr_drop->second);
+        while (ss >> token && ((idx = v->pieceToChar.find(toupper(token))) != std::string::npos))
+            v->isPriorityDrop[PieceType(idx)] = true;
+        if (DoCheck && idx == std::string::npos && token != '-')
+            std::cerr << "priorityDropTypes - Invalid piece type: " << token << std::endl;
+    }
     parse_attribute("piecePromotionOnCapture", v->piecePromotionOnCapture);
     parse_attribute("mandatoryPawnPromotion", v->mandatoryPawnPromotion);
     parse_attribute("mandatoryPiecePromotion", v->mandatoryPiecePromotion);
diff --git a/src/position.cpp b/src/position.cpp
index b9f34be44..752e97da5 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -1086,6 +1086,8 @@ bool Position::legal(Move m) const {
           if (popcount((DarkSquares & to ? DarkSquares : ~DarkSquares) & pieces(us, BISHOP)) + 1 > (count_with_hand(us, BISHOP) + 1) / 2)
               return false;
   }
+  if (type_of(m) == DROP && (!var->isPriorityDrop[type_of(moved_piece(m))]) && priorityDropCountInHand[us] > 0)
+      return false;
 
   // No legal moves from target square
   if (immobility_illegal() && (type_of(m) == DROP || type_of(m) == NORMAL) && !(PseudoMoves[0][us][type_of(moved_piece(m))][to] & board_bb()))
diff --git a/src/position.h b/src/position.h
index adaeeb6ad..b9256f456 100644
--- a/src/position.h
+++ b/src/position.h
@@ -369,6 +369,7 @@ class Position {
   bool tsumeMode;
   bool chess960;
   int pieceCountInHand[COLOR_NB][PIECE_TYPE_NB];
+  int priorityDropCountInHand[COLOR_NB];
   int virtualPieces;
   Bitboard promotedPieces;
   void add_to_hand(Piece pc);
@@ -1532,6 +1533,7 @@ inline void Position::add_to_hand(Piece pc) {
   if (variant()->freeDrops) return;
   pieceCountInHand[color_of(pc)][type_of(pc)]++;
   pieceCountInHand[color_of(pc)][ALL_PIECES]++;
+  priorityDropCountInHand[color_of(pc)] += var->isPriorityDrop[type_of(pc)];
   psq += PSQT::psq[pc][SQ_NONE];
 }
 
@@ -1539,6 +1541,7 @@ inline void Position::remove_from_hand(Piece pc) {
   if (variant()->freeDrops) return;
   pieceCountInHand[color_of(pc)][type_of(pc)]--;
   pieceCountInHand[color_of(pc)][ALL_PIECES]--;
+  priorityDropCountInHand[color_of(pc)] -= var->isPriorityDrop[type_of(pc)];
   psq -= PSQT::psq[pc][SQ_NONE];
 }
 
diff --git a/src/variant.h b/src/variant.h
index aa2738356..6de41dc74 100644
--- a/src/variant.h
+++ b/src/variant.h
@@ -90,6 +90,7 @@ struct Variant {
   bool mustCapture = false;
   bool mustDrop = false;
   PieceType mustDropType = ALL_PIECES;
+  bool isPriorityDrop[PIECE_TYPE_NB] = {};
   bool pieceDrops = false;
   bool dropLoop = false;
   bool capturesToHand = false;
diff --git a/src/variants.ini b/src/variants.ini
index 0810312c6..eb60f3dbb 100644
--- a/src/variants.ini
+++ b/src/variants.ini
@@ -212,6 +212,7 @@
 # mustCapture: captures are mandatory (check evasion still takes precedence) [bool] (default: false)
 # mustDrop: drops are mandatory (e.g., for Sittuyin setup phase) [bool] (default: false)
 # mustDropType: piece type for which piece drops are mandatory [PieceType] (default: *)
+# priorityDropTypes: piece types that must be dropped before dropping the other pieces [PieceType] (default: none)
 # pieceDrops: enable piece drops [bool] (default: false)
 # dropLoop: captures promoted pieces are not demoted [bool] (default: false)
 # capturesToHand: captured pieces go to opponent's hand [bool] (default: false)