KEY_LEFT = 37;
KEY_RIGHT = 39;
KEY_SPACE = 32;
SHIP_WIDTH = width() / 13;
SHIP_HEIGHT = SHIP_WIDTH / 2;
SPEED = SHIP_WIDTH / 6;

finished = FALSE;
score = 0;
stage = 0;
autoFlush(FALSE);

while not finished do
    x[0] = (width() - SHIP_WIDTH) / 2;
    y[0] = 10;
    red[0] = 255;
    green[0] = 255;
    blue[0] = 0;
    shot_x[0] = -1;
    shot_y[0] = -1;

    num_enemies = 0;
    next_y = 4 * SHIP_HEIGHT;
    while next_y < height() - SHIP_HEIGHT do
        num_enemies = num_enemies + 1;
        x[num_enemies] = random(0, width() - SHIP_WIDTH);
        y[num_enemies] = next_y;
        red[num_enemies] = random(50, 254);
        green[num_enemies] = random(50, 254);
        blue[num_enemies] = random(50, 254);
        dx[num_enemies] = 1;
        if random(1) == 1 then
            dx[num_enemies] = -1;
        endif;
        shot_x[num_enemies] = -1;
        shot_y[num_enemies] = -1;
        next_y = next_y + 2 * SHIP_HEIGHT + 5;
    done;
    enemies_left = num_enemies;
    stage_finished = FALSE;
    stage = stage + 1;
    println("Use left and right arrow to move, and space to fire.");
    println("Get ready for stage ", stage, ".  Please press 'a'.");
    flush();
    while readChar() != 'a' do
    done;
    while not finished and not stage_finished do
        cls();
        t = time();
    
        if keyPressed(KEY_LEFT) then
            if x[0] - SPEED >= 0 then
                x[0] = x[0] - SPEED;
            endif;
        elseif keyPressed(KEY_RIGHT) then
            if x[0] + SPEED < width() then
                x[0] = x[0] + SPEED;
            endif;
        elseif keyPressed(KEY_SPACE) then
            if shot_x[0] < 0 then
                shot_x[0] = x[0] + SHIP_WIDTH / 2;
                shot_y[0] = y[0] + SHIP_HEIGHT + 1;
            endif;
        endif;
    
        for q = 0 to num_enemies do
            if x[q] >= 0 then
                color(red[q], green[q], blue[q]);
                if q > 0 then
                    /* draw enemy */
                    fillShape(x[q] + SHIP_WIDTH / 2, y[q],
                              x[q], y[q] + SHIP_HEIGHT / 2,
                              x[q] + SHIP_WIDTH, y[q] + SHIP_HEIGHT / 2);
                    fillRect(x[q], y[q] + SHIP_HEIGHT / 2,
                             SHIP_WIDTH, SHIP_HEIGHT / 2);
                else
                    /* draw my thing */
                    fillRect(x[q], y[q], SHIP_WIDTH, SHIP_HEIGHT / 2);
                    fillShape(x[q], y[q] + SHIP_HEIGHT / 2 - 1,
                              x[q] + SHIP_WIDTH, y[q] + SHIP_HEIGHT / 2 - 1,
                              x[q] + SHIP_WIDTH / 2, y[q] + SHIP_HEIGHT);
                endif;
            endif;
        done;
        
        if shot_x[0] >= 0 then
            if not isBackground(shot_x[0], shot_y[0] + SHIP_HEIGHT / 2) then
                r = getRed(shot_x[0], shot_y[0] + SHIP_HEIGHT / 2);
                g = getGreen(shot_x[0], shot_y[0] + SHIP_HEIGHT / 2);
                b = getBlue(shot_x[0], shot_y[0] + SHIP_HEIGHT / 2);
                if r != 255 and g != 255 and b != 255 then
                    shot_x[0] = -1;
                    score = score + 10;
                    for q = 1 to num_enemies do
                        if shot_y[0] + SHIP_HEIGHT / 2 >= y[q]
                           and shot_y[0] + SHIP_HEIGHT / 2 <= y[q] + SHIP_HEIGHT then
                            x[q] = -1;
                            enemies_left = enemies_left - 1;
                            if enemies_left == 0 then
                                stage_finished = TRUE;
                            endif;
                        endif;
                    done;
                endif;
            endif;
        endif;
        if shot_x[0] >= 0 then
            color(255, 128, 128);
            line(shot_x[0], shot_y[0], shot_x[0], shot_y[0] + SHIP_HEIGHT / 2);
            shot_y[0] = shot_y[0] + SPEED;
            if shot_y[0] >= height() then
                shot_x[0] = -1;
            endif;
        endif;
 
        color(255, 255, 255);
        for q = 1 to num_enemies do
            if shot_x[q] >= 0 then
                if shot_y[q] <= y[0] + SHIP_HEIGHT then
                    r = getRed(shot_x[q], shot_y[q]);
                    g = getGreen(shot_x[q], shot_y[q]);
                    b = getBlue(shot_x[q], shot_y[q]);
                    if r == red[0] and g == green[0] and b == blue[0] then
                        finished = TRUE;
                    endif;
                endif;
                line(shot_x[q], shot_y[q], shot_x[q], shot_y[q] + SHIP_HEIGHT / 2);
                shot_y[q] = shot_y[q] - SPEED;
                if shot_y[q] < 0 then
                    shot_x[q] = -1;
                endif;
            elseif x[q] >= 0 and x[q] >= x[0] - 2 * SHIP_WIDTH
                   and x[q] <= x[0] + 3 * SHIP_WIDTH and random(20) == 0 then
                shot_x[q] = x[q] + SHIP_WIDTH / 2;
                shot_y[q] = y[q];
            endif;
        done;

        for q = 1 to num_enemies do
            if x[q] >= 0 then
                if random(70) == 1 then
                    dx[q] = -dx[q];
                endif;
                x[q] = x[q] + dx[q] * SPEED;
                if x[q] < 0 then
                    x[q] = x[q] + 2 * SPEED;;
                    dx[q] = -dx[q];
                elseif x[q] >= width() - SHIP_WIDTH then
                    x[q] = x[q] - 2 * SPEED;;
                    dx[q] = -dx[q];
                endif;
            endif;
        done;
    
        color(255, 255, 255);
        println("Score: ", score);
        flush();
        t = time() - t;
        wait(50 - t);
    done;
done;
autoFlush(TRUE);
println("Game over.  Please press 'a'.");
while readChar() != 'a' do
done;
cls();