Push Notificaiton setNotificationsTrigger

setNotificationsTrigger.ts

/**
 * This function will be called every day at 8AM pacific time.
 * Scheduled as CRON job in cloud scheduler.
 */

// This function create an https API that we can call using a GET request.
export const setNotificationsTrigger = functions.https.onRequest(async (_, response) => {

    // We're using a try catch block to take advantage of the 
    // very nice `await` syntax, while also handling errors properly.
    try {
        // First we want to get our tasks.
        // Await basically means, that we want to wait for the closure
        // result of `getIncompleteTasks` before proceeding.
        const tasks = await getIncompleteTasks()
        // Then we use our formatter function to get a dictionary.
        // [userID: [Task]]
        const convertedTasks = getFormatted(tasks)
      
        // Now we create an empty array of Promises.
        // Look at it as an Array of closures.
        // The Swift syntax could be something like:
        // let promises = [(Any) -> Void]()
        const promises: Promise<any>[] = []

        // We want to iterate over our dictionary
        for (let userID in convertedTasks) {
            // To get each user's tasks
            let userTasks = convertedTasks[userID]
            // And if we have at least 1 open task...
            if (userTasks.length > 0) {
                // We need to add the functiont to notify a user
                // to the Promises array.
                // Note: We're not adding the result of the notification function, 
                // but the actual function. 
                // We want to add the function's callback to our Array of callbacks.
                promises.push(notifyUser(userID, userTasks.length))
            }
        }

        // Lastly we await for the execution and 
        // result of ALL functions at the same time
        const result = await Promise.all(promises)
        // Here we're just sending the response to close the network request.
        response.send(result.filter((element: string) => {
            // The filter now filters out all Promises that 
            // did not return a value for the result of the message.
            // Remember, if the user.fcmToken was undefined, 
            // we did not send a notification, but returned undefined.
            return typeof element !== 'undefined' && element !== null
        }));
    } catch (error) {
        // Return the error if there was one.
        response.send(error);
    }
})