dev: refactoring Board to be simpler for Piece to use

This commit adds a bunch of getters/setters for accessing the
boardGrid. This is a simpler way to allow both Piece and all
the inherited classes to access the Board without having to
declare every single class a friend. So now when we want to
access boardGrid, we use getPieceAt() or setPieceAt(). They
are overloaded to accept rank/file, Square, or int/int.
There's also a convenience function to check if the square
is empty, though that may get re-written to use the existing
Square.isValid().

inc/Board.hpp

@@ -14,9 +14,7 @@
 #include <string>
 #include <vector>
 
-#include "Piece.hpp"
+// suggested to forward declare here, and put include in the .cpp
-
-// why do I have to forward declare all these?!
 class Piece;
 
 enum Players { PL_WHITE, PL_BLACK };
@@ -25,14 +23,61 @@ struct Square;
 class Board {
   private:
     friend class Piece; // this doesn't seem to do anything
-    Players playerTurn;
-  public:
-    // this should be protected, but even when Piece is declared as a friend,
-    // accessing it in Piece.cpp threw an error
     std::vector<std::vector<std::unique_ptr<Piece>>> boardGrid;
+    Players playerTurn;
+    // let's get super object-oriented, baby
+    // these help the getters and setters access the boardGrid
+    // and also make them shorter and less duplicative
+    inline std::unique_ptr<Piece>& at(int r, int f) {
+        return boardGrid[r][f];
+    }
+    inline const std::unique_ptr<Piece>& at(int r, int f) const {
+        return boardGrid[r][f];
+    }
+
+    inline std::unique_ptr<Piece>& at(Rank rank, File file) {
+        return boardGrid[static_cast<int>(rank)][static_cast<int>(file)];
+    }
+    inline const std::unique_ptr<Piece>& at(Rank rank, File file) const {
+        return boardGrid[static_cast<int>(rank)][static_cast<int>(file)];
+    }
+
+    inline std::unique_ptr<Piece>& at(const Square& sq) {
+        return boardGrid[static_cast<int>(sq.rank)][static_cast<int>(sq.file)];
+    }
+    inline const std::unique_ptr<Piece>& at(const Square& sq) const {
+        return boardGrid[static_cast<int>(sq.rank)][static_cast<int>(sq.file)];
+    }
+  public:
     Board();
     virtual ~Board();
 
+    // These are to allow Piece to access Board in a controlled way
+    // --- GETTERS ---
+    Piece* getPieceAt(int r, int f) { return at(r, f).get(); }
+    const Piece* getPieceAt(int r, int f) const { return at(r, f).get(); }
+
+    Piece* getPieceAt(Rank rank, File file) { return at(rank, file).get(); }
+    const Piece* getPieceAt(Rank rank, File file) const { return at(rank, file).get(); }
+
+    Piece* getPieceAt(const Square& sq) { return at(sq).get(); }
+    const Piece* getPieceAt(const Square& sq) const { return at(sq).get(); }
+
+    // --- SETTERS ---
+    void setPieceAt(int r, int f, std::unique_ptr<Piece> piece) { at(r, f) = std::move(piece); }
+    void clearSquare(int r, int f) { at(r, f).reset(); }
+
+    void setPieceAt(Rank rank, File file, std::unique_ptr<Piece> piece) { at(rank, file) = std::move(piece); }
+    void clearSquare(Rank rank, File file) { at(rank, file).reset(); }
+
+    void setPieceAt(const Square& sq, std::unique_ptr<Piece> piece) { at(sq) = std::move(piece); }
+    void clearSquare(const Square& sq) { at(sq).reset(); }
+
+    // --- CHECKERS ---
+    bool isSquareEmpty(int r, int f) const { return at(r, f) == nullptr; }
+    bool isSquareEmpty(Rank rank, File file) const { return at(rank, file) == nullptr; }
+    bool isSquareEmpty(const Square& sq) const { return at(sq) == nullptr; }
+    
     void setupInitialPosition();
 
     void clearBoard();