function percent = parfor_progress(N)
%PARFOR_PROGRESS Progress monitor (progress bar) that works with parfor.
%   PARFOR_PROGRESS works by creating a file called parfor_progress.txt in
%   your working directory, and then keeping track of the parfor loop's
%   progress within that file. This workaround is necessary because parfor
%   workers cannot communicate with one another so there is no simple way
%   to know which iterations have finished and which haven't.
%
%   PARFOR_PROGRESS(N) initializes the progress monitor for a set of N
%   upcoming calculations.
%
%   PARFOR_PROGRESS updates the progress inside your parfor loop and
%   displays an updated progress bar.
%
%   PARFOR_PROGRESS(0) deletes parfor_progress.txt and finalizes progress
%   bar.
%
%   To suppress output from any of these functions, just ask for a return
%   variable from the function calls, like PERCENT = PARFOR_PROGRESS which
%   returns the percentage of completion.
%
%   Example:
%
%      N = 100;
%      parfor_progress(N);
%      parfor i=1:N
%         pause(rand); % Replace with real code
%         parfor_progress;
%      end
%      parfor_progress(0);
%
%   See also PARFOR.

% By Jeremy Scheff - jdscheff@gmail.com - http://www.jeremyscheff.com/
% Copyright (c) 2011, Jeremy Scheff
% All rights reserved.
% 
% Redistribution and use in source and binary forms, with or without
% modification, are permitted provided that the following conditions are
% met:
% 
%     * Redistributions of source code must retain the above copyright
%       notice, this list of conditions and the following disclaimer.
%     * Redistributions in binary form must reproduce the above copyright
%       notice, this list of conditions and the following disclaimer in
%       the documentation and/or other materials provided with the distribution
% 
% THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
% AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
% IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
% ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
% LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
% CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
% SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
% INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
% CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
% ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
% POSSIBILITY OF SUCH DAMAGE.


error(nargchk(0, 1, nargin, 'struct'));

if nargin < 1
    N = -1;
end

percent = 0;
w = 50; % Width of progress bar

if N > 0
    f = fopen('parfor_progress.txt', 'w');
    if f<0
        error('Do you have write permissions for %s?', pwd);
    end
    fprintf(f, '%d\n', N); % Save N at the top of progress.txt
    fclose(f);
    
    if nargout == 0
        disp(['  0%[>', repmat(' ', 1, w), ']']);
    end
elseif N == 0
    delete('parfor_progress.txt');
    percent = 100;
    
    if nargout == 0
        disp([repmat(char(8), 1, (w+9)), char(10), '100%[', repmat('=', 1, w+1), ']']);
    end
else
    if ~exist('parfor_progress.txt', 'file')
        error('parfor_progress.txt not found. Run PARFOR_PROGRESS(N) before PARFOR_PROGRESS to initialize parfor_progress.txt.');
    end
    
    f = fopen('parfor_progress.txt', 'a');
    fprintf(f, '1\n');
    fclose(f);
    
    f = fopen('parfor_progress.txt', 'r');
    progress = fscanf(f, '%d');
    fclose(f);
    percent = (length(progress)-1)/progress(1)*100;
    
    if nargout == 0
        perc = sprintf('%3.0f%%', percent); % 4 characters wide, percentage
        disp([repmat(char(8), 1, (w+9)), char(10), perc, '[', repmat('=', 1, round(percent*w/100)), '>', repmat(' ', 1, w - round(percent*w/100)), ']']);
    end
end
