function fifteen(action)
%FIFTEEN A sliding puzzle of fifteen squares and sixteen slots.
%   Win by sequentially lining all fifteen squares up, leaving the
%   last square empty.  
%
%   Moves are made by clicking on a tile which lies in either the
%   same row or column as the open slot.  
%
%   This M-file, which implements this game, demonstrates good use
%   of "switch-yarding."  Switch-yard programming requires the GUI
%   to drive the program.  Based on the action of the GUI, it will
%   call the same function using different inputs to "switch" among
%   tasks.

% Raymond S. Norris, October 1996
% Copyright 1984-2002 The MathWorks, Inc. 
% $Revision: 1.10 $

if nargin<1
  % set up a working figure window and store it in the userdata for
  % action 'setup' to use
  figure_h=figure;
  set(figure_h,'Units','points')
  set(figure_h,'UserData',figure_h);
  action='initialize';
end

% actions to be switched on are: initialize, scramble, move, help
switch action
  
case 'initialize';
  % setup the screen
  figure_h=get(gcf,'UserData');
  
  set(figure_h,...
    'Color',[0.4 0.4 0.4],...
    'Menubar','none',...
    'Name','The Sliding Puzzle',...
    'NumberTitle','off',...
    'Position',[200 200 310 255],...
    'Resize','off');
  axis('off')
  
  % create status bar
  % set the tag to 'click' mode (set to 'winner' mode is user has won)
  status_handle=uicontrol(figure_h,...
    'BackgroundColor',[0.4 0.4 0.4],...
    'ForegroundColor',[1 1 1], ...
    'HorizontalAlignment','center',...
    'FontSize',18,...
    'Units','points',...
    'Position',[15 10 215 25],...
    'String','Click on a tile to slide it',...
    'Style','text',...
    'Tag','click');
  
  % create utility buttons (new game, help, close)
  % new_game
  new_game_h=uicontrol(figure_h,...
    'Callback','fifteen scramble',...
    'FontSize',12, ...
    'Units','points',...
    'Position',[235 175 65 30],...
    'String','New Game',...
    'Style','pushbutton');
  
  % help
  help_h=uicontrol(figure_h,...
    'Callback','fifteen help',...
    'Fontsize',12, ...
    'Units','points',...
    'Position',[235 110 65 30],...
    'String','Help',...
    'Style','pushbutton');
  
  % close
  close_h=uicontrol(figure_h,...
    'Callback','close(gcf)',...
    'Fontsize',12, ...
    'Units','points',...
    'Position',[235 45 65 30],...
    'String','Close',...
    'Style','pushbutton');
  
  % setup the game board
  irows=1;
  for counter=1:16
    jcols=rem(counter,4);
    if jcols==0
      jcols=4;
    end
    position=[40*jcols 205-40*irows 40 40];
    index=(irows-1)*4+jcols;
    if jcols==4
      irows=irows+1;
    end
    board.squares(index)=uicontrol(figure_h,...
      'FontSize',18,...
      'FontWeight','bold',...
      'Units','points',...
      'Position',position,...
      'Style','pushbutton',...
      'Tag',num2str(index));
  end
  
  % save all the handles in the figure windows userdata(over-writing the
  % handle of the figure window since we don't need it anymore)
  set(figure_h,'userdata',board);
  fifteen('scramble')
  
case 'scramble'
  score_board=randperm(16);
  % where ever the location of '16' is is where we'll start our open slot
  num_16=find(score_board==16);
  board=get(gcf,'UserData');
  set(board.squares,...
    'BackgroundColor',[0.701961 0.701961 0.701961],...
    'Enable','on',...
    'Visible','on')
  set(board.squares,{'string'},num2cell(score_board)')
  
  % change the value 16 (set it to black, disable it, and set the
  % string to empty; the color change won't take effect on the PC) and
  % turn the visibility of the board on 
  set(board.squares(num_16),...
    'BackgroundColor','black',...
    'Enable','off',...
    'String',' ');
  % keep track of where the current free square is by storing it in
  % the board struct.  we also want to keep track of the 'score'; this
  % way we know when we've won(when score(1:15)==[1:15])
  [board.free_square.x, board.free_square.y] = LocalGetXY(num_16);
  board.score=score_board;
  set(board.squares,...
    'Callback','fifteen move',...
    'Visible','on',...
    'UserData',board)
  
  % since we could be restarting an old game(i.e. winner) we need to check
  % if the 'winner' banner is up, if so change it.
  old_handle=findobj(gcf,'Tag','winner');
  if isempty(old_handle)==0
    % we're in 'winner' mode, set back to 'click' mode
    set(old_handle,...
      'String','Click on a tile to slide it',...
      'Tag','click');
  end
  
  % lets hide the objects handle from all other functions called at
  % the command line
  set(gcf,'HandleVisibility','callback');
  
case 'move'
  % check that the move is legal
  square_tag=str2double(get(gcbo,'Tag'));
  % determine the x and y coordinates of the selected tile
  [current.x, current.y] = LocalGetXY(square_tag);
  data=get(gcbo,'UserData');
  % determine the x and y coordinates of the open tile
  open.x=data.free_square.x;
  open.y=data.free_square.y;
  open_square=(open.x-1)*4+open.y;
  inc_by=0;
  if current.x==open.x          
    % the selected tile is on the same row as the open tile
    loop=abs(current.y-open.y);  % 'loop' tells us how many tiles away we are
    inc_by=open.y<current.y;     % we need to know if we are moving right -> left or left -> right
    if inc_by==0                 
      inc_by=-1;                 % we're moving right -> left
    end
  elseif current.y==open.y
    % the selected tile is in the same column as the open tile
    loop=abs(current.x-open.x);  % 'loop' tells us how many tiles away we are
    direction=open.x<current.x;  % we need to know if we are moving up or moving down
    if direction==1
      inc_by=4;                  % we're moving up
    else
      inc_by=-4;                 % we're moving down
    end
  end
  
  if inc_by~=0
    % there was a legal move
    square_handles=data.squares;
    score_board=data.score;
    set(square_handles(open_square),...
      'BackgroundColor',[0.701961 0.701961 0.701961],...
      'Enable','on');
    to_square=open_square;
    
    % make the move
    for index=1:loop
      % now slide over all the tiles between the selected tile and the
      % open tile
      from_square=to_square+inc_by;
      from_value=get(square_handles(from_square),'String');
      set(square_handles(to_square),...
        'String',from_value);
      score_board(to_square)=str2double(from_value);
      to_square=from_square;
    end
    
    data.score=score_board;
    % set up new free square
    set(gcbo,...
      'BackgroundColor','black',...
      'Enable','off',...
      'String',' ');
    
    % update the free square x and y coordinates
    data.free_square.x=current.x;
    data.free_square.y=current.y;
    set(square_handles,'userdata',data);
    
    % check for winner
    if data.score(1:15)==[1:15]
      % change from 'click' mode to 'winner' mode
      old_handle=findobj(gcf,'Tag','click');
      set(old_handle,...
        'String','WINNER!!!',...
        'Tag','winner');
    end
    
  end   % there was a legal move
  
case 'help'
  helpwin(mfilename);
  
otherwise
  disp([mfilename ': unknown action ''' action ''''])
  
end


% calculate the xrow and ycol< of the tile
function [x,y] = LocalGetXY(tile)

x=ceil(tile/4);
y=rem(tile,4);
if y==0
  y=4;
end