//! Hover color transitions are independent of tab layout and selected state.
use super::{Point, Tab, Visual};
use std::{collections::BTreeMap, time::Instant};

#[derive(Default)]
struct Fade {
    from: f32,
    target: f32,
    started: Option<Instant>,
}

impl Fade {
    fn sample(&mut self, hovered: bool, now: Instant) -> (f32, bool) {
        let t = self.started.map_or(1.0, |start| {
            (now.duration_since(start).as_secs_f32() / 0.16).min(1.0)
        });
        let value = self.from + (self.target - self.from) * (1.0 - (1.0 - t).powi(3));
        let target = if hovered { 1.0 } else { 0.0 };
        if target != self.target {
            // Reversing mid-fade starts at the currently visible color.
            self.from = value;
            self.target = target;
            self.started = Some(now);
            (value, true)
        } else {
            (value, t < 1.0)
        }
    }
}

#[derive(Default)]
pub(super) struct Hover {
    tabs: BTreeMap<u64, (Fade, Fade)>,
    plus: Fade,
}

impl Hover {
    pub fn sample(
        &mut self,
        visual: &mut Visual,
        tabs: &[Tab],
        pointer: Option<Point>,
        now: Instant,
    ) -> bool {
        let hit = pointer.and_then(|point| visual.hit(point));
        let (plus, mut animating) = self.plus.sample(
            pointer.is_some_and(|point| visual.plus.contains(point)),
            now,
        );
        visual.plus_hover = plus;
        self.tabs
            .retain(|id, _| tabs.iter().any(|tab| tab.id == *id));
        visual.hovers.clear();
        for tab in tabs {
            let (body, close) = self.tabs.entry(tab.id).or_default();
            let (body, body_animating) = body.sample(hit.is_some_and(|hit| hit.0 == tab.id), now);
            let (close, close_animating) = close.sample(hit == Some((tab.id, true)), now);
            visual.hovers.push((tab.id, body, close));
            animating |= body_animating || close_animating;
        }
        animating
    }
}