use crate::{
    ActiveData, IdLike, LayerId, Ui, Widget, WidgetData, WidgetId, WidgetRef, util::HashMap,
};
use std::{
    any::{Any, TypeId},
    ops::{Index, IndexMut},
    rc::Rc,
};

pub trait Event: Sized + 'static + Clone {
    type Data<'a> = ();
    type State: Default = ();
    #[allow(unused_variables)]
    fn should_run(&self, data: &mut Self::Data<'_>) -> bool {
        true
    }
}

pub trait EventLike {
    type Event: Event;
    fn into_event(self) -> Self::Event;
}

impl<E: Event> EventLike for E {
    type Event = Self;

    fn into_event(self) -> Self::Event {
        self
    }
}

pub struct EventCtx<'a, Ctx, Data> {
    pub ui: &'a mut Ui,
    pub state: &'a mut Ctx,
    pub data: &'a mut Data,
}

pub struct EventIdCtx<'a, Ctx, Data, W: ?Sized> {
    pub widget: WidgetRef<W>,
    pub ui: &'a mut Ui,
    pub state: &'a mut Ctx,
    pub data: &'a mut Data,
}

#[derive(Default)]
pub struct EventManager {
    types: HashMap<TypeId, Box<dyn EventManagerLike>>,
}

impl EventManager {
    pub fn get_type<E: EventLike, Ctx: 'static>(&mut self) -> &mut TypeEventManager<E::Event, Ctx> {
        self.types
            .entry(Self::type_key::<E, Ctx>())
            .or_insert(Box::new(TypeEventManager::<E::Event, Ctx>::default()))
            .as_any()
            .downcast_mut()
            .unwrap()
    }

    pub fn register<I: IdLike, E: EventLike, Ctx: 'static>(
        &mut self,
        id: I,
        event: E,
        f: impl for<'a> EventFn<Ctx, <E::Event as Event>::Data<'a>>,
    ) {
        self.get_type::<E, Ctx>().register(id, event, f);
    }

    pub fn type_key<E: EventLike, Ctx: 'static>() -> TypeId {
        TypeId::of::<TypeEventManager<E::Event, Ctx>>()
    }

    pub fn remove(&mut self, id: WidgetId) {
        for m in self.types.values_mut() {
            m.remove(id);
        }
    }

    pub fn draw(&mut self, data: &WidgetData, active: &ActiveData) {
        for t in &data.event_mgrs {
            self.types.get_mut(t).unwrap().draw(active);
        }
    }

    pub fn undraw(&mut self, data: &WidgetData, active: &ActiveData) {
        for t in &data.event_mgrs {
            self.types.get_mut(t).unwrap().undraw(active);
        }
    }
}

pub trait EventManagerLike {
    fn remove(&mut self, id: WidgetId);
    fn draw(&mut self, data: &ActiveData);
    fn undraw(&mut self, data: &ActiveData);
    fn as_any(&mut self) -> &mut dyn Any;
}

type EventData<E, Ctx> = (E, Rc<dyn for<'a> EventFn<Ctx, <E as Event>::Data<'a>>>);
pub struct TypeEventManager<E: Event, Ctx> {
    // TODO: reduce visiblity!!
    pub active: HashMap<LayerId, HashMap<WidgetId, E::State>>,
    map: HashMap<WidgetId, Vec<EventData<E, Ctx>>>,
}

impl<E: Event, Ctx: 'static> EventManagerLike for TypeEventManager<E, Ctx> {
    fn remove(&mut self, id: WidgetId) {
        self.map.remove(&id);
        for layer in self.active.values_mut() {
            layer.remove(&id);
        }
    }
    fn draw(&mut self, data: &ActiveData) {
        self.active
            .entry(data.layer)
            .or_default()
            .entry(data.id)
            .or_default();
    }
    fn undraw(&mut self, data: &ActiveData) {
        if let Some(layer) = self.active.get_mut(&data.layer) {
            layer.remove(&data.id);
        }
    }
    fn as_any(&mut self) -> &mut dyn Any {
        self
    }
}

impl<E: Event, Ctx> Default for TypeEventManager<E, Ctx> {
    fn default() -> Self {
        Self {
            active: Default::default(),
            map: Default::default(),
        }
    }
}

impl<E: Event, Ctx: 'static> TypeEventManager<E, Ctx> {
    fn register(
        &mut self,
        id: impl IdLike,
        event: impl EventLike<Event = E>,
        f: impl for<'a> EventFn<Ctx, E::Data<'a>>,
    ) {
        let event = event.into_event();
        self.map
            .entry(id.id())
            .or_default()
            .push((event, Rc::new(f)));
    }

    fn run_fn<'a>(
        &mut self,
        id: impl IdLike,
    ) -> impl for<'b> FnOnce(EventCtx<Ctx, E::Data<'b>>) + 'a {
        let fs = self.map.get(&id.id()).cloned().unwrap_or_default();
        move |ctx| {
            for (e, f) in fs {
                if e.should_run(ctx.data) {
                    f(EventCtx {
                        ui: ctx.ui,
                        state: ctx.state,
                        data: ctx.data,
                    })
                }
            }
        }
    }
}

impl<'a, Ctx, Data, W2, W: Widget> Index<WidgetRef<W>> for EventIdCtx<'a, Ctx, Data, W2> {
    type Output = W;

    fn index(&self, index: WidgetRef<W>) -> &Self::Output {
        &self.ui[index]
    }
}

impl<'a, Ctx, Data, W2, W: Widget> IndexMut<WidgetRef<W>> for EventIdCtx<'a, Ctx, Data, W2> {
    fn index_mut(&mut self, index: WidgetRef<W>) -> &mut Self::Output {
        &mut self.ui[index]
    }
}

impl<'a, Ctx, Data, W: Widget> EventIdCtx<'a, Ctx, Data, W> {
    pub fn widget(&mut self) -> &mut W {
        &mut self.ui[self.widget]
    }
}

pub trait EventFn<Ctx, Data>: Fn(EventCtx<Ctx, Data>) + 'static {}
impl<F: Fn(EventCtx<Ctx, Data>) + 'static, Ctx, Data> EventFn<Ctx, Data> for F {}

pub trait WidgetEventFn<Ctx, Data, W: ?Sized>: Fn(EventIdCtx<Ctx, Data, W>) + 'static {}
impl<F: Fn(EventIdCtx<Ctx, Data, W>) + 'static, Ctx, Data, W: ?Sized> WidgetEventFn<Ctx, Data, W>
    for F
{
}

impl Ui {
    pub fn run_event<E: EventLike, Ctx: 'static>(
        &mut self,
        ctx: &mut Ctx,
        id: impl IdLike,
        data: &mut <E::Event as Event>::Data<'_>,
    ) {
        let f = self.data.events.get_type::<E, Ctx>().run_fn(id);
        f(EventCtx {
            ui: self,
            state: ctx,
            data,
        })
    }
}