use std::cell::RefCell;
use std::rc::Rc;
use std::time::Duration;
use kiln_core::Board;
use kiln_core::game::GameState;
use crate::animation::Animation;
use crate::log::LogState;
use crate::menu::{MenuItem, MenuCloseAnimation, MenuOpenAnimation, MenuState};
use crate::scroll_overlay::{ScrollCloseAnimation, ScrollOpenAnimation, ScrollOverlayState};
use crate::transition::TransitionAnimation;

/// A pair of board `Rc`s (old board, new board) queued for transition pre-rendering.
type PendingTransition = Option<(Rc<RefCell<Board>>, Rc<RefCell<Board>>)>;

/// View-only UI state for the log panel, scroll overlay, menu, and board animations.
/// Presentation-only state; lives in the front-end, not on [`GameState`].
pub(crate) struct Ui {
    /// State for the log panel (open/closed, height, scroll position).
    pub(crate) log: LogState,
    /// Scroll offset and bounds for the fully-open scroll overlay.
    pub(crate) overlay: ScrollOverlayState,
    /// Old and new board Rcs waiting to be pre-rendered on the next `draw()` call.
    /// Populated when a portal transition is detected; consumed in `draw()`.
    pub(crate) pending_transition: PendingTransition,
    /// The currently running animation, if any. All input is suppressed while `Some`.
    pub(crate) active_animation: Option<Box<dyn Animation>>,
    /// State for the active menu overlay. `Some` while the menu is open or closing.
    pub(crate) menu: Option<MenuState>,
    /// Set by a menu action to signal that the game loop should exit after the
    /// close animation finishes.
    pub(crate) should_quit: bool,
}

impl Default for Ui {
    fn default() -> Self {
        Self {
            log: LogState::new(),
            overlay: ScrollOverlayState::default(),
            pending_transition: None,
            active_animation: None,
            menu: None,
            should_quit: false,
        }
    }
}

impl Ui {
    /// Scrolls the scroll overlay by `delta` lines, clamped to the valid range.
    pub(crate) fn scroll_lines(&mut self, delta: i32) {
        self.overlay.offset = (self.overlay.offset as i32 + delta)
            .clamp(0, self.overlay.max_scroll as i32) as u16;
    }

    /// Scrolls the menu overlay by `delta` lines, clamped to the valid range.
    pub(crate) fn scroll_menu(&mut self, delta: i32) {
        if let Some(m) = self.menu.as_mut() {
            m.offset = (m.offset as i32 + delta).clamp(0, m.max_scroll as i32) as u16;
        }
    }

    /// Opens a menu: stores the items as [`MenuState`] and starts the open animation.
    pub(crate) fn open_menu(&mut self, items: Vec<MenuItem>) {
        self.active_animation = Some(Box::new(MenuOpenAnimation::new(items.clone())));
        self.menu = Some(MenuState { items, ..Default::default() });
    }

    /// Starts the close animation using a snapshot of the current menu items.
    ///
    /// Called from within a menu item's action closure (e.g. `ui.begin_close_menu()`).
    pub(crate) fn begin_close_menu(&mut self) {
        let items = self.menu.as_ref().map(|m| m.items.clone()).unwrap_or_default();
        self.active_animation = Some(Box::new(MenuCloseAnimation::new(items)));
    }

    /// Advances all time-driven UI state by `dt` and drives the game tick.
    ///
    /// While any animation is running, `game.tick` is suppressed. When an
    /// animation finishes, [`input_mode_after`](Animation::input_mode_after) is
    /// consulted: returning to [`Board`](crate::input::InputMode::Board) mode
    /// eagerly calls [`handle_scroll`](GameState::handle_scroll) to clear any
    /// pending scroll, and clears [`menu`](Ui::menu) so the closed overlay is not
    /// rendered on the next frame.
    pub(crate) fn tick(&mut self, dt: Duration, game: &mut GameState) {
        // Advance the active animation; on completion, dispatch any mode-change effect.
        if let Some(ref mut anim) = self.active_animation {
            if anim.update(dt.as_secs_f32()) {
                let mode = anim.input_mode_after();
                self.active_animation = None;
                // Returning to Board mode: eagerly clear scroll and menu state so
                // neither renders as open for one extra frame before the game tick.
                if matches!(mode, crate::input::InputMode::Board) {
                    game.handle_scroll();
                    self.menu = None;
                }
            }
            return; // no game tick during any animation (even when just ended)
        }

        // Normal path: tick the game, then check if a scroll appeared.
        game.tick(dt);
        if let Some(scroll) = &game.active_scroll {
            let lines = scroll.lines.clone();
            self.active_animation = Some(Box::new(ScrollOpenAnimation::new(lines)));
        }
    }

    /// Sets the player's scroll choice and starts the close animation.
    ///
    /// `choice` is `None` when the player dismisses without selecting.
    pub(crate) fn begin_close(&mut self, choice: Option<String>, game: &mut GameState) {
        if let Some(scroll) = game.active_scroll.as_mut() {
            scroll.choice = choice;
        }
        let lines = game.active_scroll.as_ref()
            .map(|s| s.lines.clone())
            .unwrap_or_default();
        self.active_animation = Some(Box::new(ScrollCloseAnimation::new(lines)));
    }

    /// Initialises the board-wipe transition animation once the draw area is known.
    ///
    /// Called from `draw_board_area` when [`pending_transition`](Ui::pending_transition)
    /// is set, so the [`TransitionAnimation`] is sized to the exact inner board area.
    pub(crate) fn start_transition(&mut self, old: &Board, new: &Board, area: ratatui::layout::Rect) {
        self.active_animation = Some(Box::new(TransitionAnimation::new(old, new, area)));
    }
}