Working initial version

frontend/src/App.css

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+.App {
+  display: flex;
+  flex-direction: column;
+  gap: 2rem;
+  padding: 2rem;
+  align-items: center;
+  justify-content: start;
+  height: 100vh;
+}
+
+.panel-container {
+  display: flex;
+  flex-direction: row;
+  gap: 2rem;
+}
+
+.controls {
+  display: flex;
+  flex-direction: row;
+  align-items: center;
+  gap: 2rem;
+
+  label {
+    margin-right: 0.5rem;
+  }
+}

frontend/src/App.tsx

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+import { useState } from "react";
+import Panel from "./components/Panel";
+
+import { useQuery } from "@tanstack/react-query";
+import "./App.css";
+import ArticleSelector from "./components/ArticleSelector";
+import CelexSelector from "./components/CelexSelector";
+import { getArticleIds } from "./lib/api";
+import { Language } from "./lib/types";
+
+function App() {
+  const [celexId, setCelexId] = useState("32024R1689");
+  const [selectedArticle, setSelectedArticle] = useState<number>(1);
+  const [numPanels, setNumPanels] = useState(1);
+  const [selectedParagraphId, setSelectedParagraphId] = useState<string | null>(
+    null
+  );
+
+  const {
+    data: articleIds,
+    isPending,
+    error,
+  } = useQuery({
+    queryKey: ["articleIds", celexId],
+    queryFn: () => getArticleIds(celexId),
+    enabled: !!celexId,
+  });
+
+  if (isPending) {
+    return <div>Loading...</div>;
+  }
+  if (error) {
+    return <div>Error: {error.message}</div>;
+  }
+
+  const examples = [
+    { name: "GDPR", id: "32016R0679" },
+    { name: "AI Act", id: "32024R1689" },
+    { name: "Cyber Resilience Act", id: "32024R2847" },
+  ];
+
+  return (
+    <div className="App">
+      <div className="controls">
+        <div>
+          <label htmlFor="examples">Select example:</label>
+          <select
+            id="examples"
+            value={celexId}
+            onChange={(e) => {
+              setSelectedArticle(1);
+              setSelectedParagraphId(null);
+              setCelexId(e.currentTarget.value);
+            }}
+          >
+            {examples.map((example) => (
+              <option key={example.id} value={example.id}>
+                {example.name}
+              </option>
+            ))}
+          </select>
+        </div>
+        <CelexSelector defaultId={celexId} onSelected={setCelexId} />
+        <ArticleSelector
+          articleIds={articleIds}
+          selectedId={selectedArticle}
+          onSelected={setSelectedArticle}
+        />
+        <button onClick={() => setNumPanels((prev) => prev + 1)}>
+          Add Panel
+        </button>
+      </div>
+      <div className="panel-container">
+        {Array.from({ length: numPanels }, (_, index) => (
+          <Panel
+            key={index}
+            celexId={celexId}
+            language={
+              Object.values(Language)[index % Object.values(Language).length]
+            }
+            articleId={selectedArticle}
+            selectedParagraphId={selectedParagraphId || undefined}
+            onParagraphSelected={setSelectedParagraphId}
+          />
+        ))}
+      </div>
+    </div>
+  );
+}
+
+export default App;

frontend/src/components/ArticleSelector.tsx

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+type ArticleSelectorProps = {
+  articleIds: number[];
+  selectedId: number;
+  onSelected(articleId: number): void;
+};
+
+function ArticleSelector({
+  articleIds,
+  selectedId,
+  onSelected,
+}: ArticleSelectorProps) {
+  return (
+    <>
+      {selectedId > 1 && (
+        <button onClick={() => onSelected(selectedId - 1)}>prev</button>
+      )}
+      <select
+        value={selectedId}
+        onChange={(e) => {
+          const id = parseInt(e.currentTarget.value);
+          onSelected(id);
+        }}
+      >
+        {articleIds.map((id) => (
+          <option key={id} value={id}>
+            Article {id}
+          </option>
+        ))}
+      </select>
+      {selectedId < articleIds[articleIds.length - 1] && (
+        <button onClick={() => onSelected(selectedId + 1)}>next</button>
+      )}
+    </>
+  );
+}
+
+export default ArticleSelector;

frontend/src/components/CelexSelector.tsx

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+type CelexSelectorProps = {
+  defaultId?: string;
+  onSelected(celexId: string): void;
+};
+
+function CelexSelector({ defaultId, onSelected }: CelexSelectorProps) {
+  return (
+    <form
+      onSubmit={(e) => {
+        e.preventDefault();
+        onSelected(e.currentTarget.celexId.value);
+      }}
+    >
+      <label htmlFor="celexId">CELEX ID:</label>
+      <input type="text" id="celexId" defaultValue={defaultId} />
+    </form>
+  );
+}
+
+export default CelexSelector;

frontend/src/components/LanguageSwitcher.css

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+.language-switcher {
+  margin: 0 10px;
+  padding: 5px;
+  font-size: 14px;
+  border-radius: 4px;
+  border: 1px solid #ccc;
+}

frontend/src/components/LanguageSwitcher.tsx

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+import { Language } from "../lib/types";
+
+import "./LanguageSwitcher.css";
+
+function LanguageSwitcher({
+  defaultLang,
+  onChange,
+}: {
+  defaultLang: Language;
+  onChange: (lang: Language) => void;
+}) {
+  return (
+    <>
+      <select
+        defaultValue={defaultLang}
+        onChange={(ev) => onChange(ev.currentTarget.value as Language)}
+        className="language-switcher"
+      >
+        {Object.values(Language).map((lang) => (
+          <option key={lang} value={lang}>
+            {lang.toUpperCase()}
+          </option>
+        ))}
+      </select>
+    </>
+  );
+}
+
+export default LanguageSwitcher;

frontend/src/components/Panel.css

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+.panel {
+  flex-grow: 1;
+  padding: 1rem;
+  border-radius: 8px;
+  border: 1px solid #ccc;
+
+  .highlight {
+    background-color: rgba(100, 255, 100, 0.2);
+  }
+
+  article {
+    .list-lower-alpha {
+      list-style-type: lower-alpha;
+    }
+
+    ol .item-number {
+      display: none;
+    }
+
+    .paragraph-number {
+      float: left;
+      margin-right: 1ch;
+    }
+  }
+}

frontend/src/components/Panel.tsx

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+import { useQuery } from "@tanstack/react-query";
+import { useEffect, useRef, useState } from "react";
+import { getArticle } from "../lib/api";
+import { Language } from "../lib/types";
+import LanguageSwitcher from "./LanguageSwitcher";
+import "./Panel.css";
+
+type PanelProps = {
+  celexId: string;
+  language?: Language;
+  articleId: number;
+  selectedParagraphId?: string;
+  onParagraphSelected(paragraphId: string): void;
+};
+
+function Panel({
+  celexId,
+  language,
+  articleId,
+  onParagraphSelected,
+  selectedParagraphId,
+}: PanelProps) {
+  const [lang, setLang] = useState(language || Language.ENG);
+  const articleRef = useRef<HTMLDivElement>(null);
+  const { data, isPending, error } = useQuery({
+    queryKey: ["article", celexId, articleId, lang],
+    queryFn: () => getArticle(celexId, articleId, lang),
+    enabled: !!celexId,
+  });
+
+  useEffect(() => {
+    const articleElement = articleRef.current;
+    if (!articleElement) return;
+
+    const paragraphs = articleElement.querySelectorAll(".paragraph");
+
+    // Highlight the selected paragraph
+    paragraphs.forEach((p) => {
+      p.classList.remove("highlight");
+    });
+    if (selectedParagraphId) {
+      const selectedParagraph = Array.from(paragraphs).find(
+        (p) => p.getAttribute("data-paragraph-id") === selectedParagraphId
+      );
+      if (selectedParagraph) {
+        selectedParagraph.classList.add("highlight");
+      }
+    }
+
+    // Add click event listeners
+    const handleClick = (target: Element) => () => {
+      const paragraphId = target.getAttribute("data-paragraph-id");
+      paragraphs.forEach((p) => {
+        p.classList.remove("highlight");
+      });
+      if (!paragraphId) {
+        console.warn("No paragraph ID found for target:", target);
+        return;
+      }
+      target.classList.add("highlight");
+      onParagraphSelected(paragraphId);
+    };
+
+    paragraphs.forEach((element) => {
+      element.addEventListener("click", handleClick(element));
+    });
+
+    // Cleanup event listeners
+    return () => {
+      console.log("Cleaning up event listeners");
+      paragraphs.forEach((element) => {
+        element.removeEventListener("click", handleClick(element));
+      });
+    };
+  }, [articleRef, data, selectedParagraphId, onParagraphSelected]);
+
+  if (isPending) return "Loading...";
+  if (error) return "An error has occurred: " + error.message;
+
+  return (
+    <div className={"panel"}>
+      <LanguageSwitcher
+        defaultLang={lang}
+        onChange={setLang}
+      ></LanguageSwitcher>
+      <div
+        ref={articleRef}
+        lang={lang.substring(0, 2)}
+        className="article-text"
+        dangerouslySetInnerHTML={{ __html: data || "" }}
+      />
+    </div>
+  );
+}
+
+export default Panel;

frontend/src/index.css

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+:root {
+  font-family: system-ui, Avenir, Helvetica, Arial, sans-serif;
+  line-height: 1.5;
+  font-weight: 400;
+
+  color-scheme: light dark;
+  color: rgba(255, 255, 255, 0.87);
+  background-color: #242424;
+
+  font-synthesis: none;
+  text-rendering: optimizeLegibility;
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}
+
+a {
+  font-weight: 500;
+  color: #646cff;
+  text-decoration: inherit;
+}
+a:hover {
+  color: #535bf2;
+}
+
+body {
+  margin: 0;
+  display: flex;
+  place-items: center;
+  min-width: 320px;
+  min-height: 100vh;
+}
+
+h1 {
+  font-size: 3.2em;
+  line-height: 1.1;
+}
+
+button {
+  border-radius: 8px;
+  border: 1px solid transparent;
+  padding: 0.6em 1.2em;
+  font-size: 1em;
+  font-weight: 500;
+  font-family: inherit;
+  background-color: #1a1a1a;
+  cursor: pointer;
+  transition: border-color 0.25s;
+}
+button:hover {
+  border-color: #646cff;
+}
+button:focus,
+button:focus-visible {
+  outline: 4px auto -webkit-focus-ring-color;
+}
+
+@media (prefers-color-scheme: light) {
+  :root {
+    color: #213547;
+    background-color: #ffffff;
+  }
+  a:hover {
+    color: #747bff;
+  }
+  button {
+    background-color: #f9f9f9;
+  }
+}

frontend/src/lib/api.ts

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+const API_URL = import.meta.env.VITE_API_URL;
+
+async function getArticle(
+  celexId: string,
+  article: number,
+  language: string
+): Promise<string> {
+  console.debug(
+    `Fetching article ${article} for CELEX ID ${celexId} in ${language} language`
+  );
+  const response = await fetch(
+    `${API_URL}/${celexId}/articles/${article}/${language}`
+  );
+  return await response.text();
+}
+
+async function getArticleIds(celexId: string): Promise<number[]> {
+  console.debug(`Fetching article list for CELEX ID ${celexId}`);
+  const response = await fetch(`${API_URL}/${celexId}/articles`);
+  return await response.json();
+}
+
+export { getArticle, getArticleIds };

frontend/src/lib/types.ts

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+enum Language {
+  ENG = "eng",
+  DEU = "deu",
+  FRA = "fra",
+  ITA = "ita",
+  ESP = "esp",
+}
+
+export { Language };

frontend/src/main.tsx

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+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { ReactQueryDevtools } from "@tanstack/react-query-devtools";
+import { StrictMode } from "react";
+import { createRoot } from "react-dom/client";
+import App from "./App.tsx";
+import "./index.css";
+
+const queryClient = new QueryClient();
+
+createRoot(document.getElementById("root")!).render(
+  <StrictMode>
+    <QueryClientProvider client={queryClient}>
+      <ReactQueryDevtools />
+      <App />
+    </QueryClientProvider>
+  </StrictMode>
+);

frontend/src/vite-env.d.ts

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+/// <reference types="vite/client" />
+
+interface ImportMetaEnv {
+  readonly VITE_APP_TITLE: string;
+  readonly VITE_API_URL: string;
+}
+
+interface ImportMeta {
+  readonly env: ImportMetaEnv;
+}