From 58adf1d025bd7ff149d7fd06147b0f3e069f8c7d Mon Sep 17 00:00:00 2001
From: Martin Haug <mhaug@live.de>
Date: Sun, 12 Feb 2023 23:32:14 +0100
Subject: [PATCH] Add XMP

---
 Cargo.lock            |  6 ++++++
 Cargo.toml            |  1 +
 src/export/pdf/mod.rs | 20 ++++++++++++++++++++
 3 files changed, 27 insertions(+)

diff --git a/Cargo.lock b/Cargo.lock
index a4c224cb2..d28bb206c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1191,6 +1191,7 @@ dependencies = [
  "unicode-xid",
  "unscanny",
  "usvg",
+ "xmp-writer",
 ]
 
 [[package]]
@@ -1565,6 +1566,11 @@ version = "0.13.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4d25c75bf9ea12c4040a97f829154768bbbce366287e2dc044af160cd79a13fd"
 
+[[package]]
+name = "xmp-writer"
+version = "0.1.0"
+source = "git+https://github.com/typst/xmp-writer#a4a36967cd73c9c19548e940bbcc55583a901417"
+
 [[package]]
 name = "yaml-front-matter"
 version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
index b2db54244..8bd8e67e7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -40,6 +40,7 @@ unicode-segmentation = "1"
 unicode-xid = "0.2"
 unscanny = "0.1"
 usvg = { version = "0.22", default-features = false }
+xmp-writer = { git = "https://github.com/typst/xmp-writer" }
 
 [profile.dev]
 debug = 0
diff --git a/src/export/pdf/mod.rs b/src/export/pdf/mod.rs
index 60cd4ea2f..38433211c 100644
--- a/src/export/pdf/mod.rs
+++ b/src/export/pdf/mod.rs
@@ -11,6 +11,7 @@ use std::hash::Hash;
 
 use pdf_writer::types::Direction;
 use pdf_writer::{Finish, Name, PdfWriter, Ref, TextStr};
+use xmp_writer::{LangId, RenditionClass, XmpWriter};
 
 use self::outline::HeadingNode;
 use self::page::Page;
@@ -115,20 +116,39 @@ fn write_catalog(ctx: &mut PdfContext) {
     };
 
     // Write the document information.
+    let meta_ref = ctx.alloc.bump();
+    let mut xmp = XmpWriter::new();
+
     let mut info = ctx.writer.document_info(ctx.alloc.bump());
     if let Some(title) = &ctx.document.title {
         info.title(TextStr(title));
+        xmp.title([(None, title.as_str())]);
     }
     if let Some(author) = &ctx.document.author {
         info.author(TextStr(author));
+        xmp.creator([(author.as_str())]);
     }
     info.creator(TextStr("Typst"));
+    xmp.creator_tool("Typst");
+    xmp.num_pages(ctx.document.pages.len() as u32);
+    xmp.format("application/pdf");
+    xmp.language(ctx.languages.keys().map(|lang| LangId(lang.as_str())));
+    xmp.rendition_class(RenditionClass::Proof);
+    xmp.pdf_version("1.7");
+
     info.finish();
 
+    let xmp_buf = xmp.finish(None);
+    let mut meta_stream = ctx.writer.stream(meta_ref, &xmp_buf);
+    meta_stream.pair(Name(b"Type"), Name(b"Metadata"));
+    meta_stream.pair(Name(b"Subtype"), Name(b"XML"));
+    meta_stream.finish();
+
     // Write the document catalog.
     let mut catalog = ctx.writer.catalog(ctx.alloc.bump());
     catalog.pages(ctx.page_tree_ref);
     catalog.viewer_preferences().direction(dir);
+    catalog.pair(Name(b"Metadata"), meta_ref);
 
     if let Some(outline_root_id) = outline_root_id {
         catalog.outlines(outline_root_id);