function petriNetMutexDemo
% PETRINETMUTEXDEMO  GUI demo: two machines sharing one robot arm.
% The token moves from the central resource place to Machine A or B.

fig = figure( ...
    'Name', 'Two Machines Sharing One Robot Arm', ...
    'Color', 'w', ...
    'NumberTitle', 'off', ...
    'MenuBar', 'none', ...
    'ToolBar', 'none', ...
    'Resize', 'off', ...
    'Position', [100 100 1020 590]);

ax = axes( ...
    'Parent', fig, ...
    'Position', [0.04 0.23 0.92 0.69]);
hold(ax, 'on');
axis(ax, [0 10 0 6]);
axis(ax, 'equal');
axis(ax, 'off');

% -------------------------------------------------------------------------
% Model state
% -------------------------------------------------------------------------
state.aReady = false;
state.bReady = false;
state.aActive = false;
state.bActive = false;
state.aWaiting = false;
state.bWaiting = false;
state.resourceFree = true;
state.tokenLocation = 0; % 0=center, 1=left, 2=right
state.message = 'Press Ready A and Ready B, then fire the enabled transition.';

% -------------------------------------------------------------------------
% Layout
% -------------------------------------------------------------------------
leftPlace = [0.9 1.05 1.8 1.8];
centerPlace = [4.35 3.15 1.3 1.3];
rightPlace = [7.3 1.05 1.8 1.8];

tAPos = [3.0 2.55 0.35 0.85];
tBPos = [6.65 2.55 0.35 0.85];

leftCenter = [leftPlace(1) + leftPlace(3) / 2, leftPlace(2) + leftPlace(4) / 2];
centerCenter = [centerPlace(1) + centerPlace(3) / 2, centerPlace(2) + centerPlace(4) / 2];
rightCenter = [rightPlace(1) + rightPlace(3) / 2, rightPlace(2) + rightPlace(4) / 2];

tokenR = 0.11;

% Header
text(ax, 5.0, 5.72, ...
    'Green = executing | Yellow = enabled | Red = waiting | Token moves from center to the chosen machine', ...
    'HorizontalAlignment', 'center', 'FontSize', 11, 'FontWeight', 'bold', 'Interpreter', 'none');
text(ax, 5.0, 5.40, 'Shared robot arm token: M_0 = 1', ...
    'HorizontalAlignment', 'center', 'FontSize', 10, 'Interpreter', 'none');

% Arcs
h.arcCenterA = drawArrow([4.75 3.15], [3.18 3.40]);
h.arcAToLeft = drawArrow([3.18 2.55], [1.95 2.05]);
h.arcCenterB = drawArrow([5.25 3.15], [6.82 3.40]);
h.arcBToRight = drawArrow([6.82 2.55], [8.05 2.05]);

% Places and transitions
h.left = rectangle(ax, 'Position', leftPlace, 'Curvature', [1 1], ...
    'FaceColor', [1 1 1], 'EdgeColor', [0.25 0.25 0.25], 'LineWidth', 2);

h.center = rectangle(ax, 'Position', centerPlace, 'Curvature', [1 1], ...
    'FaceColor', [1.0 0.95 0.65], 'EdgeColor', [0.45 0.35 0.0], 'LineWidth', 2);

h.right = rectangle(ax, 'Position', rightPlace, 'Curvature', [1 1], ...
    'FaceColor', [1 1 1], 'EdgeColor', [0.25 0.25 0.25], 'LineWidth', 2);

h.tA = rectangle(ax, 'Position', tAPos, ...
    'FaceColor', [0.25 0.25 0.25], 'EdgeColor', [0.15 0.15 0.15], 'LineWidth', 1.5);

h.tB = rectangle(ax, 'Position', tBPos, ...
    'FaceColor', [0.25 0.25 0.25], 'EdgeColor', [0.15 0.15 0.15], 'LineWidth', 1.5);

% Token
h.token = rectangle(ax, ...
    'Position', [centerCenter(1) - tokenR, centerCenter(2) - tokenR, 2 * tokenR, 2 * tokenR], ...
    'Curvature', [1 1], ...
    'FaceColor', [1.0 0.85 0.1], ...
    'EdgeColor', 'none');

% Labels
text(ax, leftCenter(1), leftCenter(2) + 0.95, 'P_{machineA\_usingRobot}', ...
    'HorizontalAlignment', 'center', 'FontSize', 11, 'Interpreter', 'tex');

text(ax, centerCenter(1), centerCenter(2) + 0.95, 'P_{robotArm}', ...
    'HorizontalAlignment', 'center', 'FontSize', 11, 'Interpreter', 'tex');

text(ax, rightCenter(1), rightCenter(2) + 0.95, 'P_{machineB\_usingRobot}', ...
    'HorizontalAlignment', 'center', 'FontSize', 11, 'Interpreter', 'tex');

text(ax, 3.18, 3.72, 'T_{startA}', 'HorizontalAlignment', 'center', 'FontSize', 11, 'Interpreter', 'tex');
text(ax, 6.82, 3.72, 'T_{startB}', 'HorizontalAlignment', 'center', 'FontSize', 11, 'Interpreter', 'tex');

% Buttons
uicontrol(fig, 'Style', 'pushbutton', 'String', 'Ready A', ...
    'Position', [70 70 110 32], 'Callback', @(~, ~) makeReady(1));
uicontrol(fig, 'Style', 'pushbutton', 'String', 'Ready B', ...
    'Position', [190 70 110 32], 'Callback', @(~, ~) makeReady(2));
uicontrol(fig, 'Style', 'pushbutton', 'String', 'Fire Enabled Transition', ...
    'Position', [320 70 180 32], 'Callback', @(~, ~) fireTransition());
uicontrol(fig, 'Style', 'pushbutton', 'String', 'Complete Task', ...
    'Position', [515 70 140 32], 'Callback', @(~, ~) completeTask());
uicontrol(fig, 'Style', 'pushbutton', 'String', 'Reset', ...
    'Position', [670 70 90 32], 'Callback', @(~, ~) resetDemo());

status = uicontrol(fig, 'Style', 'text', ...
    'Position', [35 18 950 30], ...
    'BackgroundColor', 'w', ...
    'HorizontalAlignment', 'left', ...
    'FontSize', 11);

updateView();

    function makeReady(machineIdx)
        if machineIdx == 1
            if ~state.aActive
                state.aReady = true;
                state.aWaiting = false;
            end
            state.message = 'Machine A is ready to request the robot arm.';
        else
            if ~state.bActive
                state.bReady = true;
                state.bWaiting = false;
            end
            state.message = 'Machine B is ready to request the robot arm.';
        end
        updateView();
    end

    function fireTransition()
        enabled = [];

        if state.resourceFree && state.aReady && ~state.aActive
            enabled(end + 1) = 1; %#ok<AGROW>
        end
        if state.resourceFree && state.bReady && ~state.bActive
            enabled(end + 1) = 2; %#ok<AGROW>
        end

        if isempty(enabled)
            state.message = 'No enabled transition: make a machine ready and keep the robot arm free.';
            updateView();
            return;
        end

        if numel(enabled) == 2
            if rand < 0.5
                chosen = 1;
                loser = 2;
            else
                chosen = 2;
                loser = 1;
            end
            state.message = sprintf('Both transitions are enabled. T_start%d won the random choice.', chosen);
            setActive(chosen);
            setWaiting(loser);
        else
            chosen = enabled(1);
            state.message = sprintf('Only T_start%d is enabled, so it fires.', chosen);
            setActive(chosen);
        end

        state.resourceFree = false;
        animateTokenMove(chosen);
        state.tokenLocation = chosen;
        updateView();
    end

    function setActive(machineIdx)
        if machineIdx == 1
            state.aReady = false;
            state.aActive = true;
            state.aWaiting = false;
        else
            state.bReady = false;
            state.bActive = true;
            state.bWaiting = false;
        end
    end

    function setWaiting(machineIdx)
        if machineIdx == 1
            state.aWaiting = true;
        else
            state.bWaiting = true;
        end
    end

    function completeTask()
        if state.aActive
            state.aActive = false;
            state.message = 'Machine A finished. The robot arm token returns to the center.';
        elseif state.bActive
            state.bActive = false;
            state.message = 'Machine B finished. The robot arm token returns to the center.';
        else
            state.message = 'No machine is currently using the robot arm.';
            updateView();
            return;
        end

        state.resourceFree = true;
        animateTokenMove(0);
        state.tokenLocation = 0;

        if state.aWaiting
            state.aWaiting = false;
            state.aReady = true;
        end
        if state.bWaiting
            state.bWaiting = false;
            state.bReady = true;
        end

        updateView();
    end

    function resetDemo()
        state.aReady = false;
        state.bReady = false;
        state.aActive = false;
        state.bActive = false;
        state.aWaiting = false;
        state.bWaiting = false;
        state.resourceFree = true;
        state.tokenLocation = 0;
        state.message = 'Reset complete. Press Ready A and Ready B, then fire the enabled transition.';
        updateTokenPosition(0);
        updateView();
    end

    function updateView()
        enabledA = state.resourceFree && state.aReady && ~state.aActive;
        enabledB = state.resourceFree && state.bReady && ~state.bActive;

        set(h.left, 'FaceColor', getMachineColor(state.aReady, state.aActive, state.aWaiting));
        set(h.right, 'FaceColor', getMachineColor(state.bReady, state.bActive, state.bWaiting));
        set(h.center, 'FaceColor', getResourceColor(state.resourceFree));
        set(h.tA, 'FaceColor', getTransitionColor(enabledA, state.aActive, state.aWaiting));
        set(h.tB, 'FaceColor', getTransitionColor(enabledB, state.bActive, state.bWaiting));

        if state.resourceFree
            set(h.token, 'Visible', 'on');
            updateTokenPosition(0);
        else
            set(h.token, 'Visible', 'on');
            updateTokenPosition(state.tokenLocation);
        end

        if enabledA && enabledB
            setArrowStyle(h.arcCenterA, [1.0 0.55 0.0], 3.0);
            setArrowStyle(h.arcCenterB, [1.0 0.55 0.0], 3.0);
        elseif enabledA
            setArrowStyle(h.arcCenterA, [1.0 0.55 0.0], 3.0);
            setArrowStyle(h.arcCenterB, [0.65 0.65 0.65], 1.2);
        elseif enabledB
            setArrowStyle(h.arcCenterA, [0.65 0.65 0.65], 1.2);
            setArrowStyle(h.arcCenterB, [1.0 0.55 0.0], 3.0);
        else
            setArrowStyle(h.arcCenterA, [0.65 0.65 0.65], 1.2);
            setArrowStyle(h.arcCenterB, [0.65 0.65 0.65], 1.2);
        end

        setArrowStyle(h.arcAToLeft, [0.55 0.55 0.55], 1.2);
        setArrowStyle(h.arcBToRight, [0.55 0.55 0.55], 1.2);

        set(status, 'String', state.message);
        drawnow;
    end

    function updateTokenPosition(location)
        if location == 0
            c = centerCenter;
        elseif location == 1
            c = leftCenter;
        else
            c = rightCenter;
        end

        set(h.token, 'Position', [c(1) - tokenR, c(2) - tokenR, 2 * tokenR, 2 * tokenR]);
    end

    function animateTokenMove(location)
        if location == 0
            target = centerCenter;
        elseif location == 1
            target = leftCenter;
        else
            target = rightCenter;
        end

        if state.tokenLocation == 0
            start = centerCenter;
        elseif state.tokenLocation == 1
            start = leftCenter;
        else
            start = rightCenter;
        end

        nSteps = 20;
        for k = 1:nSteps
            alpha = k / nSteps;
            c = (1 - alpha) * start + alpha * target;
            set(h.token, 'Position', [c(1) - tokenR, c(2) - tokenR, 2 * tokenR, 2 * tokenR]);
            drawnow;
        end
    end

    function c = getMachineColor(isReady, isActive, isWaiting)
        if isActive
            c = [0.2 0.8 0.2];
        elseif isWaiting
            c = [0.92 0.35 0.35];
        elseif isReady
            c = [0.5 0.8 1.0];
        else
            c = [1.0 1.0 1.0];
        end
    end

    function c = getResourceColor(isFree)
        if isFree
            c = [1.0 0.95 0.65];
        else
            c = [0.82 0.82 0.82];
        end
    end

    function c = getTransitionColor(isEnabled, isActive, isWaiting)
        if isActive
            c = [0.2 0.8 0.2];
        elseif isWaiting
            c = [0.92 0.35 0.35];
        elseif isEnabled
            c = [1.0 0.85 0.25];
        else
            c = [0.25 0.25 0.25];
        end
    end

    function setArrowStyle(hArrow, color, width)
        set(hArrow.line, 'Color', color, 'LineWidth', width);
        set(hArrow.head, 'FaceColor', color, 'EdgeColor', color);
    end

    function hArrow = drawArrow(p1, p2)
        hArrow.line = plot(ax, [p1(1) p2(1)], [p1(2) p2(2)], ...
            'k-', 'LineWidth', 1.5);

        v = p2 - p1;
        u = v / norm(v);
        n = [-u(2) u(1)];

        tip = p2;
        base = p2 - 0.18 * u;
        left = base + 0.08 * n;
        right = base - 0.08 * n;

        hArrow.head = patch(ax, [tip(1) left(1) right(1)], ...
            [tip(2) left(2) right(2)], 'k', 'EdgeColor', 'k');
    end
end