floem/view/

mod.rs

//! # View and Widget Traits
//! Views are self-contained components that can be composed together to create complex UIs.
//! Views are the main building blocks of Floem.
//!
//! Views are structs that implement the [`View`] and [`Widget`] traits. Many of these structs will also contain a child field that also implements [`View`]. In this way, views can be composed together easily to create complex UIs. This is the most common way to build UIs in Floem. For more information on how to compose views check out the [views](crate::views) module.
//!
//! Creating a struct and manually implementing the [`View`] and [`Widget`] traits is typically only needed for building new widgets and for special cases. The rest of this module documentation is for help when manually implementing [`View`] and [`Widget`] on your own types.
//!
//!
//! ## The View and Widget Traits
//! The [`View`] trait is the trait that Floem uses to build  and display elements, and it builds on the [`Widget`] trait. The [`Widget`] trait contains the methods for implementing updates, styling, layout, events, and painting.
//! Eventually, the goal is for Floem to integrate the [`Widget`] trait with other rust UI libraries so that the widget layer can be shared among all compatible UI libraries.
//!
//! ## State management
//!
//! For all reactive state that your type contains, either in the form of signals or derived signals, you need to process the changes within an effect.
//! The most common pattern is to [`get`](floem_reactive::ReadSignal::get) the data in an effect and pass it in to `id.update_state()` and then handle that data in the `update` method of the View trait.
//!
//! For example a minimal slider might look like the following. First, we define the struct with the [`ViewData`] that contains the [`Id`].
//! Then, we use a function to construct the slider. As part of this function we create an effect that will be re-run every time the signals in the  `percent` closure change.
//! In the effect we send the change to the associated [`Id`]. This change can then be handled in the [`Widget::update`] method.
//! ```rust
//! use floem::ViewId;
//! use floem::reactive::*;
//!
//! struct Slider {
//!     id: ViewId,
//! }
//! pub fn slider(percent: impl Fn() -> f32 + 'static) -> Slider {
//!    let id = ViewId::new();
//!
//!    // If the following effect is not created, and `percent` is accessed directly,
//!    // `percent` will only be accessed a single time and will not be reactive.
//!    // Therefore the following `create_effect` is necessary for reactivity.
//!    create_effect(move |_| {
//!        let percent = percent();
//!        id.update_state(percent);
//!    });
//!    Slider {
//!        id,
//!    }
//! }
//! ```
//!

mod id;
mod into_iter;
pub(crate) mod stacking;
pub(crate) mod state;
mod storage;
pub mod tuple;

pub use id::{ViewId, process_pending_scope_reparents};
pub use into_iter::*;
pub use state::*;
pub(crate) use storage::*;
pub use tuple::*;

use floem_reactive::{Effect, ReadSignal, RwSignal, Scope, SignalGet, UpdaterEffect};
use peniko::kurbo::*;
use smallvec::SmallVec;
use std::any::Any;
use std::cell::Cell;
use std::hash::Hash;
use std::rc::Rc;

use crate::{
    Renderer,
    context::{EventCx, PaintCx, StyleCx, UpdateCx},
    event::EventPropagation,
    style::{LayoutProps, Style, StyleClassRef},
    unit::Length,
    views::{
        DynamicView,
        dyn_stack::{FxIndexSet, HashRun, diff},
        dyn_view,
    },
};
use state::ViewStyleProps;

/// type erased [`View`]
///
/// Views in Floem are strongly typed. [`AnyView`] allows you to escape the strong typing by converting any type implementing [`View`] into the [`AnyView`] type.
///
/// ## Bad Example
///```compile_fail
/// use floem::views::*;
/// use floem::widgets::*;
/// use floem::reactive::{RwSignal, SignalGet};
///
/// let check = true;
///
/// container(if check == true {
///     checkbox(|| true)
/// } else {
///     label(|| "no check".to_string())
/// });
/// ```
/// The above example will fail to compile because `container` is expecting a single type implementing `View` so the if and
/// the else must return the same type. However the branches return different types. The solution to this is to use the [`IntoView::into_any`] method
/// to escape the strongly typed requirement.
///
/// ```
/// use floem::reactive::{RwSignal, SignalGet};
/// use floem::views::*;
/// use floem::{IntoView, View};
///
/// let check = true;
///
/// container(if check == true {
///     checkbox(|| true).into_any()
/// } else {
///     label(|| "no check".to_string()).into_any()
/// });
/// ```
pub type AnyView = Box<dyn View>;

/// Converts a value into a [`View`].
///
/// This trait can be implemented on types which can be built into another type that implements the `View` trait.
///
/// For example, `&str` implements `IntoView` by building a `text` view and can therefore be used directly in a View tuple.
/// ```rust
/// # use floem::reactive::*;
/// # use floem::views::*;
/// # use floem::IntoView;
/// fn app_view() -> impl IntoView {
///     v_stack(("Item One", "Item Two"))
/// }
/// ```
/// Check out the [other types](#foreign-impls) that `IntoView` is implemented for.
pub trait IntoView: Sized {
    /// The final View type this converts to.
    type V: View + 'static;

    /// Intermediate type that has a [`ViewId`] before full view construction.
    ///
    /// For [`View`] types, this is `Self` (already has ViewId).
    /// For primitives, this is [`LazyView<Self>`] (creates ViewId, defers view construction).
    /// For tuples/vecs, this is the converted view type (eager conversion).
    type Intermediate: HasViewId + IntoView<V = Self::V>;

    /// Converts to the intermediate form which has a [`ViewId`].
    ///
    /// This is used by [`Decorators`](crate::views::Decorators) to get a [`ViewId`]
    /// for applying styles before the final view is constructed.
    fn into_intermediate(self) -> Self::Intermediate;

    /// Converts the value into a [`View`].
    fn into_view(self) -> Self::V {
        self.into_intermediate().into_view()
    }

    /// Converts the value into a [`AnyView`].
    fn into_any(self) -> AnyView {
        Box::new(self.into_view())
    }
}

/// A trait for types that have an associated [`ViewId`].
///
/// This is automatically implemented for all types that implement [`View`],
/// and can be manually implemented for intermediate types like [`Pending`].
pub trait HasViewId {
    /// Returns the [`ViewId`] associated with this value.
    fn view_id(&self) -> ViewId;
}

/// Blanket implementation of [`HasViewId`] for all [`View`] types.
impl<V: View> HasViewId for V {
    fn view_id(&self) -> ViewId {
        self.id()
    }
}

/// A trait for views that can accept children.
///
/// This provides a builder-pattern API for adding children to views,
/// similar to GPUI's `ParentElement` trait. Both methods append to
/// existing children rather than replacing them.
///
/// Views opt-in to this trait by implementing it. Not all views should
/// have children (e.g., `Label`, `TextInput`), so there is no blanket
/// implementation.
///
/// ## Example
/// ```rust,ignore
/// Stack::empty()
///     .child(text("Header"))
///     .children((0..5).map(|i| text(format!("Item {i}"))))
///     .child(text("Footer"))
/// ```
pub trait ParentView: HasViewId + Sized {
    /// Returns the scope associated with this view, if any.
    ///
    /// Views that need to provide context to children should:
    /// 1. Create a scope in their constructor: `Scope::new()` or `Scope::current().create_child()`
    /// 2. Provide context in that scope: `scope.provide_context(...)`
    /// 3. Override this method to return that scope
    ///
    /// When this returns `Some(scope)`, the scope is stored on the view (via `set_scope()`)
    /// so that descendants can find it via `ViewId::find_scope()`.
    fn scope(&self) -> Option<Scope> {
        None
    }

    /// Adds a single child to this view.
    ///
    /// The child is constructed lazily during the update cycle. The scope
    /// is resolved at build time by walking up the view hierarchy to find
    /// the nearest ancestor with a scope (via `ViewId::find_scope()`).
    fn child(self, child: impl IntoView + 'static) -> Self {
        // If this view provides a scope, store it for descendant lookup
        if let Some(scope) = self.scope() {
            self.view_id().set_scope(scope);
        }
        self.view_id().add_child_deferred(move || child.into_any());
        self
    }

    /// Adds multiple children to this view.
    ///
    /// Accepts arrays, tuples, vectors, and iterators of views.
    /// The children are constructed lazily during the update cycle. The scope
    /// is resolved at build time by walking up the view hierarchy to find
    /// the nearest ancestor with a scope (via `ViewId::find_scope()`).
    fn children(self, children: impl IntoViewIter + 'static) -> Self {
        // If this view provides a scope, store it for descendant lookup
        if let Some(scope) = self.scope() {
            self.view_id().set_scope(scope);
        }
        self.view_id()
            .add_children_deferred(move || children.into_view_iter().collect());
        self
    }

    /// Adds reactive children that update when signals change.
    ///
    /// The children function is called initially and re-called whenever
    /// its reactive dependencies change, replacing all children.
    ///
    /// The scope is resolved at build time by walking up the view hierarchy
    /// to find the nearest ancestor with a scope (via `ViewId::find_scope()`).
    ///
    /// ## Example
    /// ```rust,ignore
    /// use floem::prelude::*;
    /// use floem::views::Stem;
    ///
    /// let items = RwSignal::new(vec!["a", "b", "c"]);
    ///
    /// Stem::new().derived_children(move || {
    ///     items.get().into_iter().map(|item| text(item))
    /// });
    /// ```
    fn derived_children<CF, C>(self, children_fn: CF) -> Self
    where
        CF: Fn() -> C + 'static,
        C: IntoViewIter + 'static,
    {
        let id = self.view_id();

        // If this view provides a scope, store it for descendant lookup
        if let Some(scope) = self.scope() {
            id.set_scope(scope);
        }

        // Defer the entire setup to message processing
        // The scope is resolved via find_scope() when the message is processed
        id.setup_reactive_children_deferred(move || {
            let children_fn = Box::new(
                Scope::current()
                    .enter_child(move |_| children_fn().into_view_iter().collect::<Vec<_>>()),
            );

            let (initial_children, initial_scope) = UpdaterEffect::new(
                move || children_fn(()),
                move |(new_children, new_scope): (Vec<AnyView>, Scope)| {
                    // Dispose old scope and remove old children
                    if let Some(old_scope) = id.take_children_scope() {
                        old_scope.dispose();
                    }
                    // Set new children and store new scope
                    id.set_children_vec(new_children);
                    id.set_children_scope(new_scope);
                    id.request_all();
                },
            );

            // Set initial children and scope
            id.set_children_vec(initial_children);
            id.set_children_scope(initial_scope);
        });
        self
    }

    /// Adds a single reactive child with explicit state tracking.
    ///
    /// Takes two closures: one that tracks reactive dependencies and returns state,
    /// and another that builds a view from that state. When the state changes,
    /// only the managed child is replaced while preserving any other siblings.
    /// This allows mixing static children with a reactive child.
    ///
    /// For a simpler API where a single closure both tracks deps and returns a view,
    /// use `derived_child` instead.
    ///
    /// The scope is resolved at build time by walking up the view hierarchy
    /// to find the nearest ancestor with a scope (via `ViewId::find_scope()`).
    ///
    /// ## Example
    /// ```rust,ignore
    /// use floem::prelude::*;
    /// use floem::views::Stem;
    ///
    /// #[derive(Clone)]
    /// enum ViewType { One, Two }
    ///
    /// let view_type = RwSignal::new(ViewType::One);
    ///
    /// Stem::new().stateful_child(
    ///     move || view_type.get(),
    ///     |value| match value {
    ///         ViewType::One => text("One"),
    ///         ViewType::Two => text("Two"),
    ///     }
    /// );
    /// ```
    fn stateful_child<S, SF, CF, V>(self, state_fn: SF, child_fn: CF) -> Self
    where
        SF: Fn() -> S + 'static,
        CF: Fn(S) -> V + 'static,
        V: IntoView + 'static,
        S: 'static,
    {
        let id = self.view_id();

        // If this view provides a scope, store it for descendant lookup
        if let Some(scope) = self.scope() {
            id.set_scope(scope);
        }

        // Track the managed child's ViewId and Scope (append/track mode)
        let managed_child: Rc<Cell<Option<(ViewId, Scope)>>> = Rc::new(Cell::new(None));
        let managed_child_clone = managed_child.clone();

        // Defer the entire setup to message processing
        id.setup_reactive_children_deferred(move || {
            let child_fn: Rc<dyn Fn(S) -> (AnyView, Scope)> =
                Rc::new(Scope::current().enter_child(move |state: S| child_fn(state).into_any()));

            let child_fn_for_effect = child_fn.clone();
            let managed_child_for_effect = managed_child_clone.clone();

            let initial_state = UpdaterEffect::new(state_fn, move |new_state: S| {
                // Get and dispose old managed child
                if let Some((old_child_id, old_scope)) = managed_child_for_effect.take() {
                    old_scope.dispose();

                    // Remove old child from children list
                    let mut current_children = id.children();
                    let pos = current_children
                        .iter()
                        .position(|&c| c == old_child_id)
                        .unwrap_or(current_children.len());

                    if pos < current_children.len() {
                        current_children.remove(pos);
                        id.request_remove_views(vec![old_child_id]);
                    }

                    // Create and insert new child
                    let (new_child, new_scope) = child_fn_for_effect(new_state);
                    let new_child_id = new_child.id();
                    new_child_id.set_parent(id);
                    new_child_id.set_view(new_child);

                    let insert_pos = pos.min(current_children.len());
                    current_children.insert(insert_pos, new_child_id);

                    id.set_children_ids(current_children);
                    managed_child_for_effect.set(Some((new_child_id, new_scope)));
                }
                id.request_all();
            });

            // Create initial child and append to existing children
            let (initial_child, initial_scope) = child_fn(initial_state);
            let child_id = initial_child.id();
            child_id.set_parent(id);
            child_id.set_view(initial_child);

            let mut current_children = id.children();
            current_children.push(child_id);
            id.set_children_ids(current_children);

            managed_child_clone.set(Some((child_id, initial_scope)));
        });
        self
    }

    /// Adds keyed reactive children that efficiently update when signals change.
    ///
    /// Unlike `derived_children` which recreates all children on every update,
    /// `keyed_children` uses keys to identify items and only creates/removes
    /// children that actually changed. Views for unchanged items are reused.
    ///
    /// The scope is resolved at build time by walking up the view hierarchy
    /// to find the nearest ancestor with a scope (via `ViewId::find_scope()`).
    ///
    /// ## Arguments
    /// - `items_fn`: A function that returns an iterator of items
    /// - `key_fn`: A function that extracts a unique key from each item
    /// - `view_fn`: A function that creates a view from an item
    ///
    /// ## Example
    /// ```rust,ignore
    /// use floem::prelude::*;
    /// use floem::views::Stem;
    ///
    /// let items = RwSignal::new(vec!["a", "b", "c"]);
    ///
    /// Stem::new().keyed_children(
    ///     move || items.get(),
    ///     |item| *item,  // key by the item itself
    ///     |item| text(item),
    /// );
    /// ```
    fn keyed_children<IF, I, T, K, KF, VF, V>(self, items_fn: IF, key_fn: KF, view_fn: VF) -> Self
    where
        IF: Fn() -> I + 'static,
        I: IntoIterator<Item = T>,
        KF: Fn(&T) -> K + 'static,
        K: Eq + Hash + 'static,
        VF: Fn(T) -> V + 'static,
        V: IntoView + 'static,
        T: 'static,
    {
        let id = self.view_id();

        // If this view provides a scope, store it for descendant lookup
        if let Some(scope) = self.scope() {
            id.set_scope(scope);
        }

        // Defer the entire setup to message processing
        // The scope is resolved via find_scope() when the message is processed
        id.setup_reactive_children_deferred(move || {
            // Wrap view_fn to create scoped views - each child gets its own scope
            let view_fn = Scope::current().enter_child(move |item: T| view_fn(item).into_any());

            // Initialize keyed children state
            id.set_keyed_children(Vec::new());

            Effect::new(move |prev_hash_run: Option<HashRun<FxIndexSet<K>>>| {
                let items: SmallVec<[T; 128]> = items_fn().into_iter().collect();
                let new_keys: FxIndexSet<K> = items.iter().map(&key_fn).collect();

                // Take current children state
                let mut children: Vec<Option<(ViewId, Scope)>> = id
                    .take_keyed_children()
                    .unwrap_or_default()
                    .into_iter()
                    .map(Some)
                    .collect();

                if let Some(HashRun(prev_keys)) = prev_hash_run {
                    // Compute diff between old and new keys
                    let mut diff_result = diff::<K, T>(&prev_keys, &new_keys);

                    // Prepare items for added entries
                    let mut items: SmallVec<[Option<T>; 128]> =
                        items.into_iter().map(Some).collect();
                    for added in &mut diff_result.added {
                        added.view = items[added.at].take();
                    }

                    // Apply diff operations (returns views to remove)
                    let views_to_remove =
                        apply_keyed_diff(id, &mut children, diff_result, &view_fn);

                    // Request removal via message (processed during update phase)
                    id.request_remove_views(views_to_remove);
                } else {
                    // First run - create all children
                    for item in items {
                        let (view, scope) = view_fn(item);
                        let child_id = view.id();
                        child_id.set_parent(id);
                        child_id.set_view(view);
                        children.push(Some((child_id, scope)));
                    }
                }

                // Update the actual children list
                let children_ids: Vec<ViewId> = children
                    .iter()
                    .filter_map(|c| Some(c.as_ref()?.0))
                    .collect();
                id.set_children_ids(children_ids);

                // Store updated children state (convert back from Option)
                let children_vec: Vec<(ViewId, Scope)> = children.into_iter().flatten().collect();
                id.set_keyed_children(children_vec);

                id.request_all();
                HashRun(new_keys)
            });
        });

        self
    }

    /// Adds a single reactive child that updates when signals change.
    ///
    /// The closure both tracks reactive dependencies and returns a view.
    /// When any tracked dependency changes, only the managed child is replaced
    /// while preserving any other siblings. This allows mixing static children
    /// with a reactive child.
    ///
    /// This is consistent with `derived_children` which also takes a single
    /// closure. For explicit state tracking with separate closures, use
    /// `stateful_child` instead.
    ///
    /// The scope is resolved at build time by walking up the view hierarchy
    /// to find the nearest ancestor with a scope (via `ViewId::find_scope()`).
    ///
    /// ## Example
    /// ```rust,ignore
    /// use floem::prelude::*;
    /// use floem::views::Stem;
    ///
    /// #[derive(Clone)]
    /// enum ViewType { One, Two }
    ///
    /// let view_type = RwSignal::new(ViewType::One);
    ///
    /// Stem::new().derived_child(move || {
    ///     match view_type.get() {  // tracking happens here
    ///         ViewType::One => text("One").into_any(),
    ///         ViewType::Two => text("Two").into_any(),
    ///     }
    /// });
    /// ```
    fn derived_child<CF, V>(self, child_fn: CF) -> Self
    where
        CF: Fn() -> V + 'static,
        V: IntoView + 'static,
    {
        let id = self.view_id();

        // If this view provides a scope, store it for descendant lookup
        if let Some(scope) = self.scope() {
            id.set_scope(scope);
        }

        // Track the managed child's ViewId and Scope (append/track mode)
        let managed_child: Rc<Cell<Option<(ViewId, Scope)>>> = Rc::new(Cell::new(None));
        let managed_child_clone = managed_child.clone();

        // Defer the entire setup to message processing
        id.setup_reactive_children_deferred(move || {
            let child_fn =
                Box::new(Scope::current().enter_child(move |_: ()| child_fn().into_any()));

            let managed_child_for_effect = managed_child_clone.clone();

            let (initial_child, initial_scope) = UpdaterEffect::new(
                move || child_fn(()),
                move |(new_child, new_scope): (AnyView, Scope)| {
                    // Get and dispose old managed child
                    if let Some((old_child_id, old_scope)) = managed_child_for_effect.take() {
                        old_scope.dispose();

                        // Remove old child from children list
                        let mut current_children = id.children();
                        let pos = current_children
                            .iter()
                            .position(|&c| c == old_child_id)
                            .unwrap_or(current_children.len());

                        if pos < current_children.len() {
                            current_children.remove(pos);
                            id.request_remove_views(vec![old_child_id]);
                        }

                        // Add new child at the same position (or end if not found)
                        let new_child_id = new_child.id();
                        new_child_id.set_parent(id);
                        new_child_id.set_view(new_child);

                        // Insert at the old position or append
                        let insert_pos = pos.min(current_children.len());
                        current_children.insert(insert_pos, new_child_id);

                        id.set_children_ids(current_children);
                        managed_child_for_effect.set(Some((new_child_id, new_scope)));
                    }
                    id.request_all();
                },
            );

            // Append initial child to existing children
            let child_id = initial_child.id();
            child_id.set_parent(id);
            child_id.set_view(initial_child);

            let mut current_children = id.children();
            current_children.push(child_id);
            id.set_children_ids(current_children);

            managed_child_clone.set(Some((child_id, initial_scope)));
        });
        self
    }
}

/// Apply keyed diff operations to children.
///
/// Returns a list of ViewIds to remove (removal is deferred via message).
fn apply_keyed_diff<T, VF>(
    parent_id: ViewId,
    children: &mut Vec<Option<(ViewId, Scope)>>,
    diff: crate::views::dyn_stack::Diff<T>,
    view_fn: &VF,
) -> Vec<ViewId>
where
    VF: Fn(T) -> (AnyView, Scope),
{
    use crate::views::dyn_stack::{DiffOpAdd, DiffOpMove, DiffOpRemove};

    let mut views_to_remove = Vec::new();

    // Resize children if needed
    if diff.added.len() > diff.removed.len() {
        let target_size = children.len() + diff.added.len() - diff.removed.len();
        children.resize_with(target_size, || None);
    }

    // Items to move (deferred to avoid overwriting)
    let mut items_to_move = Vec::with_capacity(diff.moved.len());

    // 1. Clear all if requested
    if diff.clear {
        for child in &mut *children {
            if let Some((view_id, scope)) = child.take() {
                views_to_remove.push(view_id);
                scope.dispose();
            }
        }
    }

    // 2. Remove items (collect for deferred removal)
    for DiffOpRemove { at } in diff.removed {
        if let Some((view_id, scope)) = children[at].take() {
            views_to_remove.push(view_id);
            scope.dispose();
        }
    }

    // 3. Collect items to move
    for DiffOpMove { from, to } in diff.moved {
        if let Some(item) = children[from].take() {
            items_to_move.push((to, item));
        }
    }

    // 4. Add new items
    for DiffOpAdd { at, view } in diff.added {
        if let Some(item) = view {
            let (view, scope) = view_fn(item);
            let child_id = view.id();
            child_id.set_parent(parent_id);
            child_id.set_view(view);
            children[at] = Some((child_id, scope));
        }
    }

    // 5. Apply moves
    for (to, item) in items_to_move {
        children[to] = Some(item);
    }

    // 6. Remove holes
    children.retain(|c| c.is_some());

    views_to_remove
}

/// A wrapper type for lazy view construction.
///
/// `LazyView<T>` wraps a value that will eventually be converted into a [`View`],
/// but creates its [`ViewId`] eagerly. This allows decorators to be applied
/// before the actual view is constructed.
///
/// ## Example
/// ```rust
/// use floem::views::*;
/// use floem::{IntoView, LazyView};
///
/// // The ViewId is created when LazyView is constructed,
/// // but the Label is only created when into_view() is called
/// let lazy = LazyView::new("Hello");
/// let view = lazy.style(|s| s.padding(10.0)).into_view();
/// ```
pub struct LazyView<T> {
    /// The ViewId created eagerly for this lazy view.
    pub id: ViewId,
    /// The content that will be converted into a view.
    pub content: T,
}

impl<T> LazyView<T> {
    /// Creates a new `LazyView` wrapper with an eagerly-created [`ViewId`].
    pub fn new(content: T) -> Self {
        Self {
            id: ViewId::new(),
            content,
        }
    }

    /// Creates a new `LazyView` wrapper with an existing [`ViewId`].
    pub fn with_id(id: ViewId, content: T) -> Self {
        Self { id, content }
    }
}

impl<T> HasViewId for LazyView<T> {
    fn view_id(&self) -> ViewId {
        self.id
    }
}

impl<IV: IntoView + 'static> IntoView for Box<dyn Fn() -> IV> {
    type V = DynamicView;
    type Intermediate = DynamicView;

    fn into_intermediate(self) -> Self::Intermediate {
        dyn_view(self)
    }
}

impl<T: IntoView + Clone + 'static> IntoView for RwSignal<T> {
    type V = DynamicView;
    type Intermediate = DynamicView;

    fn into_intermediate(self) -> Self::Intermediate {
        dyn_view(move || self.get())
    }
}

impl<T: IntoView + Clone + 'static> IntoView for ReadSignal<T> {
    type V = DynamicView;
    type Intermediate = DynamicView;

    fn into_intermediate(self) -> Self::Intermediate {
        dyn_view(move || self.get())
    }
}

impl<VW: View + 'static> IntoView for VW {
    type V = VW;
    type Intermediate = Self;

    fn into_intermediate(self) -> Self::Intermediate {
        self
    }

    fn into_view(self) -> Self::V {
        self
    }
}

impl IntoView for i32 {
    type V = crate::views::Label;
    type Intermediate = LazyView<i32>;

    fn into_intermediate(self) -> Self::Intermediate {
        LazyView::new(self)
    }
}

impl IntoView for usize {
    type V = crate::views::Label;
    type Intermediate = LazyView<usize>;

    fn into_intermediate(self) -> Self::Intermediate {
        LazyView::new(self)
    }
}

impl IntoView for &str {
    type V = crate::views::Label;
    type Intermediate = LazyView<String>;

    fn into_intermediate(self) -> Self::Intermediate {
        LazyView::new(self.to_string())
    }
}

impl IntoView for String {
    type V = crate::views::Label;
    type Intermediate = LazyView<String>;

    fn into_intermediate(self) -> Self::Intermediate {
        LazyView::new(self)
    }
}

impl IntoView for () {
    type V = crate::views::Empty;
    type Intermediate = LazyView<()>;

    fn into_intermediate(self) -> Self::Intermediate {
        LazyView::new(self)
    }
}

impl<IV: IntoView + 'static> IntoView for Vec<IV> {
    type V = crate::views::Stack;
    type Intermediate = LazyView<Vec<IV>>;

    fn into_intermediate(self) -> Self::Intermediate {
        LazyView::new(self)
    }
}

impl<IV: IntoView + 'static> IntoView for LazyView<Vec<IV>> {
    type V = crate::views::Stack;
    type Intermediate = Self;

    fn into_intermediate(self) -> Self::Intermediate {
        self
    }

    fn into_view(self) -> Self::V {
        crate::views::from_iter_with_id(self.id, self.content, None)
    }
}

// IntoView implementations for LazyView<T> types
// These use the pre-created ViewId from LazyView
// LazyView is its own Intermediate since it already has a ViewId

impl IntoView for LazyView<i32> {
    type V = crate::views::Label;
    type Intermediate = Self;

    fn into_intermediate(self) -> Self::Intermediate {
        self
    }

    fn into_view(self) -> Self::V {
        crate::views::Label::with_id(self.id, self.content)
    }
}

impl IntoView for LazyView<usize> {
    type V = crate::views::Label;
    type Intermediate = Self;

    fn into_intermediate(self) -> Self::Intermediate {
        self
    }

    fn into_view(self) -> Self::V {
        crate::views::Label::with_id(self.id, self.content)
    }
}

impl IntoView for LazyView<&str> {
    type V = crate::views::Label;
    type Intermediate = Self;

    fn into_intermediate(self) -> Self::Intermediate {
        self
    }

    fn into_view(self) -> Self::V {
        crate::views::Label::with_id(self.id, self.content)
    }
}

impl IntoView for LazyView<String> {
    type V = crate::views::Label;
    type Intermediate = Self;

    fn into_intermediate(self) -> Self::Intermediate {
        self
    }

    fn into_view(self) -> Self::V {
        crate::views::Label::with_id(self.id, self.content)
    }
}

impl IntoView for LazyView<()> {
    type V = crate::views::Empty;
    type Intermediate = Self;

    fn into_intermediate(self) -> Self::Intermediate {
        self
    }

    fn into_view(self) -> Self::V {
        crate::views::Empty::with_id(self.id)
    }
}

/// The View trait contains the methods for implementing updates, styling, layout, events, and painting.
///
/// The [`id`](View::id) method must be implemented.
/// The other methods may be implemented as necessary to implement the functionality of the View.
/// ## State Management in a Custom View
///
/// For all reactive state that your type contains, either in the form of signals or derived signals, you need to process the changes within an effect.
/// The most common pattern is to [`get`](floem_reactive::SignalGet::get) the data in an effect and pass it in to `id.update_state()` and then handle that data in the `update` method of the `View` trait.
///
/// For example a minimal slider might look like the following. First, we define the struct that contains the [`ViewId`](crate::ViewId).
/// Then, we use a function to construct the slider. As part of this function we create an effect that will be re-run every time the signals in the  `percent` closure change.
/// In the effect we send the change to the associated [`ViewId`](crate::ViewId). This change can then be handled in the [`View::update`](crate::View::update) method.
/// ```rust
/// # use floem::{*, views::*, reactive::*};
///
/// struct Slider {
///     id: ViewId,
///     percent: f32,
/// }
/// pub fn slider(percent: impl Fn() -> f32 + 'static) -> Slider {
///     let id = ViewId::new();
///
///     // If the following effect is not created, and `percent` is accessed directly,
///     // `percent` will only be accessed a single time and will not be reactive.
///     // Therefore the following `create_effect` is necessary for reactivity.
///     create_effect(move |_| {
///         let percent = percent();
///         id.update_state(percent);
///     });
///     Slider { id, percent: 0.0 }
/// }
/// impl View for Slider {
///     fn id(&self) -> ViewId {
///         self.id
///     }
///
///     fn update(&mut self, cx: &mut floem::context::UpdateCx, state: Box<dyn std::any::Any>) {
///         if let Ok(percent) = state.downcast::<f32>() {
///             self.percent = *percent;
///             self.id.request_layout();
///         }
///     }
/// }
/// ```
pub trait View {
    fn id(&self) -> ViewId;

    fn view_style(&self) -> Option<Style> {
        None
    }

    fn view_class(&self) -> Option<StyleClassRef> {
        None
    }

    fn debug_name(&self) -> std::borrow::Cow<'static, str> {
        core::any::type_name::<Self>().into()
    }

    /// Use this method to react to changes in view-related state.
    /// You will usually send state to this hook manually using the `View`'s `Id` handle
    ///
    /// ```ignore
    /// self.id.update_state(SomeState)
    /// ```
    ///
    /// You are in charge of downcasting the state to the expected type.
    ///
    /// If the update needs other passes to run you're expected to call
    /// `_cx.window_state_mut().request_changes`.
    fn update(&mut self, cx: &mut UpdateCx, state: Box<dyn Any>) {
        // these are here to just ignore these arguments in the default case
        let _ = cx;
        let _ = state;
    }

    /// Use this method to style the view's children.
    ///
    /// If the style changes needs other passes to run you're expected to call
    /// `cx.window_state.style_dirty.insert(view_id)`.
    fn style_pass(&mut self, cx: &mut StyleCx<'_>) {
        let _ = cx;
    }

    /// Handles an event during the **capture phase** of event propagation.
    ///
    /// The capture phase runs **from the root of the dispatch path down toward
    /// the target element**, before the target itself receives the event. This
    /// method is invoked for each element encountered during that downward
    /// traversal.
    ///
    /// In contrast, [`Self::event`] runs during the **target and bubble phases**,
    /// after the event reaches the target and begins propagating back up the
    /// ancestor chain.
    ///
    /// Capture handlers are useful when an element must observe or influence an
    /// event **before the target processes it**. This can be necessary when:
    ///
    /// - the ancestor needs an opportunity to intercept or block the event before
    ///   it reaches the target
    /// - the ancestor must coordinate state across a subtree before the target
    ///   reacts
    /// - the event must be transformed or redirected before normal handling occurs
    ///
    /// Returning [`EventPropagation::Stop`] prevents the event from propagating to
    /// additional elements further along the dispatch path. The current element’s
    /// handlers will still complete.
    ///
    /// This differs from [`EventCx::stop_immediate_propagation`], which halts
    /// dispatch **immediately**, preventing any remaining handlers on the current
    /// element from running.
    ///
    /// Calling [`EventCx::prevent_default`] marks the event as having its default
    /// behavior suppressed. This flag is shared across all phases of dispatch,
    /// allowing capture handlers to prevent the default action before the event
    /// reaches the target.
    ///
    /// # See also
    ///
    /// - [`Self::event`] — handles the same event during the target and bubble phases.
    ///
    /// # Default behavior
    ///
    /// The default implementation ignores the event and allows propagation to
    /// continue.
    fn event_capture(&mut self, _cx: &mut EventCx) -> EventPropagation {
        EventPropagation::Continue
    }

    /// Handles an event during the **target and bubble phases** of event propagation.
    ///
    /// After the capture phase completes, the event is delivered to the **target
    /// element** and then propagates upward through its ancestors. This method is
    /// invoked for the target and for each ancestor encountered during that upward
    /// traversal.
    ///
    /// In contrast, [`Self::event_capture`] runs earlier during the **capture phase**
    /// while the event travels downward toward the target.
    ///
    /// Returning [`EventPropagation::Stop`] prevents the event from propagating to
    /// additional elements further along the dispatch path. The current element’s
    /// handlers will still complete.
    ///
    /// This differs from [`EventCx::stop_immediate_propagation`], which stops
    /// dispatch immediately and prevents any remaining handlers on the current
    /// element from executing.
    ///
    /// Calling [`EventCx::prevent_default`] suppresses the event’s default behavior.
    /// This flag is shared across all phases of dispatch and can be set in either
    /// [`Self::event_capture`] or [`Self::event`].
    ///
    /// # Propagation behavior
    ///
    /// Event dispatch proceeds in this order:
    ///
    /// 1. [`Self::event_capture`] on ancestors from root → target
    /// 2. [`Self::event`] on the target
    /// 3. [`Self::event`] on ancestors from target → root
    ///
    /// Propagation may be stopped at any point by returning
    /// [`EventPropagation::Stop`] or by calling
    /// [`EventCx::stop_immediate_propagation`].
    ///
    /// # Default behavior
    ///
    /// The default implementation ignores the event and allows propagation to
    /// continue.
    fn event(&mut self, _cx: &mut EventCx) -> EventPropagation {
        EventPropagation::Continue
    }

    /// `View`-specific implementation. Called during paint traversal for this view.
    /// Children are painted automatically by Floem.
    /// Views should only paint their own content (backgrounds, borders, custom drawing).
    fn paint(&mut self, cx: &mut PaintCx) {
        let _ = cx;
        // Default implementation: no custom painting
        // Children are painted automatically by traversal
    }

    fn post_paint(&mut self, cx: &mut PaintCx) {
        let _ = cx;
    }
}

impl View for Box<dyn View> {
    fn id(&self) -> ViewId {
        (**self).id()
    }

    fn view_style(&self) -> Option<Style> {
        (**self).view_style()
    }

    fn view_class(&self) -> Option<StyleClassRef> {
        (**self).view_class()
    }

    fn debug_name(&self) -> std::borrow::Cow<'static, str> {
        (**self).debug_name()
    }

    fn update(&mut self, cx: &mut UpdateCx, state: Box<dyn Any>) {
        (**self).update(cx, state)
    }

    fn style_pass(&mut self, cx: &mut StyleCx) {
        (**self).style_pass(cx)
    }

    fn event_capture(&mut self, cx: &mut EventCx) -> EventPropagation {
        (**self).event_capture(cx)
    }

    fn event(&mut self, cx: &mut EventCx) -> EventPropagation {
        (**self).event(cx)
    }

    fn paint(&mut self, cx: &mut PaintCx) {
        (**self).paint(cx)
    }

    fn post_paint(&mut self, cx: &mut PaintCx) {
        (**self).paint(cx)
    }
}

pub(crate) fn border_radius(
    radius: crate::unit::Length,
    size: f64,
    resolve_cx: &crate::unit::FontSizeCx,
) -> f64 {
    radius.resolve(size, resolve_cx)
}

fn border_to_radii_view(
    style: &ViewStyleProps,
    size: Size,
    resolve_cx: &crate::unit::FontSizeCx,
) -> RoundedRectRadii {
    let border_radii = style.border_radius();
    RoundedRectRadii {
        top_left: border_radius(
            border_radii.top_left.unwrap_or(Length::Pt(0.0)),
            size.min_side(),
            resolve_cx,
        ),
        top_right: border_radius(
            border_radii.top_right.unwrap_or(Length::Pt(0.0)),
            size.min_side(),
            resolve_cx,
        ),
        bottom_left: border_radius(
            border_radii.bottom_left.unwrap_or(Length::Pt(0.0)),
            size.min_side(),
            resolve_cx,
        ),
        bottom_right: border_radius(
            border_radii.bottom_right.unwrap_or(Length::Pt(0.0)),
            size.min_side(),
            resolve_cx,
        ),
    }
}

pub(crate) fn paint_bg(cx: &mut PaintCx, style: &ViewStyleProps, rect: Rect) {
    let radii = border_to_radii_view(style, rect.size(), &cx.font_size_cx);
    if radii_max(radii) > 0.0 {
        paint_box_shadow(cx, style, rect, Some(radii));
        let bg = match style.background() {
            Some(color) => color,
            None => return,
        };
        let rounded_rect = rect.to_rounded_rect(radii);
        cx.fill(&rounded_rect, &bg, 0.0);
    } else {
        paint_box_shadow(cx, style, rect, None);
        let bg = match style.background() {
            Some(color) => color,
            None => return,
        };
        cx.fill(&rect, &bg, 0.0);
    }
}

fn paint_box_shadow(
    cx: &mut PaintCx,
    style: &ViewStyleProps,
    rect: Rect,
    rect_radius: Option<RoundedRectRadii>,
) {
    for shadow in &style.shadow() {
        let min = rect.size().min_side();
        let left_offset = shadow.left_offset.resolve(min, &cx.font_size_cx);
        let right_offset = shadow.right_offset.resolve(min, &cx.font_size_cx);
        let top_offset = shadow.top_offset.resolve(min, &cx.font_size_cx);
        let bottom_offset = shadow.bottom_offset.resolve(min, &cx.font_size_cx);
        let spread = shadow.spread.resolve(min, &cx.font_size_cx);
        let blur_radius = shadow.blur_radius.resolve(min, &cx.font_size_cx);
        let inset = Insets::new(
            left_offset / 2.0,
            top_offset / 2.0,
            right_offset / 2.0,
            bottom_offset / 2.0,
        );
        let rect = rect.inflate(spread, spread).inset(inset);
        if let Some(radii) = rect_radius {
            let rounded_rect = RoundedRect::from_rect(rect, radii_add(radii, spread));
            cx.fill(&rounded_rect, shadow.color, blur_radius);
        } else {
            cx.fill(&rect, shadow.color, blur_radius);
        }
    }
}
pub(crate) fn paint_outline(cx: &mut PaintCx, style: &ViewStyleProps, rect: Rect) {
    if cx.is_vger() {
        let outline = &style.outline();
        if outline.width == 0. {
            return;
        }
        let half = outline.width / 2.0;
        let rect = rect.inflate(half, half);
        let border_radii = border_to_radii_view(style, rect.size(), &cx.font_size_cx);
        cx.stroke(
            &rect.to_rounded_rect(radii_add(border_radii, half)),
            &style.outline_color(),
            outline,
        );
        return;
    }

    use crate::{
        paint::{BorderPath, BorderPathEvent},
        unit::Pct,
    };

    let outlines = [
        (style.outline(), style.outline_color()),
        (style.outline(), style.outline_color()),
        (style.outline(), style.outline_color()),
        (style.outline(), style.outline_color()),
    ];

    // Early return if no outlines
    if outlines.iter().any(|o| o.0.width == 0.0) {
        return;
    }

    let outline_color = style.outline_color();
    let Pct(outline_progress) = style.outline_progress();

    let half_width = outlines[0].0.width / 2.0;
    let rect = rect.inflate(half_width, half_width);

    let radii = radii_map(
        border_to_radii_view(style, rect.size(), &cx.font_size_cx),
        |r| (r + half_width).max(0.0),
    );

    let mut outline_path = BorderPath::new(rect, radii);

    // Only create subsegment if needed
    if outline_progress < 100. {
        outline_path.subsegment(0.0..(outline_progress.clamp(0.0, 100.) / 100.));
    }

    let mut current_path = Vec::new();
    for event in outline_path.path_elements(&outlines, 0.1) {
        match event {
            BorderPathEvent::PathElement(el) => current_path.push(el),
            BorderPathEvent::NewStroke(stroke) => {
                // Render current path with previous stroke if any
                if !current_path.is_empty() {
                    cx.stroke(&current_path.as_slice(), &outline_color, &stroke.0);
                    current_path.clear();
                }
            }
        }
    }
    assert!(current_path.is_empty());
}

pub(crate) fn paint_border(
    cx: &mut PaintCx,
    layout_style: &LayoutProps,
    style: &ViewStyleProps,
    rect: Rect,
) {
    if cx.is_vger() {
        let border = layout_style.border();

        let left = border.left.unwrap_or(Stroke::new(0.));
        let top = border.top.unwrap_or(Stroke::new(0.));
        let right = border.right.unwrap_or(Stroke::new(0.));
        let bottom = border.bottom.unwrap_or(Stroke::new(0.));

        if left.width == top.width
            && top.width == right.width
            && right.width == bottom.width
            && bottom.width == left.width
            && left.width > 0.0
            && style.border_color().left.is_some()
            && style.border_color().top.is_some()
            && style.border_color().right.is_some()
            && style.border_color().bottom.is_some()
            && style.border_color().left == style.border_color().top
            && style.border_color().top == style.border_color().right
            && style.border_color().right == style.border_color().bottom
        {
            let half = left.width / 2.0;
            let rect = rect.inflate(-half, -half);
            let radii = border_to_radii_view(style, rect.size(), &cx.font_size_cx);
            if let Some(color) = style.border_color().left {
                if radii_max(radii) > 0.0 {
                    let radii = radii_map(radii, |r| (r - half).max(0.0));
                    cx.stroke(&rect.to_rounded_rect(radii), &color, &left);
                } else {
                    cx.stroke(&rect, &color, &left);
                }
            }
        } else {
            if left.width > 0.0
                && let Some(color) = style.border_color().left
            {
                let half = left.width / 2.0;
                cx.stroke(
                    &Line::new(Point::new(half, 0.0), Point::new(half, rect.height())),
                    &color,
                    &left,
                );
            }
            if right.width > 0.0
                && let Some(color) = style.border_color().right
            {
                let half = right.width / 2.0;
                cx.stroke(
                    &Line::new(
                        Point::new(rect.width() - half, 0.0),
                        Point::new(rect.width() - half, rect.height()),
                    ),
                    &color,
                    &right,
                );
            }
            if top.width > 0.0
                && let Some(color) = style.border_color().top
            {
                let half = top.width / 2.0;
                cx.stroke(
                    &Line::new(Point::new(0.0, half), Point::new(rect.width(), half)),
                    &color,
                    &top,
                );
            }
            if bottom.width > 0.0
                && let Some(color) = style.border_color().bottom
            {
                let half = bottom.width / 2.0;
                cx.stroke(
                    &Line::new(
                        Point::new(0.0, rect.height() - half),
                        Point::new(rect.width(), rect.height() - half),
                    ),
                    &color,
                    &bottom,
                );
            }
        }
        return;
    }

    use crate::{
        paint::{BorderPath, BorderPathEvent},
        unit::Pct,
    };

    let border = layout_style.border();
    let borders = [
        (
            border.top.unwrap_or(Stroke::new(0.)),
            style.border_color().top.unwrap_or_default(),
        ),
        (
            border.right.unwrap_or(Stroke::new(0.)),
            style.border_color().right.unwrap_or_default(),
        ),
        (
            border.bottom.unwrap_or(Stroke::new(0.)),
            style.border_color().bottom.unwrap_or_default(),
        ),
        (
            border.left.unwrap_or(Stroke::new(0.)),
            style.border_color().left.unwrap_or_default(),
        ),
    ];

    // Early return if no borders
    if borders.iter().all(|b| b.0.width == 0.0) {
        return;
    }

    let Pct(border_progress) = style.border_progress();

    let half_width = borders[0].0.width / 2.0;
    let rect = rect.inflate(-half_width, -half_width);

    let radii = radii_map(
        border_to_radii_view(style, rect.size(), &cx.font_size_cx),
        |r| (r - half_width).max(0.0),
    );

    let mut border_path = BorderPath::new(rect, radii);

    // Only create subsegment if needed
    if border_progress < 100. {
        border_path.subsegment(0.0..(border_progress.clamp(0.0, 100.) / 100.));
    }

    // optimize for maximum which is 12 paths and a single move to
    let mut current_path = smallvec::SmallVec::<[_; 13]>::new();
    for event in border_path.path_elements(&borders, 0.1) {
        match event {
            BorderPathEvent::PathElement(el) => {
                if !current_path.is_empty() && matches!(el, PathEl::MoveTo(_)) {
                    // extra move to's will mess up dashed patterns
                    continue;
                }
                current_path.push(el)
            }
            BorderPathEvent::NewStroke(stroke) => {
                // Render current path with previous stroke if any
                if !current_path.is_empty() && stroke.0.width > 0. {
                    cx.stroke(&current_path.as_slice(), &stroke.1, &stroke.0);
                    current_path.clear();
                } else if stroke.0.width == 0. {
                    current_path.clear();
                }
            }
        }
    }
    assert!(current_path.is_empty());
}

// Helper functions for futzing with RoundedRectRadii. These should probably be in kurbo.

fn radii_map(radii: RoundedRectRadii, f: impl Fn(f64) -> f64) -> RoundedRectRadii {
    RoundedRectRadii {
        top_left: f(radii.top_left),
        top_right: f(radii.top_right),
        bottom_left: f(radii.bottom_left),
        bottom_right: f(radii.bottom_right),
    }
}

pub(crate) const fn radii_max(radii: RoundedRectRadii) -> f64 {
    radii
        .top_left
        .max(radii.top_right)
        .max(radii.bottom_left)
        .max(radii.bottom_right)
}

fn radii_add(radii: RoundedRectRadii, offset: f64) -> RoundedRectRadii {
    radii_map(radii, |r| r + offset)
}