From 88fa756ab96ccfc882e3f689ba9f62e221225b9f Mon Sep 17 00:00:00 2001
From: Silvano Cerza <silvanocerza@gmail.com>
Date: Sat, 22 Feb 2025 11:03:16 +0100
Subject: [PATCH] Handle scrollable editors in the ActionsGutter

---
 .../conflicts-resolution/actions-gutter.tsx    | 18 ++++++++++++++----
 src/views/conflicts-resolution/component.tsx   | 10 ++++++++++
 src/views/conflicts-resolution/editor-pane.tsx | 16 ++++++++++++++--
 3 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/src/views/conflicts-resolution/actions-gutter.tsx b/src/views/conflicts-resolution/actions-gutter.tsx
index 1abe582..97364e5 100644
--- a/src/views/conflicts-resolution/actions-gutter.tsx
+++ b/src/views/conflicts-resolution/actions-gutter.tsx
@@ -11,6 +11,9 @@ interface ActionsGutterProps {
   // This is essential to correctly draw the lines between
   // the left and right editor
   lineHeight: number;
+  // These two properties are necessary to handle editors scrolling
+  leftEditorTopOffset: number;
+  rightEditorTopLineOffset: number;
   onAcceptLeft: (chunk: DiffChunk) => void;
   onAcceptRight: (chunk: DiffChunk) => void;
   onReject: (chunk: DiffChunk) => void;
@@ -19,6 +22,8 @@ interface ActionsGutterProps {
 const ActionsGutter: React.FC<ActionsGutterProps> = ({
   diffChunks,
   lineHeight,
+  leftEditorTopOffset: leftEditorTopLineOffset,
+  rightEditorTopLineOffset: rightEditorTopOffset,
   onAcceptLeft,
   onAcceptRight,
   onReject,
@@ -39,10 +44,15 @@ const ActionsGutter: React.FC<ActionsGutterProps> = ({
   }, []);
 
   const drawChunk = (chunk: DiffChunk, index: number) => {
-    const topLeft = (chunk.startLeftLine - 1) * lineHeight;
-    const bottomLeft = (chunk.endLeftLine - 1) * lineHeight;
-    const topRight = (chunk.startRightLine - 1) * lineHeight;
-    const bottomRight = (chunk.endRightLine - 1) * lineHeight;
+    // The offsets are substracted to compensate the editors scrolling
+    const topLeft =
+      (chunk.startLeftLine - 1) * lineHeight - leftEditorTopLineOffset;
+    const bottomLeft =
+      (chunk.endLeftLine - 1) * lineHeight - leftEditorTopLineOffset;
+    const topRight =
+      (chunk.startRightLine - 1) * lineHeight - rightEditorTopOffset;
+    const bottomRight =
+      (chunk.endRightLine - 1) * lineHeight - rightEditorTopOffset;
     const color =
       chunk.type == "add"
         ? "var(--color-green)"
diff --git a/src/views/conflicts-resolution/component.tsx b/src/views/conflicts-resolution/component.tsx
index 91281f2..fca0198 100644
--- a/src/views/conflicts-resolution/component.tsx
+++ b/src/views/conflicts-resolution/component.tsx
@@ -42,6 +42,12 @@ const DiffView: React.FC<DiffViewProps> = ({
   const handleEditorReady = (editor: EditorView) => {
     setLineHeight(editor.defaultLineHeight);
   };
+
+  const [leftEditorTopOffset, setLeftEditorTopOffset] =
+    React.useState<number>(0);
+  const [rightEditorTopOffset, setRightEditorTopOffset] =
+    React.useState<number>(0);
+
   const diffs = diff(oldText, newText);
 
   return (
@@ -62,12 +68,15 @@ const DiffView: React.FC<DiffViewProps> = ({
           }}
           onEditorUpdate={handleEditorReady}
           onContentChange={onOldTextChange}
+          onScrollTopUpdate={setLeftEditorTopOffset}
         />
       </div>
       <div style={{ minWidth: "160px", width: "auto" }}>
         <ActionsGutter
           diffChunks={diffs}
           lineHeight={lineHeight}
+          leftEditorTopOffset={leftEditorTopOffset}
+          rightEditorTopLineOffset={rightEditorTopOffset}
           onAcceptLeft={(chunk: DiffChunk) => {
             if (chunk.type === "add") {
               const oldLines = oldText.split("\n");
@@ -141,6 +150,7 @@ const DiffView: React.FC<DiffViewProps> = ({
             isOriginal: false,
           }}
           onContentChange={onNewTextChange}
+          onScrollTopUpdate={setRightEditorTopOffset}
         />
       </div>
     </div>
diff --git a/src/views/conflicts-resolution/editor-pane.tsx b/src/views/conflicts-resolution/editor-pane.tsx
index 86c3de0..4367466 100644
--- a/src/views/conflicts-resolution/editor-pane.tsx
+++ b/src/views/conflicts-resolution/editor-pane.tsx
@@ -12,11 +12,18 @@ interface EditorPaneProps {
   highlightPluginSpec: DiffHighlightPluginSpec;
   onEditorUpdate?: (editor: EditorView) => void;
   onContentChange: (content: string) => void;
+  // Used to track the offset of the first line when the editor scrolls
+  onScrollTopUpdate?: (topOffset: number) => void;
 }
 
 const EditorPane: React.FC<EditorPaneProps> = (props) => {
-  const { content, highlightPluginSpec, onEditorUpdate, onContentChange } =
-    props;
+  const {
+    content,
+    highlightPluginSpec,
+    onEditorUpdate,
+    onContentChange,
+    onScrollTopUpdate,
+  } = props;
   const extensions = React.useMemo(() => {
     return [
       // basicSetup minus line numbers
@@ -45,6 +52,11 @@ const EditorPane: React.FC<EditorPaneProps> = (props) => {
         },
       }),
       markdown(),
+      EditorView.domEventObservers({
+        scroll(event) {
+          onScrollTopUpdate?.(event.target.scrollTop);
+        },
+      }),
     ];
   }, [highlightPluginSpec]);