% Modeling and Simulating Social Systems with MATLAB
% http://www.soms.ethz.ch/matlab
% Author: Stefano Balietti and Karsten Donnay, 2012

function [density, flow] = simulate_cars(moveProb, inFlow, withGraphics)
% This function is simulating cars on a highway
% INPUT: 
%   moveProb: the probability for a car to move forwards, 0..1
%   inFlowProb: The inflow volume to the road, 0..1
%   withGraphics: Should the road be animated? true/false
% OUTPUT:
%   density: the average vehicle density, 0..1
%   flow: the average flow of cars, 0..1


% set parameter values
N=40;            % road length
nIter=100;      % number of iterations


% define road (1=car, 0=no car)
x = rand(1,N)<inFlow;


% set statistical variables
movedCars=0;
density=0;

if (withGraphics)
    % Get the handle of the figure
    h = figure();
    % Prepare the new file.
    vidObj = VideoWriter('video.avi');
    open(vidObj);
end

% main loop, iterating the time variable, t
for t=1:nIter
    
    % THIS IS WHERE THE MODEL IS

    % save old state of the road
    x0=x;    
    % update position x(0):
    if ( rand<inFlow )
        x(1)=1;
    end
    % update positions x(1..N-1)
    for i=1:(N-1)
        if ( x0(i) && ~x0(i+1) && rand<moveProb)
            x(i)=0;
            x(i+1)=1;
            movedCars=movedCars+1;  % keep track of how many cars are moved forwards. Needed for calculating the flow later on.
        end
    end
    % update position x(N)
    if ( rand<moveProb )
        x(N)=0;
    end


    % update statistics
    density = density + sum(x)/N;

    
    % animate
    if ( withGraphics )
        clf; hold on;
        plot(0:N, 0*(0:N), 'Color', [.75 .75 .75], 'LineWidth', 5)
        xlim([0 N+1])
        ylim([-N/4 N/4])
        for i=1:N
            if ( x(i) )
                draw_car(i, 0, 0.8, 0.2);
            end
        end
        % STORE VIDEO FRAMES
        % Get the very last frame    
        currFrame = getframe(h);
        writeVideo(vidObj,currFrame);
        
        pause(.01)
    end

end


% rescale statistical vaiables before returing them
density = density/nIter;
flow = movedCars/(N*nIter);

if (withGraphics)
    % SAVE VIDEO FRAMES TO FILE
    close(vidObj);
end