Send SMS with Rails

Add SMS sending to this Rails project with TextKit.

- Docs for this stack: https://jointextkit.com/docs/send-with-rails.md
- API: POST https://api.jointextkit.com/v1/messages with `Authorization: Bearer
  <key>` and a JSON body `{"to": "+1...", "body": "..."}`.
- There is no Ruby gem: POST JSON to https://api.jointextkit.com/v1/messages
  with Net::HTTP from a service object, and call it from an Active Job.
- Read the key from the `TEXTKIT_API_KEY` environment variable. Never hardcode
  it or send it to the browser.
- Phone numbers are E.164 and US or Canada only (`+1` followed by 10 digits).
- A test key (`ssms_sk_test_`) simulates: `+15005550006` always ends `delivered`
  and no phone gets a text.
- Errors are JSON: `{"error": {"code", "message", "param"}}` with a 4xx status.
  On `429`, wait `Retry-After` seconds and retry.
- Send only from server code that runs after a real event (a signup, an order).
  Never expose an endpoint that texts any number a visitor types.

export TEXTKIT_API_KEY=ssms_sk_test_...

require "net/http"

class Textkit
  ENDPOINT = URI("https://api.jointextkit.com/v1/messages")

  class Error < StandardError; end

  def self.send_sms(to:, body:)
    req = Net::HTTP::Post.new(ENDPOINT)
    req["Authorization"] = "Bearer #{ENV.fetch("TEXTKIT_API_KEY")}"
    req["Content-Type"] = "application/json"
    req.body = { to: to, body: body }.to_json

    res = Net::HTTP.start(ENDPOINT.hostname, ENDPOINT.port, use_ssl: true) { |http| http.request(req) }
    data = JSON.parse(res.body)
    raise Error, "#{data.dig("error", "code")}: #{data.dig("error", "message")}" unless res.is_a?(Net::HTTPSuccess)

    data
  end
end

bin/rails runner 'puts Textkit.send_sms(to: "+15005550006", body: "Hello from TextKit")["id"]'

class SendSmsJob < ApplicationJob
  queue_as :default

  def perform(to, body)
    Textkit.send_sms(to: to, body: body)
  end
end

SendSmsJob.perform_later(user.phone, "Your order shipped.")