Firebase cloud function for Slack button actions in medium article https://medium.com/evenbit/151c1c98641d

database_trigger.ts

export const on_actions = functions.database.ref("actions/{id}").onWrite(async (event) => {
    if (!event.data.exists()) {
        return "Nothing to do for deletion of processed commands.";
    }

    // Start by deleting the action request itself from the queue
    await event.data.ref.remove();

    const action = event.data.val();

    if (action.callback_id !== "ping-pong") {
        console.error("Only ping pong actions are implemented!");
        return;
    }

    const pongId = admin.database().ref("pong").push().key;
    const pingId = action.actions[0].value;
    const pingRef = admin.database().ref("ping").child(pingId);
    const transactionResult = await pingRef.transaction((ping) => {
        if (!ping) {
            return null;
        }

        if (ping.pongs && Object.keys(ping.pongs).length >= 3) {
            // Only count the first three pings!
            console.log(`User ${action.user.name}@${action.team.domain} was too late to reply to ping ${pingId}`);
            return;
        }

        ping.pongs = ping.pongs || {};
        // Slack timestamps comes as Unix Epoch in SECONDS with milliseconds in fraction
        ping.pongs[pongId] = Math.round(parseFloat(action.action_ts) * 1000);
        return ping;
    });

    const committed = transactionResult.committed;
    const ping = transactionResult.snapshot.exists() ? transactionResult.snapshot.val() : null;
    if (!committed) {
        return "Not your luck today";
    }

    const pongTime = ping.pongs[pongId];
    const pong: Pong = {
        ponged_at: pongTime,
        ping_pong_time: pongTime - ping.pinged_at,
        user_id: action.user.id,
        user_name: action.user.name,
        team: action.team.id,
        ping: pingId
    };

    await admin.database().ref("pong").child(pongId).set(pong);

    const numberOfPongs = Object.keys(ping.pongs).length;
    if (numberOfPongs < 3) {
        return "Waiting for more pongs";
    }

    return sendPingPongScore(pingId);
});