iris/core/src/orientation/len.rs

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

#[derive(Debug, Default, Clone, Copy, PartialEq)]
pub struct Size {
    pub x: LayoutLen,
    pub y: LayoutLen,
}

/// What a widget asks for along one axis: a [`Len`] -- pixels and a fraction
/// of the box it is given -- plus a share of whatever is left over once
/// everything fixed has been taken. The parts add up rather than choosing
/// between one another.
///
/// Only a container dividing its room can answer a share, so a length nobody
/// divides is a `Len`: a position, a padding, a cap, anything already
/// resolved.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct LayoutLen {
    pub px: Px,
    pub rel: Rel,
    pub leftover: Weight,
}

/// A bare number is pixels, which is the one length that needs no box to be
/// read in.
impl<N: UiNum> From<N> for Len {
    fn from(value: N) -> Self {
        Len::px(value.to_f32())
    }
}

impl<N: UiNum> From<N> for LayoutLen {
    fn from(value: N) -> Self {
        LayoutLen::px(value.to_f32())
    }
}

impl<Nx: UiNum, Ny: UiNum> From<(Nx, Ny)> for Size {
    fn from((x, y): (Nx, Ny)) -> Self {
        Self {
            x: x.into(),
            y: y.into(),
        }
    }
}

/// A length with no share in it is a length a container does not have to
/// divide, which is one it can always give.
impl From<Len> for LayoutLen {
    fn from(len: Len) -> Self {
        Self {
            px: len.px,
            rel: len.rel,
            leftover: Weight::ZERO,
        }
    }
}

impl From<LayoutLen> for Size {
    fn from(value: LayoutLen) -> Self {
        Self { x: value, y: value }
    }
}

impl Size {
    pub const ZERO: Self = Self {
        x: LayoutLen::ZERO,
        y: LayoutLen::ZERO,
    };

    pub const LEFTOVER: Self = Self {
        x: LayoutLen::LEFTOVER,
        y: LayoutLen::LEFTOVER,
    };

    /// From something measured outside layout -- a texture, a shaped line --
    /// which is where a size in floats comes from.
    pub fn px(v: Vec2) -> Self {
        Self::from_px(PxVec2::from_f32(v))
    }

    pub const fn from_px(v: PxVec2) -> Self {
        Self {
            x: LayoutLen {
                px: v.x,
                ..LayoutLen::ZERO
            },
            y: LayoutLen {
                px: v.y,
                ..LayoutLen::ZERO
            },
        }
    }

    pub fn rel(v: Vec2) -> Self {
        Self {
            x: LayoutLen::rel(v.x),
            y: LayoutLen::rel(v.y),
        }
    }

    pub fn leftover(v: Vec2) -> Self {
        Self {
            x: LayoutLen::leftover(v.x),
            y: LayoutLen::leftover(v.y),
        }
    }

    pub fn to_uivec2(self) -> UiVec2 {
        UiVec2 {
            x: self.x.apply_leftover(),
            y: self.y.apply_leftover(),
        }
    }

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

impl LayoutLen {
    pub const ZERO: Self = Self {
        px: Px::ZERO,
        rel: Rel::ZERO,
        leftover: Weight::ZERO,
    };

    pub const LEFTOVER: Self = Self {
        px: Px::ZERO,
        rel: Rel::ZERO,
        leftover: Weight::ONE,
    };

    /// The whole of what is left over counts as the whole box, which is what
    /// a length means to something that is not dividing a box between
    /// siblings -- a scroll asking how long its content is.
    pub fn apply_leftover(&self) -> Len {
        let share = match self.leftover > Weight::ZERO {
            true => Rel::ONE,
            false => Rel::ZERO,
        };
        Len::from_parts(self.rel.add(share), self.px)
    }

    /// Only pixels: the same number of them whatever box it lands in, and
    /// whatever anyone else in the row asks for. A length that is any part
    /// of a box or of what is left over is not one.
    pub fn is_px(&self) -> bool {
        self.rel == Rel::ZERO && self.leftover == Weight::ZERO
    }

    /// Nothing but a claim on what is left over, so there is no length here
    /// at all where nothing is.
    pub fn is_only_leftover(&self) -> bool {
        self.leftover > Weight::ZERO && self.without_leftover() == Len::ZERO
    }

    /// This as a length of a box, where it is one. `leftover` is not: a
    /// share of what is left over is a length only to whoever divides one,
    /// so it passes up in the reported size instead and is resolved there.
    pub fn declared(&self) -> Option<Len> {
        (self.leftover == Weight::ZERO).then(|| self.without_leftover())
    }

    /// What this takes whatever is left over: the reading of a length for
    /// anyone not dividing a box between siblings, where a share is a claim
    /// on someone else's room rather than a length of its own.
    /// [`Self::apply_leftover`] is the opposite reading of the same value.
    pub const fn without_leftover(&self) -> Len {
        Len::from_parts(self.rel, self.px)
    }

    /// This length, given as a part of a box `len` long, as a part of the
    /// box `len` is itself a part of. The share is untouched: it is a claim
    /// on whoever divides the room, not a fraction of anything.
    pub const fn within_len(self, len: Len) -> Self {
        let part = self.without_leftover().within_len(len);
        Self {
            px: part.px,
            rel: part.rel,
            leftover: self.leftover,
        }
    }

    pub fn px(px: impl UiNum) -> Self {
        Self {
            px: Px::from_num(px),
            ..Self::ZERO
        }
    }
    pub fn rel(rel: impl UiNum) -> Self {
        Self {
            rel: Rel::from_num(rel),
            ..Self::ZERO
        }
    }
    pub fn leftover(ratio: impl UiNum) -> Self {
        Self {
            leftover: Weight::from_num(ratio),
            ..Self::ZERO
        }
    }
}

pub mod len_fns {
    use super::*;

    pub fn px(px: impl UiNum) -> LayoutLen {
        LayoutLen::px(px)
    }
    pub fn rel(rel: impl UiNum) -> LayoutLen {
        LayoutLen::rel(rel)
    }
    pub fn leftover(ratio: impl UiNum) -> LayoutLen {
        LayoutLen::leftover(ratio)
    }
}

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

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

impl Default for LayoutLen {
    fn default() -> Self {
        Self::leftover(1.0)
    }
}

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

impl std::fmt::Display for LayoutLen {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        // A part that is zero is left out, so a length that is zero all
        // through would print as nothing -- which reads as no length at all
        // wherever one is printed beside something that has none.
        if *self == Self::ZERO {
            return write!(f, "0 px;");
        }
        if self.px != Px::ZERO {
            write!(f, "{} px;", self.px)?;
        }
        if self.rel != Rel::ZERO {
            write!(f, "{} rel;", self.rel)?;
        }
        if self.leftover != Weight::ZERO {
            write!(f, "{} leftover;", self.leftover)?;
        }
        Ok(())
    }
}

impl_axis_index!(Size => LayoutLen);

#[cfg(test)]
mod tests {
    use super::*;

    /// What a request prints as is how a failing case is read and written out
    /// again, and a length that printed as nothing could not be told from a
    /// widget that has no rule at all.
    #[test]
    fn every_length_prints_as_something() {
        for len in [
            LayoutLen::ZERO,
            LayoutLen::px(8),
            LayoutLen::rel(0.5),
            LayoutLen::LEFTOVER,
        ] {
            assert!(!len.to_string().is_empty(), "{len:?} printed as nothing");
        }
        assert_eq!(LayoutLen::ZERO.to_string(), "0 px;");
    }
}