use crate::*;
use Azimuth::*;

/// Where is [0, 0] located?
///
/// ```
/// use tengri::*;
/// use Azimuth::*;
/// let _ = "".align(NW);
/// ```
#[cfg_attr(test, derive(Arbitrary))]
#[derive(Debug, Copy, Clone, Default)] pub enum Azimuth {
    #[default] C, X, Y, NW, N, NE, E, SE, S, SW, W
}

pub struct Origin<T>(
    pub(crate) Option<Azimuth>,
    pub(crate) T
);

impl_draw!(<S: Screen, T: Draw<S>,>|self: Origin<T>, _to: S|{
    todo!()
});

/// Something that has `[0, 0]` at a particular point.
pub trait HasOrigin {
    fn origin (&self) -> Azimuth;
}

impl<T: AsRef<Azimuth>> HasOrigin for T {
    fn origin (&self) -> Azimuth {
        *self.as_ref()
    }
}

fn_kw_layout!(kw_align |state, output, expr| {
    let head = expr.head();
    let mut frags = head.src()?.unwrap_or_default().split("/");
    Ok(matches!(frags.next(), Some("align")).then(||{
        draw(move|output: &mut O|{state.interpret(output, &expr.tail().head())}).align(
            eval_enum!("align", output, state,
                expr.head().src()?.unwrap_or_default().split("/").skip(1).next(),
                Azimuth {
                    "c" => C, "x" => X, "y" => Y,
                    "n" => N, "s" => S, "e" => E, "w" => W,
                    "nw" => NW, "sw" => SW, "ne" => NE, "se" => SE,
                })
        ).draw(output)
    }).transpose()?.flatten())
});

impl<S: Screen, T: Draw<S>> CanAlign<S> for T {}

pub trait CanAlign<S: Screen>: Draw<S> + Sized {
    fn align (self, azimuth: impl Into<Option<Azimuth>>) -> Align<Self> {
        Align(azimuth.into(), self)
    }
    fn align_c (self) -> Align<Self> {
        Align(Some(Azimuth::C), self)
    }
    fn align_x (self) -> Align<Self> {
        Align(Some(Azimuth::X), self)
    }
    fn align_y (self) -> Align<Self> {
        Align(Some(Azimuth::Y), self)
    }
    fn align_n (self) -> Align<Self> {
        Align(Some(Azimuth::N), self)
    }
    fn align_s (self) -> Align<Self> {
        Align(Some(Azimuth::S), self)
    }
    fn align_e (self) -> Align<Self> {
        Align(Some(Azimuth::E), self)
    }
    fn align_w (self) -> Align<Self> {
        Align(Some(Azimuth::W), self)
    }
    fn align_ne (self) -> Align<Self> {
        Align(Some(Azimuth::NE), self)
    }
    fn align_se (self) -> Align<Self> {
        Align(Some(Azimuth::SE), self)
    }
    fn align_nw (self) -> Align<Self> {
        Align(Some(Azimuth::NW), self)
    }
    fn align_sw (self) -> Align<Self> {
        Align(Some(Azimuth::SW), self)
    }
}

pub struct Align<T>(
    pub(crate) Option<Azimuth>,
    pub(crate) T,
);

impl<S: Screen, T: Draw<S>> Draw<S> for Align<T> {
    fn draw (&self, to: &mut S) -> Perhaps<XYWH<S::Unit>> {
        let Self(azimuth, item) = self;
        let area0 = to.area();
        let size  = to.size(area0, item)?;
        let area1 = align::<S>(area0, size, *azimuth);
        //println!("\n\r{azimuth:?} {area0:?} {size:?}=>{area1:?}");
        Ok(if let Some(area) = area1 {
            to.draw(area, &item)?
        } else {
            None
        })
    }
}

fn align <S: Screen> (
    area0: XYWH<S::Unit>, area: Option<XYWH<S::Unit>>, azimuth: Option<Azimuth>
) -> Option<XYWH<S::Unit>> {
    area.map(|XYWH(x, y, w, h)|{
        let XYWH(x0, y0, w0, h0) = area0;
        match azimuth {
            Some(NW) => XYWH(x0,                          y0,                          w, h),
            Some(N)  => XYWH(x0 + w0.minus(w) / 2.into(), y0,                          w, h),
            Some(NE) => XYWH((x0 + w0).minus(w),          y0,                          w, h),
            Some(W)  => XYWH(x0,                          y0 + h0.minus(h) / 2.into(), w, h),
            Some(C)  => XYWH(x0 + w0.minus(w) / 2.into(), y0 + h0.minus(h) / 2.into(), w, h),
            Some(E)  => XYWH((x0 + w0).minus(w),          y0 + h0.minus(h) / 2.into(), w, h),
            Some(SW) => XYWH(x0,                          (y0 + h0).minus(h),          w, h),
            Some(S)  => XYWH(x0 + w0.minus(w) / 2.into(), (y0 + h0).minus(h),          w, h),
            Some(SE) => XYWH((x0 + w0).minus(w),          (y0 + h0).minus(h),          w, h),
            Some(X)  => XYWH(x0 + w0.minus(w) / 2.into(), y,                           w, h),
            Some(Y)  => XYWH(x,                           y0 + h0.minus(h) / 2.into(), w, h),
            None     => XYWH(x, y, w, h)
        }
    })
}

fn_kw_layout!(kw_split |state, output, expr| {
    let head = expr.head();
    let mut frags = head.src()?.unwrap_or_default().split("/");
    Ok(matches!(frags.next(), Some("bsp")).then(||{
        eval_enum!("bsp", output, state, frags.next(), Split {
            "n" => North,
            "s" => South,
            "e" => East,
            "w" => West,
            "a" => Above,
            "b" => Below
        }).stack(
            draw(move|output: &mut O|{
                state.interpret(output, &expr.tail().head()?)
            }),
            draw(move|output: &mut O|{
                state.interpret(output, &expr.tail().tail().head()?)
            }),
        ).draw(output)
    }).transpose()?.flatten())
});

/// Split along an axis. Direction determines order.
#[cfg_attr(test, derive(Arbitrary))]
#[derive(Copy, Clone, PartialEq, Debug, Default)] pub enum Split {
    North,
    South,
    East,
    West,
    Above,
    #[default] Below
}

pub struct Pair<S: Screen, A: Draw<S>, B: Draw<S>>(Split, A, B, PhantomData<S>);

pub fn split <S: Screen, A: Draw<S>, B: Draw<S>> (
    split: Split, a: A, b: B
) -> Pair<S, A, B> {
    Pair(split, a, b, PhantomData)
}

impl<S: Screen, A: Draw<S>, B: Draw<S>> Draw<S> for Pair<S, A, B> {
    fn draw (&self, to: &mut S) -> Drawn<S::Unit> {
        let Self(split, a, b, ..) = self;
        let (area_a, area_b) = stack_areas(split, to, a, b)?;
        let (drawn_a, drawn_b) = draw_stacks(split, to, a, area_a, None, b, area_b, None)?;
        Ok(stack_drawn(split, drawn_a, drawn_b))
    }
}

fn draw_stacks <S: Screen> (
    split:    &Split,
    to:       &mut S,
    a:        impl Draw<S>,
    area_a:   impl Into<Option<XYWH<S::Unit>>>,
    origin_a: impl Into<Option<Azimuth>>,
    b:        impl Draw<S>,
    area_b:   impl Into<Option<XYWH<S::Unit>>>,
    origin_b: impl Into<Option<Azimuth>>,
) -> Usually<(Option<XYWH<S::Unit>>, Option<XYWH<S::Unit>>)> {
    let draw_a = |to: &mut S|Ok::<_, Box<dyn Error>>(match origin_a.into() {
        Some(origin_a) => to.draw(area_a.into(), a.align(origin_a))?,
        None => to.draw(area_a.into(), a)?
    });
    let draw_b = |to: &mut S|Ok::<_, Box<dyn Error>>(match origin_b.into() {
        Some(origin_b) => to.draw(area_b.into(), b.align(origin_b))?,
        None => to.draw(area_b.into(), b)?
    });
    Ok(if matches!(split, Split::Below) {
        let drawn_b = draw_b(to)?;
        let drawn_a = draw_a(to)?;
        (drawn_a, drawn_b)
    } else {
        (draw_a(to)?, draw_b(to)?)
    })
}

pub fn stack_areas <S: Screen> (
    split: &Split,
    to:    &mut S,
    a:     impl Draw<S>,
    b:     impl Draw<S>,
) -> Usually<(Option<XYWH<S::Unit>>, Option<XYWH<S::Unit>>)> {
    let area_a = to.size(None, a)?;
    Ok(match split {
        Split::South => (
            area_a,
            area_a
                .map(|used|to.size(XYWH(to.x(), to.y() + used.h(), to.w(), to.h().minus(used.h())), b))
                .transpose()?
                .flatten()
        ),
        Split::East  => (
            area_a,
            area_a.map(|used|to.size(XYWH(to.x() + used.w(), to.y(), to.w().minus(used.w()), to.h()), b))
                .transpose()?
                .flatten()
        ),
        Split::North => (
            area_a.map(|used|XYWH(used.x(), (to.y() + to.h()).minus(used.h()), used.w(), used.h())),
            if let Some(used) = area_a {
                to.size(XYWH(to.x(), to.y(), to.w(), to.h().minus(used.h())), b)?
            } else {
                to.size(None, b)?
                    .map(|area_b|XYWH(area_b.x(), area_b.y() + area_b.h(), area_b.w(), area_b.h()))
            }
        ),
        Split::West => (
            area_a.map(|used|XYWH((to.x() + to.w()).minus(used.w()), used.y(), used.w(), used.h())),
            if let Some(used) = area_a {
                to.size(XYWH(to.x(), to.y(), to.w().minus(used.w()), to.h()), b)?
            } else {
                to.size(None, b)?
                    .map(|area_b|XYWH(area_b.x() + area_b.w(), area_b.y(), area_b.w(), area_b.h()))
            }
        ),
        Split::Above | Split::Below => (
            area_a,
            to.size(None, b)?,
        ),
    })
}

fn stack_drawn <S: Coord> (
    split:   &Split,
    drawn_a: Option<XYWH<S>>,
    drawn_b: Option<XYWH<S>>,
) -> Option<XYWH<S>> {
    if let (Some(XYWH(xa, ya, wa, ha)), Some(XYWH(xb, yb, wb, hb))) = (drawn_a, drawn_b) {
        match split {
            Split::South => Some(XYWH(xa.min(xb), ya, wa.max(wb), ha + hb)),
            Split::East  => Some(XYWH(xa, ya.min(yb), wa + wb, ha.max(hb))),
            Split::North => Some(XYWH(xa.min(xb), yb, wa.max(wb), ha + hb)),
            Split::West  => Some(XYWH(xb, ya.min(yb), wa + wb, ha.max(hb))),
            Split::Above | Split::Below =>
                Some(XYWH(xa.min(xb), ya.min(yb), wa.max(wb), ha.max(hb))),
        }
    } else if let Some(a) = drawn_a {
        Some(a)
    } else if let Some(b) = drawn_b {
        Some(b)
    } else {
        None
    }
}

impl Split {

    /// ```
    /// use tengri::*;
    /// let _ = Split::Above.stack(&"", &"");
    /// let _ = Split::Below.stack(&"", &"");
    /// let _ = Split::North.stack(&"", &"");
    /// let _ = Split::South.stack(&"", &"");
    /// let _ = Split::East.stack(&"", &"");
    /// let _ = Split::West.stack(&"", &"");
    /// ```
    pub const fn stack <S: Screen, A: Draw<S>, B: Draw<S>> (&self, a: A, b: B) -> impl Draw<S> {
        Pair(*self, a, b, PhantomData)
    }

    /// ```
    /// use tengri::*;
    /// let _ = Split::Above.half(&"", &"");
    /// let _ = Split::Below.half(&"", &"");
    /// let _ = Split::North.half(&"", &"");
    /// let _ = Split::South.half(&"", &"");
    /// let _ = Split::East.half(&"", &"");
    /// let _ = Split::West.half(&"", &"");
    /// ```
    pub const fn half <S: Screen, A: Draw<S>, B: Draw<S>> (&self, a: &A, b: &B) -> impl Draw<S> {
        draw(move|to: &mut S|{
            let (area_a,   area_b)   = to.xywh().split_half(self);
            let (origin_a, origin_b) = self.origins();
            let (drawn_a,  drawn_b)  = draw_stacks(self, to, a, area_a, origin_a, b, area_b, origin_b)?;
            Ok(stack_drawn(self, drawn_a, drawn_b))
        })
    }

    /// Newly split areas begin at the center of the split
    /// to maintain centeredness in the user's field of view.
    ///
    /// Use [align] to override that and always start
    /// at the top, bottom, etc.
    ///
    /// ```
    /// /*
    ///
    ///  Split east:   Split south:
    ///  |    |    |   |    A    |
    ///  | <-A|B-> |   |---------|
    ///  |    |    |   |    B    |
    ///
    /// */
    /// ```
    const fn origins (&self) -> (Azimuth, Azimuth) {
        use Azimuth::*;
        match self {
            Self::South => (S, N),
            Self::East  => (E, W),
            Self::North => (N, S),
            Self::West  => (W, E),
            Self::Above => (C, C),
            Self::Below => (C, C),
        }
    }

    ///// ```
    ///// use tengri::*;
    ///// let _ = Split::Below.iter([
    /////     "Leftbar"
    /////         .min_w(10).max_w(15).align(Azimuth::NW),
    /////     "Rightbar"
    /////         .min_w(10).max_w(12).align(Azimuth::NE),
    /////     "Center"
    /////         .min_w(20).max_w(40).align(Azimuth::C),
    ///// ].iter());
    ///// ```
    //pub fn iter <S: Screen, T: Draw<S>> (&self, _: impl Iterator<Item = T>) {
        //todo!()
    //}

}

pub const fn east <S: Screen, A: Draw<S>, B: Draw<S>> (a: A, b: B) -> impl Draw<S> {
    Pair(Split::East, a, b, PhantomData)
}

pub const fn north <S: Screen, A: Draw<S>, B: Draw<S>> (a: A, b: B) -> impl Draw<S> {
    Pair(Split::North, a, b, PhantomData)
}

pub const fn west <S: Screen, A: Draw<S>, B: Draw<S>> (a: A, b: B) -> impl Draw<S> {
    Pair(Split::West, a, b, PhantomData)
}

pub const fn south <S: Screen, A: Draw<S>, B: Draw<S>> (a: A, b: B) -> impl Draw<S> {
    Pair(Split::South, a, b, PhantomData)
}

pub const fn above <S: Screen, A: Draw<S>, B: Draw<S>> (a: A, b: B) -> impl Draw<S> {
    Pair(Split::Above, a, b, PhantomData)
}

pub const fn below <S: Screen, A: Draw<S>, B: Draw<S>> (a: A, b: B) -> impl Draw<S> {
    Pair(Split::Below, a, b, PhantomData)
}

#[macro_export] macro_rules! north {
    ($head:expr $(,)?) => { $head };
    ($head:expr, $($tail:expr),* $(,)?) => { north($head, north!($($tail,)*)) };
}

#[macro_export] macro_rules! south {
    ($head:expr $(,)?) => { $head };
    ($head:expr, $($tail:expr),* $(,)?) => { south($head, south!($($tail,)*)) };
}

#[macro_export] macro_rules! east {
    ($head:expr $(,)?) => { $head };
    ($head:expr, $($tail:expr),* $(,)?) => { east($head, east!($($tail,)*)) };
}

#[macro_export] macro_rules! west {
    ($head:expr $(,)?) => { $head };
    ($head:expr $(, $tail:expr)* $(,)?) => { west($head, west!($($tail,)*)) };
}

#[macro_export] macro_rules! above {
    ($head:expr $(,)?) => { $head };
    ($head:expr $(, $tail:expr)* $(,)?) => { above($head, above!($($tail,)*)) };
}

#[macro_export] macro_rules! below {
    ($head:expr $(,)?) => { $head };
    ($head:expr, $($tail:expr),* $(,)?) => { below($head, below!($($tail,)*)) };
}

#[cfg(test)] #[test] fn test_stack_areas () -> Usually<()> {
    let area = XYWH(0u16, 0, 80, 25);

    assert_eq!(stack_areas(&Split::East, &mut Tui::Layout(area), &"foo", &"bar")?, (
        Some(XYWH(0u16, 0, 3, 1)),
        Some(XYWH(3u16, 0, 3, 1)),
    ));

    assert_eq!(stack_areas(&Split::South, &mut Tui::Layout(area), &"foo", &"bar")?, (
        Some(XYWH(0u16, 0, 3, 1)),
        Some(XYWH(0u16, 1, 3, 1)),
    ));

    Ok(())
}

#[cfg(test)] #[test] fn test_split_stack () -> Usually<()> {
    use Split::*;
    fn size_of <A: Draw<Tui>, B: Draw<Tui>> (stack: &Pair<Tui, A, B>) -> Perhaps<XYWH<u16>> {
        Tui::Layout(XYWH(0, 0, 80, 25)).size(None, stack)
    }
    assert_eq!(size_of(&split(East, "foo", "bar"))?,
        Some(XYWH(0, 0, 6, 1)));
    assert_eq!(size_of(&split(South, "foo", "bar"))?,
        Some(XYWH(0, 0, 3, 2)));
    assert_eq!(size_of(&split(South, split(East, "foo", "bar"), "baz"))?,
        Some(XYWH(0, 0, 6, 2)));
    assert_eq!(size_of(&split(East, split(South, "foo", "bar"), "baz"))?,
        Some(XYWH(0, 0, 6, 2)));
    return Ok(());
}

#[cfg(test)] #[test] fn test_align () -> Usually<()> {
    let mut screen = Tui::Layout(XYWH(0, 0, 80, 25));
    assert_eq!("FOOBAR\nKILROY".draw(&mut screen)?, Some(XYWH(0, 0, 6, 2)));
    assert_eq!("FOOBAR\nKILROY".align_nw().draw(&mut screen)?, Some(XYWH(0,   0, 6, 2)));
    assert_eq!("FOOBAR\nKILROY".align_n().draw(&mut screen)?,  Some(XYWH(37,  0, 6, 2)));
    assert_eq!("FOOBAR\nKILROY".align_ne().draw(&mut screen)?, Some(XYWH(74,  0, 6, 2)));
    assert_eq!("FOOBAR\nKILROY".align_w().draw(&mut screen)?,  Some(XYWH(0,  11, 6, 2)));
    assert_eq!("FOOBAR\nKILROY".align_c().draw(&mut screen)?,  Some(XYWH(37, 11, 6, 2)));
    assert_eq!("FOOBAR\nKILROY".align_e().draw(&mut screen)?,  Some(XYWH(74, 11, 6, 2)));
    assert_eq!("FOOBAR\nKILROY".align_sw().draw(&mut screen)?, Some(XYWH(0,  23, 6, 2)));
    assert_eq!("FOOBAR\nKILROY".align_s().draw(&mut screen)?,  Some(XYWH(37, 23, 6, 2)));
    assert_eq!("FOOBAR\nKILROY".align_se().draw(&mut screen)?, Some(XYWH(74, 23, 6, 2)));
    Ok(())
}