Introducting ScrollSpy component

Signed-off-by: Alex Andreev <alex.andreev.email@gmail.com>

src/renderer/components/+preferences/preferences.tsx

@@ -38,9 +38,9 @@ export class Preferences extends React.Component {
         contentGaps={false}
         header={header}
       >
-        <section>
+        <section id="application">
           <h1>Application</h1>
-          <section>
+          <section id="appearance">
             <h2>Appearance</h2>
             <SubTitle title="Theme"/>
             <Select

src/renderer/components/layout/page-layout.tsx

@@ -5,6 +5,7 @@ import { observer } from "mobx-react";
 import { autobind, cssNames, IClassName } from "../../utils";
 import { Icon } from "../icon";
 import { navigation } from "../../navigation";
+import { ScrollSpy } from "../scroll-spy/scroll-spy";
 
 export interface PageLayoutProps extends React.DOMAttributes<any> {
   className?: IClassName;
@@ -63,33 +64,35 @@ export class PageLayout extends React.Component<PageLayoutProps> {
     const className = cssNames("PageLayout", { showOnTop, showNavigation }, this.props.className);
 
     return (
-      <div {...elemProps} className={className}>
-        <div className={cssNames("header flex gaps align-center", headerClass)}>
-          {header}
-          {provideBackButtonNavigation && (
-            <Icon
-              big material="close"
-              className="back box right"
-              onClick={this.back}
-            />
-          )}
-        </div>
-        <div className="content-scrollable-area">
-          <div className="content-wrapper">
-            { showNavigation && (
-              <div className="content-navigation">
-                <ul>
-                  <li>Section 1</li>
-                  <li>Section 2</li>
-                </ul>
-              </div>
+      <ScrollSpy render={navigation => (
+        <div {...elemProps} className={className}>
+          <div className={cssNames("header flex gaps align-center", headerClass)}>
+            {header}
+            {provideBackButtonNavigation && (
+              <Icon
+                big material="close"
+                className="back box right"
+                onClick={this.back}
+              />
             )}
-            <div className={cssNames("content", contentGaps && "flex column gaps", contentClass)}>
-              {children}
+          </div>
+          <div className="content-scrollable-area">
+            <div className="content-wrapper">
+              { showNavigation && (
+                <div className="content-navigation">
+                  <ul>
+                    <li>Section 1</li>
+                    <li>Section 2</li>
+                    <li>{navigation.toString()}</li>
+                  </ul>
+                </div>
+              )}
+              <div className={cssNames("content", contentGaps && "flex column gaps", contentClass)}>
+                {children}
+              </div>
             </div>
           </div>
         </div>
-      </div>
-    );
+      )} />);
   }
 }

src/renderer/components/scroll-spy/scroll-spy.tsx

@@ -0,0 +1,59 @@
+import React, { useEffect } from "react";
+
+interface Props extends React.DOMAttributes<any> {
+  render: (data: any) => any
+}
+
+export function ScrollSpy(props: Props) {
+  let navigationData: any = {};
+
+  const updateNavigation = () => {
+    const firstSection = document.querySelector("section");
+
+    if (!firstSection) {
+      throw new Error("No <section/> tag founded! Content should be placed inside <section></section> elements to activate navigation.");
+    }
+
+    navigationData = {
+      id: "root",
+      name: "Parent",
+      children: getNavigation(firstSection.parentElement)
+    };
+
+    console.log(navigationData);
+  };
+
+  const getNavigation = (element: Element) => {
+    const sections = element.querySelectorAll(":scope > section"); // Searching only direct children of an element. Impossible without :scope
+    const children: any = [];
+
+    sections.forEach(section => {
+      const id = section.getAttribute("id");
+      const name = section.querySelector(":first-child").textContent;
+
+      if (!name || !id) {
+        return;
+      }
+
+      children.push({
+        id,
+        name,
+        children: getNavigation(section)
+      });
+    });
+
+    return children;
+  };
+
+  useEffect(() => {
+    updateNavigation();
+    // element.current.addEventListener("scroll", updateActive);
+    // TODO: Attach on dom change event
+  }, []);
+
+  return (
+    <div className="ScrollSpy">
+      {props.render(navigationData)}
+    </div>
+  );
+}