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use super::*;
use crate::drawing::backend::DrawingBackend;
use std::borrow::Borrow;
use std::iter::{once, Once};
use std::marker::PhantomData;
use std::ops::Add;

/// An empty composibable element, which is the start point of an ad-hoc composible element
pub struct EmptyElement<Coord, DB: DrawingBackend> {
    coord: Coord,
    phantom: PhantomData<DB>,
}

impl<Coord, DB: DrawingBackend> EmptyElement<Coord, DB> {
    pub fn at(coord: Coord) -> Self {
        Self {
            coord,
            phantom: PhantomData,
        }
    }
}

impl<Coord, Other, DB: DrawingBackend> Add<Other> for EmptyElement<Coord, DB>
where
    Other: Drawable<DB>,
    for<'a> &'a Other: PointCollection<'a, BackendCoord>,
{
    type Output = BoxedElement<Coord, DB, Other>;
    fn add(self, other: Other) -> Self::Output {
        BoxedElement {
            offset: self.coord,
            inner: other,
            phantom: PhantomData,
        }
    }
}

impl<'a, Coord, DB: DrawingBackend> PointCollection<'a, Coord> for &'a EmptyElement<Coord, DB> {
    type Borrow = &'a Coord;
    type IntoIter = Once<&'a Coord>;
    fn point_iter(self) -> Self::IntoIter {
        once(&self.coord)
    }
}

impl<Coord, DB: DrawingBackend> Drawable<DB> for EmptyElement<Coord, DB> {
    fn draw<I: Iterator<Item = BackendCoord>>(
        &self,
        _pos: I,
        _backend: &mut DB,
    ) -> Result<(), DrawingErrorKind<DB::ErrorType>> {
        Ok(())
    }
}

/// An composed element has only one component
pub struct BoxedElement<Coord, DB: DrawingBackend, A: Drawable<DB>> {
    inner: A,
    offset: Coord,
    phantom: PhantomData<DB>,
}

impl<'b, Coord, DB: DrawingBackend, A: Drawable<DB>> PointCollection<'b, Coord>
    for &'b BoxedElement<Coord, DB, A>
{
    type Borrow = &'b Coord;
    type IntoIter = Once<&'b Coord>;
    fn point_iter(self) -> Self::IntoIter {
        once(&self.offset)
    }
}

impl<Coord, DB: DrawingBackend, A> Drawable<DB> for BoxedElement<Coord, DB, A>
where
    for<'a> &'a A: PointCollection<'a, BackendCoord>,
    A: Drawable<DB>,
{
    fn draw<I: Iterator<Item = BackendCoord>>(
        &self,
        mut pos: I,
        backend: &mut DB,
    ) -> Result<(), DrawingErrorKind<DB::ErrorType>> {
        if let Some((x0, y0)) = pos.next() {
            self.inner.draw(
                self.inner.point_iter().into_iter().map(|p| {
                    let p = p.borrow();
                    (p.0 + x0, p.1 + y0)
                }),
                backend,
            )?;
        }
        Ok(())
    }
}

impl<Coord, DB: DrawingBackend, My, Yours> Add<Yours> for BoxedElement<Coord, DB, My>
where
    My: Drawable<DB>,
    for<'a> &'a My: PointCollection<'a, BackendCoord>,
    Yours: Drawable<DB>,
    for<'a> &'a Yours: PointCollection<'a, BackendCoord>,
{
    type Output = ComposedElement<Coord, DB, My, Yours>;
    fn add(self, yours: Yours) -> Self::Output {
        ComposedElement {
            offset: self.offset,
            first: self.inner,
            second: yours,
            phantom: PhantomData,
        }
    }
}

/// The composed element which has at least two components
pub struct ComposedElement<Coord, DB: DrawingBackend, A, B>
where
    A: Drawable<DB>,
    B: Drawable<DB>,
{
    first: A,
    second: B,
    offset: Coord,
    phantom: PhantomData<DB>,
}

impl<'b, Coord, DB: DrawingBackend, A, B> PointCollection<'b, Coord>
    for &'b ComposedElement<Coord, DB, A, B>
where
    A: Drawable<DB>,
    B: Drawable<DB>,
{
    type Borrow = &'b Coord;
    type IntoIter = Once<&'b Coord>;
    fn point_iter(self) -> Self::IntoIter {
        once(&self.offset)
    }
}

impl<Coord, DB: DrawingBackend, A, B> Drawable<DB> for ComposedElement<Coord, DB, A, B>
where
    for<'a> &'a A: PointCollection<'a, BackendCoord>,
    for<'b> &'b B: PointCollection<'b, BackendCoord>,
    A: Drawable<DB>,
    B: Drawable<DB>,
{
    fn draw<I: Iterator<Item = BackendCoord>>(
        &self,
        mut pos: I,
        backend: &mut DB,
    ) -> Result<(), DrawingErrorKind<DB::ErrorType>> {
        if let Some((x0, y0)) = pos.next() {
            self.first.draw(
                self.first.point_iter().into_iter().map(|p| {
                    let p = p.borrow();
                    (p.0 + x0, p.1 + y0)
                }),
                backend,
            )?;
            self.second.draw(
                self.second.point_iter().into_iter().map(|p| {
                    let p = p.borrow();
                    (p.0 + x0, p.1 + y0)
                }),
                backend,
            )?;
        }
        Ok(())
    }
}

impl<Coord, DB: DrawingBackend, A, B, C> Add<C> for ComposedElement<Coord, DB, A, B>
where
    A: Drawable<DB>,
    for<'a> &'a A: PointCollection<'a, BackendCoord>,
    B: Drawable<DB>,
    for<'a> &'a B: PointCollection<'a, BackendCoord>,
    C: Drawable<DB>,
    for<'a> &'a C: PointCollection<'a, BackendCoord>,
{
    type Output = ComposedElement<Coord, DB, A, ComposedElement<BackendCoord, DB, B, C>>;
    fn add(self, rhs: C) -> Self::Output {
        ComposedElement {
            offset: self.offset,
            first: self.first,
            second: ComposedElement {
                offset: (0, 0),
                first: self.second,
                second: rhs,
                phantom: PhantomData,
            },
            phantom: PhantomData,
        }
    }
}