use std::f32::consts::TAU;

use bevy::prelude::*;

use bevy::input::mouse::AccumulatedMouseMotion;
use bevy::window::{CursorGrabMode, CursorOptions};

pub fn cursor_grab(
    mut mouse_button_input: ResMut<ButtonInput<MouseButton>>,
    key_input: Res<ButtonInput<KeyCode>>,
    window: Single<(&mut Window, &mut CursorOptions)>,
) {
    let (mut window, mut cursor) = window.into_inner();

    let is_grabbed = cursor.grab_mode != CursorGrabMode::None;
    let request_grab = mouse_button_input.any_just_pressed([MouseButton::Left, MouseButton::Right]);
    let request_ungrab = !window.focused || key_input.just_pressed(KeyCode::Escape);

    if !is_grabbed && request_grab && !request_ungrab {
        cursor.grab_mode = CursorGrabMode::Locked;

        // To prevent other systems (such as `place_break_blocks`)
        // from seeing the mouse button inputs, clear the state here.
        mouse_button_input.clear();
    }

    if is_grabbed && request_ungrab && !request_grab {
        cursor.grab_mode = CursorGrabMode::None;
    }

    if is_grabbed && !request_ungrab {
        // Set the cursor position to the center of the window, so that when
        // it is ungrabbed, it will reappear there. Because `is_grabbed` is
        // not updated on grab, this block is delayed by one frame.
        //
        // 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`, and would log an error.
        //
        // 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 is
        // not supported at all, so this would instead log a bunch of errors.
        let center = window.resolution.size() / 2.;
        #[cfg(not(target_family = "wasm"))] // skip on web
        window.set_cursor_position(Some(center));
    }

    // Keep cursor visbility in sync with `grab_mode`.
    cursor.visible = cursor.grab_mode == CursorGrabMode::None;
}

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

#[derive(Component, Debug)]
pub struct CameraFreeLook {
    /// The mouse sensitivity, in radians per pixel.
    pub sensitivity: Vec2,
    /// How far the camera can be tilted up and down.
    pub pitch_limit: std::ops::RangeInclusive<f32>,

    /// Upon initialization, `pitch` and `yaw` will
    /// be set from the camera transform's rotation.
    initialized: bool,
    /// The current yaw (right/left) of the camera, in radians.
    pub yaw: f32,
    /// The current pitch (tilt) of the camera, in radians.
    pub pitch: f32,
}

impl Default for CameraFreeLook {
    fn default() -> Self {
        Self {
            sensitivity: Vec2::splat(0.2).map(f32::to_radians),
            pitch_limit: -(TAU / 4.0)..=(TAU / 4.0),
            initialized: false,
            yaw: 0.0,
            pitch: 0.0,
        }
    }
}

pub fn camera_look(
    accumulated_mouse_motion: Res<AccumulatedMouseMotion>,
    camera: Single<(&mut Transform, &mut CameraFreeLook)>,
) {
    let (mut transform, mut look) = camera.into_inner();

    // Ensure the yaw and pitch are initialized once
    // from the camera transform's current rotation.
    if !look.initialized {
        (look.yaw, look.pitch, _) = transform.rotation.to_euler(EulerRot::YXZ);
        look.initialized = true;
    }

    // Update the current camera state's internal yaw and pitch.
    let motion = accumulated_mouse_motion.delta * look.sensitivity;
    let (min, max) = look.pitch_limit.clone().into_inner();
    look.yaw = (look.yaw - motion.x).rem_euclid(TAU); // keep within 0°..360°
    look.pitch = (look.pitch - motion.y).clamp(min, max);

    // Override the camera transform's rotation.
    transform.rotation = Quat::from_euler(EulerRot::ZYX, 0.0, look.yaw, look.pitch);
}

#[derive(Component)]
pub struct Crosshair;

pub fn setup_crosshair(mut commands: Commands, assets: Res<AssetServer>) {
    commands.spawn((
        Node {
            width: percent(100),
            height: percent(100),
            align_items: AlignItems::Center,
            justify_content: JustifyContent::Center,
            ..default()
        },
        children![(
            Crosshair,
            Node {
                width: px(64),
                height: px(64),
                ..default()
            },
            ImageNode {
                image: assets.load("crosshair.png"),
                ..default()
            },
            // Hidden by default, because cursor shouldn't be grabbed at startup either.
            Visibility::Hidden,
        )],
    ));
}

pub fn update_crosshair_visibility(
    cursor: Single<&CursorOptions, Changed<CursorOptions>>,
    crosshair: Single<&mut Visibility, With<Crosshair>>,
) {
    let is_grabbed = cursor.grab_mode != CursorGrabMode::None;
    let mut crosshair_visibility = crosshair.into_inner();
    *crosshair_visibility = (!is_grabbed || cursor.visible)
        .then_some(Visibility::Hidden)
        .unwrap_or_default();
}