From 3d075e55f59f02a518bef68b9a7218f0dfb8b7b4 Mon Sep 17 00:00:00 2001
From: Linus Groh <mail@linusgroh.de>
Date: Mon, 6 Mar 2023 21:17:19 +0000
Subject: [PATCH] LibWeb/HTML: Port Window.scrollBy() to IDL

---
 Userland/Libraries/LibWeb/HTML/Window.cpp | 91 ++++++++++-------------
 Userland/Libraries/LibWeb/HTML/Window.h   |  4 +-
 Userland/Libraries/LibWeb/HTML/Window.idl |  2 +
 3 files changed, 43 insertions(+), 54 deletions(-)

diff --git a/Userland/Libraries/LibWeb/HTML/Window.cpp b/Userland/Libraries/LibWeb/HTML/Window.cpp
index bb3a4ad6334..6d6ae49cdd6 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Window.cpp
@@ -1017,8 +1017,6 @@ WebIDL::ExceptionOr<void> Window::initialize_web_interfaces(Badge<WindowEnvironm
     define_native_function(realm, "fetch", Bindings::fetch, 1, attr);
 
     // FIXME: These properties should be [Replaceable] according to the spec, but [Writable+Configurable] is the closest we have.
-    define_native_function(realm, "scrollBy", scroll_by, 2, attr);
-
     define_native_accessor(realm, "screenX", screen_x_getter, {}, attr);
     define_native_accessor(realm, "screenY", screen_y_getter, {}, attr);
     define_native_accessor(realm, "screenLeft", screen_left_getter, {}, attr);
@@ -1417,12 +1415,51 @@ void Window::scroll(double x, double y)
     auto options = ScrollToOptions {};
 
     // 2. Let x and y be the arguments, respectively.
+
     options.left = x;
     options.top = y;
 
     scroll(options);
 }
 
+// https://w3c.github.io/csswg-drafts/cssom-view/#dom-window-scrollby
+void Window::scroll_by(ScrollToOptions options)
+{
+    // 2. Normalize non-finite values for the left and top dictionary members of options.
+    auto x = options.left.value_or(0);
+    auto y = options.top.value_or(0);
+    x = JS::Value(x).is_finite_number() ? x : 0;
+    y = JS::Value(y).is_finite_number() ? y : 0;
+
+    // 3. Add the value of scrollX to the left dictionary member.
+    options.left = x + scroll_x();
+
+    // 4. Add the value of scrollY to the top dictionary member.
+    options.top = y + scroll_y();
+
+    // 5. Act as if the scroll() method was invoked with options as the only argument.
+    scroll(options);
+}
+
+// https://w3c.github.io/csswg-drafts/cssom-view/#dom-window-scrollby
+void Window::scroll_by(double x, double y)
+{
+    // 1. If invoked with two arguments, follow these substeps:
+
+    // 1. Let options be null converted to a ScrollToOptions dictionary. [WEBIDL]
+    auto options = ScrollToOptions {};
+
+    // 2. Let x and y be the arguments, respectively.
+
+    // 3. Let the left dictionary member of options have the value x.
+    options.left = x;
+
+    // 4. Let the top dictionary member of options have the value y.
+    options.top = y;
+
+    scroll_by(options);
+}
+
 // https://w3c.github.io/hr-time/#dom-windoworworkerglobalscope-performance
 WebIDL::ExceptionOr<JS::NonnullGCPtr<HighResolutionTime::Performance>> Window::performance()
 {
@@ -1643,56 +1680,6 @@ JS_DEFINE_NATIVE_FUNCTION(Window::get_selection)
     return impl->associated_document().get_selection();
 }
 
-// https://www.w3.org/TR/cssom-view/#dom-window-scrollby
-JS_DEFINE_NATIVE_FUNCTION(Window::scroll_by)
-{
-    auto& realm = *vm.current_realm();
-
-    auto* impl = TRY(impl_from(vm));
-    if (!impl->page())
-        return JS::js_undefined();
-    auto& page = *impl->page();
-
-    JS::Object* options = nullptr;
-
-    if (vm.argument_count() == 0) {
-        options = JS::Object::create(realm, nullptr);
-    } else if (vm.argument_count() == 1) {
-        options = TRY(vm.argument(0).to_object(vm));
-    } else if (vm.argument_count() >= 2) {
-        // We ignore arguments 2+ in line with behavior of Chrome and Firefox
-        options = JS::Object::create(realm, nullptr);
-        MUST(options->set("left", vm.argument(0), ShouldThrowExceptions::No));
-        MUST(options->set("top", vm.argument(1), ShouldThrowExceptions::No));
-        MUST(options->set("behavior", MUST_OR_THROW_OOM(JS::PrimitiveString::create(vm, "auto"sv)), ShouldThrowExceptions::No));
-    }
-
-    auto left_value = TRY(options->get("left"));
-    auto left = TRY(left_value.to_double(vm));
-
-    auto top_value = TRY(options->get("top"));
-    auto top = TRY(top_value.to_double(vm));
-
-    left = JS::Value(left).is_finite_number() ? left : 0.0;
-    top = JS::Value(top).is_finite_number() ? top : 0.0;
-
-    auto current_scroll_position = page.top_level_browsing_context().viewport_scroll_offset().to_type<float>();
-    left = left + static_cast<double>(current_scroll_position.x());
-    top = top + static_cast<double>(current_scroll_position.y());
-
-    auto behavior_string_value = TRY(options->get("behavior"));
-    auto behavior_string = behavior_string_value.is_undefined() ? "auto" : TRY(behavior_string_value.to_deprecated_string(vm));
-    if (behavior_string != "smooth" && behavior_string != "auto")
-        return vm.throw_completion<JS::TypeError>("Behavior is not one of 'smooth' or 'auto'"sv);
-    auto behavior = (behavior_string == "smooth") ? Bindings::ScrollBehavior::Smooth : Bindings::ScrollBehavior::Auto;
-
-    // FIXME: Spec wants us to call scroll(options) here.
-    //        The only difference is that would invoke the viewport calculations that scroll()
-    //        is not actually doing yet, so this is the same for now.
-    perform_a_scroll(page, left, top, nullptr, behavior);
-    return JS::js_undefined();
-}
-
 JS_DEFINE_NATIVE_FUNCTION(Window::screen_left_getter)
 {
     auto* impl = TRY(impl_from(vm));
diff --git a/Userland/Libraries/LibWeb/HTML/Window.h b/Userland/Libraries/LibWeb/HTML/Window.h
index 3e89d3ae28c..96fcabad917 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.h
+++ b/Userland/Libraries/LibWeb/HTML/Window.h
@@ -177,6 +177,8 @@ public:
     double scroll_y() const;
     void scroll(ScrollToOptions const&);
     void scroll(double x, double y);
+    void scroll_by(ScrollToOptions);
+    void scroll_by(double x, double y);
 
     WebIDL::ExceptionOr<JS::NonnullGCPtr<HighResolutionTime::Performance>> performance();
 
@@ -246,8 +248,6 @@ private:
 
     JS_DECLARE_NATIVE_FUNCTION(device_pixel_ratio_getter);
 
-    JS_DECLARE_NATIVE_FUNCTION(scroll_by);
-
     JS_DECLARE_NATIVE_FUNCTION(screen_x_getter);
     JS_DECLARE_NATIVE_FUNCTION(screen_y_getter);
     JS_DECLARE_NATIVE_FUNCTION(screen_left_getter);
diff --git a/Userland/Libraries/LibWeb/HTML/Window.idl b/Userland/Libraries/LibWeb/HTML/Window.idl
index b7ba3282332..be6e2b4cef1 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.idl
+++ b/Userland/Libraries/LibWeb/HTML/Window.idl
@@ -61,6 +61,8 @@ interface Window : EventTarget {
     undefined scroll(unrestricted double x, unrestricted double y);
     [ImplementedAs=scroll] undefined scrollTo(optional ScrollToOptions options = {});
     [ImplementedAs=scroll] undefined scrollTo(unrestricted double x, unrestricted double y);
+    undefined scrollBy(optional ScrollToOptions options = {});
+    undefined scrollBy(unrestricted double x, unrestricted double y);
 
     // FIXME: Everything from here on should be shared through WindowOrWorkerGlobalScope
     // https://w3c.github.io/hr-time/#the-performance-attribute