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use std::mem;

use super::Compose;
use bevy::prelude::*;

pub fn flex<C: Compose>(content: C) -> Flex<C> {
    Flex {
        content,
        on_click: None,
        on_hover: None,
    }
}

type HandlerFn = Box<dyn FnMut(&mut World) + Send + Sync>;

pub struct Flex<C> {
    content: C,
    on_click: Option<HandlerFn>,
    on_hover: Option<HandlerFn>,
}

impl<C> Flex<C> {
    pub fn on_click<Marker>(mut self, system: impl IntoSystem<(), (), Marker>) -> Self {
        let mut cell = Some(IntoSystem::<(), (), Marker>::into_system(system));
        let mut id_cell = None;
        self.on_click = Some(Box::new(move |world| {
            if let Some(system) = cell.take() {
                let id = world.register_system(system);
                id_cell = Some(id);
            }

            let id = id_cell.unwrap();
            world.run_system(id).unwrap();
        }));
        self
    }

    pub fn on_hover<Marker>(mut self, system: impl IntoSystem<(), (), Marker>) -> Self {
        let mut cell = Some(IntoSystem::<(), (), Marker>::into_system(system));
        let mut id_cell = None;
        self.on_hover = Some(Box::new(move |world| {
            if let Some(system) = cell.take() {
                let id = world.register_system(system);
                id_cell = Some(id);
            }

            let id = id_cell.unwrap();
            world.run_system(id).unwrap();
        }));
        self
    }
}

impl<C: Compose> Compose for Flex<C> {
    type State = (Entity, C::State, Vec<Entity>);

    fn build(&mut self, world: &mut World, children: &mut Vec<Entity>) -> Self::State {
        let parent_children = mem::take(children);
        let content_state = self.content.build(world, children);
        let my_children = mem::replace(children, parent_children);

        let mut entity = world.spawn(ButtonBundle {
            style: Style {
                width: Val::Px(150.0),
                height: Val::Px(65.0),
                border: UiRect::all(Val::Px(5.0)),
                justify_content: JustifyContent::Center,
                align_items: AlignItems::Center,
                ..default()
            },
            background_color: BackgroundColor(Color::BLACK),
            ..default()
        });
        entity.push_children(&my_children);

        let id = entity.id();
        children.push(id);

        if let Some(handler) = self.on_click.take() {
            entity.insert(ClickHandler {
                handler: Some(handler),
            });
        }

        if let Some(handler) = self.on_hover.take() {
            entity.insert(HoverHandler {
                handler: Some(handler),
            });
        }

        (id, content_state, my_children)
    }

    fn rebuild(
        &mut self,
        target: &mut Self,
        state: &mut Self::State,
        world: &mut World,
        children: &mut Vec<Entity>,
    ) {
        let parent_children = mem::take(children);
        self.content
            .rebuild(&mut target.content, &mut state.1, world, children);
        let my_children = mem::replace(children, parent_children);

        if my_children != state.2 {
            world.entity_mut(state.0).replace_children(&my_children);
            state.2 = my_children;
        }

        children.push(state.0);
    }
}

#[derive(Component)]
pub struct ClickHandler {
    handler: Option<HandlerFn>,
}

#[derive(Component)]
pub struct HoverHandler {
    handler: Option<HandlerFn>,
}

pub fn handler_system(world: &mut World) {
    let mut query = world.query_filtered::<(
        &Interaction,
        Option<&mut ClickHandler>,
        Option<&mut HoverHandler>,
    ), Changed<Interaction>>();

    let mut handlers: Vec<_> = query
        .iter_mut(world)
        .map(|(interaction, click_handler, hover_handler)| {
            (
                *interaction,
                click_handler.and_then(|mut h| h.handler.take()),
                hover_handler.and_then(|mut h| h.handler.take()),
            )
        })
        .collect();

    for (interaction, click_handler, hover_handler) in &mut handlers {
        match interaction {
            Interaction::Pressed => {
                if let Some(ref mut f) = click_handler {
                    f(world)
                }
            }
            Interaction::Hovered => {
                if let Some(ref mut f) = hover_handler {
                    f(world)
                }
            }
            Interaction::None => {}
        }
    }

    for (idx, (_, mut click_handler, mut hover_handler)) in query.iter_mut(world).enumerate() {
        if let Some(ref mut click_handler) = click_handler {
            click_handler.handler = handlers[idx].1.take();
        }

        if let Some(ref mut hover_handler) = hover_handler {
            hover_handler.handler = handlers[idx].2.take();
        }
    }
}