// Renders image behind widget, and otherwise passes through all behavior

use cosmic::{
    iced::{
        advanced::{
            layout::{self},
            mouse, overlay, renderer,
            widget::{tree, Operation, OperationOutputWrapper, Tree},
            Clipboard, Layout, Shell, Widget,
        },
        event::{self, Event},
        widget::image::{FilterMethod, Handle},
        ContentFit, Length, Rectangle, Size, Vector,
    },
    iced_core::Renderer,
};

use std::marker::PhantomData;

pub fn image_bg<'a, Msg, T: Into<cosmic::Element<'a, Msg>>>(content: T) -> ImageBg<'a, Msg> {
    ImageBg {
        content: content.into(),
        _msg: PhantomData,
    }
}

pub struct ImageBg<'a, Msg> {
    content: cosmic::Element<'a, Msg>,
    _msg: PhantomData<Msg>,
}

impl<'a, Msg> Widget<Msg, cosmic::Theme, cosmic::Renderer> for ImageBg<'a, Msg> {
    delegate::delegate! {
        to self.content.as_widget() {
            fn tag(&self) -> tree::Tag;
            fn state(&self) -> tree::State;
            fn children(&self) -> Vec<Tree>;
            fn size(&self) -> Size<Length>;
            fn size_hint(&self) -> Size<Length>;
            fn layout(
                    &self,
                    tree: &mut Tree,
                    renderer: &cosmic::Renderer,
                    limits: &layout::Limits,
                ) -> layout::Node;
            fn operate(
                    &self,
                    tree: &mut Tree,
                    layout: Layout<'_>,
                    renderer: &cosmic::Renderer,
                    operation: &mut dyn Operation<OperationOutputWrapper<Msg>>,
                );
            fn mouse_interaction(
                &self,
                tree: &Tree,
                layout: Layout<'_>,
                cursor: mouse::Cursor,
                viewport: &Rectangle,
                renderer: &cosmic::Renderer,
            ) -> mouse::Interaction;
        }

        to self.content.as_widget_mut() {
            fn diff(&mut self, tree: &mut Tree);
            fn on_event(
                &mut self,
                tree: &mut Tree,
                event: Event,
                layout: Layout<'_>,
                cursor: mouse::Cursor,
                renderer: &cosmic::Renderer,
                clipboard: &mut dyn Clipboard,
                shell: &mut Shell<'_, Msg>,
                viewport: &Rectangle,
            ) -> event::Status;
            fn overlay<'b>(
                &'b mut self,
                tree: &'b mut Tree,
                layout: Layout<'_>,
                renderer: &cosmic::Renderer,
            ) -> Option<overlay::Element<'b, Msg, cosmic::Theme, cosmic::Renderer>>;
        }
    }

    fn draw(
        &self,
        state: &Tree,
        renderer: &mut cosmic::Renderer,
        theme: &cosmic::Theme,
        style: &renderer::Style,
        layout: Layout<'_>,
        cursor: mouse::Cursor,
        viewport: &Rectangle,
    ) {
        use cosmic::iced_core::image::Renderer;

        // TODO desktop background?
        let handle =
            Handle::from_path("/usr/share/backgrounds/pop/kate-hazen-COSMIC-desktop-wallpaper.png");

        let Size { width, height } = renderer.dimensions(&handle);
        let image_size = Size::new(width as f32, height as f32);

        let bounds = layout.bounds();
        let adjusted_fit = ContentFit::Cover.fit(image_size, bounds.size());

        let offset = Vector::new(
            (bounds.width - adjusted_fit.width).max(0.0) / 2.0,
            (bounds.height - adjusted_fit.height).max(0.0) / 2.0,
        );

        let drawing_bounds = Rectangle {
            width: adjusted_fit.width,
            height: adjusted_fit.height,
            ..bounds
        };

        renderer.draw(
            handle.clone(),
            FilterMethod::default(),
            drawing_bounds + offset,
            [0.0, 0.0, 0.0, 0.0],
        );

        renderer.with_layer(bounds, |renderer| {
            self.content
                .as_widget()
                .draw(state, renderer, theme, style, layout, cursor, viewport)
        });
    }
}

impl<'a, Msg: 'static> From<ImageBg<'a, Msg>> for cosmic::Element<'a, Msg> {
    fn from(widget: ImageBg<'a, Msg>) -> Self {
        cosmic::Element::new(widget)
    }
}