Track QWord current page in status bar

src/features/qword/QWord.tsx

@@ -45,6 +45,7 @@ interface QWordProps {
 }
 
 export interface QWordStatus {
+  currentPage: number;
   pageCount: number;
   wordCount: number;
 }
@@ -155,14 +156,42 @@ function pageHeightFromStyles(element: HTMLElement) {
   return Number.isFinite(pageHeight) && pageHeight > 0 ? pageHeight : defaultPageViewHeight;
 }
 
+export function qwordCurrentPageFromViewport(input: { stageTop: number; paperTop: number; pageHeight: number; pageCount: number; zoom: number }) {
+  const pageCount = Math.max(1, input.pageCount);
+  const zoom = Number.isFinite(input.zoom) && input.zoom > 0 ? input.zoom : 1;
+  const visualPageHeight = Math.max(1, input.pageHeight * zoom);
+  const visiblePaperOffset = Math.max(0, input.stageTop - input.paperTop);
+  return Math.min(pageCount, Math.max(1, Math.floor(visiblePaperOffset / visualPageHeight) + 1));
+}
+
 export function QWord({ document, zoom = 100, onChange, onStatusChange }: QWordProps) {
+  const stageRef = useRef<HTMLElement>(null);
   const editorRef = useRef<HTMLDivElement>(null);
   const fileInputRef = useRef<HTMLInputElement>(null);
   const imageInputRef = useRef<HTMLInputElement>(null);
-  const [pageView, setPageView] = useState({ count: 1, height: defaultPageViewHeight });
+  const [pageView, setPageView] = useState({ count: 1, current: 1, height: defaultPageViewHeight });
   const wordCount = useMemo(() => countWords(document.html), [document.html]);
   const stageStyle = { "--qword-zoom": String(zoom / 100) } as CSSProperties;
 
+  function currentPageFromStage(pageCount: number, pageHeight: number) {
+    const stage = stageRef.current;
+    const editor = editorRef.current;
+    if (!stage || !editor) {
+      return 1;
+    }
+
+    const stageRect = stage.getBoundingClientRect();
+    const paperRect = editor.getBoundingClientRect();
+    const currentZoom = Number.parseFloat(window.getComputedStyle(stage).getPropertyValue("--qword-zoom"));
+    return qwordCurrentPageFromViewport({
+      stageTop: stageRect.top,
+      paperTop: paperRect.top,
+      pageHeight,
+      pageCount,
+      zoom: Number.isFinite(currentZoom) ? currentZoom : 1
+    });
+  }
+
   function refreshPageView() {
     window.requestAnimationFrame(() => {
       const editor = editorRef.current;
@@ -172,7 +201,10 @@ export function QWord({ document, zoom = 100, onChange, onStatusChange }: QWordP
 
       const height = pageHeightFromStyles(editor);
       const count = Math.max(1, Math.ceil(editor.scrollHeight / height));
-      setPageView((current) => (current.count === count && current.height === height ? current : { count, height }));
+      const currentPage = currentPageFromStage(count, height);
+      setPageView((current) =>
+        current.count === count && current.height === height && current.current === currentPage ? current : { count, current: currentPage, height }
+      );
     });
   }
 
@@ -189,8 +221,8 @@ export function QWord({ document, zoom = 100, onChange, onStatusChange }: QWordP
   }, [document.html, zoom]);
 
   useLayoutEffect(() => {
-    onStatusChange?.({ pageCount: pageView.count, wordCount });
-  }, [onStatusChange, pageView.count, wordCount]);
+    onStatusChange?.({ currentPage: pageView.current, pageCount: pageView.count, wordCount });
+  }, [onStatusChange, pageView.count, pageView.current, wordCount]);
 
   function runCommand(command: string, value?: string) {
     editorRef.current?.focus();
@@ -371,7 +403,7 @@ export function QWord({ document, zoom = 100, onChange, onStatusChange }: QWordP
 
   return (
     <div className="editor-layout qword-layout">
-      <section className="document-stage" style={stageStyle} aria-label="Редактор QWord">
+      <section ref={stageRef} className="document-stage" style={stageStyle} onScroll={refreshPageView} aria-label="Редактор QWord">
         <div className="module-toolbar word-module-toolbar">
           <input
             ref={fileInputRef}