[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, 118 insertions, 0 deletions

diff --git a/client/simple/src/js/main/00_toolkit.ts b/client/simple/src/js/main/00_toolkit.ts
new file mode 100644
index 000000000..05cfc4b6b
--- /dev/null
+++ b/client/simple/src/js/main/00_toolkit.ts
@@ -0,0 +1,118 @@
+import type { KeyBindingLayout } from "./keyboard.ts";
+
+type Settings = {
+  theme_static_path?: string;
+  method?: string;
+  hotkeys?: KeyBindingLayout;
+  infinite_scroll?: boolean;
+  autocomplete?: boolean;
+  autocomplete_min?: number;
+  search_on_category_select?: boolean;
+  translations?: Record<string, string>;
+  [key: string]: unknown;
+};
+
+type ReadyOptions = {
+  // all values must be truthy for the callback to be executed
+  on?: (boolean | undefined)[];
+};
+
+const getEndpoint = (): string => {
+  const endpointClass = Array.from(document.body.classList).find((className) => className.endsWith("_endpoint"));
+  return endpointClass?.split("_")[0] ?? "";
+};
+
+const getSettings = (): Settings => {
+  const settings = document.querySelector("script[client_settings]")?.getAttribute("client_settings");
+  if (!settings) return {};
+
+  try {
+    return JSON.parse(atob(settings));
+  } catch (error) {
+    console.error("Failed to load client_settings:", error);
+    return {};
+  }
+};
+
+type AssertElement = (element?: Element | null) => asserts element is Element;
+export const assertElement: AssertElement = (element?: Element | null): asserts element is Element => {
+  if (!element) {
+    throw new Error("Bad assertion: DOM element not found");
+  }
+};
+
+export const searxng = {
+  // dynamic functions
+  closeDetail: undefined as (() => void) | undefined,
+  scrollPageToSelected: undefined as (() => void) | undefined,
+  selectImage: undefined as ((resultElement: Element) => void) | undefined,
+  selectNext: undefined as ((openDetailView?: boolean) => void) | undefined,
+  selectPrevious: undefined as ((openDetailView?: boolean) => void) | undefined,
+
+  endpoint: getEndpoint(),
+
+  http: async (method: string, url: string | URL, data?: BodyInit): Promise<Response> => {
+    const controller = new AbortController();
+    const timeoutId = setTimeout(() => controller.abort(), 30000);
+
+    const res = await fetch(url, {
+      body: data,
+      method,
+      signal: controller.signal
+    }).finally(() => clearTimeout(timeoutId));
+    if (!res.ok) {
+      throw new Error(res.statusText);
+    }
+
+    return res;
+  },
+
+  listen: <K extends keyof DocumentEventMap, E extends Element>(
+    type: string | K,
+    target: string | Document | E,
+    listener: (this: E, event: DocumentEventMap[K]) => void,
+    options?: AddEventListenerOptions
+  ): void => {
+    if (typeof target !== "string") {
+      target.addEventListener(type, listener as EventListener, options);
+      return;
+    }
+
+    document.addEventListener(
+      type,
+      (event: Event) => {
+        for (const node of event.composedPath()) {
+          if (node instanceof Element && node.matches(target)) {
+            try {
+              listener.call(node as E, event as DocumentEventMap[K]);
+            } catch (error) {
+              console.error(error);
+            }
+            break;
+          }
+        }
+      },
+      options
+    );
+  },
+
+  ready: (callback: () => void, options?: ReadyOptions): void => {
+    for (const condition of options?.on ?? []) {
+      if (!condition) {
+        return;
+      }
+    }
+
+    if (document.readyState !== "loading") {
+      callback();
+    } else {
+      searxng.listen("DOMContentLoaded", document, callback, { once: true });
+    }
+  },
+
+  settings: getSettings()
+};
+
+searxng.listen("click", ".close", function (this: Element) {
+  (this.parentNode as Element)?.classList.add("invisible");
+});