Add the background script.

package.json

@@ -70,8 +70,7 @@
       {
         "files": "tests/**/*.test.ts",
         "rules": {
-          "@typescript-eslint/triple-slash-reference": "off",
-          "no-await-in-loop": "off"
+          "@typescript-eslint/triple-slash-reference": "off"
         }
       }
     ],
@@ -79,7 +78,8 @@
     "rules": {
       "@typescript-eslint/consistent-type-definitions": "off",
       "@typescript-eslint/consistent-type-imports": "off",
-      "n/file-extension-in-import": "off"
+      "n/file-extension-in-import": "off",
+      "no-await-in-loop": "off"
     },
     "space": true
   }

source/background-scripts/initialize.ts

@@ -0,0 +1,36 @@
+import browser from 'webextension-polyfill';
+
+import {parseRedirect} from '../redirect/exports.js';
+
+async function browserActionClicked() {
+  await browser.runtime.openOptionsPage();
+}
+
+if (import.meta.env.VITE_BROWSER === 'chromium') {
+  browser.action.onClicked.addListener(browserActionClicked);
+} else {
+  browser.browserAction.onClicked.addListener(browserActionClicked);
+}
+
+browser.runtime.onInstalled.addListener(async () => {
+  if (import.meta.env.DEV) {
+    await browser.runtime.openOptionsPage();
+  }
+});
+
+browser.webNavigation.onBeforeNavigate.addListener(async (details) => {
+  const url = new URL(details.url);
+
+  for (const parameters of Object.values(await browser.storage.local.get())) {
+    const redirect = parseRedirect(parameters);
+    if (redirect === undefined) {
+      continue;
+    }
+
+    if (redirect.isMatch(url)) {
+      const redirectedUrl = redirect.redirect(url);
+      await browser.tabs.update({url: redirectedUrl.href});
+      break;
+    }
+  }
+});