This is a draft and will likely get updated constantly.

Background/Research

Frequently, my friends and I go to trivia at a local bar in Seattle. This bar posts it’s trivia categories weekly, and then I copy and paste the categories into a group chat I have with my friends. Ocasionally I forget to do this, or it takes a while. This begs to be automated.

Getting the Categories

This is super easy - Facebook has a Graph API which lets you easily get the posts, as well as a webhook which goes back to a URL I can control. Then I can do whatever (like call a post API).

Sending the Message

This is unfortunately not super easy - the only APIs Facebook has for sending messages are through it’s Messanger Platform, which only let’s you send messages to people who subscribe. It would be nice if it just had an API to post a message to an arbitrary conversation - that’s all I really want.

Approach

I’m going to make a Facebook bot that allows a user to subscribe to get a message anytime a page posts an update that meets a particular regex. They’ll be able to specify the page and the regex in the API. I’ll have a page where my friends can just click to get the already prepoulated messanger sending it to them.

I’ll create a web app, which will have one page, where you can click to sign up to recieve messages from a specific regex for a specific page. I’ll start (and likely end) with only supporting Cha Cha, so I will create the web hook subscription by hand. I’ll start with hard coding my regex in the web app, but the backend will have an argument for that.

When the user signs up, they will use the checkbox plugin to authenticate. In the database, I’ll have a users table with a GUID primary key, which I will pass to facebook as the ref field. In that table, I’ll have a one to many relationship to the regexes table. Each regex will be identified by a GUID primary key, and will have a many to one relationship to the pages table. The pages table will use the facebook page-id as the primary key. In my MVP, I’ll only need the users table, since the regex and the page will be defined by me, to send the trivia categories to my firneds.

The webhook callback will hit an endpoint /pages/[page-id]/post, with the content of the post. Each page will have a list of regexes, and each regex will have a list of user accounts. I’ll then send a push notification using the bot send api using the NON_PROMOTIONAL_SUBSCRIPTION message type, to the user_ref we store when the users signs up and authenticates.