Refactor logic of email notification handling

[gondzo]

Extract logic of email notification handling to a separate handler instead of directly coding it in app.js.

[maxceem]

1. Regarding source code, notifications are being sent by email only after they are saved in the DB.

models.Notification.create({
 ...
 })
 .then(() => {
   // send email
 })

I don't see any reasons why these actions couldn't be done in parrallel. Even if saving notification to the DB fails, looks like there are no reasons to stop sending email.

@gondzo Do you know any reasons I'm missing not to make it parrallel?

[vikasrohit]

Yes @maxceem, you are right. That is what the purpose of this issue/task is. However, right now while saving notifications in database, code validates different events and might alter the event type e.g. in case of a user's handle in mentioned in a post, it changes the event type to MENTIONED_IN_POST from POST_CREATED and the email sending logic is using that updated event type.
What we are thinking is to have post handlers (like we have handlers for all events) which handles the notifications saved in database and do additional things like email, slack etc. However, we are still open for any other good approach which removes the clutter from app.js and makes the code more maitainable.

[maxceem]

2. For general understanding.
   As I know notifications/src project initially supposed to be an independent project without any specific logic for connectNotificationServerver. We just keep tc-notifications/src and tc-notifications/connect together in one repo because it's easier.
   Should we still keep tc-notifications/src independent from connect stuff?
   Is tc-notifications/src being used somewhere else, or going to be used?

[vikasrohit]

Excellent question @maxceem In fact that is my intention in getting this refactoring done. Ideally this code in app.js should belong to the connectNotificationServer. Right now I am not sure how we are going to separate the specific implementation of notification servers, but I think we can definitely utilize https://github.com/topcoder-platform/tc-connect-notifications to host the connectNotificationServer. @gondzo @mtwomey what do you think?

[maxceem]

@vikasrohit great, so far I've moved all the code related to connect from /src to /connect.