# HG changeset patch
# User Laman
# Date 2017-04-17 20:28:13
# Node ID 2fcaffe8cb708aba3d370157caebea66b7c7421d
# Parent  0d57edb8be11235ce0f3fa1662bb6e028ee90316

checking for a legal position

diff --git a/src/core.py b/src/core.py
--- a/src/core.py
+++ b/src/core.py
@@ -6,7 +6,7 @@ import PIL
 from util import MsgQueue
 from gui import gui
 from imageanalyzer import ImageAnalyzer
-from go import Go
+from go import Go, isLegalPosition
 import config as cfg
 
 
@@ -47,7 +47,10 @@ class Core:
 
 	def analyze(self):
 		if self.detector.analyze(self._frame):
-			self._guiMessages.send("setGameState",(self.detector.board,))
+			if isLegalPosition(self.detector.board):
+				self._guiMessages.send("setGameState",(self.detector.board,))
+			else:
+				log.info("illegal position detected")
 
 	def listen(self):
 		listenerThread=threading.Thread(target=lambda: self._ownMessages.listen())
diff --git a/src/go.py b/src/go.py
--- a/src/go.py
+++ b/src/go.py
@@ -1,4 +1,4 @@
-EMPTY=0
+EMPTY=0
 BLACK=1
 WHITE=-1
 
@@ -7,7 +7,8 @@ class Go:
 	## Initializes self.board to a list[r][c]=EMPTY.
 	def __init__(self,boardSize=19):
 		self.boardSize=boardSize
-		self.board=[[EMPTY]*self.boardSize for x in range(boardSize)]
+		self.board=[[EMPTY]*boardSize for x in range(boardSize)]
+		self._temp=[[EMPTY]*boardSize for x in range(boardSize)]
 
 	## Executes a move.
 	#
@@ -22,11 +23,11 @@ class Go:
 
 		# capture neighbors
 		for r,c in ((-1,0),(1,0),(0,-1),(0,1)):
-			self.temp=[[False]*self.boardSize for x in self.board]
+			self._clearTemp()
 			if not self._floodFill(-color,row+r,col+c): self._remove()
 
 		# check for suicide
-		self.temp=[[False]*self.boardSize for x in self.board]
+		self._clearTemp()
 		if not self._floodFill(color,row,col):
 			self.board[row][col]=EMPTY
 			return False
@@ -39,19 +40,52 @@ class Go:
 	#  @return True if alive, False if captured
 	def _floodFill(self,color,row,col):
 		if col<0 or col>=self.boardSize or row<0 or row>=self.boardSize: return False # out of range
-		if self.temp[row][col]: return False # already visited
+		if self._temp[row][col]: return False # already visited
 		if self.board[row][col]==EMPTY: return True # found a liberty
 		if self.board[row][col]!=color: return False # opponent's stone
-		self.temp[row][col]=True # set visited
+		self._temp[row][col]=True # set visited
 		return self._floodFill(color,row,col-1) or self._floodFill(color,row,col+1) or self._floodFill(color,row-1,col) or self._floodFill(color,row+1,col) # check neighbors
 
 	## Removes stones at coordinates marked with True in self.temp.
 	def _remove(self):
 		for r in range(self.boardSize):
 			for c in range(self.boardSize):
-				if self.temp[r][c]: self.board[r][c]=EMPTY
+				if self._temp[r][c]: self.board[r][c]=EMPTY
 
+	def _clearTemp(self):
+		for i in range(self.boardSize):
+			for j in range(self.boardSize):
+				self._temp[i][j]=EMPTY
 
 def exportBoard(board):
 	substitutions={EMPTY:".", BLACK:"X", WHITE:"O"}
 	return "\n".join("".join(substitutions.get(x,"?") for x in row) for row in board)
+
+
+def isLegalPosition(board):
+	boardSize=len(board)
+	temp=[[None]*boardSize for x in range(boardSize)]
+
+	for r in range(boardSize):
+		for c in range(boardSize):
+			if board[r][c]==EMPTY: continue
+			if temp[r][c]: continue
+			if not dfs([(r,c)],board,temp): return False
+	return True
+
+
+def dfs(stack,board,mask):
+	boardSize=len(board)
+	(r,c)=stack[0]
+	color=board[r][c]
+
+	while len(stack)>0:
+		(r,c)=stack.pop()
+		if board[r][c]==EMPTY: return True
+		elif board[r][c]!=color: continue
+		elif mask[r][c]: return True
+		mask[r][c]=True
+		for (x,y) in ((0,-1),(-1,0),(0,1),(1,0)):
+			if 0<=r+y<boardSize and 0<=c+x<boardSize:
+				stack.append((r+y,c+x))
+	return False
diff --git a/src/tests/__init__.py b/src/tests/__init__.py
new file mode 100644
diff --git a/src/tests/testGo.py b/src/tests/testGo.py
new file mode 100644
--- /dev/null
+++ b/src/tests/testGo.py
@@ -0,0 +1,25 @@
+from unittest import TestCase
+
+from go import isLegalPosition
+
+
+class TestLegal(TestCase):
+	def testLegal(self):
+		board=[
+			[0,0,0,0,0],
+			[1,1,1,1,1],
+			[-1,-1,0,1,0],
+			[0,0,0,-1,-1],
+			[0,-1,0,-1,0]
+		]
+		self.assertTrue(isLegalPosition(board))
+
+	def testIllegal(self):
+		board=[
+			[0,1,0,0,0],
+			[1,-1,1,0,0],
+			[0,1,0,0,0],
+			[0,0,0,0,0],
+			[0,0,0,0,0]
+		]
+		self.assertFalse(isLegalPosition(board))