1 files changed, 104 insertions, 0 deletions
diff --git a/crates/typst-html/src/encode.rs b/crates/typst-html/src/encode.rs
new file mode 100644
index 00000000..d4ff83d6
--- /dev/null
+++ b/crates/typst-html/src/encode.rs
@@ -0,0 +1,104 @@
+use std::fmt::Write;
+
+use typst_library::diag::{bail, At, SourceResult, StrResult};
+use typst_library::foundations::Repr;
+use typst_library::html::{charsets, tag, HtmlDocument, HtmlElement, HtmlNode};
+use typst_library::layout::Frame;
+use typst_syntax::Span;
+
+/// Encodes an HTML document into a string.
+pub fn html(document: &HtmlDocument) -> SourceResult<String> {
+    let mut w = Writer { buf: String::new() };
+    w.buf.push_str("<!DOCTYPE html>");
+    write_element(&mut w, &document.root)?;
+    Ok(w.buf)
+}
+
+struct Writer {
+    buf: String,
+}
+
+/// Encode an HTML node into the writer.
+fn write_node(w: &mut Writer, node: &HtmlNode) -> SourceResult<()> {
+    match node {
+        HtmlNode::Tag(_) => {}
+        HtmlNode::Text(text, span) => write_text(w, text, *span)?,
+        HtmlNode::Element(element) => write_element(w, element)?,
+        HtmlNode::Frame(frame) => write_frame(w, frame),
+    }
+    Ok(())
+}
+
+/// Encode plain text into the writer.
+fn write_text(w: &mut Writer, text: &str, span: Span) -> SourceResult<()> {
+    for c in text.chars() {
+        if charsets::is_valid_in_normal_element_text(c) {
+            w.buf.push(c);
+        } else {
+            write_escape(w, c).at(span)?;
+        }
+    }
+    Ok(())
+}
+
+/// Encode one element into the write.
+fn write_element(w: &mut Writer, element: &HtmlElement) -> SourceResult<()> {
+    w.buf.push('<');
+    w.buf.push_str(&element.tag.resolve());
+
+    for (attr, value) in &element.attrs.0 {
+        w.buf.push(' ');
+        w.buf.push_str(&attr.resolve());
+        w.buf.push('=');
+        w.buf.push('"');
+        for c in value.chars() {
+            if charsets::is_valid_in_attribute_value(c) {
+                w.buf.push(c);
+            } else {
+                write_escape(w, c).at(element.span)?;
+            }
+        }
+        w.buf.push('"');
+    }
+
+    w.buf.push('>');
+
+    if tag::is_void(element.tag) {
+        return Ok(());
+    }
+
+    for node in &element.children {
+        write_node(w, node)?;
+    }
+
+    w.buf.push_str("</");
+    w.buf.push_str(&element.tag.resolve());
+    w.buf.push('>');
+
+    Ok(())
+}
+
+/// Escape a character.
+fn write_escape(w: &mut Writer, c: char) -> StrResult<()> {
+    // See <https://html.spec.whatwg.org/multipage/syntax.html#syntax-charref>
+    match c {
+        '&' => w.buf.push_str("&amp;"),
+        '<' => w.buf.push_str("&lt;"),
+        '>' => w.buf.push_str("&gt;"),
+        '"' => w.buf.push_str("&quot;"),
+        '\'' => w.buf.push_str("&apos;"),
+        c if charsets::is_w3c_text_char(c) && c != '\r' => {
+            write!(w.buf, "&#x{:x};", c as u32).unwrap()
+        }
+        _ => bail!("the character {} cannot be encoded in HTML", c.repr()),
+    }
+    Ok(())
+}
+
+/// Encode a laid out frame into the writer.
+fn write_frame(w: &mut Writer, frame: &Frame) {
+    // FIXME: This string replacement is obviously a hack.
+    let svg = typst_svg::svg_frame(frame)
+        .replace("<svg class", "<svg style=\"overflow: visible;\" class");
+    w.buf.push_str(&svg);
+}