Add timezone to PDF's default timestamp. (#5564)

Co-authored-by: Laurenz <laurmaedje@gmail.com>

3 files changed, 144 insertions, 18 deletions

diff --git a/crates/typst-cli/src/compile.rs b/crates/typst-cli/src/compile.rs
index 3aa3aa3b..adeef0f2 100644
--- a/crates/typst-cli/src/compile.rs
+++ b/crates/typst-cli/src/compile.rs
@@ -17,7 +17,7 @@ use typst::html::HtmlDocument;
 use typst::layout::{Frame, Page, PageRanges, PagedDocument};
 use typst::syntax::{FileId, Source, Span};
 use typst::WorldExt;
-use typst_pdf::{PdfOptions, PdfStandards};
+use typst_pdf::{PdfOptions, PdfStandards, Timestamp};
 
 use crate::args::{
     CompileArgs, CompileCommand, DiagnosticFormat, Input, Output, OutputFormat,
@@ -55,7 +55,7 @@ pub struct CompileConfig {
     pub output_format: OutputFormat,
     /// Which pages to export.
     pub pages: Option<PageRanges>,
-    /// The document's creation date formatted as a UNIX timestamp.
+    /// The document's creation date formatted as a UNIX timestamp, with UTC suffix.
     pub creation_timestamp: Option<DateTime<Utc>>,
     /// The format to emit diagnostics in.
     pub diagnostic_format: DiagnosticFormat,
@@ -271,11 +271,23 @@ fn export_paged(document: &PagedDocument, config: &CompileConfig) -> SourceResul
 
 /// Export to a PDF.
 fn export_pdf(document: &PagedDocument, config: &CompileConfig) -> SourceResult<()> {
+    // If the timestamp is provided through the CLI, use UTC suffix,
+    // else, use the current local time and timezone.
+    let timestamp = match config.creation_timestamp {
+        Some(timestamp) => convert_datetime(timestamp).map(Timestamp::new_utc),
+        None => {
+            let local_datetime = chrono::Local::now();
+            convert_datetime(local_datetime).and_then(|datetime| {
+                Timestamp::new_local(
+                    datetime,
+                    local_datetime.offset().local_minus_utc() / 60,
+                )
+            })
+        }
+    };
     let options = PdfOptions {
         ident: Smart::Auto,
-        timestamp: convert_datetime(
-            config.creation_timestamp.unwrap_or_else(chrono::Utc::now),
-        ),
+        timestamp,
         page_ranges: config.pages.clone(),
         standards: config.pdf_standards.clone(),
     };
@@ -289,7 +301,9 @@ fn export_pdf(document: &PagedDocument, config: &CompileConfig) -> SourceResult<
 }
 
 /// Convert [`chrono::DateTime`] to [`Datetime`]
-fn convert_datetime(date_time: chrono::DateTime<chrono::Utc>) -> Option<Datetime> {
+fn convert_datetime<Tz: chrono::TimeZone>(
+    date_time: chrono::DateTime<Tz>,
+) -> Option<Datetime> {
     Datetime::from_ymd_hms(
         date_time.year(),
         date_time.month().try_into().ok()?,
diff --git a/crates/typst-pdf/src/catalog.rs b/crates/typst-pdf/src/catalog.rs
index 753b8cb6..c4b0e2e8 100644
--- a/crates/typst-pdf/src/catalog.rs
+++ b/crates/typst-pdf/src/catalog.rs
@@ -9,10 +9,10 @@ use typst_library::foundations::{Datetime, Smart};
 use typst_library::layout::Dir;
 use typst_library::text::Lang;
 use typst_syntax::Span;
-use xmp_writer::{DateTime, LangId, RenditionClass, Timezone, XmpWriter};
+use xmp_writer::{DateTime, LangId, RenditionClass, XmpWriter};
 
 use crate::page::PdfPageLabel;
-use crate::{hash_base64, outline, TextStrExt, WithEverything};
+use crate::{hash_base64, outline, TextStrExt, Timezone, WithEverything};
 
 /// Write the document catalog.
 pub fn write_catalog(
@@ -87,8 +87,17 @@ pub fn write_catalog(
         xmp.pdf_keywords(&joined);
     }
 
-    let date = ctx.document.info.date.unwrap_or(ctx.options.timestamp);
-    let tz = ctx.document.info.date.is_auto();
+    // (1) If the `document.date` is set to specific `datetime` or `none`, use it.
+    // (2) If the `document.date` is set to `auto` or not set, try to use the
+    //     date from the options.
+    // (3) Otherwise, we don't write date metadata.
+    let (date, tz) = match (ctx.document.info.date, ctx.options.timestamp) {
+        (Smart::Custom(date), _) => (date, None),
+        (Smart::Auto, Some(timestamp)) => {
+            (Some(timestamp.datetime), Some(timestamp.timezone))
+        }
+        _ => (None, None),
+    };
     if let Some(date) = date {
         if let Some(pdf_date) = pdf_date(date, tz) {
             info.creation_date(pdf_date);
@@ -281,7 +290,7 @@ pub(crate) fn write_page_labels(
 }
 
 /// Converts a datetime to a pdf-writer date.
-fn pdf_date(datetime: Datetime, tz: bool) -> Option<pdf_writer::Date> {
+fn pdf_date(datetime: Datetime, tz: Option<Timezone>) -> Option<pdf_writer::Date> {
     let year = datetime.year().filter(|&y| y >= 0)? as u16;
 
     let mut pdf_date = pdf_writer::Date::new(year);
@@ -306,16 +315,36 @@ fn pdf_date(datetime: Datetime, tz: bool) -> Option<pdf_writer::Date> {
         pdf_date = pdf_date.second(s);
     }
 
-    if tz {
-        pdf_date = pdf_date.utc_offset_hour(0).utc_offset_minute(0);
+    match tz {
+        Some(Timezone::UTC) => {
+            pdf_date = pdf_date.utc_offset_hour(0).utc_offset_minute(0)
+        }
+        Some(Timezone::Local { hour_offset, minute_offset }) => {
+            pdf_date =
+                pdf_date.utc_offset_hour(hour_offset).utc_offset_minute(minute_offset)
+        }
+        None => {}
     }
 
     Some(pdf_date)
 }
 
 /// Converts a datetime to an xmp-writer datetime.
-fn xmp_date(datetime: Datetime, tz: bool) -> Option<xmp_writer::DateTime> {
+fn xmp_date(
+    datetime: Datetime,
+    timezone: Option<Timezone>,
+) -> Option<xmp_writer::DateTime> {
     let year = datetime.year().filter(|&y| y >= 0)? as u16;
+    let timezone = timezone.map(|tz| match tz {
+        Timezone::UTC => xmp_writer::Timezone::Utc,
+        Timezone::Local { hour_offset, minute_offset } => {
+            // The xmp-writer use signed integers for the minute offset, which
+            // can be buggy if the minute offset is negative. And because our
+            // minute_offset is ensured to be `0 <= minute_offset < 60`, we can
+            // safely cast it to a signed integer.
+            xmp_writer::Timezone::Local { hour: hour_offset, minute: minute_offset as i8 }
+        }
+    });
     Some(DateTime {
         year,
         month: datetime.month(),
@@ -323,6 +352,6 @@ fn xmp_date(datetime: Datetime, tz: bool) -> Option<xmp_writer::DateTime> {
         hour: datetime.hour(),
         minute: datetime.minute(),
         second: datetime.second(),
-        timezone: if tz { Some(Timezone::Utc) } else { None },
+        timezone,
     })
 }
diff --git a/crates/typst-pdf/src/lib.rs b/crates/typst-pdf/src/lib.rs
index c315684d..f45c62bb 100644
--- a/crates/typst-pdf/src/lib.rs
+++ b/crates/typst-pdf/src/lib.rs
@@ -89,9 +89,9 @@ pub struct PdfOptions<'a> {
     /// `Auto`, a hash of the document's title and author is used instead (which
     /// is reasonably unique and stable).
     pub ident: Smart<&'a str>,
-    /// If not `None`, shall be the creation date of the document as a UTC
-    /// datetime. It will only be used if `set document(date: ..)` is `auto`.
-    pub timestamp: Option<Datetime>,
+    /// If not `None`, shall be the creation timestamp of the document. It will
+    /// only be used if `set document(date: ..)` is `auto`.
+    pub timestamp: Option<Timestamp>,
     /// Specifies which ranges of pages should be exported in the PDF. When
     /// `None`, all pages should be exported.
     pub page_ranges: Option<PageRanges>,
@@ -99,6 +99,51 @@ pub struct PdfOptions<'a> {
     pub standards: PdfStandards,
 }
 
+/// A timestamp with timezone information.
+#[derive(Debug, Clone, Copy)]
+pub struct Timestamp {
+    /// The datetime of the timestamp.
+    pub(crate) datetime: Datetime,
+    /// The timezone of the timestamp.
+    pub(crate) timezone: Timezone,
+}
+
+impl Timestamp {
+    /// Create a new timestamp with a given datetime and UTC suffix.
+    pub fn new_utc(datetime: Datetime) -> Self {
+        Self { datetime, timezone: Timezone::UTC }
+    }
+
+    /// Create a new timestamp with a given datetime, and a local timezone offset.
+    pub fn new_local(datetime: Datetime, whole_minute_offset: i32) -> Option<Self> {
+        let hour_offset = (whole_minute_offset / 60).try_into().ok()?;
+        // Note: the `%` operator in Rust is the remainder operator, not the
+        // modulo operator. The remainder operator can return negative results.
+        // We can simply apply `abs` here because we assume the `minute_offset`
+        // will have the same sign as `hour_offset`.
+        let minute_offset = (whole_minute_offset % 60).abs().try_into().ok()?;
+        match (hour_offset, minute_offset) {
+            // Only accept valid timezone offsets with `-23 <= hours <= 23`,
+            // and `0 <= minutes <= 59`.
+            (-23..=23, 0..=59) => Some(Self {
+                datetime,
+                timezone: Timezone::Local { hour_offset, minute_offset },
+            }),
+            _ => None,
+        }
+    }
+}
+
+/// A timezone.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Timezone {
+    /// The UTC timezone.
+    UTC,
+    /// The local timezone offset from UTC. And the `minute_offset` will have
+    /// same sign as `hour_offset`.
+    Local { hour_offset: i8, minute_offset: u8 },
+}
+
 /// Encapsulates a list of compatible PDF standards.
 #[derive(Clone)]
 pub struct PdfStandards {
@@ -612,3 +657,41 @@ fn transform_to_array(ts: Transform) -> [f32; 6] {
         ts.ty.to_f32(),
     ]
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_timestamp_new_local() {
+        let dummy_datetime = Datetime::from_ymd_hms(2024, 12, 17, 10, 10, 10).unwrap();
+        let test = |whole_minute_offset, expect_timezone| {
+            assert_eq!(
+                Timestamp::new_local(dummy_datetime, whole_minute_offset)
+                    .unwrap()
+                    .timezone,
+                expect_timezone
+            );
+        };
+
+        // Valid timezone offsets
+        test(0, Timezone::Local { hour_offset: 0, minute_offset: 0 });
+        test(480, Timezone::Local { hour_offset: 8, minute_offset: 0 });
+        test(-480, Timezone::Local { hour_offset: -8, minute_offset: 0 });
+        test(330, Timezone::Local { hour_offset: 5, minute_offset: 30 });
+        test(-210, Timezone::Local { hour_offset: -3, minute_offset: 30 });
+        test(-720, Timezone::Local { hour_offset: -12, minute_offset: 0 }); // AoE
+
+        // Corner cases
+        test(315, Timezone::Local { hour_offset: 5, minute_offset: 15 });
+        test(-225, Timezone::Local { hour_offset: -3, minute_offset: 45 });
+        test(1439, Timezone::Local { hour_offset: 23, minute_offset: 59 });
+        test(-1439, Timezone::Local { hour_offset: -23, minute_offset: 59 });
+
+        // Invalid timezone offsets
+        assert!(Timestamp::new_local(dummy_datetime, 1440).is_none());
+        assert!(Timestamp::new_local(dummy_datetime, -1440).is_none());
+        assert!(Timestamp::new_local(dummy_datetime, i32::MAX).is_none());
+        assert!(Timestamp::new_local(dummy_datetime, i32::MIN).is_none());
+    }
+}