Improve markdown TOC scrolling (#349)

Use a better system for scrolling using scrollTo on the
OverlayScrollbars ref. This lets me get the heading as close to the top
of the viewport as possible without the convoluted CSS tricks I was
trying before.

frontend/app/element/markdown.less

@@ -17,7 +17,6 @@
         font-size: 14px;
         overflow-wrap: break-word;
         margin-bottom: 10px;
-        --half-contents-height: 10em;
 
         .heading {
             &:first-of-type {
@@ -26,7 +25,6 @@
             color: var(--app-text-color);
             margin-top: 16px;
             margin-bottom: 8px;
-            scroll-margin-block-end: var(--half-contents-height);
         }
 
         strong {

frontend/app/element/markdown.tsx

@@ -8,13 +8,12 @@ import * as util from "@/util/util";
 import { useAtomValueSafe } from "@/util/util";
 import { clsx } from "clsx";
 import { Atom } from "jotai";
-import { OverlayScrollbarsComponent } from "overlayscrollbars-react";
-import React, { CSSProperties, useCallback, useMemo, useRef } from "react";
+import { OverlayScrollbarsComponent, OverlayScrollbarsComponentRef } from "overlayscrollbars-react";
+import React, { CSSProperties, useRef } from "react";
 import ReactMarkdown from "react-markdown";
 import rehypeRaw from "rehype-raw";
 import RemarkFlexibleToc, { TocItem } from "remark-flexible-toc";
 import remarkGfm from "remark-gfm";
-import { useHeight } from "../hook/useHeight";
 import "./markdown.less";
 
 const Link = ({ href, children }: { href: string; children: React.ReactNode }) => {
@@ -148,23 +147,23 @@ const Markdown = ({ text, textAtom, showTocAtom, style, className, resolveOpts,
     const textAtomValue = useAtomValueSafe(textAtom);
     const tocRef = useRef<TocItem[]>([]);
     const showToc = useAtomValueSafe(showTocAtom) ?? false;
-    const contentsRef = useRef<HTMLDivElement>(null);
-    const contentsHeight = useHeight(contentsRef, 200);
+    const contentsOsRef = useRef<OverlayScrollbarsComponentRef>(null);
 
-    const halfContentsHeight = useMemo(() => {
-        return `${contentsHeight / 2}px`;
-    }, [contentsHeight]);
-
-    const onTocClick = useCallback((data: string) => {
-        if (contentsRef.current) {
-            const headings = contentsRef.current.getElementsByClassName("heading");
+    const onTocClick = (data: string) => {
+        if (contentsOsRef.current && contentsOsRef.current.osInstance()) {
+            const { viewport } = contentsOsRef.current.osInstance().elements();
+            const headings = viewport.getElementsByClassName("heading");
             for (const heading of headings) {
                 if (heading.textContent === data) {
-                    heading.scrollIntoView({ inline: "nearest", block: "end" });
+                    const headingBoundingRect = heading.getBoundingClientRect();
+                    const viewportBoundingRect = viewport.getBoundingClientRect();
+                    const headingTop = headingBoundingRect.top - viewportBoundingRect.top;
+                    viewport.scrollBy({ top: headingTop });
+                    break;
                 }
             }
         }
-    }, []);
+    };
 
     const markdownComponents = {
         a: Link,
@@ -180,30 +179,19 @@ const Markdown = ({ text, textAtom, showTocAtom, style, className, resolveOpts,
         pre: (props: any) => <CodeBlock {...props} onClickExecute={onClickExecute} />,
     };
 
-    const toc = useMemo(() => {
-        if (showToc && tocRef.current.length > 0) {
-            return tocRef.current.map((item) => {
-                return (
-                    <a
-                        key={item.href}
-                        className="toc-item"
-                        style={{ "--indent-factor": item.depth } as CSSProperties}
-                        onClick={() => onTocClick(item.value)}
-                    >
-                        {item.value}
-                    </a>
-                );
-            });
-        }
-    }, [showToc, tocRef]);
+    // const toc = useMemo(() => {
+    //     if (showToc && tocRef.current.length > 0) {
+    //         return
+    //     }
+    // }, [showToc, tocRef]);
 
     text = textAtomValue ?? text;
 
     return (
-        <div className={clsx("markdown", className)} style={style} ref={contentsRef}>
+        <div className={clsx("markdown", className)} style={style}>
             <OverlayScrollbarsComponent
+                ref={contentsOsRef}
                 className="content"
-                style={{ "--half-contents-height": halfContentsHeight } as CSSProperties}
                 options={{ scrollbars: { autoHide: "leave" } }}
             >
                 <ReactMarkdown
@@ -218,7 +206,18 @@ const Markdown = ({ text, textAtom, showTocAtom, style, className, resolveOpts,
                 <OverlayScrollbarsComponent className="toc" options={{ scrollbars: { autoHide: "leave" } }}>
                     <div className="toc-inner">
                         <h4>Table of Contents</h4>
-                        {toc}
+                        {tocRef.current.map((item) => {
+                            return (
+                                <a
+                                    key={item.href}
+                                    className="toc-item"
+                                    style={{ "--indent-factor": item.depth } as CSSProperties}
+                                    onClick={() => onTocClick(item.value)}
+                                >
+                                    {item.value}
+                                </a>
+                            );
+                        })}
                     </div>
                 </OverlayScrollbarsComponent>
             )}