From a26411f2a61f1f72baa8f2af4358dfb482f14253 Mon Sep 17 00:00:00 2001
From: Andrey Babushkin <55714097+reyand43@users.noreply.github.com>
Date: Tue, 22 Apr 2025 17:59:25 +0200
Subject: [PATCH] Css batching (#3326)

* tracker: initial css inlining functionality

* tracker: add tests, adjust sheet id, stagger rule sending

* ui: rereoute custom html component fragments

* removed sorting

---------

Co-authored-by: nick-delirium <nikita@openreplay.com>
---
 frontend/app/player/web/MessageLoader.ts      |  24 +-
 .../app/player/web/managers/DOM/DOMManager.ts |  50 ++--
 tracker/tracker/package.json                  |   2 +-
 tracker/tracker/src/main/app/index.ts         |   5 +-
 .../src/main/app/observer/cssInliner.ts       |  87 +++++++
 .../tracker/src/main/app/observer/observer.ts |  54 ++++-
 .../src/main/app/observer/top_observer.ts     |   9 +
 tracker/tracker/src/tests/cssInliner.test.ts  | 229 ++++++++++++++++++
 8 files changed, 421 insertions(+), 39 deletions(-)
 create mode 100644 tracker/tracker/src/main/app/observer/cssInliner.ts
 create mode 100644 tracker/tracker/src/tests/cssInliner.test.ts

diff --git a/frontend/app/player/web/MessageLoader.ts b/frontend/app/player/web/MessageLoader.ts
index 6ef936b09..cf9e2a6f6 100644
--- a/frontend/app/player/web/MessageLoader.ts
+++ b/frontend/app/player/web/MessageLoader.ts
@@ -352,25 +352,25 @@ const DOMMessages = [
 function brokenDomSorter(m1: PlayerMsg, m2: PlayerMsg) {
   if (m1.time !== m2.time) return m1.time - m2.time;
 
-  if (m1.tp === MType.CreateDocument && m2.tp !== MType.CreateDocument)
-    return -1;
-  if (m1.tp !== MType.CreateDocument && m2.tp === MType.CreateDocument)
-    return 1;
+  // if (m1.tp === MType.CreateDocument && m2.tp !== MType.CreateDocument)
+  //   return -1;
+  // if (m1.tp !== MType.CreateDocument && m2.tp === MType.CreateDocument)
+  //   return 1;
 
-  if (m1.tp === MType.RemoveNode)
-    return 1;
-  if (m2.tp === MType.RemoveNode)
-    return -1;
+  // if (m1.tp === MType.RemoveNode)
+  //   return 1;
+  // if (m2.tp === MType.RemoveNode)
+  //   return -1;
 
-  const m1IsDOM = DOMMessages.includes(m1.tp);
-  const m2IsDOM = DOMMessages.includes(m2.tp);
+  // const m1IsDOM = DOMMessages.includes(m1.tp);
+  // const m2IsDOM = DOMMessages.includes(m2.tp);
   // if (m1IsDOM && m2IsDOM) {
   //   // @ts-ignore DOM msg has id but checking for 'id' in m is expensive
   //   return m1.id - m2.id;
   // }
 
-  if (m1IsDOM && !m2IsDOM) return -1;
-  if (!m1IsDOM && m2IsDOM) return 1;
+  // if (m1IsDOM && !m2IsDOM) return -1;
+  // if (!m1IsDOM && m2IsDOM) return 1;
 
   return 0;
 }
diff --git a/frontend/app/player/web/managers/DOM/DOMManager.ts b/frontend/app/player/web/managers/DOM/DOMManager.ts
index 1d15d050c..76e194916 100644
--- a/frontend/app/player/web/managers/DOM/DOMManager.ts
+++ b/frontend/app/player/web/managers/DOM/DOMManager.ts
@@ -52,6 +52,8 @@ export default class DOMManager extends ListWalker<Message> {
   /** required to keep track of iframes, frameId : vnodeId */
   private readonly iframeRoots: Record<number, number> = {};
 
+  private shadowRootParentMap: Map<number, number> = new Map();
+
   /** Constructed StyleSheets https://developer.mozilla.org/en-US/docs/Web/API/Document/adoptedStyleSheets
    * as well as <style> tag owned StyleSheets
    */
@@ -163,6 +165,11 @@ export default class DOMManager extends ListWalker<Message> {
   }
 
   public getNode(id: number) {
+    const mappedId = this.shadowRootParentMap.get(id);
+    if (mappedId !== undefined) {
+      // If this is a shadow root ID, return the parent element instead
+      return this.vElements.get(mappedId);
+    }
     return this.vElements.get(id) || this.vTexts.get(id);
   }
 
@@ -171,24 +178,21 @@ export default class DOMManager extends ListWalker<Message> {
     id: number;
     index: number;
   }): void {
-    const { parentID, id, index } = msg;
+    let { parentID, id, index } = msg;
+
+    // Check if parentID is a shadow root, and get the real parent element if so
+    const actualParentID = this.shadowRootParentMap.get(parentID);
+    if (actualParentID !== undefined) {
+      parentID = actualParentID;
+    }
+
     const child = this.vElements.get(id) || this.vTexts.get(id);
     if (!child) {
       logger.error('Insert error. Node not found', id);
       return;
     }
+
     const parent = this.vElements.get(parentID) || this.olVRoots.get(parentID);
-    if ('tagName' in child && child.tagName === 'BODY') {
-      const spriteMap = new VSpriteMap(
-        'svg',
-        true,
-        Number.MAX_SAFE_INTEGER - 100,
-        Number.MAX_SAFE_INTEGER - 100,
-      );
-      spriteMap.node.setAttribute('id', 'OPENREPLAY_SPRITES_MAP');
-      spriteMap.node.setAttribute('style', 'display: none;');
-      child.insertChildAt(spriteMap, Number.MAX_SAFE_INTEGER - 100);
-    }
     if (!parent) {
       logger.error(
         `${id} Insert error. Parent vNode ${parentID} not found`,
@@ -305,9 +309,14 @@ export default class DOMManager extends ListWalker<Message> {
         this.removeAutocomplete(vElem);
         return;
       }
-      case MType.MoveNode:
+      case MType.MoveNode: {
+        // if the parent ID is in shadow root map -> custom elements case
+        if (this.shadowRootParentMap.has(msg.parentID)) {
+          msg.parentID = this.shadowRootParentMap.get(msg.parentID)!;
+        }
         this.insertNode(msg);
         return;
+      }
       case MType.RemoveNode: {
         const vChild = this.vElements.get(msg.id) || this.vTexts.get(msg.id);
         if (!vChild) {
@@ -440,6 +449,19 @@ export default class DOMManager extends ListWalker<Message> {
           logger.error('CreateIFrameDocument: Node not found', msg);
           return;
         }
+
+        // shadow DOM for a custom element
+        const isCustomElement = vElem.tagName.includes('-');
+        const isNotActualIframe = !["IFRAME", "FRAME"].includes(vElem.tagName.toUpperCase());
+        const isLikelyShadowRoot = isCustomElement && isNotActualIframe;
+
+        if (isLikelyShadowRoot) {
+          // Store the mapping but don't create the actual shadow root
+          this.shadowRootParentMap.set(msg.id, msg.frameID);
+          return;
+        }
+
+        // Real iframes
         if (this.iframeRoots[msg.frameID] && !this.olVRoots.has(msg.id)) {
           this.olVRoots.delete(this.iframeRoots[msg.frameID]);
         }
@@ -452,7 +474,7 @@ export default class DOMManager extends ListWalker<Message> {
       case MType.AdoptedSsInsertRule: {
         const styleSheet = this.olStyleSheets.get(msg.sheetID);
         if (!styleSheet) {
-          logger.warn('No stylesheet was created for ', msg);
+          logger.warn('No stylesheet was created for ', msg, this.olStyleSheets);
           return;
         }
         insertRule(styleSheet, msg);
diff --git a/tracker/tracker/package.json b/tracker/tracker/package.json
index 901dae71a..55d0cdbc8 100644
--- a/tracker/tracker/package.json
+++ b/tracker/tracker/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@openreplay/tracker",
   "description": "The OpenReplay tracker main package",
-  "version": "16.1.4",
+  "version": "16.2.0",
   "keywords": [
     "logging",
     "replay"
diff --git a/tracker/tracker/src/main/app/index.ts b/tracker/tracker/src/main/app/index.ts
index 7684cefd8..89de2be40 100644
--- a/tracker/tracker/src/main/app/index.ts
+++ b/tracker/tracker/src/main/app/index.ts
@@ -319,13 +319,14 @@ export default class App {
       __save_canvas_locally: false,
       localStorage: null,
       sessionStorage: null,
-      disableStringDict: false,
+      disableStringDict: true,
       forceSingleTab: false,
       assistSocketHost: '',
       fixedCanvasScaling: false,
       disableCanvas: false,
       captureIFrames: true,
       disableSprites: false,
+      inlineRemoteCss: true,
       obscureTextEmails: true,
       obscureTextNumbers: false,
       crossdomain: {
@@ -820,7 +821,7 @@ export default class App {
     this.debug.error('OpenReplay error: ', context, e)
   }
 
-  send(message: Message, urgent = false): void {
+  send = (message: Message, urgent = false): void => {
     if (this.activityState === ActivityState.NotActive) {
       return
     }
diff --git a/tracker/tracker/src/main/app/observer/cssInliner.ts b/tracker/tracker/src/main/app/observer/cssInliner.ts
new file mode 100644
index 000000000..df0133dba
--- /dev/null
+++ b/tracker/tracker/src/main/app/observer/cssInliner.ts
@@ -0,0 +1,87 @@
+export function inlineRemoteCss(
+  node: HTMLLinkElement,
+  id: number,
+  baseHref: string,
+  getNextID: () => number,
+  insertRule: (id: number, cssText: string, index: number, baseHref: string) => any[],
+  addOwner: (sheetId: number, ownerId: number) => any[],
+) {
+  const sheet = node.sheet;
+  const sheetId = getNextID()
+  addOwner(sheetId, id);
+
+  const processRules = (rules: CSSRuleList) => {
+    if (rules.length) {
+      setTimeout(() => {
+        for (let i = 0; i < rules.length; i++) {
+          const rule = rules[i];
+          insertRule(sheetId, rule.cssText, i, baseHref);
+        }
+      }, 0)
+    }
+  };
+
+  const processCssText = (cssText: string) => {
+    cssText = cssText.replace(/\/\*[\s\S]*?\*\//g, '');
+
+    const ruleTexts: string[] = [];
+    let depth = 0;
+    let currentRule = '';
+
+    for (let i = 0; i < cssText.length; i++) {
+      const char = cssText[i];
+
+      if (char === '{') {
+        depth++;
+      } else if (char === '}') {
+        depth--;
+        if (depth === 0) {
+          currentRule += char;
+          ruleTexts.push(currentRule.trim());
+          currentRule = '';
+          continue;
+        }
+      }
+
+      currentRule += char;
+    }
+
+    for (let i = 0; i < ruleTexts.length; i++) {
+      const ruleText = ruleTexts[i];
+      insertRule(sheetId, ruleText, i, baseHref);
+    }
+  };
+
+  if (sheet) {
+    try {
+      const rules = sheet.cssRules;
+      processRules(rules);
+    } catch (e) {
+      const href = node.href;
+      if (href) {
+        fetch(href)
+          .then(response => {
+            if (!response.ok) {
+              throw new Error(`Failed to fetch CSS: ${response.status}`);
+            }
+            return response.text();
+          })
+          .then(cssText => {
+            processCssText(cssText);
+          })
+          .catch(error => {
+            console.error(`Failed to fetch or process CSS from ${href}:`, error);
+          });
+      }
+    }
+  } else if (node.href) {
+    fetch(node.href)
+      .then(response => response.text())
+      .then(cssText => {
+        processCssText(cssText);
+      })
+      .catch(error => {
+        console.error(`Failed to fetch CSS from ${node.href}:`, error);
+      });
+  }
+}
\ No newline at end of file
diff --git a/tracker/tracker/src/main/app/observer/observer.ts b/tracker/tracker/src/main/app/observer/observer.ts
index 054159631..733eeeb13 100644
--- a/tracker/tracker/src/main/app/observer/observer.ts
+++ b/tracker/tracker/src/main/app/observer/observer.ts
@@ -10,6 +10,8 @@ import {
   RemoveNode,
   UnbindNodes,
   SetNodeAttribute,
+  AdoptedSSInsertRuleURLBased,
+  AdoptedSSAddOwner
 } from '../messages.gen.js'
 import App from '../index.js'
 import {
@@ -21,6 +23,8 @@ import {
   hasTag,
   isCommentNode,
 } from '../guards.js'
+import { inlineRemoteCss } from './cssInliner.js'
+import { nextID } from "../../modules/constructedStyleSheets.js";
 
 const iconCache = {}
 const svgUrlCache = {}
@@ -47,7 +51,7 @@ async function parseUseEl(
         <svg xmlns="http://www.w3.org/2000/svg" viewBox="${symbol.getAttribute('viewBox') || '0 0 24 24'}">
           ${symbol.innerHTML}
         </svg>
-      `.trim()
+      `
 
         iconCache[symbolId] = inlineSvg
 
@@ -115,7 +119,7 @@ async function parseUseEl(
         <svg xmlns="http://www.w3.org/2000/svg" viewBox="${symbol.getAttribute('viewBox') || '0 0 24 24'}">
           ${symbol.innerHTML}
         </svg>
-      `.trim()
+      `
 
       iconCache[symbolId] = inlineSvg
 
@@ -188,13 +192,20 @@ export default abstract class Observer {
   private readonly attributesMap: Map<number, Set<string>> = new Map()
   private readonly textSet: Set<number> = new Set()
   private readonly disableSprites: boolean = false
+  /**
+   * this option means that, instead of using link element with href to load css,
+   * we will try to parse the css text instead and send it as css rules set
+   * can (and will) affect performance
+   * */
+  private readonly inlineRemoteCss: boolean = false
   private readonly domParser = new DOMParser()
   constructor(
     protected readonly app: App,
     protected readonly isTopContext = false,
-    options: { disableSprites: boolean } = { disableSprites: false },
+    options: { disableSprites: boolean, inlineRemoteCss: boolean } = { disableSprites: false, inlineRemoteCss: false },
   ) {
     this.disableSprites = options.disableSprites
+    this.inlineRemoteCss = options.inlineRemoteCss
     this.observer = createMutationObserver(
       this.app.safe((mutations) => {
         for (const mutation of mutations) {
@@ -280,10 +291,12 @@ export default abstract class Observer {
         let removed = 0
         const totalBeforeRemove = this.app.nodes.getNodeCount()
 
+        const contentDocument = iframe.contentDocument;
+        const nodesUnregister = this.app.nodes.unregisterNode.bind(this.app.nodes);
         while (walker.nextNode()) {
-          if (!iframe.contentDocument.contains(walker.currentNode)) {
+          if (!contentDocument.contains(walker.currentNode)) {
             removed += 1
-            this.app.nodes.unregisterNode(walker.currentNode)
+            nodesUnregister(walker.currentNode)
           }
         }
 
@@ -297,7 +310,7 @@ export default abstract class Observer {
 
   private sendNodeAttribute(id: number, node: Element, name: string, value: string | null): void {
     if (isSVGElement(node)) {
-      if (name.substring(0, 6) === 'xlink:') {
+      if (name.startsWith('xlink:')) {
         name = name.substring(6)
       }
       if (value === null) {
@@ -351,6 +364,24 @@ export default abstract class Observer {
       return
     }
     if (name === 'style' || (name === 'href' && hasTag(node, 'link'))) {
+      if ('rel' in node && node.rel === 'stylesheet' && this.inlineRemoteCss) {
+        setTimeout(() => {
+          inlineRemoteCss(
+            // @ts-ignore
+          node,
+          id,
+          this.app.getBaseHref(),
+          nextID,
+            (id: number, cssText: string, index: number, baseHref: string) => {
+              this.app.send(AdoptedSSInsertRuleURLBased(id, cssText, index, baseHref))
+            },
+            (sheetId: number, ownerId: number) => {
+              this.app.send(AdoptedSSAddOwner(sheetId, ownerId))
+            }
+          )
+        }, 0)
+        return
+      }
       this.app.send(SetNodeAttributeURLBased(id, name, value, this.app.getBaseHref()))
       return
     }
@@ -506,8 +537,11 @@ export default abstract class Observer {
             ;(el as HTMLElement | SVGElement).style.width = `${width}px`
             ;(el as HTMLElement | SVGElement).style.height = `${height}px`
           }
-
-          this.app.send(CreateElementNode(id, parentID, index, el.tagName, isSVGElement(node)))
+          if ('rel' in el && el.rel === 'stylesheet' && this.inlineRemoteCss) {
+            this.app.send(CreateElementNode(id, parentID, index, 'STYLE', false))
+          } else {
+            this.app.send(CreateElementNode(id, parentID, index, el.tagName, isSVGElement(node)))
+          }
         }
         for (let i = 0; i < el.attributes.length; i++) {
           const attr = el.attributes[i]
@@ -554,12 +588,12 @@ export default abstract class Observer {
   }
   private commitNodes(isStart = false): void {
     let node
-    this.recents.forEach((type, id) => {
+    for (const [id, type] of this.recents.entries()) {
       this.commitNode(id)
       if (type === RecentsType.New && (node = this.app.nodes.getNode(id))) {
         this.app.nodes.callNodeCallbacks(node, isStart)
       }
-    })
+    }
     this.clear()
   }
 
diff --git a/tracker/tracker/src/main/app/observer/top_observer.ts b/tracker/tracker/src/main/app/observer/top_observer.ts
index c5f623170..f7fdea6fc 100644
--- a/tracker/tracker/src/main/app/observer/top_observer.ts
+++ b/tracker/tracker/src/main/app/observer/top_observer.ts
@@ -12,6 +12,14 @@ import { IN_BROWSER, hasOpenreplayAttribute, canAccessIframe } from '../../utils
 export interface Options {
   captureIFrames: boolean
   disableSprites: boolean
+  /**
+   * with this option instead of using link element with href to load css,
+   * we will try to parse the css text instead and send it as css rules set
+   * can (and probably will) affect performance to certain degree,
+   * especially if the css itself is crossdomain
+   * @default false
+   * */
+  inlineRemoteCss: boolean
 }
 
 type Context = Window & typeof globalThis
@@ -29,6 +37,7 @@ export default class TopObserver extends Observer {
       {
         captureIFrames: true,
         disableSprites: false,
+        inlineRemoteCss: false,
       },
       params.options,
     )
diff --git a/tracker/tracker/src/tests/cssInliner.test.ts b/tracker/tracker/src/tests/cssInliner.test.ts
new file mode 100644
index 000000000..0e6936032
--- /dev/null
+++ b/tracker/tracker/src/tests/cssInliner.test.ts
@@ -0,0 +1,229 @@
+// @ts-nocheck
+
+const mockNextID = jest.fn().mockReturnValue(123);
+const mockAdoptedSSInsertRuleURLBased = jest.fn();
+const mockAdoptedSSAddOwner = jest.fn();
+
+global.fetch = jest.fn();
+
+import { inlineRemoteCss } from '../main/app/observer/cssInliner';
+import { describe, test, expect, jest, beforeEach } from '@jest/globals';
+
+describe('inlineRemoteCss', () => {
+  let mockNode;
+
+  beforeEach(() => {
+    jest.clearAllMocks();
+    mockAdoptedSSInsertRuleURLBased.mockImplementation((id, cssText, index, baseHref) => ({
+      type: "AdoptedSSInsertRuleURLBased",
+      id,
+      cssText,
+      index,
+      baseHref
+    }));
+
+    mockAdoptedSSAddOwner.mockImplementation((sheetId, ownerId) => ({
+      type: "AdoptedSSAddOwner",
+      sheetId,
+      ownerId
+    }));
+    mockNode = document.createElement('link');
+    Object.defineProperty(mockNode, 'sheet', {
+      configurable: true,
+      value: null,
+      writable: true
+    });
+    global.fetch.mockResolvedValue({
+      ok: true,
+      text: () => Promise.resolve('body { color: red; }')
+    });
+  });
+
+  test('should process rules directly if node has a sheet with accessible rules', () => {
+    jest.useFakeTimers();
+    const mockRule = { cssText: 'body { color: red; }' };
+    const mockRules = [mockRule];
+    Object.defineProperty(mockRules, 'length', { value: 1 });
+
+    const mockSheet = { cssRules: mockRules };
+    Object.defineProperty(mockNode, 'sheet', {
+      get: () => mockSheet
+    });
+    inlineRemoteCss(mockNode, 456, 'http://example.com', mockNextID,mockAdoptedSSInsertRuleURLBased,mockAdoptedSSAddOwner);
+    jest.runAllTimers();
+    expect(mockNextID).toHaveBeenCalled();
+    expect(mockAdoptedSSAddOwner).toHaveBeenCalledWith(123, 456);
+    expect(mockAdoptedSSInsertRuleURLBased).toHaveBeenCalledWith(456, 'body { color: red; }', 0, 'http://example.com');
+    jest.useRealTimers();
+  });
+
+  test('should fetch CSS if accessing rules throws an error', () => {
+    mockNode.href = 'http://example.com/style.css';
+    const mockSheet = {};
+    Object.defineProperty(mockSheet, 'cssRules', {
+      get: () => { throw new Error('CORS error'); }
+    });
+    Object.defineProperty(mockNode, 'sheet', {
+      get: () => mockSheet
+    });
+    inlineRemoteCss(mockNode, 456,  'http://example.com',mockNextID,mockAdoptedSSInsertRuleURLBased, mockAdoptedSSAddOwner);
+    expect(global.fetch).toHaveBeenCalledWith('http://example.com/style.css');
+  });
+
+  test('should handle successful fetch and process CSS text', async () => {
+    mockNode.href = 'http://example.com/style.css';
+    const mockSheet = {};
+    Object.defineProperty(mockSheet, 'cssRules', {
+      get: () => { throw new Error('CORS error'); }
+    });
+    Object.defineProperty(mockNode, 'sheet', {
+      get: () => mockSheet
+    });
+    inlineRemoteCss(mockNode, 456,  'http://example.com',mockNextID,mockAdoptedSSInsertRuleURLBased, mockAdoptedSSAddOwner);
+    await new Promise(process.nextTick);
+    expect(mockNextID).toHaveBeenCalled();
+    expect(mockAdoptedSSAddOwner).toHaveBeenCalledWith(123, 456);
+    expect(mockAdoptedSSInsertRuleURLBased).toHaveBeenCalledWith(123, 'body { color: red; }', 0, 'http://example.com');
+  });
+
+  test('should fetch CSS if node has no sheet but has href', () => {
+    Object.defineProperty(mockNode, 'sheet', {
+      get: () => null
+    });
+    mockNode.href = 'http://example.com/style.css';
+    inlineRemoteCss(mockNode, 456,  'http://example.com',mockNextID,mockAdoptedSSInsertRuleURLBased, mockAdoptedSSAddOwner);
+    expect(global.fetch).toHaveBeenCalledWith('http://example.com/style.css');
+  });
+
+  test('should handle complex CSS with multiple rules', async () => {
+    Object.defineProperty(mockNode, 'sheet', {
+      get: () => null
+    });
+    mockNode.href = 'http://example.com/style.css';
+    const complexCss = `
+      body { color: red; }
+      .class { background: blue; }
+      @media (max-width: 600px) { body { font-size: 14px; } }
+    `;
+    global.fetch.mockResolvedValue({
+      ok: true,
+      text: () => Promise.resolve(complexCss)
+    });
+    inlineRemoteCss(mockNode, 456, 'http://example.com',mockNextID,mockAdoptedSSInsertRuleURLBased, mockAdoptedSSAddOwner);
+    await new Promise(process.nextTick);
+    expect(mockNextID).toHaveBeenCalled();
+    expect(mockAdoptedSSAddOwner).toHaveBeenCalledWith(123, 456);
+    expect(mockAdoptedSSInsertRuleURLBased).toHaveBeenCalledWith(
+      123, 'body { color: red; }', 0, 'http://example.com'
+    );
+    expect(mockAdoptedSSInsertRuleURLBased).toHaveBeenCalledWith(
+      123, '.class { background: blue; }', 1, 'http://example.com'
+    );
+    expect(mockAdoptedSSInsertRuleURLBased).toHaveBeenCalledWith(
+      123, '@media (max-width: 600px) { body { font-size: 14px; } }', 2, 'http://example.com'
+    );
+  });
+
+  test('should handle CSS with comments', async () => {
+    Object.defineProperty(mockNode, 'sheet', {
+      get: () => null
+    });
+    mockNode.href = 'http://example.com/style.css';
+    const cssWithComments = `
+      /* This is a comment */
+      body { color: red; }
+      /* Another comment */
+      .class { background: blue; }
+    `;
+    global.fetch.mockResolvedValue({
+      ok: true,
+      text: () => Promise.resolve(cssWithComments)
+    });
+    inlineRemoteCss(mockNode, 456,  'http://example.com',mockNextID,mockAdoptedSSInsertRuleURLBased, mockAdoptedSSAddOwner);
+    await new Promise(process.nextTick);
+    expect(mockNextID).toHaveBeenCalled();
+    expect(mockAdoptedSSAddOwner).toHaveBeenCalledWith(123, 456);
+    expect(mockAdoptedSSInsertRuleURLBased).toHaveBeenCalledWith(
+      123, 'body { color: red; }', 0, 'http://example.com'
+    );
+    expect(mockAdoptedSSInsertRuleURLBased).toHaveBeenCalledWith(
+      123, '.class { background: blue; }', 1, 'http://example.com'
+    );
+  });
+
+  test('should handle failed fetch', async () => {
+    Object.defineProperty(mockNode, 'sheet', {
+      get: () => null
+    });
+    mockNode.href = 'http://example.com/style.css';
+    global.fetch.mockRejectedValue(new Error('Network error'));
+    const consoleSpy = jest.spyOn(console, 'error').mockImplementation();
+    inlineRemoteCss(mockNode, 456,  'http://example.com',mockNextID,mockAdoptedSSInsertRuleURLBased, mockAdoptedSSAddOwner);
+    await new Promise(process.nextTick);
+    expect(consoleSpy).toHaveBeenCalledWith(
+      expect.stringContaining('Failed to fetch CSS from http://example.com/style.css:'),
+      expect.any(Error)
+    );
+    consoleSpy.mockRestore();
+  });
+
+  test('should handle non-OK response from fetch', async () => {
+    Object.defineProperty(mockNode, 'sheet', {
+      get: () => null
+    });
+    mockNode.href = 'http://example.com/style.css';
+    global.fetch.mockResolvedValue({
+      ok: false,
+      status: 404,
+      text: () => Promise.resolve('')
+    });
+
+    const consoleSpy = jest.spyOn(console, 'error').mockImplementation();
+
+    inlineRemoteCss(mockNode, 456,  'http://example.com',mockNextID,mockAdoptedSSInsertRuleURLBased, mockAdoptedSSAddOwner);
+
+    await new Promise(process.nextTick);
+    expect.any(Error)
+    consoleSpy.mockRestore();
+  });
+
+  test('should handle nested CSS rules correctly', async () => {
+    Object.defineProperty(mockNode, 'sheet', {
+      get: () => null
+    });
+    mockNode.href = 'http://example.com/style.css';
+    const nestedCss = `
+      @media (max-width: 600px) {
+        .header {
+          font-size: 14px;
+        }
+        .footer {
+          font-size: 12px;
+        }
+      }
+      .container {
+        padding: 20px;
+      }
+    `;
+    global.fetch.mockResolvedValue({
+      ok: true,
+      text: () => Promise.resolve(nestedCss)
+    });
+    inlineRemoteCss(mockNode, 456, 'http://example.com',mockNextID,mockAdoptedSSInsertRuleURLBased, mockAdoptedSSAddOwner);
+    await new Promise(process.nextTick);
+    expect(mockNextID).toHaveBeenCalled();
+    expect(mockAdoptedSSAddOwner).toHaveBeenCalledWith(123, 456);
+    expect(mockAdoptedSSInsertRuleURLBased).toHaveBeenCalledWith(
+      123,
+      '@media (max-width: 600px) {\n        .header {\n          font-size: 14px;\n        }\n        .footer {\n          font-size: 12px;\n        }\n      }',
+      0,
+      'http://example.com'
+    );
+    expect(mockAdoptedSSInsertRuleURLBased).toHaveBeenCalledWith(
+      123,
+      '.container {\n        padding: 20px;\n      }',
+      1,
+      'http://example.com'
+    );
+  });
+});
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