iced/lazy/src/component.rs

//! Build and reuse custom widgets using The Elm Architecture.
use crate::{Cache, CacheBuilder};

use iced_native::event;
use iced_native::layout::{self, Layout};
use iced_native::mouse;
use iced_native::overlay;
use iced_native::renderer;
use iced_native::{
    Clipboard, Element, Length, Point, Rectangle, Shell, Size, Widget,
};

use ouroboros::self_referencing;
use std::cell::RefCell;
use std::marker::PhantomData;

/// A reusable, custom widget that uses The Elm Architecture.
///
/// A [`Component`] allows you to implement custom widgets as if they were
/// `iced` applications with encapsulated state.
///
/// In other words, a [`Component`] allows you to turn `iced` applications into
/// custom widgets and embed them without cumbersome wiring.
///
/// A [`Component`] produces widgets that may fire an [`Event`](Component::Event)
/// and update the internal state of the [`Component`].
///
/// Additionally, a [`Component`] is capable of producing a `Message` to notify
/// the parent application of any relevant interactions.
pub trait Component<Message, Renderer> {
    /// The type of event this [`Component`] handles internally.
    type Event;

    /// Processes an [`Event`](Component::Event) and updates the [`Component`] state accordingly.
    ///
    /// It can produce a `Message` for the parent application.
    fn update(&mut self, event: Self::Event) -> Option<Message>;

    /// Produces the widgets of the [`Component`], which may trigger an [`Event`](Component::Event)
    /// on user interaction.
    fn view(&mut self) -> Element<Self::Event, Renderer>;
}

/// Turns an implementor of [`Component`] into an [`Element`] that can be
/// embedded in any application.
pub fn view<'a, C, Message, Renderer>(
    component: C,
) -> Element<'a, Message, Renderer>
where
    C: Component<Message, Renderer> + 'a,
    Message: 'a,
    Renderer: iced_native::Renderer + 'a,
{
    Element::new(Instance {
        state: RefCell::new(Some(
            StateBuilder {
                component: Box::new(component),
                message: PhantomData,
                cache_builder: |state| {
                    Some(
                        CacheBuilder {
                            element: state.view(),
                            overlay_builder: |_| None,
                        }
                        .build(),
                    )
                },
            }
            .build(),
        )),
    })
}

struct Instance<'a, Message, Renderer, Event> {
    state: RefCell<Option<State<'a, Message, Renderer, Event>>>,
}

#[self_referencing]
struct State<'a, Message: 'a, Renderer: 'a, Event: 'a> {
    component: Box<dyn Component<Message, Renderer, Event = Event> + 'a>,
    message: PhantomData<Message>,

    #[borrows(mut component)]
    #[covariant]
    cache: Option<Cache<'this, Event, Renderer>>,
}

impl<'a, Message, Renderer, Event> Instance<'a, Message, Renderer, Event> {
    fn with_element<T>(
        &self,
        f: impl FnOnce(&Element<'_, Event, Renderer>) -> T,
    ) -> T {
        self.with_element_mut(|element| f(element))
    }

    fn with_element_mut<T>(
        &self,
        f: impl FnOnce(&mut Element<'_, Event, Renderer>) -> T,
    ) -> T {
        self.state
            .borrow_mut()
            .as_mut()
            .unwrap()
            .with_cache_mut(|cache| {
                let mut element = cache.take().unwrap().into_heads().element;
                let result = f(&mut element);

                *cache = Some(
                    CacheBuilder {
                        element,
                        overlay_builder: |_| None,
                    }
                    .build(),
                );

                result
            })
    }
}

impl<'a, Message, Renderer, Event> Widget<Message, Renderer>
    for Instance<'a, Message, Renderer, Event>
where
    Renderer: iced_native::Renderer,
{
    fn width(&self) -> Length {
        self.with_element(|element| element.width())
    }

    fn height(&self) -> Length {
        self.with_element(|element| element.height())
    }

    fn layout(
        &self,
        renderer: &Renderer,
        limits: &layout::Limits,
    ) -> layout::Node {
        self.with_element(|element| element.layout(renderer, limits))
    }

    fn on_event(
        &mut self,
        event: iced_native::Event,
        layout: Layout<'_>,
        cursor_position: Point,
        renderer: &Renderer,
        clipboard: &mut dyn Clipboard,
        shell: &mut Shell<'_, Message>,
    ) -> event::Status {
        let mut local_messages = Vec::new();
        let mut local_shell = Shell::new(&mut local_messages);

        let event_status = self.with_element_mut(|element| {
            element.on_event(
                event,
                layout,
                cursor_position,
                renderer,
                clipboard,
                &mut local_shell,
            )
        });

        local_shell.revalidate_layout(|| shell.invalidate_layout());

        if !local_messages.is_empty() {
            let mut component = self
                .state
                .borrow_mut()
                .take()
                .unwrap()
                .into_heads()
                .component;

            for message in local_messages
                .into_iter()
                .filter_map(|message| component.update(message))
            {
                shell.publish(message);
            }

            *self.state.borrow_mut() = Some(
                StateBuilder {
                    component,
                    message: PhantomData,
                    cache_builder: |state| {
                        Some(
                            CacheBuilder {
                                element: state.view(),
                                overlay_builder: |_| None,
                            }
                            .build(),
                        )
                    },
                }
                .build(),
            );

            shell.invalidate_layout();
        }

        event_status
    }

    fn draw(
        &self,
        renderer: &mut Renderer,
        style: &renderer::Style,
        layout: Layout<'_>,
        cursor_position: Point,
        viewport: &Rectangle,
    ) {
        self.with_element(|element| {
            element.draw(renderer, style, layout, cursor_position, viewport);
        });
    }

    fn mouse_interaction(
        &self,
        layout: Layout<'_>,
        cursor_position: Point,
        viewport: &Rectangle,
        renderer: &Renderer,
    ) -> mouse::Interaction {
        self.with_element(|element| {
            element.mouse_interaction(
                layout,
                cursor_position,
                viewport,
                renderer,
            )
        })
    }

    fn overlay(
        &mut self,
        layout: Layout<'_>,
        renderer: &Renderer,
    ) -> Option<overlay::Element<'_, Message, Renderer>> {
        let has_overlay = self
            .state
            .borrow_mut()
            .as_mut()
            .unwrap()
            .with_cache_mut(|cache| {
                let element = cache.take().unwrap().into_heads().element;

                *cache = Some(
                    CacheBuilder {
                        element,
                        overlay_builder: |element| {
                            element.overlay(layout, renderer)
                        },
                    }
                    .build(),
                );

                cache
                    .as_ref()
                    .unwrap()
                    .borrow_overlay()
                    .as_ref()
                    .map(|overlay| overlay.position())
            });

        has_overlay.map(|position| {
            overlay::Element::new(
                position,
                Box::new(Overlay { instance: self }),
            )
        })
    }
}

struct Overlay<'a, 'b, Message, Renderer, Event> {
    instance: &'b mut Instance<'a, Message, Renderer, Event>,
}

impl<'a, 'b, Message, Renderer, Event>
    Overlay<'a, 'b, Message, Renderer, Event>
{
    fn with_overlay_maybe<T>(
        &self,
        f: impl FnOnce(&overlay::Element<'_, Event, Renderer>) -> T,
    ) -> Option<T> {
        self.instance
            .state
            .borrow()
            .as_ref()
            .unwrap()
            .borrow_cache()
            .as_ref()
            .unwrap()
            .borrow_overlay()
            .as_ref()
            .map(f)
    }

    fn with_overlay_mut_maybe<T>(
        &self,
        f: impl FnOnce(&mut overlay::Element<'_, Event, Renderer>) -> T,
    ) -> Option<T> {
        self.instance
            .state
            .borrow_mut()
            .as_mut()
            .unwrap()
            .with_cache_mut(|cache| {
                cache
                    .as_mut()
                    .unwrap()
                    .with_overlay_mut(|overlay| overlay.as_mut().map(f))
            })
    }
}

impl<'a, 'b, Message, Renderer, Event> overlay::Overlay<Message, Renderer>
    for Overlay<'a, 'b, Message, Renderer, Event>
where
    Renderer: iced_native::Renderer,
{
    fn layout(
        &self,
        renderer: &Renderer,
        bounds: Size,
        position: Point,
    ) -> layout::Node {
        self.with_overlay_maybe(|overlay| {
            let vector = position - overlay.position();

            overlay.layout(renderer, bounds).translate(vector)
        })
        .unwrap_or_default()
    }

    fn draw(
        &self,
        renderer: &mut Renderer,
        style: &renderer::Style,
        layout: Layout<'_>,
        cursor_position: Point,
    ) {
        self.with_overlay_maybe(|overlay| {
            overlay.draw(renderer, style, layout, cursor_position);
        });
    }

    fn mouse_interaction(
        &self,
        layout: Layout<'_>,
        cursor_position: Point,
        viewport: &Rectangle,
        renderer: &Renderer,
    ) -> mouse::Interaction {
        self.with_overlay_maybe(|overlay| {
            overlay.mouse_interaction(
                layout,
                cursor_position,
                viewport,
                renderer,
            )
        })
        .unwrap_or_default()
    }

    fn on_event(
        &mut self,
        event: iced_native::Event,
        layout: Layout<'_>,
        cursor_position: Point,
        renderer: &Renderer,
        clipboard: &mut dyn Clipboard,
        shell: &mut Shell<'_, Message>,
    ) -> iced_native::event::Status {
        let mut local_messages = Vec::new();
        let mut local_shell = Shell::new(&mut local_messages);

        let event_status = self
            .with_overlay_mut_maybe(|overlay| {
                overlay.on_event(
                    event,
                    layout,
                    cursor_position,
                    renderer,
                    clipboard,
                    &mut local_shell,
                )
            })
            .unwrap_or_else(|| iced_native::event::Status::Ignored);

        local_shell.revalidate_layout(|| shell.invalidate_layout());

        if !local_messages.is_empty() {
            let mut component =
                self.instance.state.take().unwrap().into_heads().component;

            for message in local_messages
                .into_iter()
                .filter_map(|message| component.update(message))
            {
                shell.publish(message);
            }

            self.instance.state = RefCell::new(Some(
                StateBuilder {
                    component,
                    message: PhantomData,
                    cache_builder: |state| {
                        Some(
                            CacheBuilder {
                                element: state.view(),
                                overlay_builder: |element| {
                                    element.overlay(layout, renderer)
                                },
                            }
                            .build(),
                        )
                    },
                }
                .build(),
            ));

            shell.invalidate_layout();
        }

        event_status
    }
}