use cursive::{
    view::Position,
    views::{LayerPosition, TextView},
    Cursive,
};

/// Moves top layer by the specified amount
fn move_top(c: &mut Cursive, x_in: isize, y_in: isize) {
    // Step 1. Get the current position of the layer.
    let s = c.screen_mut();
    let l = LayerPosition::FromFront(0);

    // Step 2. add the specifed amount
    let pos = s
        .layer_offset(LayerPosition::FromFront(0))
        .unwrap()
        .saturating_add((x_in, y_in));

    // convert the new x and y into a position
    let p = Position::absolute(pos);

    // Step 3. Apply the new position
    s.reposition_layer(l, p);
}

fn main() {
    let mut siv = cursive::default();

    // We can quit by pressing `q`
    siv.add_global_callback('q', Cursive::quit);
    // Next Gen FPS Controls.
    siv.add_global_callback('w', |s| move_top(s, 0, -1));
    siv.add_global_callback('a', |s| move_top(s, -1, 0));
    siv.add_global_callback('s', |s| move_top(s, 0, 1));
    siv.add_global_callback('d', |s| move_top(s, 1, 0));

    // Add window to fly around.
    siv.add_layer(TextView::new(
        "Press w,a,s,d to move the window.\n\
         Press q to quit the application.",
    ));

    // Run the event loop
    siv.run();
}