Fix fen placement string, disambiguate moves from san

src/lx_chess.cr

@@ -39,7 +39,9 @@ term = LxChess::Terminal.new
 
 loop do
   term.move 0, 0
-  puts fen.placement
+  print fen.placement
+  term.trunc
+  puts
   puts
   gb.draw
   puts
@@ -68,7 +70,10 @@ rescue e : LxChess::Notation::InvalidNotation | LxChess::Game::SanError
   end
 ensure
   puts
-  log.each { |l| puts l }
+  log.each { |l| print l; term.trunc; puts }
+  until log.size < 8
+    log.pop
+  end
 end
 
 # gb.flip!

src/lx_chess/board.cr

@@ -68,7 +68,7 @@ module LxChess
     # Convert human *cord* into an index on the board.
     # Ex: `A1` => `0`
     def index(cord : String)
-      x = LETTERS.index(cord[0]) || 0
+      x = LETTERS.index(cord[0].downcase) || 0
       y = cord[1].to_i - 1
       index(x, y)
     end
@@ -102,11 +102,16 @@ module LxChess
       index + (@width - dist_left) - 1
     end
 
-    def rank(index)
+    def rank(index : Int16)
       rank, _ = index.divmod(@width)
       rank
     end
 
+    def file(index : Int16)
+      _, file = index.divmod(@width)
+      file
+    end
+
     def move(from : (String | Int), to : (String | Int))
       piece = self[from.to_i16]
       self[from.to_i16] = nil

src/lx_chess/fen.cr

@@ -73,10 +73,10 @@ module LxChess
     end
 
     def placement
-      @board.map { |piece| piece ? piece.fen_symbol : nil }
+      rows = @board.map { |piece| piece ? piece.fen_symbol : nil }
         .each_slice(@board.width)
-        .map { |row| row.chunks { |r| r.nil? }.map { |chunked, values| chunked ? values.size : values.join }.first }
+        .map { |row| row.chunks { |r| r.nil? }.map { |chunked, values| chunked ? values.size : values.join }.join }
-        .join('/')
+        .to_a.reverse.join('/')
     end
   end
 end

src/lx_chess/game.cr

@@ -37,7 +37,10 @@ module LxChess
         end
       end
 
-      raise SanError.new("Ambiguous SAN") if pieces.size > 1
+      if pieces.size > 1
+        pieces = disambiguate_candidates(notation, pieces)
+      end
+      raise SanError.new("#{notation.to_s} is ambiguous") if pieces.size > 1
       if piece = pieces.first?
         # from, to
         [piece.index, index]
@@ -46,6 +49,32 @@ module LxChess
       end
     end
 
+    # Attempt to reduce ambiguities in candidate moves
+    def disambiguate_candidates(notation : Notation, pieces : Array(Piece | Nil))
+      return pieces unless origin = notation.origin
+      case origin
+      when /[a-z]\d/
+        piece = @board[origin]
+        pieces.select { |c| c == piece }
+      when /[a-z]/
+        file = Board::LETTERS.index(origin[0].downcase) || 0
+        pieces.select do |c|
+          next unless c
+          next unless index = c.index
+          @board.file(index) == file
+        end
+      when /\d/
+        rank = origin.to_i16
+        pieces.select do |c|
+          next unless c
+          next unless index = c.index
+          @board.rank(index) == rank
+        end
+      else
+        pieces
+      end
+    end
+
     # Generate the psuedo-legal moves for a given *square*
     # TODO: add en passant, add boundaries, remove illegal moves
     def moves(square : (String | Int))