use crate::util::impl_axis_index;
use std::{fmt::Display, marker::Destruct};

use super::*;
use crate::{Px, PxVec2, Rel, UiNum, util::impl_op};

#[repr(C)]
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, bytemuck::Pod, bytemuck::Zeroable, Default)]
pub struct UiVec2 {
    pub x: Len,
    pub y: Len,
}

impl UiVec2 {
    pub const ZERO: Self = Self {
        x: Len::ZERO,
        y: Len::ZERO,
    };

    pub const fn new(x: Len, y: Len) -> Self {
        Self { x, y }
    }

    pub const fn px(px: impl const Into<Vec2>) -> Self {
        let px = px.into();
        Self {
            x: Len::px(px.x),
            y: Len::px(px.y),
        }
    }

    /// From lengths already on the grid, with no fraction of a box.
    pub const fn from_px(px: PxVec2) -> Self {
        Self {
            x: Len::from_parts(Rel::ZERO, px.x),
            y: Len::from_parts(Rel::ZERO, px.y),
        }
    }

    pub const fn rel(rel: impl const Into<Vec2>) -> Self {
        let rel = rel.into();
        Self {
            x: Len::rel(rel.x),
            y: Len::rel(rel.y),
        }
    }

    pub const fn shift(&mut self, offset: impl const Into<UiVec2>) {
        let offset = offset.into();
        *self += offset;
    }

    pub const fn offset(mut self, offset: impl const Into<UiVec2>) -> Self {
        self.shift(offset);
        self
    }

    pub const fn within(&self, region: &UiRegion) -> UiVec2 {
        UiVec2 {
            x: self.x.within(&region.x),
            y: self.y.within(&region.y),
        }
    }

    /// Resolved against a box of `size`, which is where a fraction stops
    /// being one and becomes a place.
    pub fn to_px(&self, size: PxVec2) -> PxVec2 {
        PxVec2::new(self.x.to_px(size.x), self.y.to_px(size.y))
    }

    pub const FULL_SIZE: Self = Self::rel(Vec2::ONE);

    pub const fn from_axis(axis: Axis, aligned: Len, ortho: Len) -> Self {
        match axis {
            Axis::X => Self {
                x: aligned,
                y: ortho,
            },
            Axis::Y => Self {
                x: ortho,
                y: aligned,
            },
        }
    }

    pub fn get_px(&self) -> Vec2 {
        (self.x.px.to_f32(), self.y.px.to_f32()).into()
    }

    pub fn get_rel(&self) -> Vec2 {
        (self.x.rel.to_f32(), self.y.rel.to_f32()).into()
    }
}

impl Display for UiVec2 {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "rel{};px{}", self.get_rel(), self.get_px())
    }
}

impl_op!(same UiVec2 Add add; x y);
impl_op!(same UiVec2 Sub sub; x y);

const impl From<Vec2> for UiVec2 {
    fn from(px: Vec2) -> Self {
        Self::px(px)
    }
}

const impl<T: const UiNum, U: const UiNum> From<(T, U)> for UiVec2
where
    (T, U): const Destruct,
{
    fn from(px: (T, U)) -> Self {
        Self::px(px)
    }
}

/// A length along one axis: a fraction of the box it is measured in plus an
/// offset, `rel * box + px`. A position is the same number -- the length from
/// the start of the box to the point -- which is why a [`UiSpan`] is two of
/// these. Both parts are fixed point, so composing one through a chain of
/// boxes rounds only where it multiplies, and lands on the same number as any
/// other route to the same place.
///
/// It carries no claim on what a container has left over. That is
/// [`crate::LayoutLen`], which is this plus a weight, and which means nothing
/// to anyone but whoever divides the room.
#[repr(C)]
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, bytemuck::Pod, Default, bytemuck::Zeroable)]
pub struct Len {
    pub rel: Rel,
    pub px: Px,
}

impl_op!(same Len Add add; rel px);
impl_op!(same Len Sub sub; rel px);

impl Len {
    pub const ZERO: Self = Self {
        rel: Rel::ZERO,
        px: Px::ZERO,
    };
    pub const FULL: Self = Self {
        rel: Rel::ONE,
        px: Px::ZERO,
    };

    pub const fn new(rel: f32, px: f32) -> Self {
        Self::from_parts(Rel::from_f32(rel), Px::from_f32(px))
    }

    /// From parts already on the grid, rather than numbers to be put on it.
    pub const fn from_parts(rel: Rel, px: Px) -> Self {
        Self { rel, px }
    }

    pub const fn rel(rel: f32) -> Self {
        Self::from_parts(Rel::from_f32(rel), Px::ZERO)
    }

    pub const fn px(px: f32) -> Self {
        Self::from_parts(Rel::ZERO, Px::from_f32(px))
    }

    pub const fn max(&self, other: Self) -> Self {
        Self {
            rel: self.rel.max(other.rel),
            px: self.px.max(other.px),
        }
    }

    pub const fn min(&self, other: Self) -> Self {
        Self {
            rel: self.rel.min(other.rel),
            px: self.px.min(other.px),
        }
    }

    /// Both parts by the same fraction, which is what a part of a length
    /// means when the length is part pixels and part a fraction of a box.
    pub const fn scale(&self, by: Rel) -> Self {
        Self {
            rel: self.rel.mul(by),
            px: self.px.mul(by),
        }
    }

    pub const fn offset(mut self, amt: Px) -> Self {
        self.px = self.px.add(amt);
        self
    }

    pub const fn within(&self, span: &UiSpan) -> Self {
        Self {
            rel: self.rel.lerp(span.start.rel, span.end.rel),
            px: self.px.add(self.rel.lerp(span.start.px, span.end.px)),
        }
    }

    pub const fn within_len(&self, len: Len) -> Self {
        self.within(&UiSpan {
            start: Len::ZERO,
            end: len,
        })
    }

    pub const fn flip(&mut self) {
        self.rel = Rel::ONE.sub(self.rel);
        self.px = self.px.neg();
    }

    pub const fn to(&self, end: Self) -> UiSpan {
        UiSpan { start: *self, end }
    }

    /// Resolved against a box of `len`, which is the only place a fraction
    /// becomes a number of pixels.
    pub const fn to_px(&self, len: Px) -> Px {
        self.px.add(len.mul(self.rel))
    }
}

#[repr(C)]
#[derive(Debug, Copy, Clone, PartialEq, bytemuck::Pod, bytemuck::Zeroable)]
pub struct UiSpan {
    pub start: Len,
    pub end: Len,
}

impl UiSpan {
    pub const FULL: Self = Self {
        start: Len::ZERO,
        end: Len::FULL,
    };

    pub const fn rel(rel: f32) -> Self {
        Self {
            start: Len::rel(rel),
            end: Len::rel(rel),
        }
    }

    pub const fn new(start: Len, end: Len) -> Self {
        Self { start, end }
    }

    pub const fn flip(&mut self) {
        self.start.flip();
        self.end.flip();
        std::mem::swap(&mut self.start.rel, &mut self.end.rel);
        std::mem::swap(&mut self.start.px, &mut self.end.px);
    }

    pub const fn shift(&mut self, offset: Len) {
        self.start += offset;
        self.end += offset;
    }

    /// Composing a box through the one it sits in, and the hottest line in
    /// layout. It used to skip the multiplies where a span was the whole of
    /// its parent or the parent the whole of its own; both come out of the
    /// multiply unchanged anyway, and the body those comparisons cost was
    /// what kept the inliner from taking this at all.
    pub const fn within(&self, parent: &Self) -> Self {
        Self {
            start: self.start.within(parent),
            end: self.end.within(parent),
        }
    }

    /// A box `len` long inside this one, on the side `align` says. Both must
    /// be lengths of the same rel base: it subtracts one from the other
    /// rather than composing it in, which is what keeps a fraction the same
    /// fraction however long this box turns out to be.
    pub const fn place(self, len: Len, align: AxisAlign) -> Self {
        let start = self.start + (self.len() - len).scale(align.rel());
        Self::new(start, start + len)
    }

    pub const fn len(&self) -> Len {
        self.end - self.start
    }
}

#[repr(C)]
#[derive(Debug, Copy, Clone, PartialEq, bytemuck::Pod, bytemuck::Zeroable)]
pub struct UiRegion {
    pub x: UiSpan,
    pub y: UiSpan,
}

impl UiRegion {
    pub const FULL: Self = Self {
        x: UiSpan::FULL,
        y: UiSpan::FULL,
    };

    pub const fn new(x: UiSpan, y: UiSpan) -> Self {
        Self { x, y }
    }

    pub const fn rel(rel: Vec2) -> Self {
        Self {
            x: UiSpan::rel(rel.x),
            y: UiSpan::rel(rel.y),
        }
    }
    pub const fn within(&self, parent: &Self) -> Self {
        Self {
            x: self.x.within(&parent.x),
            y: self.y.within(&parent.y),
        }
    }
    pub const fn flip(&mut self, axis: Axis) {
        match axis {
            Axis::X => self.x.flip(),
            Axis::Y => self.y.flip(),
        }
    }

    pub fn shift(&mut self, offset: impl Into<UiVec2>) {
        let offset = offset.into();
        self.x.shift(offset.x);
        self.y.shift(offset.y);
    }

    pub fn offset(mut self, offset: impl Into<UiVec2>) -> Self {
        self.shift(offset);
        self
    }

    pub fn to_px(&self, size: PxVec2) -> PixelRegion {
        PixelRegion {
            top_left: self.top_left().to_px(size),
            bot_right: self.bot_right().to_px(size),
        }
    }

    pub const fn center(&self) -> UiVec2 {
        Align::CENTER.pos().within(self)
    }

    pub const fn size(&self) -> UiVec2 {
        UiVec2 {
            x: self.x.len(),
            y: self.y.len(),
        }
    }

    pub const fn top_left(&self) -> UiVec2 {
        UiVec2 {
            x: self.x.start,
            y: self.y.start,
        }
    }

    pub const fn bot_right(&self) -> UiVec2 {
        UiVec2 {
            x: self.x.end,
            y: self.y.end,
        }
    }

    pub const fn from_axis(axis: Axis, aligned: UiSpan, ortho: UiSpan) -> Self {
        Self {
            x: match axis {
                Axis::X => aligned,
                Axis::Y => ortho,
            },
            y: match axis {
                Axis::X => ortho,
                Axis::Y => aligned,
            },
        }
    }
}

impl Display for UiRegion {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "{} -> {} (size: {})",
            self.top_left(),
            self.bot_right(),
            self.size()
        )
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct PixelRegion {
    pub top_left: PxVec2,
    pub bot_right: PxVec2,
}

impl PixelRegion {
    pub fn contains(&self, pos: PxVec2) -> bool {
        pos.x >= self.top_left.x
            && pos.x <= self.bot_right.x
            && pos.y >= self.top_left.y
            && pos.y <= self.bot_right.y
    }

    pub fn size(&self) -> PxVec2 {
        self.bot_right - self.top_left
    }
}

impl Display for PixelRegion {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{} -> {}", self.top_left, self.bot_right)
    }
}

impl_axis_index!(UiVec2 => Len);
impl_axis_index!(UiRegion => UiSpan);