From e578d09e1a120f812ac5baffcd550e0fa6dd98b8 Mon Sep 17 00:00:00 2001
From: Vasily Vlasov <vvlasov@brightgrove.com>
Date: Wed, 16 Oct 2019 12:18:12 +0300
Subject: [PATCH] add FEN-string validator based on regular expression

---
 fen_validator.py | 36 ++++++++++++++++++++++++++++++++++++
 pystockfish.py   |  8 ++++++++
 2 files changed, 44 insertions(+)
 create mode 100644 fen_validator.py

diff --git a/fen_validator.py b/fen_validator.py
new file mode 100644
index 0000000..81ac27b
--- /dev/null
+++ b/fen_validator.py
@@ -0,0 +1,36 @@
+import re
+
+def fenPass(fen):
+    regexMatch=re.match('\s*^(((?:[rnbqkpRNBQKP1-8]+\/){7})[rnbqkpRNBQKP1-8]+)\s([b|w])\s([K|Q|k|q]{1,4})\s(-|[a-h][1-8])\s(\d+\s\d+)$', fen)
+    if  regexMatch:
+        regexList = regexMatch.groups()
+        fen = regexList[0].split("/")
+        if len(fen) != 8:
+            raise ValueError("expected 8 rows in position part of fen: {0}".format(repr(fen)))
+
+        for fenPart in fen:
+            field_sum = 0
+            previous_was_digit, previous_was_piece = False,False
+
+            for c in fenPart:
+                if c in ["1", "2", "3", "4", "5", "6", "7", "8"]:
+                    if previous_was_digit:
+                        raise ValueError("two subsequent digits in position part of fen: {0}".format(repr(fen)))
+                    field_sum += int(c)
+                    previous_was_digit = True
+                    previous_was_piece = False
+                elif c == "~":
+                    if not previous_was_piece:
+                        raise ValueError("~ not after piece in position part of fen: {0}".format(repr(fen)))
+                    previous_was_digit, previous_was_piece = False,False
+                elif c.lower() in ["p", "n", "b", "r", "q", "k"]:
+                    field_sum += 1
+                    previous_was_digit = False
+                    previous_was_piece = True
+                else:
+                    raise ValueError("invalid character in position part of fen: {0}".format(repr(fen)))
+
+            if field_sum != 8:
+                raise ValueError("expected 8 columns per row in position part of fen: {0}".format(repr(fen)))
+
+    else: raise ValueError("fen doesn`t match follow this example: rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1 ")
diff --git a/pystockfish.py b/pystockfish.py
index 3da9fe8..22e8f4a 100644
--- a/pystockfish.py
+++ b/pystockfish.py
@@ -14,6 +14,9 @@
 import re
 import subprocess
 from random import randint
+
+from fen_validator import fenPass
+
 MAX_MOVES = 200
 UCI_MOVE_REGEX = "[a-h]\d[a-h]\d[qrnb]?"
 PV_REGEX = " pv (?P<move_list>{0}( {0})*)".format(UCI_MOVE_REGEX)
@@ -195,6 +198,11 @@ def setfenposition(self, fen):
         """
         set position in fen notation.  Input is a FEN string i.e. "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1"
         """
+        try:
+            fenPass(fen)
+        except ValueError as e:
+            print(e.message)
+
         self.put('position fen %s' % fen)
         self.isready()