use std::ops::DerefMut;

use crate::{
    GameState,
    config::{UI_BUTTON_HOVERED, UI_BUTTON_NORMAL, UI_BUTTON_PRESSED},
    despawn,
    resources::{Lives, Score},
};

use bevy::{
    color::palettes::css::{BLACK, DARK_GRAY, GREEN, LIGHT_BLUE, RED, WHITE},
    prelude::*,
};

/// Plugin for the main menu
pub struct PluginGameMenu;

impl Plugin for PluginGameMenu {
    fn build(&self, app: &mut App) {
        app.add_systems(OnEnter(GameState::TitleScreen), spawn_menu)
            .add_systems(OnExit(GameState::TitleScreen), despawn::<MarkerMainMenu>)
            .add_systems(
                Update,
                (handle_spacebar, operate_buttons).run_if(in_state(GameState::TitleScreen)),
            );
    }
}

/// Plugin for the "get ready" period as gameplay starts.
pub struct PluginGetReady;

impl Plugin for PluginGetReady {
    fn build(&self, app: &mut App) {
        app.add_systems(OnEnter(GameState::GetReady), spawn_get_ready)
            .add_systems(OnExit(GameState::GetReady), despawn::<OnReadySetGo>)
            .add_systems(
                Update,
                (animate_get_ready_widget).run_if(in_state(GameState::GetReady)),
            )
            .insert_resource(ReadySetGoTimer(Timer::from_seconds(3.0, TimerMode::Once)));
    }
}

/// Plugin for the in-game HUD
pub struct PluginGameHud;

impl Plugin for PluginGameHud {
    fn build(&self, app: &mut App) {
        app.add_systems(OnEnter(GameState::Playing), spawn_ui)
            .add_systems(OnExit(GameState::Playing), despawn::<MarkerHUD>)
            .add_systems(Update, (operate_ui).run_if(in_state(GameState::Playing)));
    }
}

/// Plugin for the game-over screen
pub struct PluginGameOver;

impl Plugin for PluginGameOver {
    fn build(&self, app: &mut App) {
        app.add_systems(OnEnter(GameState::GameOver), spawn_gameover_ui)
            .add_systems(OnExit(GameState::GameOver), despawn::<MarkerGameOver>)
            .add_systems(
                Update,
                operate_buttons.run_if(in_state(GameState::GameOver)),
            );
    }
}

// Marker component for the title screen UI entity.
// This way, a query for the TitleUI can be used to despawn the title screen
#[derive(Component)]
struct MarkerMainMenu;

/// Marker component for things on the get-ready indicator
#[derive(Component)]
struct OnReadySetGo;

/// Marker for things on the game-over screen
#[derive(Component)]
struct MarkerGameOver;

/// Marker for things on the HUD (the in-game UI elements)
#[derive(Component)]
struct MarkerHUD;

/// Action specifier for the game-over menu's buttons.
///
/// Attach this component to a button and [`PluginGameOver`] will use it to
/// decide what to do when that button is pressed.
#[derive(Component)]
enum ButtonMenuAction {
    ToMainMenu,
    StartGame,
    Quit,
}

/// Newtype wrapper for `Timer`. Used to count down during the "get ready" phase.
#[derive(Deref, DerefMut, Resource)]
struct ReadySetGoTimer(Timer);

/// Marker for the counter text segment
#[derive(Component)]
struct CountdownText;

/// Marker for the counter bar segment
#[derive(Component)]
struct CountdownBar;

/// Utility function for creating a standard button.
fn button_bundle(text: &str) -> impl Bundle {
    (
        Button,
        // TODO: Generic action
        Node {
            width: Val::Px(150.0),
            height: Val::Px(65.0),
            border: UiRect::all(Val::Px(2.0)),
            justify_content: JustifyContent::Center,
            align_items: AlignItems::Center,
            margin: UiRect::all(Val::Px(5.0)),
            ..default()
        },
        BorderColor(Color::BLACK),
        BorderRadius::MAX,
        BackgroundColor(UI_BUTTON_NORMAL),
        children![(
            Text::new(text),
            TextColor(Color::srgb(0.9, 0.9, 0.9)),
            TextShadow::default(),
        )],
    )
}

fn spawn_menu(mut commands: Commands) {
    commands
        .spawn((
            MarkerMainMenu,
            Node {
                width: Val::Percent(100.0),
                height: Val::Percent(100.0),
                align_items: AlignItems::Center,
                justify_content: JustifyContent::Center,
                flex_direction: FlexDirection::Column,
                ..Default::default()
            },
        ))
        .with_children(|cmds| {
            cmds.spawn((
                Text::new("Robert's Bad Asteroids Game"),
                TextFont::from_font_size(50.0),
                TextLayout::new_with_justify(JustifyText::Center),
                TextShadow::default(),
            ));
            cmds.spawn((
                Text::new("Press space to begin"),
                TextFont::from_font_size(20.0),
                TextColor(Color::srgb(0.7, 0.7, 0.7)),
                TextShadow::default(),
            ));
            cmds.spawn((button_bundle("Start Game"), ButtonMenuAction::StartGame));
            cmds.spawn((button_bundle("Quit"), ButtonMenuAction::Quit));
        });
}

fn spawn_get_ready(mut commands: Commands, mut timer: ResMut<ReadySetGoTimer>) {
    timer.reset();
    commands.spawn((
        OnReadySetGo, // marker, so this can be de-spawned properly
        Node {
            align_self: AlignSelf::Center,
            justify_self: JustifySelf::Center,
            align_items: AlignItems::Center,
            justify_content: JustifyContent::Center,
            flex_direction: FlexDirection::Column,
            width: Val::Percent(30.),
            height: Val::Percent(30.),
            ..default()
        },
        BackgroundColor(LIGHT_BLUE.into()),
        children![
            (Text::new("Get Ready!"), TextColor(BLACK.into())),
            (
                CountdownBar,
                Node {
                    width: Val::Percent(90.0),
                    height: Val::Percent(10.),
                    ..default()
                },
                BackgroundColor(GREEN.into()),
            ),
            (
                CountdownText,
                Text::new("<uninit timer>"),
                TextColor(RED.into()),
            )
        ],
    ));
}

/// Spawns the game over screen.
///
/// Used by [`PluginGameOver`] when entering the [`GameState::GameOver`] state.
fn spawn_gameover_ui(mut commands: Commands) {
    commands.spawn((
        MarkerGameOver, // Marker, so `despawn<T>` can remove this on state exit.
        Node {
            width: Val::Percent(100.0),
            height: Val::Percent(100.0),
            align_items: AlignItems::Center,
            justify_content: JustifyContent::Center,
            flex_direction: FlexDirection::Column,
            ..default()
        },
        children![
            (button_bundle("Main Menu"), ButtonMenuAction::ToMainMenu,),
            (button_bundle("Quit"), ButtonMenuAction::Quit),
        ],
    ));
}

fn animate_get_ready_widget(
    mut text_segment: Single<&mut Text, With<CountdownText>>,
    mut bar_segment: Single<&mut Node, With<CountdownBar>>,
    time: Res<Time>,
    mut timer: ResMut<ReadySetGoTimer>,
    mut game_state: ResMut<NextState<GameState>>,
) {
    // Advance the timer, read the remaining time and write it onto the label.
    timer.tick(time.delta());

    // Add one to the visual value so the countdown starts at 3 and stops at 1.
    // Otherwise it starts at 2 and disappears after showing 0.
    // That feels wrong even though it's functionally identical.
    let tval = timer.0.remaining().as_secs() + 1;
    **text_segment = format!("{tval}").into();

    // Shrink the progress bar Node
    bar_segment.width = Val::Percent(100.0 * (1.0 - timer.fraction()));

    // If the timer has expired, change state to playing.
    if timer.finished() {
        game_state.set(GameState::Playing);
    }
}

/// Handles interactions with the menu buttons.
///
/// The buttons are used by the main menu and the game-over menu to change
/// between game states.
///
/// Button animation and action handling is done entirely within this system.
///
/// There are no checks for current state. If a "quit" button was put somewhere
/// on the HUD, this system would quit the game. The same will happen for
/// returning to the title screen. This should be useful for making a pause
/// menu, too.
fn operate_buttons(
    mut interactions: Query<
        (
            &Interaction,
            &mut BackgroundColor,
            &mut BorderColor,
            &ButtonMenuAction,
        ),
        (Changed<Interaction>, With<Button>),
    >,
    mut game_state: ResMut<NextState<GameState>>,
    mut app_exit_events: EventWriter<AppExit>,
) {
    // TODO: Better colors. These are taken from the example and they're ugly.
    for (interaction, mut color, mut border_color, menu_action) in &mut interactions {
        match *interaction {
            Interaction::Pressed => {
                *color = UI_BUTTON_PRESSED.into();
                border_color.0 = DARK_GRAY.into();
                match menu_action {
                    ButtonMenuAction::ToMainMenu => {
                        game_state.set(GameState::TitleScreen);
                    }
                    ButtonMenuAction::StartGame => {
                        game_state.set(GameState::GetReady);
                    }
                    ButtonMenuAction::Quit => {
                        app_exit_events.write(AppExit::Success);
                    }
                }
            }
            Interaction::Hovered => {
                *color = UI_BUTTON_HOVERED.into();
                border_color.0 = WHITE.into();
            }
            Interaction::None => {
                *color = UI_BUTTON_NORMAL.into();
                border_color.0 = BLACK.into();
            }
        }
    }
}

/// Main menu input listener. Starts game when the spacebar is pressed.
fn handle_spacebar(input: Res<ButtonInput<KeyCode>>, mut game_state: ResMut<NextState<GameState>>) {
    if input.just_pressed(KeyCode::Space) {
        game_state.set(GameState::GetReady);
    }
}

pub fn spawn_ui(mut commands: Commands, score: Res<Score>, lives: Res<Lives>) {
    let score = score.0;
    let lives = lives.0;
    commands.spawn((
        MarkerHUD,
        Node {
            width: Val::Percent(100.0),
            height: Val::Percent(100.0),
            align_items: AlignItems::Start,
            justify_content: JustifyContent::SpaceBetween,
            padding: UiRect::all(Val::Px(5.0)),
            ..default()
        },
        children![
            (
                Text::new(format!("Score: {score}")),
                TextFont::from_font_size(25.0),
                TextShadow::default(),
            ),
            (
                Text::new(format!("Lives: {lives}")),
                TextFont::from_font_size(25.0),
                TextShadow::default(),
            )
        ],
    ));
}

/// Updates the HUD with the current score & life count
///
/// TODO: some kind of event-based thing. Touching the text nodes every frame
/// seems expensive.
fn operate_ui(
    mut query: Single<(&Node, &Children), With<MarkerHUD>>,
    mut text_query: Query<&mut Text>,
    lives: Res<Lives>,
    score: Res<Score>,
) {
    let (_node, children) = query.deref_mut();
    let score = score.0;
    let lives = lives.0;
    // TODO: Something smarter than `unwrap()`
    let mut score_text = text_query.get_mut(children[0]).unwrap();
    **score_text = format!("Score: {score}");

    let mut lives_text = text_query.get_mut(children[1]).unwrap();
    **lives_text = format!("Lives: {lives}");
}