cranpose-navigation 0.9.42

use cranpose_animation::{AnimationType, Easing, tween};
use cranpose_coroflow::ProvideViewModelStore;
use cranpose_services::{BackGesture, PredictiveBackHandler, ProvideSaveableScope};
use cranpose_ui::{CrossfadeSeek, SeekableCrossfade, composable};

use crate::controller::{Entry, NavController};

/// How long Compose's `NavHost` fades between destinations.
const DEFAULT_TRANSITION_MILLIS: u64 = 700;

/// Shows the screen on top of `controller`'s back stack — Android's
/// `NavHost`.
///
/// `content` receives the route and composes its screen, usually with a
/// `match`, so the compiler checks that every route has one:
///
/// ```
/// use cranpose_navigation::{NavHost, rememberNavController};
///
/// #[derive(Clone, PartialEq)]
/// enum Screen {
///     Home,
///     Detail { id: u32 },
/// }
///
/// # #[allow(non_snake_case)]
/// fn App() {
///     let nav = rememberNavController(Screen::Home);
///     NavHost(nav, move |screen| match screen {
///         Screen::Home => HomeScreen(move |id| nav.navigate(Screen::Detail { id })),
///         Screen::Detail { id } => DetailScreen(id),
///     });
/// }
/// # #[allow(non_snake_case)]
/// # fn HomeScreen(_open: impl Fn(u32) + 'static) {}
/// # #[allow(non_snake_case)]
/// # fn DetailScreen(_id: u32) {}
/// ```
///
/// Screens crossfade the way Compose's do. The platform back gesture pops the
/// back stack while there is a screen beneath the top one. While an
/// interactive back gesture moves (Android's predictive back, the iOS edge
/// swipe), the screen beneath shows through as far as the gesture went; when
/// the user lets go, the fade finishes or goes back from there. Every entry has
/// its own view model store: `viewModel` in a screen finds the screen's view
/// models, which are kept while other screens cover it and dropped once it is
/// popped and has faded out. Every entry also has its own
/// [`SaveableScope`](cranpose_services::SaveableScope), so `rememberSaveable`
/// in a screen keeps that visit's state while it is covered and forgets it
/// once it is popped.
#[composable(no_skip)]
pub fn NavHost<R, F>(controller: NavController<R>, content: F)
where
    R: Clone + PartialEq + 'static,
    F: FnMut(R) + 'static,
{
    NavHostWith(
        controller,
        tween(DEFAULT_TRANSITION_MILLIS, Easing::FastOutSlowInEasing),
        content,
    );
}

/// [`NavHost`] with its own `transition` between screens — Compose's
/// `NavHost(enterTransition, exitTransition)` for a fade.
#[composable(no_skip)]
pub fn NavHostWith<R, F>(controller: NavController<R>, transition: AnimationType, mut content: F)
where
    R: Clone + PartialEq + 'static,
    F: FnMut(R) + 'static,
{
    let (top, beneath, can_pop) = controller
        .stack
        .read(|stack| (stack.top(), stack.beneath_top(), stack.can_pop()));
    let gesture = cranpose_core::rememberMutableStateOf(|| None::<f32>);
    PredictiveBackHandler(
        can_pop,
        move |step| {
            gesture.set(match step {
                BackGesture::Started(event) | BackGesture::Progressed(event) => {
                    Some(event.progress)
                }
                BackGesture::Cancelled => None,
            });
        },
        move || {
            gesture.set(None);
            controller.navigate_up();
        },
    );
    let seek = gesture
        .get()
        .zip(beneath)
        .map(|(fraction, beneath)| CrossfadeSeek {
            toward: Some(beneath),
            fraction,
        });
    SeekableCrossfade(top, seek, transition, move |entry| {
        if let Some(Entry {
            route,
            store,
            saveables,
            ..
        }) = entry
        {
            ProvideSaveableScope(saveables, || {
                ProvideViewModelStore(store, || content(route));
            });
        }
    });
}