cranpose_core/

callbacks.rs

use std::{cell::RefCell, rc::Rc};

use crate::{Composer, ComposerCore, RecomposeScope, composer_context};

/// The parameters of one composable call, kept in a slot between recompositions so the call can
/// skip its body when they are unchanged. Generated by the `#[composable]` macro.
pub struct ParamState<T> {
    pub(crate) value: Option<T>,
}

/// A parameter that points at a shared allocation: two that point at the
/// same one are equal without comparing what it holds.
pub trait SharedParam {
    /// Whether `self` and `other` point at the same allocation.
    fn same_allocation(&self, other: &Self) -> bool;
}

impl<T: ?Sized> SharedParam for Rc<T> {
    fn same_allocation(&self, other: &Self) -> bool {
        Rc::ptr_eq(self, other)
    }
}

impl<T: ?Sized> SharedParam for std::sync::Arc<T> {
    fn same_allocation(&self, other: &Self) -> bool {
        std::sync::Arc::ptr_eq(self, other)
    }
}

impl<T> ParamState<T> {
    /// Brings a call's stored parameters up to date: `fresh` stores them on
    /// the call's first composition, and `refresh` updates each stored field
    /// that differs and says whether any did. Unchanged fields are not
    /// cloned again.
    pub fn update_fields(
        &mut self,
        fresh: impl FnOnce() -> T,
        refresh: impl FnOnce(&mut T) -> bool,
    ) -> bool {
        match self.value.as_mut() {
            Some(stored) => refresh(stored),
            None => {
                self.value = Some(fresh());
                true
            }
        }
    }

    /// Returns a clone of the stored parameters, or `None` before any composition stored them.
    pub fn value(&self) -> Option<T>
    where
        T: Clone,
    {
        self.value.clone()
    }
}

/// A call's stored parameters and the value its body last returned, held in
/// one slot: a call that skips its body finds both with one lookup.
pub struct ParamReturnState<T, R> {
    params: ParamState<T>,
    returned: Option<R>,
}

impl<T, R> ParamReturnState<T, R> {
    /// [`ParamState::update_fields`] for the stored parameters.
    pub fn update_fields(
        &mut self,
        fresh: impl FnOnce() -> T,
        refresh: impl FnOnce(&mut T) -> bool,
    ) -> bool {
        self.params.update_fields(fresh, refresh)
    }

    /// Returns a clone of the stored parameters, or `None` before any composition stored them.
    pub fn value(&self) -> Option<T>
    where
        T: Clone,
    {
        self.params.value()
    }

    /// The value the call's body returned last.
    pub fn returned(&self) -> Option<R>
    where
        R: Clone,
    {
        self.returned.clone()
    }

    /// Stores the value the call's body returned, replacing the previous one.
    pub fn store_return(&mut self, value: R) {
        self.returned = Some(value);
    }
}

impl<T, R> Default for ParamReturnState<T, R> {
    fn default() -> Self {
        Self {
            params: ParamState::default(),
            returned: None,
        }
    }
}

/// Updates one stored parameter to `new` and says whether it differed,
/// reusing the stored value's allocations where `Clone::clone_from` can.
pub fn refresh_param<T: PartialEq + Clone>(stored: &mut T, new: &T) -> bool {
    if stored == new {
        return false;
    }
    stored.clone_from(new);
    true
}

/// Stores `new` as a parameter without comparing, and says it changed: for a
/// call that runs its body whatever its parameters, as one with a callback
/// does, a comparison would decide nothing. A `Modifier` compares element by
/// element.
pub fn store_param<T: Clone>(stored: &mut T, new: &T) -> bool {
    stored.clone_from(new);
    true
}

/// [`refresh_param`] for an `Rc` or `Arc` parameter: the same allocation is
/// unchanged without comparing its contents, which `PartialEq` on a pointer
/// to a type that is not `Eq` otherwise walks in full on every recomposition.
pub fn refresh_shared_param<T: SharedParam + PartialEq + Clone>(stored: &mut T, new: &T) -> bool {
    if stored.same_allocation(new) || stored == new {
        return false;
    }
    stored.clone_from(new);
    true
}

/// ParamSlot holds function/closure parameters by ownership (no PartialEq/Clone required).
/// Used by the `#[composable]` macro to store Fn-like parameters in the slot table.
pub struct ParamSlot<T> {
    val: RefCell<Option<T>>,
}

impl<T> Default for ParamSlot<T> {
    fn default() -> Self {
        Self {
            val: RefCell::new(None),
        }
    }
}

impl<T> ParamSlot<T> {
    /// Stores `v` as the held value, replacing the previous one.
    pub fn set(&self, v: T) {
        *self.val.borrow_mut() = Some(v);
    }

    /// Takes the value out temporarily for a recomposition callback.
    pub fn take(&self) -> Option<T> {
        self.val.borrow_mut().take()
    }
}

type CallbackCell = Rc<RefCell<Option<Box<dyn FnMut()>>>>;
type CallbackScopeCell = Rc<RefCell<Option<RecomposeScope>>>;

struct CallbackScopeGuard {
    core: Rc<ComposerCore>,
}

impl CallbackScopeGuard {
    fn push(composer: &Composer, scope: RecomposeScope) -> Self {
        composer.core.scope_stack.borrow_mut().push(scope);
        Self {
            core: composer.clone_core(),
        }
    }
}

impl Drop for CallbackScopeGuard {
    fn drop(&mut self) {
        self.core.scope_stack.borrow_mut().pop();
    }
}

fn with_callback_scope<R>(scope: &CallbackScopeCell, f: impl FnOnce() -> R) -> R {
    let captured_scope = scope.borrow().clone();
    if let Some(saved_scope) = captured_scope
        && let Some(composer) = composer_context::current_composer()
    {
        let _scope_guard = CallbackScopeGuard::push(&composer, saved_scope);
        return f();
    }

    f()
}

fn callback_owner_is_active(scope: &CallbackScopeCell) -> bool {
    scope
        .borrow()
        .as_ref()
        .is_none_or(RecomposeScope::is_effectively_active)
}

fn callback_owner_scope(composer: &Composer) -> Option<RecomposeScope> {
    composer.core.scope_stack.borrow().last().cloned()
}

/// Keeps the latest zero-argument callback alive across recompositions. The forwarder from
/// `clone_rc` always calls the callback stored last, and does nothing once the scope that stored
/// it is no longer active.
#[derive(Clone)]
pub struct CallbackHolder {
    rc: CallbackCell,
    creator_scope: CallbackScopeCell,
}

impl CallbackHolder {
    /// Create a new holder with a no-op callback so that callers can immediately invoke it.
    pub fn new() -> Self {
        Self::default()
    }

    /// Replace the stored callback with a new closure provided by the caller.
    pub fn update<F>(&self, f: F)
    where
        F: FnMut() + 'static,
    {
        self.update_boxed(Box::new(f));
    }

    /// Boxed form of [`Self::update`]: lets generated composable helpers take
    /// callbacks type-erased at the public-fn boundary, so helper bodies are
    /// compiled once instead of once per caller closure type.
    pub fn update_boxed(&self, f: Box<dyn FnMut() + 'static>) {
        *self.rc.borrow_mut() = Some(f);
        *self.creator_scope.borrow_mut() =
            composer_context::try_with_composer(callback_owner_scope).flatten();
    }

    /// Produce a forwarder closure that keeps the holder alive and forwards calls to it.
    pub fn clone_rc(&self) -> impl Fn() + 'static + use<> {
        let rc = self.rc.clone();
        let creator_scope = self.creator_scope.clone();
        move || {
            if !callback_owner_is_active(&creator_scope) {
                return;
            }
            with_callback_scope(&creator_scope, || {
                if let Some(callback) = rc.borrow_mut().as_mut() {
                    callback();
                }
            });
        }
    }
}

impl Default for CallbackHolder {
    fn default() -> Self {
        Self {
            rc: Rc::new(RefCell::new(None)),
            creator_scope: Rc::new(RefCell::new(None)),
        }
    }
}

/// CallbackHolder1 keeps the latest single-argument callback closure alive across recompositions.
/// It mirrors [`CallbackHolder`] but supports callbacks that receive one argument.
#[derive(Clone)]
pub struct CallbackHolder1<A: 'static> {
    #[expect(clippy::type_complexity)]
    rc: Rc<RefCell<Option<Box<dyn FnMut(A)>>>>,
    creator_scope: CallbackScopeCell,
}

impl<A: 'static> CallbackHolder1<A> {
    /// Create a new holder with a no-op callback so callers can invoke it immediately.
    pub fn new() -> Self {
        Self::default()
    }

    /// Replace the stored callback with a new closure provided by the caller.
    pub fn update<F>(&self, f: F)
    where
        F: FnMut(A) + 'static,
    {
        *self.rc.borrow_mut() = Some(Box::new(f));
        *self.creator_scope.borrow_mut() =
            composer_context::try_with_composer(callback_owner_scope).flatten();
    }

    /// Produce a forwarder closure that keeps the holder alive and forwards calls to it.
    pub fn clone_rc(&self) -> impl Fn(A) + 'static {
        let rc = self.rc.clone();
        let creator_scope = self.creator_scope.clone();
        move |arg| {
            if !callback_owner_is_active(&creator_scope) {
                return;
            }
            with_callback_scope(&creator_scope, || {
                if let Some(callback) = rc.borrow_mut().as_mut() {
                    callback(arg);
                }
            });
        }
    }
}

impl<A: 'static> Default for CallbackHolder1<A> {
    fn default() -> Self {
        Self {
            rc: Rc::new(RefCell::new(None)),
            creator_scope: Rc::new(RefCell::new(None)),
        }
    }
}

/// Holds the value a composable call returned, so a later composition that skips the call can
/// return it again.
pub struct ReturnSlot<T> {
    value: Option<T>,
}

impl<T: Clone> ReturnSlot<T> {
    /// Stores `value` as the call's latest return value.
    pub fn store(&mut self, value: T) {
        self.value = Some(value);
    }

    /// Returns a clone of the stored return value, or `None` if the call has not returned one yet.
    pub fn get(&self) -> Option<T> {
        self.value.clone()
    }
}

impl<T> Default for ParamState<T> {
    fn default() -> Self {
        Self { value: None }
    }
}

impl<T> Default for ReturnSlot<T> {
    fn default() -> Self {
        Self { value: None }
    }
}

#[cfg(test)]
#[path = "tests/callbacks_callback_holder_tests.rs"]
mod callback_holder_tests;

#[cfg(test)]
#[path = "tests/callbacks_param_state_tests.rs"]
mod param_state_tests;