repose_core/

state.rs

use std::any::Any;
use std::cell::{Ref, RefCell, RefMut};
use std::rc::Rc;

use crate::{
    Signal, on_unmount, reactive, remember_with_key, request_frame, scoped_effect, signal,
};

pub struct MutableState<T: Clone + 'static> {
    inner: Signal<T>,
    saver: Option<Box<dyn StateSaver<T>>>,
}
pub trait StateSaver<T>: 'static {
    fn save(&self, value: &T) -> Box<dyn Any>;
    fn restore(&self, saved: &dyn Any) -> Option<T>;
}

pub fn remember_derived<T: Clone + 'static>(
    key: impl Into<String>,
    producer: impl Fn() -> T + 'static + Clone,
) -> std::rc::Rc<crate::Signal<T>> {
    let key: String = key.into();
    produce_state(format!("derived:{key}"), producer)
}

// State holder pattern
pub trait StateHolder: 'static {
    type State: Clone;
    type Event;

    fn initial_state() -> Self::State;
    fn reduce(state: &Self::State, event: Self::Event) -> Self::State;
}

/// Lazily produces a Signal<T> (remembered by key) and keeps it up to date
/// by re-running `producer` under the reactive graph whenever its dependencies change.
///
/// - Runs an initial compute immediately to establish dependencies.
pub fn produce_state<T: Clone + 'static>(
    key: impl Into<String>,
    producer: impl Fn() -> T + 'static + Clone,
) -> Rc<Signal<T>> {
    produce_state_inner(key.into(), producer, |out, v| out.set(v))
}

/// Like [`produce_state`], but only writes the output signal when the computed
/// value actually changed (`T: PartialEq`), skipping invalidations/frame
/// requests when the derived value is unchanged.
pub fn produce_state_eq<T: Clone + PartialEq + 'static>(
    key: impl Into<String>,
    producer: impl Fn() -> T + 'static + Clone,
) -> Rc<Signal<T>> {
    produce_state_inner(key.into(), producer, |out, v| out.set_neq(v))
}

fn produce_state_inner<T: Clone + 'static>(
    key: String,
    producer: impl Fn() -> T + 'static + Clone,
    write: impl Fn(Signal<T>, T) + 'static + Copy,
) -> Rc<Signal<T>> {
    remember_with_key(format!("produce:{key}"), || {
        let out: Signal<T> = signal(producer());
        let out_clone = out.clone();

        let obs_id = reactive::new_observer({
            let producer = producer.clone();
            move || {
                let v = producer();
                write(out_clone.clone(), v);
            }
        });

        // Establish initial deps and value
        reactive::run_observer_now(obs_id);

        scoped_effect(move || {
            on_unmount(move || {
                reactive::remove_observer(obs_id);
            })
        });

        out
    })
}

/// Local widget state that drives recomposition on every write.
///
/// Unlike [`crate::remember_state`] (a bare `Rc<RefCell<T>>` that never requests
/// a frame), `Mutable` calls [`request_frame`] on `set`/`update` so async /
/// timer / layout-callback mutations reliably re-render. Prefer [`Signal`] for
/// shared/derived state; use `Mutable` for widget-local state that should
/// always recompose.
pub struct Mutable<T: 'static>(Rc<RefCell<T>>);

// Manual impl: `#[derive(Clone)]` would require `T: Clone`, but `Rc<RefCell<T>>`
// is unconditionally cloneable and local widget state must not need `T: Clone`.
impl<T: 'static> Clone for Mutable<T> {
    fn clone(&self) -> Self {
        Self(self.0.clone())
    }
}

impl<T: 'static> Mutable<T> {
    pub fn new(v: T) -> Self {
        Self(Rc::new(RefCell::new(v)))
    }

    pub fn get(&self) -> Ref<'_, T> {
        self.0.borrow()
    }

    /// Read the current value without holding the borrow across the closure.
    pub fn with<R>(&self, f: impl FnOnce(&T) -> R) -> R {
        f(&*self.0.borrow())
    }

    pub fn set(&self, v: T) {
        *self.0.borrow_mut() = v;
        crate::signal_fired();
        request_frame();
    }

    /// Like [`set`], but skips the frame request + signal when the value is
    /// unchanged (`T: PartialEq`).
    pub fn set_neq(&self, v: T)
    where
        T: PartialEq,
    {
        {
            let mut b = self.0.borrow_mut();
            if *b == v {
                return;
            }
            *b = v;
        }
        crate::signal_fired();
        request_frame();
    }

    pub fn update(&self, f: impl FnOnce(&mut T)) {
        f(&mut *self.0.borrow_mut());
        crate::signal_fired();
        request_frame();
    }

    /// Like [`update`], but only requests a frame + fires the signal when the
    /// value actually changed (`T: PartialEq + Clone`).
    pub fn update_neq(&self, f: impl FnOnce(&mut T))
    where
        T: PartialEq + Clone,
    {
        let changed = {
            let mut b = self.0.borrow_mut();
            let before = (*b).clone();
            f(&mut *b);
            *b != before
        };
        if changed {
            crate::signal_fired();
            request_frame();
        }
    }

    /// Escape hatch when batching many writes; call [`request_frame`] yourself.
    pub fn borrow_mut_silent(&self) -> RefMut<'_, T> {
        self.0.borrow_mut()
    }

    pub fn as_rc(&self) -> Rc<RefCell<T>> {
        self.0.clone()
    }
}

/// Remember a [`Mutable`] in the current composition slot.
#[track_caller]
pub fn remember_mutable<T: 'static>(init: impl FnOnce() -> T) -> Mutable<T> {
    crate::remember(|| Mutable::new(init())).as_ref().clone()
}

/// Key-based variant of [`remember_mutable`]; stable across conditional branches.
#[track_caller]
pub fn remember_mutable_with_key<T: 'static>(
    key: impl Into<String>,
    init: impl FnOnce() -> T,
) -> Mutable<T> {
    remember_with_key(key, || Mutable::new(init()))
        .as_ref()
        .clone()
}

/// Remember a reducer-backed local state. Returns a [`Mutable`] snapshot reader
/// plus a dispatch closure that runs `H::reduce` and writes the result back.
///
/// Prefer this for multi-field widget state over many loose `Mutable`s; it keeps
/// the state shape and all mutations in one place.
#[track_caller]
pub fn remember_reducer<H: StateHolder>() -> (Mutable<H::State>, impl Fn(H::Event) + Clone)
where
    H::State: 'static,
    H::Event: 'static,
{
    let state = remember_mutable(|| H::initial_state());
    let dispatch = {
        let state = state.clone();
        move |ev: H::Event| {
            state.update(|s| *s = H::reduce(s, ev));
        }
    };
    (state, dispatch)
}

/// Key-based variant of [`remember_reducer`]; stable across conditional branches.
#[track_caller]
pub fn remember_reducer_with_key<H: StateHolder>(
    key: impl Into<String>,
) -> (Mutable<H::State>, impl Fn(H::Event) + Clone)
where
    H::State: 'static,
    H::Event: 'static,
{
    let state = remember_mutable_with_key(key, || H::initial_state());
    let dispatch = {
        let state = state.clone();
        move |ev: H::Event| {
            state.update(|s| *s = H::reduce(s, ev));
        }
    };
    (state, dispatch)
}