use bevy::prelude::*;

use bevy::input::common_conditions::input_just_pressed;
use bevy::picking::pointer::{PointerId, PointerLocation};
use bevy::window::{CursorGrabMode, CursorOptions};

use crate::Screen;

pub fn plugin(app: &mut App) {
    app.add_systems(OnEnter(Screen::Gameplay), add_window_click_observer);
    app.add_systems(PreUpdate, center_cursor.run_if(is_cursor_grabbed));
    app.add_systems(
        Update,
        ungrab_cursor.run_if(
            is_cursor_grabbed.and(input_just_pressed(KeyCode::Escape).or(not(is_window_focused))),
        ),
    );
}

fn add_window_click_observer(window: Single<Entity, With<Window>>, mut commands: Commands) {
    commands.entity(*window).observe(
        |mut event: On<Pointer<Click>>, mut cursor: Single<&mut CursorOptions>| {
            cursor.grab_mode = CursorGrabMode::Locked;
            cursor.visible = false;
            event.propagate(false);
        },
    );
}

fn ungrab_cursor(mut cursor: Single<&mut CursorOptions>) {
    cursor.grab_mode = CursorGrabMode::None;
    cursor.visible = true;
}

/// Sets the cursor (and pointer) position to the center of the
/// window, so that once it is ungrabbed, it will reappear there.
fn center_cursor(
    mut window: Single<&mut Window>,
    pointers: Query<(&PointerId, &mut PointerLocation)>,
) {
    let center = window.resolution.size() / 2.;

    // On Wayland, since the cursor is locked into place, this only needs to be
    // done once. Unfortunately, for some reason, this doesn't work in the same
    // frame as setting `grab_mode`, logging an error. This system is scheduled
    // on `PreUpdate`, so it runs with one frame delay.
    //
    // On X11, the cursor can't be locked into place, only confined to the
    // window bounds, so we repeatedly move the cursor back to the center
    // while it's grabbed.
    //
    // On the web, the cursor can be locked, but setting its position isn't
    // supported at all, so this would instead log a bunch of errors.
    #[cfg(not(target_family = "wasm"))]
    window.set_cursor_position(Some(center));

    // Update the `PointerLocation` for the mouse to be at the center
    // of the window. Otherwise it might use the last known position.
    for (id, mut pointer) in pointers {
        if id.is_mouse() {
            if let Some(location) = pointer.location.as_mut() {
                location.position = center;
            }
        }
    }
}

pub fn is_cursor_grabbed(cursor: Single<&CursorOptions>) -> bool {
    cursor.grab_mode != CursorGrabMode::None
}

pub fn is_window_focused(window: Single<&Window>) -> bool {
    window.focused
}