Requirements

Core

Send an SMS to a phone number. SMS is paged out.

Desirable

Restrict SMS functionality to known numbers.
Restrict web page functionality to Twilio source.
Retain log of all messages sent

Nice-to-have

Support multiple units
Ability to update phone numbers
Provide pageing log via webpage

Design

Components

Twilio for incoming and outgoing SMS control
AWS Lambda instance running Flask to process incoming SMS
AWS Lambda instance running Flask to perform admin tasks
DynamoDB tables for data storage

Twilio

Twilio owns number
Twilio contacts web page on incoming SMS
Reply SMS sent on error

Lambda to process incoming SMS

Test for twilio signature to ensure origin
Lookup phonenumber to ensure permission to use
Lookup unit to get pager number
Send admin page with sms body to unit number
On success, no response
On error and twilio signature, send SMS reply with details

Lambda to process admin

Log in using Microsoft login
Lookup contact in contacts table
Use permissions to determine access level
Only show content and links if permission is granted
Try and keep it all in one page if possible
Basic CRUD REST APIs might be the way to go

DynamoDB tables

contacts
- phone number (hash)
- unit
- name
- member id (GSI hash)
- permissions (json dict)
  - page log read
  - contacts read
  - contacts write
  - unit admin
  - site admin
page log
- unit (hash)
- timestamp (range)
- phone number
- body
unit
- name (hash)
- page id