use piston_window::grid::Grid;
use piston_window::rectangle::{Border, Rectangle};
use piston_window::*;
use sdl2_window::Sdl2Window;
use std::cmp;

pub const MIN_PIXELS_PER_M: f64 = 0.5;
pub const MAX_PIXELS_PER_M: f64 = 10_000.;
pub const STANDARD_PIXELS_PER_M: f64 = 64.;

/// Helper function to turn two given points into a rectangle. The order of the two points is not
/// important, they are considered two endpoints of a diagonal and therefore identify the rectangle
/// unambiguously.
fn bounding_box(p0: [f64; 2], p1: [f64; 2]) -> [f64; 4] {
    let min_x = p0[0].min(p1[0]);
    let min_y = p0[1].min(p1[1]);
    let max_x = p0[0].max(p1[0]);
    let max_y = p0[1].max(p1[1]);

    [min_x, min_y, max_x - min_x, max_y - min_y]
}

fn main() {
    let mut window: PistonWindow<Sdl2Window> = WindowSettings::new("Hello there!", [1000, 1000])
        .build()
        .expect("Could not initialise window");

    // The amount of on-screen pixels used to represent a meter of actual terrain.
    let mut pixels_per_m = STANDARD_PIXELS_PER_M;

    /* Create a rectangle that is used to draw all rectangles that were created by the user. It has
     * a thicc blacc border and white colour.
     */
    let render_rect = Rectangle::new([0.7, 0.7, 0.7, 1.]).border(Border {
        color: [0.5, 0.5, 0.5, 1.],
        radius: 2.,
    });
    // The point the user has clicked. This is where they want the rectangle to start.
    let mut starting_rect_point: Option<[f64; 2]> = None;
    let mut rectangles = Vec::new();

    // Line used to draw the square grid.
    let grid_line = Line::new([1., 1., 1., 0.3], 1.5);

    let mut mouse_pos = [0., 0.];
    let mut events = Events::new(EventSettings::new().lazy(true));
    while let Some(e) = events.next(&mut window) {
        // Update the mouse cursor position
        e.mouse_cursor(|pos| {
            mouse_pos = pos;
        });

        // The zoom factor is changed with the mouse wheel.
        e.mouse_scroll(|[_, y]| {
            let scale_changed = if y < 0. && MAX_PIXELS_PER_M > pixels_per_m {
                pixels_per_m *= 1.2;
                true
            } else if y > 0. && MIN_PIXELS_PER_M < pixels_per_m {
                pixels_per_m /= 1.2;
                true
            } else {
                false
            };

            /* Make sure that the scale factors stay very close to the normal scale factors, even
             * when the user zooms in and out very often, at least when they zoom over the standard
             * zoom factor.
             */
            if pixels_per_m > STANDARD_PIXELS_PER_M - 5.
                && pixels_per_m < STANDARD_PIXELS_PER_M + 5.
            {
                pixels_per_m = STANDARD_PIXELS_PER_M;
            }

            // Notify the user of the change if there was any
            if scale_changed {
                println!("Changed scale to {} pixels per m.", pixels_per_m);
            }
        });

        // Handle drawing a rectangle or finishing the rectangle when clicking with the mouse.
        if let Some(Button::Mouse(MouseButton::Left)) = e.press_args() {
            if let Some(first_point) = starting_rect_point {
                rectangles.push(bounding_box(first_point, mouse_pos));
                starting_rect_point = None;
            } else {
                starting_rect_point = Some(mouse_pos);
            }
        }

        // Close the window when the user presses escape
        if let Some(Button::Keyboard(Key::Escape)) = e.press_args() {
            window.set_should_close(true);
        }

        /* Update the Grid draw size to the actual window draw size.
         * TODO: Currently, the window canvas draw size is never updated. This has to be changed in
         * order to deal with the user resizing the window.
         */
        let win_size = window.draw_size();
        let grid = Grid {
            cols: (win_size.width / pixels_per_m) as u32 + 1,
            rows: (win_size.height / pixels_per_m) as u32 + 1,
            units: pixels_per_m,
        };

        window.draw_2d(&e, |c, g, _device| {
            clear([0.4, 0.2, 0., 1.], g);

            grid.draw(&grid_line, &c.draw_state, c.transform, g);

            // Draw all rectangles that are part of the map
            for &rect in &rectangles {
                render_rect.draw(rect, &c.draw_state, c.transform, g);
            }

            // Draw the current rectangle that is being drawn, but not part of the map
            if let Some(starting_rect_point) = starting_rect_point {
                render_rect.draw(
                    bounding_box(starting_rect_point, mouse_pos),
                    &c.draw_state,
                    c.transform,
                    g,
                );
            }
        });
    }
}