1 files changed, 343 insertions, 0 deletions
diff --git a/crates/typst-library/src/layout/sides.rs b/crates/typst-library/src/layout/sides.rs
new file mode 100644
index 00000000..e04b63d9
--- /dev/null
+++ b/crates/typst-library/src/layout/sides.rs
@@ -0,0 +1,343 @@
+use std::fmt::{self, Debug, Formatter};
+use std::ops::Add;
+
+use typst_utils::Get;
+
+use crate::diag::{bail, HintedStrResult};
+use crate::foundations::{
+    cast, AlternativeFold, CastInfo, Dict, Fold, FromValue, IntoValue, Reflect, Resolve,
+    StyleChain, Value,
+};
+use crate::layout::{Abs, Alignment, Axes, Axis, Corner, Rel, Size};
+
+/// A container with left, top, right and bottom components.
+#[derive(Default, Copy, Clone, Eq, PartialEq, Hash)]
+pub struct Sides<T> {
+    /// The value for the left side.
+    pub left: T,
+    /// The value for the top side.
+    pub top: T,
+    /// The value for the right side.
+    pub right: T,
+    /// The value for the bottom side.
+    pub bottom: T,
+}
+
+impl<T> Sides<T> {
+    /// Create a new instance from the four components.
+    pub const fn new(left: T, top: T, right: T, bottom: T) -> Self {
+        Self { left, top, right, bottom }
+    }
+
+    /// Create an instance with four equal components.
+    pub fn splat(value: T) -> Self
+    where
+        T: Clone,
+    {
+        Self {
+            left: value.clone(),
+            top: value.clone(),
+            right: value.clone(),
+            bottom: value,
+        }
+    }
+
+    /// Map the individual fields with `f`.
+    pub fn map<F, U>(self, mut f: F) -> Sides<U>
+    where
+        F: FnMut(T) -> U,
+    {
+        Sides {
+            left: f(self.left),
+            top: f(self.top),
+            right: f(self.right),
+            bottom: f(self.bottom),
+        }
+    }
+
+    /// Convert from `&Sides<T>` to `Sides<&T>`.
+    pub fn as_ref(&self) -> Sides<&T> {
+        Sides {
+            left: &self.left,
+            top: &self.top,
+            right: &self.right,
+            bottom: &self.bottom,
+        }
+    }
+
+    /// Zip two instances into one.
+    pub fn zip<U>(self, other: Sides<U>) -> Sides<(T, U)> {
+        Sides {
+            left: (self.left, other.left),
+            top: (self.top, other.top),
+            right: (self.right, other.right),
+            bottom: (self.bottom, other.bottom),
+        }
+    }
+
+    /// An iterator over the sides, starting with the left side, clockwise.
+    pub fn iter(&self) -> impl Iterator<Item = &T> {
+        [&self.left, &self.top, &self.right, &self.bottom].into_iter()
+    }
+
+    /// Whether all sides are equal.
+    pub fn is_uniform(&self) -> bool
+    where
+        T: PartialEq,
+    {
+        self.left == self.top && self.top == self.right && self.right == self.bottom
+    }
+}
+
+impl<T: Add> Sides<T> {
+    /// Sums up `left` and `right` into `x`, and `top` and `bottom` into `y`.
+    pub fn sum_by_axis(self) -> Axes<T::Output> {
+        Axes::new(self.left + self.right, self.top + self.bottom)
+    }
+}
+
+impl<T> Sides<Option<T>> {
+    /// Unwrap-or-default the individual sides.
+    pub fn unwrap_or_default(self) -> Sides<T>
+    where
+        T: Default,
+    {
+        self.map(Option::unwrap_or_default)
+    }
+}
+
+impl Sides<Rel<Abs>> {
+    /// Evaluate the sides relative to the given `size`.
+    pub fn relative_to(&self, size: Size) -> Sides<Abs> {
+        Sides {
+            left: self.left.relative_to(size.x),
+            top: self.top.relative_to(size.y),
+            right: self.right.relative_to(size.x),
+            bottom: self.bottom.relative_to(size.y),
+        }
+    }
+
+    /// Whether all sides are zero.
+    pub fn is_zero(&self) -> bool {
+        self.left.is_zero()
+            && self.top.is_zero()
+            && self.right.is_zero()
+            && self.bottom.is_zero()
+    }
+}
+
+impl<T> Get<Side> for Sides<T> {
+    type Component = T;
+
+    fn get_ref(&self, side: Side) -> &T {
+        match side {
+            Side::Left => &self.left,
+            Side::Top => &self.top,
+            Side::Right => &self.right,
+            Side::Bottom => &self.bottom,
+        }
+    }
+
+    fn get_mut(&mut self, side: Side) -> &mut T {
+        match side {
+            Side::Left => &mut self.left,
+            Side::Top => &mut self.top,
+            Side::Right => &mut self.right,
+            Side::Bottom => &mut self.bottom,
+        }
+    }
+}
+
+impl<T: Debug + PartialEq> Debug for Sides<T> {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        if self.is_uniform() {
+            f.write_str("Sides::splat(")?;
+            self.left.fmt(f)?;
+            f.write_str(")")
+        } else {
+            f.debug_struct("Sides")
+                .field("left", &self.left)
+                .field("top", &self.top)
+                .field("right", &self.right)
+                .field("bottom", &self.bottom)
+                .finish()
+        }
+    }
+}
+
+impl<T: Reflect> Reflect for Sides<Option<T>> {
+    fn input() -> CastInfo {
+        T::input() + Dict::input()
+    }
+
+    fn output() -> CastInfo {
+        T::output() + Dict::output()
+    }
+
+    fn castable(value: &Value) -> bool {
+        Dict::castable(value) || T::castable(value)
+    }
+}
+
+impl<T> IntoValue for Sides<Option<T>>
+where
+    T: PartialEq + IntoValue,
+{
+    fn into_value(self) -> Value {
+        if self.is_uniform() {
+            if let Some(left) = self.left {
+                return left.into_value();
+            }
+        }
+
+        let mut dict = Dict::new();
+        let mut handle = |key: &str, component: Option<T>| {
+            if let Some(c) = component {
+                dict.insert(key.into(), c.into_value());
+            }
+        };
+
+        handle("left", self.left);
+        handle("top", self.top);
+        handle("right", self.right);
+        handle("bottom", self.bottom);
+
+        Value::Dict(dict)
+    }
+}
+
+impl<T> FromValue for Sides<Option<T>>
+where
+    T: Default + FromValue + Clone,
+{
+    fn from_value(mut value: Value) -> HintedStrResult<Self> {
+        let expected_keys = ["left", "top", "right", "bottom", "x", "y", "rest"];
+        if let Value::Dict(dict) = &mut value {
+            if dict.is_empty() {
+                return Ok(Self::splat(None));
+            } else if dict.iter().any(|(key, _)| expected_keys.contains(&key.as_str())) {
+                let mut take = |key| dict.take(key).ok().map(T::from_value).transpose();
+                let rest = take("rest")?;
+                let x = take("x")?.or_else(|| rest.clone());
+                let y = take("y")?.or_else(|| rest.clone());
+                let sides = Sides {
+                    left: take("left")?.or_else(|| x.clone()),
+                    top: take("top")?.or_else(|| y.clone()),
+                    right: take("right")?.or_else(|| x.clone()),
+                    bottom: take("bottom")?.or_else(|| y.clone()),
+                };
+
+                dict.finish(&expected_keys)?;
+                return Ok(sides);
+            }
+        }
+
+        if T::castable(&value) {
+            Ok(Self::splat(Some(T::from_value(value)?)))
+        } else if let Value::Dict(dict) = &value {
+            let keys = dict.iter().map(|kv| kv.0.as_str()).collect();
+            // Do not hint at expected_keys, because T may be castable from Dict
+            // objects with other sets of expected keys.
+            Err(Dict::unexpected_keys(keys, None).into())
+        } else {
+            Err(Self::error(&value))
+        }
+    }
+}
+
+impl<T: Resolve> Resolve for Sides<T> {
+    type Output = Sides<T::Output>;
+
+    fn resolve(self, styles: StyleChain) -> Self::Output {
+        self.map(|v| v.resolve(styles))
+    }
+}
+
+impl<T: Fold> Fold for Sides<Option<T>> {
+    fn fold(self, outer: Self) -> Self {
+        // Usually, folding an inner `None` with an `outer` prefers the
+        // explicit `None`. However, here `None` means unspecified and thus
+        // we want `outer`, so we use `fold_or` to opt into such behavior.
+        self.zip(outer).map(|(inner, outer)| inner.fold_or(outer))
+    }
+}
+
+/// The four sides of objects.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
+pub enum Side {
+    /// The left side.
+    Left,
+    /// The top side.
+    Top,
+    /// The right side.
+    Right,
+    /// The bottom side.
+    Bottom,
+}
+
+impl Side {
+    /// The opposite side.
+    pub fn inv(self) -> Self {
+        match self {
+            Self::Left => Self::Right,
+            Self::Top => Self::Bottom,
+            Self::Right => Self::Left,
+            Self::Bottom => Self::Top,
+        }
+    }
+
+    /// The next side, clockwise.
+    pub fn next_cw(self) -> Self {
+        match self {
+            Self::Left => Self::Top,
+            Self::Top => Self::Right,
+            Self::Right => Self::Bottom,
+            Self::Bottom => Self::Left,
+        }
+    }
+
+    /// The next side, counter-clockwise.
+    pub fn next_ccw(self) -> Self {
+        match self {
+            Self::Left => Self::Bottom,
+            Self::Top => Self::Left,
+            Self::Right => Self::Top,
+            Self::Bottom => Self::Right,
+        }
+    }
+
+    /// The first corner of the side in clockwise order.
+    pub fn start_corner(self) -> Corner {
+        match self {
+            Self::Left => Corner::BottomLeft,
+            Self::Top => Corner::TopLeft,
+            Self::Right => Corner::TopRight,
+            Self::Bottom => Corner::BottomRight,
+        }
+    }
+
+    /// The second corner of the side in clockwise order.
+    pub fn end_corner(self) -> Corner {
+        self.next_cw().start_corner()
+    }
+
+    /// Return the corresponding axis.
+    pub fn axis(self) -> Axis {
+        match self {
+            Self::Left | Self::Right => Axis::Y,
+            Self::Top | Self::Bottom => Axis::X,
+        }
+    }
+}
+
+cast! {
+    Side,
+    self => Alignment::from(self).into_value(),
+    align: Alignment => match align {
+        Alignment::LEFT => Self::Left,
+        Alignment::RIGHT => Self::Right,
+        Alignment::TOP => Self::Top,
+        Alignment::BOTTOM => Self::Bottom,
+        _ => bail!("cannot convert this alignment to a side"),
+    },
+}