From 668b0ed30cd45426fa29ec9a43054f980477a83f Mon Sep 17 00:00:00 2001
From: Mark Bluemer <bluemer.mark@gmail.com>
Date: Tue, 18 Apr 2017 21:10:49 -0400
Subject: [PATCH] Basic minimax search implemented, not tested

---
 include/BitBoard.h      |  1 +
 include/MinimaxSearch.h | 21 +++++++++++++++++
 src/BitBoard.cpp        |  6 +++++
 src/MinimaxSearch.cpp   | 51 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 79 insertions(+)
 create mode 100644 include/MinimaxSearch.h
 create mode 100644 src/MinimaxSearch.cpp

diff --git a/include/BitBoard.h b/include/BitBoard.h
index f360b92..42290be 100644
--- a/include/BitBoard.h
+++ b/include/BitBoard.h
@@ -90,6 +90,7 @@ class BitBoard
   std::string const player();
   std::vector<Move> const actions();
   BitBoard const result(Move move);
+  double utility(std::string player);
   void const printState();
 };
 
diff --git a/include/MinimaxSearch.h b/include/MinimaxSearch.h
new file mode 100644
index 0000000..053d588
--- /dev/null
+++ b/include/MinimaxSearch.h
@@ -0,0 +1,21 @@
+#ifndef MINIMAX_SEARCH_H
+#define MINIMAX_SEARCH_H
+
+#include <string>
+#include "Move.h"
+#include "BitBoard.h"
+
+class MinimaxSearch
+{
+private:
+  static const int maxDepth = 5;
+
+  double minValue(BitBoard board, int currentDepth);
+  double maxValue(BitBoard board, int currentDepth);
+
+public:
+  Move minimaxDecision(BitBoard &board);
+
+};
+
+#endif
diff --git a/src/BitBoard.cpp b/src/BitBoard.cpp
index 199e3cb..1de01ae 100644
--- a/src/BitBoard.cpp
+++ b/src/BitBoard.cpp
@@ -224,6 +224,12 @@ BitBoard const BitBoard::result(Move move)
   return currBoard;
 }
 
+double BitBoard::utility(std::string player)
+{
+  // TODO: Do something useful here
+  return 0.0;
+}
+
 void const BitBoard::printState()
 {
   std::cout<<"-"<<pieceToString(11)<<"-"<<pieceToString(5)<<"-"<<pieceToString(31)<<"-"<<pieceToString(25)<<std::endl;
diff --git a/src/MinimaxSearch.cpp b/src/MinimaxSearch.cpp
new file mode 100644
index 0000000..8dc4341
--- /dev/null
+++ b/src/MinimaxSearch.cpp
@@ -0,0 +1,51 @@
+#include <string>
+#include <limits>
+#include <algorithm>
+#include "BitBoard.h"
+#include "Move.h"
+#include "MinimaxSearch.h"
+
+/* Private Functions */
+
+double MinimaxSearch::minValue(BitBoard board, int currentDepth)
+{
+  if (currentDepth == maxDepth) return board.utility(board.player());
+  double v = std::numeric_limits<double>::lowest();
+  for (Move move : board.actions()) {
+    v = std::min(v, maxValue(board.result(move), ++currentDepth));
+  }
+  return v;
+}
+
+double MinimaxSearch::maxValue(BitBoard board, int currentDepth)
+{
+  if (currentDepth == maxDepth) return board.utility(board.player());
+  double v = std::numeric_limits<double>::max();
+  for (Move move : board.actions()) {
+    v = std::max(v, minValue(board.result(move), ++currentDepth));
+  }
+  return v;
+}
+
+/* Public Functions */
+
+Move MinimaxSearch::minimaxDecision(BitBoard &board)
+{
+  Move bestMove;
+  double bestMoveValue{0.0};
+
+  for (Move move : board.actions()) {
+    if (bestMove.isEmpty()) {
+      bestMove = move;
+      bestMoveValue = minValue(board.result(bestMove), 0);
+    } else {
+      double nextMoveValue = minValue(board.result(move), 0);
+      if (bestMoveValue < nextMoveValue) {
+        bestMove = move;
+        bestMoveValue = nextMoveValue;
+      }
+    }
+  }
+  return bestMove;
+}
+