//! Keep behavior field state within one editing session and reset it on replacement.
use iced::advanced::widget::{Operation, Tree, tree};
use iced::advanced::{Clipboard, Layout, Shell, Widget, layout, overlay, renderer};
use iced::{Element, Event, Length, Rectangle, Size, Theme, Vector, mouse};
use oa_core::Id;

struct Identity(Id);

struct Session<'a, Message, R: renderer::Renderer> {
    identity: Id,
    content: Element<'a, Message, Theme, R>,
}

pub(super) fn reset_on_change<'a, Message: 'a, R: renderer::Renderer + 'a>(
    identity: Id,
    content: impl Into<Element<'a, Message, Theme, R>>,
) -> Element<'a, Message, Theme, R> {
    Element::new(Session {
        identity,
        content: content.into(),
    })
}

impl<Message, R: renderer::Renderer> Widget<Message, Theme, R> for Session<'_, Message, R> {
    fn tag(&self) -> tree::Tag {
        tree::Tag::of::<Identity>()
    }

    fn state(&self) -> tree::State {
        tree::State::new(Identity(self.identity))
    }

    fn children(&self) -> Vec<Tree> {
        vec![Tree::new(self.content.as_widget())]
    }

    fn diff(&self, tree: &mut Tree) {
        let retained = tree.state.downcast_mut::<Identity>();
        if retained.0 != self.identity {
            retained.0 = self.identity;
            // Iced's keyed column preserves same-length child replacements.
            // An editing-session replacement must instead get fresh field state.
            tree.children = self.children();
        } else {
            tree.diff_children(std::slice::from_ref(&self.content));
        }
    }

    fn size(&self) -> Size<Length> {
        self.content.as_widget().size()
    }

    fn layout(&mut self, tree: &mut Tree, renderer: &R, limits: &layout::Limits) -> layout::Node {
        self.content
            .as_widget_mut()
            .layout(&mut tree.children[0], renderer, limits)
    }

    fn operate(
        &mut self,
        tree: &mut Tree,
        layout: Layout<'_>,
        renderer: &R,
        operation: &mut dyn Operation,
    ) {
        self.content
            .as_widget_mut()
            .operate(&mut tree.children[0], layout, renderer, operation);
    }

    fn update(
        &mut self,
        tree: &mut Tree,
        event: &Event,
        layout: Layout<'_>,
        cursor: mouse::Cursor,
        renderer: &R,
        clipboard: &mut dyn Clipboard,
        shell: &mut Shell<'_, Message>,
        viewport: &Rectangle,
    ) {
        self.content.as_widget_mut().update(
            &mut tree.children[0],
            event,
            layout,
            cursor,
            renderer,
            clipboard,
            shell,
            viewport,
        );
    }

    fn draw(
        &self,
        tree: &Tree,
        renderer: &mut R,
        theme: &Theme,
        style: &renderer::Style,
        layout: Layout<'_>,
        cursor: mouse::Cursor,
        viewport: &Rectangle,
    ) {
        self.content.as_widget().draw(
            &tree.children[0],
            renderer,
            theme,
            style,
            layout,
            cursor,
            viewport,
        );
    }

    fn mouse_interaction(
        &self,
        tree: &Tree,
        layout: Layout<'_>,
        cursor: mouse::Cursor,
        viewport: &Rectangle,
        renderer: &R,
    ) -> mouse::Interaction {
        self.content.as_widget().mouse_interaction(
            &tree.children[0],
            layout,
            cursor,
            viewport,
            renderer,
        )
    }

    fn overlay<'b>(
        &'b mut self,
        tree: &'b mut Tree,
        layout: Layout<'b>,
        renderer: &R,
        viewport: &Rectangle,
        translation: Vector,
    ) -> Option<overlay::Element<'b, Message, Theme, R>> {
        self.content.as_widget_mut().overlay(
            &mut tree.children[0],
            layout,
            renderer,
            viewport,
            translation,
        )
    }
}