ShortenLink.ts

// shorten invite link
export let shortenLink = functions
    .database
    .ref('/groups/{groupId}/inviteLink')
    .onWrite(event => shortenInviteLink(event));

// Shortens invite link and saves it in place of the original long link.
async function shortenInviteLink(event: Event<DeltaSnapshot>)
{
    let link: string = event.data.val(); 
  
    // link is already short
    if (!isLongLink(link))
    {
        return;
    }

    var config = functions.config() as Config;
    var options = 
    {
        method: 'POST',
        uri: 'https://firebasedynamiclinks.googleapis.com/v1/shortLinks',
        qs: {
            key: config.local.apikey
        },
        headers: {
            'Content-Type': 'application/json'
        },
        body: {
            'longDynamicLink': link,
            'suffix': { 'option': 'UNGUESSABLE' }
        },
        json: true 
    };

    let result = await request(options);
    await event.data.ref.set(result.shortLink);
}

// Checks whether the link is long or already shortened.
function isLongLink(link: string)
{ 
    return link.indexOf('?link') > 0;
}

interface Config {
    local: {
        apikey: string;
    }
}