#include <ncurses.h>

struct vec2 {
    int x;
    int y;
};

struct borders {
    int top;
    int bottom;
    int left;
    int right;
};

int main()
{
    initscr(); // initialise screen
    clear(); // clear the empty buffer just in case
    noecho(); // disable the direct typing to the terminal so it doesn't mess with the application

    // here we define utility variables

    // borders for a pen point
    struct borders b;
    b.bottom = LINES;
    b.top = -1;
    b.left = -1;
    b.right = COLS;
    
    // pen point position
    struct vec2 position;
    position.x = COLS;
    position.y = LINES - 1;

    // pen point direction
    struct vec2 direction;
    direction.x = -1;
    direction.y = 0;
    
    // here we start the drawing
    for (int i = 0; i < COLS*LINES; i++)
    {
        // move & paint
        position.x += direction.x;
        position.y += direction.y;
        mvaddch(position.y, position.x, '*');

        // flush the buffer to show result on the screen
        refresh();
        
        // check if we are about to meet the border
        if (position.x + direction.x <= b.left) { // if yes, then...
            // turn right
            direction.x = 0;
            direction.y = -1;

            // grab the border and pull it towards us as bit
            b.bottom--;
        }
        // and then repeat for every single border we have...
        else if (position.y + direction.y <= b.top) {
            direction.x = 1;
            direction.y = 0;

            b.left++;
        }
        else if (position.x + direction.x >= b.right) {
            direction.x = 0;
            direction.y = 1;

            b.top++;
        }
        else if (position.y + direction.y >= b.bottom) {
            direction.x = -1;
            direction.y = 0;

            b.right--;
        }
        
        // and we wait... wait... wait...
        napms(20);
    }
    
    // hold the buffer until the keypress
    getch();

    // finish & cleanup
    endwin();
    return 0;
}