From cac6d0ae3132c5c877db755431aa5f97eeb68ffe Mon Sep 17 00:00:00 2001
From: Jan-Bulthuis <git@bulthuis.dev>
Date: Sun, 19 Jul 2026 15:38:52 +0200
Subject: [PATCH] feat: perform highlighting

---
 src/syntax.rs | 86 ++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 81 insertions(+), 5 deletions(-)

diff --git a/src/syntax.rs b/src/syntax.rs
index d1b5e7d..2b72150 100644
--- a/src/syntax.rs
+++ b/src/syntax.rs
@@ -5,15 +5,22 @@ use std::{
     fs,
     path::Path,
     sync::OnceLock,
+    time::Duration,
 };
 
+use ropey::Rope;
 use tracing::{info, warn};
 use tree_house::{
-    InjectionLanguageMarker, Language, LanguageConfig, LanguageLoader, highlighter::Highlight,
+    InjectionLanguageMarker, Language, LanguageConfig, LanguageLoader, Syntax,
+    highlighter::{Highlight, HighlightEvent, Highlighter},
     read_query,
 };
 use tree_house_bindings::Grammar;
-use typst::foundations::{Func, NativeFunc, func};
+use typst::{
+    foundations::{Content, Func, NativeElement, NativeFunc, func},
+    text::TextElem,
+};
+use typst_html::{HtmlAttr, HtmlElem, attr, tag};
 
 use crate::AppConfig;
 
@@ -183,7 +190,76 @@ fn highlight(
     #[named]
     #[default(None)]
     lang: Option<String>,
-) -> String {
-    let rev = text.chars().rev();
-    rev.collect()
+) -> Content {
+    let highlighted = highlight_code(&text, lang.as_deref()).unwrap_or(TextElem::packed(text));
+
+    if block {
+        HtmlElem::new(tag::pre)
+            .with_body(Some(highlighted))
+            .with_attr(HtmlAttr::constant("class"), "code-block")
+            .pack()
+    } else {
+        HtmlElem::new(tag::code)
+            .with_body(Some(highlighted))
+            .with_attr(HtmlAttr::constant("class"), "code-inline")
+            .pack()
+    }
+}
+
+/// Highlights `source` as `lang`.
+fn highlight_code(source: &str, lang: Option<&str>) -> Option<Content> {
+    let registry = REGISTRY.get()?;
+    let language = *registry.by_name.get(lang?)?;
+
+    let rope = Rope::from_str(source);
+    let slice = rope.slice(..);
+    let syntax = Syntax::new(slice, language, Duration::from_millis(500), registry).ok()?;
+    let mut hl = Highlighter::new(&syntax, slice, registry, 0..source.len() as u32);
+
+    let src = source.as_bytes();
+    let src_len = source.len() as u32;
+    let mut pos: u32 = 0;
+    let mut classes = String::new();
+    let mut nodes = Vec::<Content>::new();
+
+    loop {
+        let next = hl.next_event_offset().min(src_len);
+
+        if next > pos {
+            let text = std::str::from_utf8(&src[pos as usize..next as usize]).ok()?;
+            let node = TextElem::packed(text);
+            nodes.push(if classes.is_empty() {
+                node
+            } else {
+                HtmlElem::new(tag::span)
+                    .with_attr(attr::class, classes.clone())
+                    .with_body(Some(node))
+                    .pack()
+            });
+            pos = next;
+        }
+
+        if pos >= src_len {
+            break;
+        }
+
+        let (event, highlights) = hl.advance();
+        let base = match event {
+            // Replace the active highlights
+            HighlightEvent::Refresh => String::new(),
+            // Extend the active highlights
+            HighlightEvent::Push => classes.clone(),
+        };
+        classes = highlights.fold(base, |mut acc, h| {
+            let name = HIGHLIGHT_NAMES[h.idx()].replace('.', "-");
+            if !acc.is_empty() {
+                acc.push(' ');
+            }
+            acc.push_str("hl-");
+            acc.push_str(&name);
+            acc
+        });
+    }
+
+    Some(Content::sequence(nodes))
 }