[mod] theme/simple: migrate codebase to TypeScript

TypeScript is a superset of JavaScript, converting the entire theme to
TypeScript allows us to receive much more feedback on possible issues made in
package updates or our own typos, furthermore, it allows to transpile properly
to lower specs. This PR couldn't be done in smaller commits, a lot of work
needed to make everything *work properly*:

- A browser baseline has been set that requires minimum **Chromium 93, Firefox
  92 and Safari 15** (proper visuals/operation on older browser versions is not
  guaranteed)
- LightningCSS now handles minification and prefix creation for CSS.
- All hardcoded polyfills and support for previous browser baseline versions
  have been removed.
- Convert codebase to TypeScript.
- Convert IIFE to ESM, handling globals with IIFE is cumbersome, ESM is the
  standard for virtually any use of JS nowadays.
- Vite now builds the theme without the need for `vite-plugin-static-copy`.
- `searxng.ready` now accepts an array of conditions for the callback to be
  executed.
- Replace `leaflet` with `ol` as there were some issues with proper Vite
  bundling.
- Merged `head` with `main` script, as head was too small now.
- Add `assertElement` to properly check the existence of critical DOM elements.
- `searxng.on` renamed to `searxng.listen` with some handling improvements.

1 files changed, 108 insertions, 0 deletions

diff --git a/client/simple/src/js/main/infinite_scroll.ts b/client/simple/src/js/main/infinite_scroll.ts
new file mode 100644
index 000000000..e9f931e51
--- /dev/null
+++ b/client/simple/src/js/main/infinite_scroll.ts
@@ -0,0 +1,108 @@
+import { assertElement, searxng } from "./00_toolkit";
+
+const newLoadSpinner = (): HTMLDivElement => {
+  return Object.assign(document.createElement("div"), {
+    className: "loader"
+  });
+};
+
+const loadNextPage = async (onlyImages: boolean, callback: () => void): Promise<void> => {
+  const searchForm = document.querySelector<HTMLFormElement>("#search");
+  assertElement(searchForm);
+
+  const form = document.querySelector<HTMLFormElement>("#pagination form.next_page");
+  assertElement(form);
+
+  const formData = new FormData(form);
+
+  const action = searchForm.getAttribute("action");
+  if (!action) {
+    console.error("Form action not found");
+    return;
+  }
+
+  const paginationElement = document.querySelector<HTMLElement>("#pagination");
+  assertElement(paginationElement);
+
+  paginationElement.replaceChildren(newLoadSpinner());
+
+  try {
+    const res = await searxng.http("POST", action, formData);
+    const nextPage = await res.text();
+    if (!nextPage) return;
+
+    const nextPageDoc = new DOMParser().parseFromString(nextPage, "text/html");
+    const articleList = nextPageDoc.querySelectorAll<HTMLElement>("#urls article");
+    const nextPaginationElement = nextPageDoc.querySelector<HTMLElement>("#pagination");
+
+    document.querySelector("#pagination")?.remove();
+
+    const urlsElement = document.querySelector<HTMLElement>("#urls");
+    if (!urlsElement) {
+      console.error("URLs element not found");
+      return;
+    }
+
+    if (articleList.length > 0 && !onlyImages) {
+      // do not add <hr> element when there are only images
+      urlsElement.appendChild(document.createElement("hr"));
+    }
+
+    urlsElement.append(...Array.from(articleList));
+
+    if (nextPaginationElement) {
+      const results = document.querySelector<HTMLElement>("#results");
+      results?.appendChild(nextPaginationElement);
+      callback();
+    }
+  } catch (error) {
+    console.error("Error loading next page:", error);
+
+    const errorElement = Object.assign(document.createElement("div"), {
+      textContent: searxng.settings.translations?.error_loading_next_page ?? "Error loading next page",
+      className: "dialog-error"
+    });
+    errorElement.setAttribute("role", "alert");
+    document.querySelector("#pagination")?.replaceChildren(errorElement);
+  }
+};
+
+searxng.ready(
+  () => {
+    const resultsElement = document.getElementById("results");
+    if (!resultsElement) {
+      console.error("Results element not found");
+      return;
+    }
+
+    const onlyImages = resultsElement.classList.contains("only_template_images");
+    const observedSelector = "article.result:last-child";
+
+    const intersectionObserveOptions: IntersectionObserverInit = {
+      rootMargin: "320px"
+    };
+
+    const observer = new IntersectionObserver(async (entries: IntersectionObserverEntry[]) => {
+      const [paginationEntry] = entries;
+
+      if (paginationEntry?.isIntersecting) {
+        observer.unobserve(paginationEntry.target);
+
+        await loadNextPage(onlyImages, () => {
+          const nextObservedElement = document.querySelector<HTMLElement>(observedSelector);
+          if (nextObservedElement) {
+            observer.observe(nextObservedElement);
+          }
+        });
+      }
+    }, intersectionObserveOptions);
+
+    const initialObservedElement = document.querySelector<HTMLElement>(observedSelector);
+    if (initialObservedElement) {
+      observer.observe(initialObservedElement);
+    }
+  },
+  {
+    on: [searxng.endpoint === "results", searxng.settings.infinite_scroll]
+  }
+);