use std::{
    any::{Any, TypeId},
    marker::PhantomData,
};

use crate::{Painter, Ui, util::Id};

pub trait Widget<Ctx>: Any {
    fn draw(&self, painter: &mut Painter<Ctx>);
}

pub struct AnyWidget;

/// An identifier for a widget.
/// Can index a UI to get the associated widget.
///
/// W does not need to implement widget so that AnyWidget is valid;
/// Instead, add generic bounds on methods that take an ID if they need specific data.
#[repr(C)]
#[derive(Eq, Hash, PartialEq)]
pub struct WidgetId<W = AnyWidget> {
    pub(super) ty: TypeId,
    pub(super) id: Id,
    _pd: PhantomData<W>,
}

impl<W> std::fmt::Debug for WidgetId<W> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        self.id.fmt(f)
    }
}

// TODO: temp
impl<W> Clone for WidgetId<W> {
    fn clone(&self) -> Self {
        Self::new(self.id.duplicate(), self.ty)
    }
}

impl<W> WidgetId<W> {
    pub(super) fn new(id: Id, ty: TypeId) -> Self {
        Self {
            ty,
            id,
            _pd: PhantomData,
        }
    }

    pub fn erase_type(self) -> WidgetId<AnyWidget> {
        self.cast_type()
    }

    pub fn as_any(&self) -> &WidgetId<AnyWidget> {
        // safety: self is repr(C) and generic only used for phantom data
        unsafe { std::mem::transmute(self) }
    }

    fn cast_type<W2>(self) -> WidgetId<W2> {
        WidgetId {
            ty: self.ty,
            id: self.id,
            _pd: PhantomData,
        }
    }
}

pub struct WidgetTag;
pub struct FnTag;
pub struct IdTag;

pub trait WidgetLike<Ctx, Tag> {
    type Widget: 'static;
    fn add(self, ui: &mut Ui<Ctx>) -> WidgetId<Self::Widget>;
    fn with_id<W2>(
        self,
        f: impl FnOnce(&mut Ui<Ctx>, WidgetId<Self::Widget>) -> WidgetId<W2>,
    ) -> impl WidgetIdFn<W2, Ctx>
    where
        Self: Sized,
    {
        move |ui| {
            let id = self.add(ui);
            f(ui, id)
        }
    }
}

/// A function that returns a widget given a UI.
/// Useful for defining trait functions on widgets that create a parent widget so that the children
/// don't need to be IDs yet
pub trait WidgetFn<W: Widget<Ctx>, Ctx> = FnOnce(&mut Ui<Ctx>) -> W;
pub trait WidgetIdFn<W, Ctx> = FnOnce(&mut Ui<Ctx>) -> WidgetId<W>;

pub trait Idable<Ctx, Tag> {
    type Widget: Widget<Ctx>;
    fn set(self, ui: &mut Ui<Ctx>, id: &WidgetId<Self::Widget>);
    fn id<'a>(
        self,
        id: &WidgetId<Self::Widget>,
    ) -> impl WidgetIdFn<Self::Widget, Ctx> + use<'a, Self, Ctx, Tag>
    where
        Self: Sized,
    {
        let id = id.clone();
        move |ui| {
            self.set(ui, &id);
            id
        }
    }
}

impl<W: Widget<Ctx>, Ctx> Idable<Ctx, WidgetTag> for W {
    type Widget = W;

    fn set(self, ui: &mut Ui<Ctx>, id: &WidgetId<Self::Widget>) {
        ui.set(id, self);
    }
}

impl<F: FnOnce(&mut Ui<Ctx>) -> W, W: Widget<Ctx>, Ctx> Idable<Ctx, FnTag> for F {
    type Widget = W;

    fn set(self, ui: &mut Ui<Ctx>, id: &WidgetId<Self::Widget>) {
        let w = self(ui);
        ui.set(id, w);
    }
}

impl<W: Widget<Ctx>, Ctx, F: FnOnce(&mut Ui<Ctx>) -> W> WidgetLike<Ctx, FnTag> for F {
    type Widget = W;
    fn add(self, ui: &mut Ui<Ctx>) -> WidgetId<W> {
        let w = self(ui);
        ui.add(w)
    }
}

impl<W: 'static, F: FnOnce(&mut Ui<Ctx>) -> WidgetId<W>, Ctx> WidgetLike<Ctx, IdTag> for F {
    type Widget = W;
    fn add(self, ui: &mut Ui<Ctx>) -> WidgetId<W> {
        self(ui)
    }
}

impl<W: Widget<Ctx>, Ctx> WidgetLike<Ctx, WidgetTag> for W {
    type Widget = W;
    fn add(self, ui: &mut Ui<Ctx>) -> WidgetId<W> {
        ui.add_widget(self)
    }
}

impl<W: 'static, Ctx> WidgetLike<Ctx, FnTag> for WidgetId<W> {
    type Widget = W;
    fn add(self, _: &mut Ui<Ctx>) -> WidgetId<W> {
        self
    }
}

pub struct WidgetArr<const LEN: usize, Ws> {
    pub arr: [WidgetId; LEN],
    _pd: PhantomData<Ws>,
}

impl<const LEN: usize, Ws> WidgetArr<LEN, Ws> {
    pub fn new(arr: [WidgetId; LEN]) -> Self {
        Self {
            arr,
            _pd: PhantomData,
        }
    }
}

pub struct ArrTag;
pub trait WidgetArrLike<const LEN: usize, Ctx, Tags> {
    type Ws;
    fn ui(self, ui: &mut Ui<Ctx>) -> WidgetArr<LEN, Self::Ws>;
}

impl<const LEN: usize, Ws, Ctx> WidgetArrLike<LEN, Ctx, ArrTag> for WidgetArr<LEN, Ws> {
    type Ws = Ws;
    fn ui(self, _: &mut Ui<Ctx>) -> WidgetArr<LEN, Ws> {
        self
    }
}

impl<W: WidgetLike<Ctx, WidgetTag>, Ctx> WidgetArrLike<1, Ctx, WidgetTag> for W {
    type Ws = (W::Widget,);
    fn ui(self, ui: &mut Ui<Ctx>) -> WidgetArr<1, (W::Widget,)> {
        WidgetArr::new([self.add(ui).erase_type()])
    }
}

// I hate this language it's so bad why do I even use it
macro_rules! impl_widget_arr {
    ($n:expr;$($W:ident)*) => {
        impl_widget_arr!($n;$($W)*;$(${concat($W,Tag)})*);
    };
    ($n:expr;$($W:ident)*;$($Tag:ident)*) => {
        impl<$($W: WidgetLike<Ctx, $Tag>,$Tag,)* Ctx> WidgetArrLike<$n, Ctx, ($($Tag,)*)> for ($($W,)*) {
            type Ws = ($($W::Widget,)*);
            fn ui(self, ui: &mut Ui<Ctx>) -> WidgetArr<$n, ($($W::Widget,)*)> {
                #[allow(non_snake_case)]
                let ($($W,)*) = self;
                WidgetArr::new(
                    [$($W.add(ui).cast_type(),)*],
                )
            }
        }
    };
}

impl_widget_arr!(1;A);
impl_widget_arr!(2;A B);
impl_widget_arr!(3;A B C);
impl_widget_arr!(4;A B C D);
impl_widget_arr!(5;A B C D E);
impl_widget_arr!(6;A B C D E F);
impl_widget_arr!(7;A B C D E F G);
impl_widget_arr!(8;A B C D E F G H);
impl_widget_arr!(9;A B C D E F G H I);
impl_widget_arr!(10;A B C D E F G H I J);
impl_widget_arr!(11;A B C D E F G H I J K);
impl_widget_arr!(12;A B C D E F G H I J K L);