diff --git a/gmcr.js b/gmcr.js
index e69de29..7f0bfe4 100644
--- a/gmcr.js
+++ b/gmcr.js
@@ -0,0 +1,81 @@
+let lastNotification = "";
+function surroundText(haystack, wordList, padding) {
+	let surroundingText = "";
+	wordList.forEach(word => {
+		if (word.idx < 0)
+			return;
+		const start = Math.max(0, word.idx - padding);
+		const end = word.idx + word.length + padding;
+		if (start > 0)
+			surroundingText += "...";
+		surroundingText += haystack.slice(start, end).trim();
+		if (end < haystack.length)
+			surroundingText += "...";
+
+		surroundingText += "<br>";
+		console.log(start, end, surroundingText);
+	});
+	return surroundingText.trim();
+}
+
+function simpleMatch(captions, words) {
+	const wordList = words.map(word => ({
+		idx: captions.toLowerCase().indexOf(word.toLowerCase()),
+		length: word.length
+	})).filter(i => i.idx >= 0);
+	const surroundingText = surroundText(captions, wordList, 10);
+	return [ wordList.length, surroundingText ];
+}
+
+function advancedMatch(captions, regex, flags) {
+	const reg = RegExp(regex, flags);
+	let wordList = [];
+	if (reg.global) {
+		wordList = [...captions.matchAll(reg)].map(i => ({ idx: i.index, length: i[0].length }));
+	} else {
+		const match = captions.match(reg);
+		if (match.length)
+			wordList = [ {idx: match.index, length: match[0].length} ];
+	}
+	const surroundingText = surroundText(captions, wordList, 10);
+	return [ Boolean(wordList.length), surroundingText ];
+}
+
+function captionUpdate() {
+	const captions = [...document.querySelector(".a4cQT").children].map(i => i.innerText).reduce((i, j) => i + "\n" + j);
+	browser.storage.local.get(["advanced", "flags", "regex", "words"])
+		.then(storage => {
+			let surroundingText = "";
+			let matched = false;
+			if (storage.advanced) {
+				[ matched, surroundingText ] = advancedMatch(captions, storage.regex, storage.flags);
+			} else {
+				[ matched, surroundingText ] = simpleMatch(captions, storage.words);
+			}
+			console.log(matched, surroundingText);
+			/* The lastNotification prevents repetitive notifications because
+			 * of constant updates.
+			 */
+			if (matched && surroundingText !== lastNotification) {
+				new Notification("Match found", {body: surroundingText});
+				lastNotification = surroundingText;
+			}
+		})
+}
+
+/* The script gets injected when the "Ask to join" page. However, captions
+ * element isn't shown until you actually join the meeting, so a 0.5s loop lets
+ * us add a listener whenever it shows up.
+ */
+function setupListener() {
+	const captionElement = document.querySelector(".a4cQT");
+	if (captionElement === null) {
+		setTimeout(setupListener, 500);
+		return;
+	}
+	const config = { subtree: true, childList: true };
+	const observer = new MutationObserver(captionUpdate);
+	observer.observe(captionElement, config);
+}
+
+setupListener();