From ce341c0230aa216bcbb2a81e75873d38d5d7a717 Mon Sep 17 00:00:00 2001
From: Shannon Booth <shannon@serenityos.org>
Date: Mon, 1 Apr 2024 22:18:00 +0200
Subject: [PATCH] LibWeb: Add support for document.lastModified

---
 Userland/Libraries/LibWeb/DOM/Document.cpp | 34 ++++++++++++++++++++++
 Userland/Libraries/LibWeb/DOM/Document.h   |  7 ++++-
 Userland/Libraries/LibWeb/DOM/Document.idl |  1 +
 3 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/Userland/Libraries/LibWeb/DOM/Document.cpp b/Userland/Libraries/LibWeb/DOM/Document.cpp
index 257987d39d2..5a14f3ca9c6 100644
--- a/Userland/Libraries/LibWeb/DOM/Document.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Document.cpp
@@ -301,6 +301,10 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<Document>> Document::create_and_initialize(
 
     document->m_window = window;
 
+    // NOTE: Non-standard: Pull out the Last-Modified header for use in the lastModified property.
+    if (auto maybe_last_modified = MUST(navigation_params.response->header_list()->get("Last-Modified"sv.bytes())); maybe_last_modified.has_value())
+        document->m_last_modified = Core::DateTime::parse("%a, %d %b %Y %H:%M:%S %Z"sv, maybe_last_modified.value());
+
     // 11. Set window's associated Document to document.
     window->set_associated_document(*document);
 
@@ -2158,6 +2162,36 @@ void Document::update_readiness(HTML::DocumentReadyState readiness_value)
     }
 }
 
+// https://html.spec.whatwg.org/multipage/dom.html#dom-document-lastmodified
+String Document::last_modified() const
+{
+    // The lastModified attribute, on getting, must return the date and time of the Document's source file's
+    // last modification, in the user's local time zone, in the following format:
+
+    // 1. The month component of the date.
+    // 2. A U+002F SOLIDUS character (/).
+    // 3. The day component of the date.
+    // 4. A U+002F SOLIDUS character (/).
+    // 5. The year component of the date.
+    // 6. A U+0020 SPACE character.
+    // 7. The hours component of the time.
+    // 8. A U+003A COLON character (:).
+    // 9. The minutes component of the time.
+    // 10. A U+003A COLON character (:).
+    // 11. The seconds component of the time.
+
+    // The Document's source file's last modification date and time must be derived from relevant features
+    // of the networking protocols used, e.g. from the value of the HTTP `Last-Modified` header of the document,
+    // or from metadata in the file system for local files. If the last modification date and time are not known,
+    // the attribute must return the current date and time in the above format.
+    constexpr auto format_string = "%m/%d/%Y %H:%M:%S"sv;
+
+    if (m_last_modified.has_value())
+        return MUST(m_last_modified.value().to_string(format_string));
+
+    return MUST(Core::DateTime::now().to_string(format_string));
+}
+
 Page& Document::page()
 {
     return m_page;
diff --git a/Userland/Libraries/LibWeb/DOM/Document.h b/Userland/Libraries/LibWeb/DOM/Document.h
index b16b315aec2..2c1436fdd16 100644
--- a/Userland/Libraries/LibWeb/DOM/Document.h
+++ b/Userland/Libraries/LibWeb/DOM/Document.h
@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2018-2023, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2021-2023, Linus Groh <linusg@serenityos.org>
- * Copyright (c) 2023, Shannon Booth <shannon@serenityos.org>
+ * Copyright (c) 2023-2024, Shannon Booth <shannon@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -14,6 +14,7 @@
 #include <AK/String.h>
 #include <AK/Vector.h>
 #include <AK/WeakPtr.h>
+#include <LibCore/DateTime.h>
 #include <LibCore/Forward.h>
 #include <LibJS/Forward.h>
 #include <LibURL/URL.h>
@@ -323,6 +324,8 @@ public:
     HTML::DocumentReadyState readiness() const { return m_readiness; }
     void update_readiness(HTML::DocumentReadyState);
 
+    String last_modified() const;
+
     [[nodiscard]] JS::GCPtr<HTML::Window> window() const { return m_window; }
 
     void set_window(HTML::Window&);
@@ -872,6 +875,8 @@ private:
 
     Vector<JS::NonnullGCPtr<DOM::ShadowRoot>> m_shadow_roots;
 
+    Optional<Core::DateTime> m_last_modified;
+
     u64 m_dom_tree_version { 0 };
 
     // https://drafts.csswg.org/css-position-4/#document-top-layer
diff --git a/Userland/Libraries/LibWeb/DOM/Document.idl b/Userland/Libraries/LibWeb/DOM/Document.idl
index d6247efec8d..584609ea87a 100644
--- a/Userland/Libraries/LibWeb/DOM/Document.idl
+++ b/Userland/Libraries/LibWeb/DOM/Document.idl
@@ -103,6 +103,7 @@ interface Document : Node {
     readonly attribute HTMLHeadElement? head;
     readonly attribute HTMLScriptElement? currentScript;
 
+    readonly attribute DOMString lastModified;
     readonly attribute DOMString readyState;
 
     [CEReactions] attribute DOMString title;