async function getAccessToken()

in packages/hub/src/utils/XetBlob.ts [593:662]
58 lines of code
10 McCabe index (conditional complexity)

async function getAccessToken(
	initialAccessToken: string | undefined,
	customFetch: typeof fetch,
	refreshUrl: string
): Promise<{ accessToken: string; casUrl: string }> {
	const key = cacheKey({ refreshUrl, initialAccessToken });

	const jwt = jwts.get(key);

	if (jwt && jwt.expiresAt > new Date(Date.now() + JWT_SAFETY_PERIOD)) {
		return { accessToken: jwt.accessToken, casUrl: jwt.casUrl };
	}

	// If we already have a promise for this repo, return it
	const existingPromise = jwtPromises.get(key);
	if (existingPromise) {
		return existingPromise;
	}

	const promise = (async () => {
		const resp = await customFetch(refreshUrl, {
			headers: {
				...(initialAccessToken
					? {
							Authorization: `Bearer ${initialAccessToken}`,
					  }
					: {}),
			},
		});

		if (!resp.ok) {
			throw new Error(`Failed to get JWT token: ${resp.status} ${await resp.text()}`);
		}

		const json: { accessToken: string; casUrl: string; exp: number } = await resp.json();
		const jwt = {
			accessToken: json.accessToken,
			expiresAt: new Date(json.exp * 1000),
			initialAccessToken,
			refreshUrl,
			casUrl: json.casUrl,
		};

		jwtPromises.delete(key);

		for (const [key, value] of jwts.entries()) {
			if (value.expiresAt < new Date(Date.now() + JWT_SAFETY_PERIOD)) {
				jwts.delete(key);
			} else {
				break;
			}
		}
		if (jwts.size >= JWT_CACHE_SIZE) {
			const keyToDelete = jwts.keys().next().value;
			if (keyToDelete) {
				jwts.delete(keyToDelete);
			}
		}
		jwts.set(key, jwt);

		return {
			accessToken: json.accessToken,
			casUrl: json.casUrl,
		};
	})();

	jwtPromises.set(key, promise);

	return promise;
}