Port PageLabel conversion

crates/typst-pdf/src/paint.rs

@@ -1,7 +1,10 @@
 //! Convert paint types from typst to krilla.
 
+use std::num::NonZeroUsize;
 use krilla::geom::NormalizedF32;
+use krilla::page::{NumberingStyle, PageLabel};
 use typst_library::layout::Abs;
+use typst_library::model::Numbering;
 use typst_library::visualize::{ColorSpace, DashPattern, FillRule, FixedStroke, Paint};
 
 use crate::AbsExt;
@@ -54,4 +57,59 @@ fn paint(paint: &Paint) -> (krilla::paint::Paint, u8) {
         Paint::Gradient(_) => (krilla::color::rgb::Color::black().into(), 255),
         Paint::Pattern(_) => (krilla::color::rgb::Color::black().into(), 255),
     }
+}
+
+pub(crate) trait PageLabelExt {
+    fn generate(numbering: &Numbering, number: usize) -> Option<PageLabel>;
+    fn arabic(number: usize) -> PageLabel;
+}
+
+impl PageLabelExt for PageLabel {
+    /// Create a new `PageLabel` from a `Numbering` applied to a page
+    /// number.
+    fn generate(numbering: &Numbering, number: usize) -> Option<PageLabel> {
+        {
+            let Numbering::Pattern(pat) = numbering else {
+                return None;
+            };
+
+            let (prefix, kind) = pat.pieces.first()?;
+
+            // If there is a suffix, we cannot use the common style optimisation,
+            // since PDF does not provide a suffix field.
+            let style = if pat.suffix.is_empty() {
+                use typst_library::model::NumberingKind as Kind;
+                use krilla::page::NumberingStyle as Style;
+                match kind {
+                    Kind::Arabic => Some(Style::Arabic),
+                    Kind::LowerRoman => Some(Style::LowerRoman),
+                    Kind::UpperRoman => Some(Style::UpperRoman),
+                    Kind::LowerLatin if number <= 26 => Some(Style::LowerAlpha),
+                    Kind::LowerLatin if number <= 26 => Some(Style::UpperAlpha),
+                    _ => None,
+                }
+            } else {
+                None
+            };
+
+            // Prefix and offset depend on the style: If it is supported by the PDF
+            // spec, we use the given prefix and an offset. Otherwise, everything
+            // goes into prefix.
+            let prefix = if style.is_none() {
+                Some(pat.apply(&[number]))
+            } else {
+                (!prefix.is_empty()).then(|| prefix.clone())
+            };
+
+            let offset = style.and(NonZeroUsize::new(number));
+            Some(PageLabel::new(style, prefix.map(|s| s.to_string()), offset))
+        }
+    }
+
+    /// Creates an arabic page label with the specified page number.
+    /// For example, this will display page label `11` when given the page
+    /// number 11.
+    fn arabic(number: usize) -> PageLabel {
+        PageLabel::new(Some(NumberingStyle::Arabic), None, NonZeroUsize::new(number))
+    }
 }