Send email from Rails

require 'net/http'
require 'json'
require 'uri'

module Emailssh
  # ActionMailer calls #deliver! with a Mail::Message. Everything ActionMailer
  # already does (views, layouts, attachments, multipart) happens before this,
  # so all that is left is turning the message into one HTTP request.
  class DeliveryMethod
    ENDPOINT = URI('https://emails.sh/v1/emails').freeze

    attr_accessor :settings

    def initialize(settings = {})
      self.settings = settings
    end

    def deliver!(message)
      payload = {
        from: message[:from].to_s,
        to: Array(message.to),
        subject: message.subject,
        html: html_part(message),
        text: text_part(message),
        cc: Array(message.cc),
        bcc: Array(message.bcc),
        reply_to: message[:reply_to]&.to_s
      }.compact

      request = Net::HTTP::Post.new(ENDPOINT)
      request['Authorization'] = "Bearer #{settings.fetch(:api_key)}"
      request['Content-Type'] = 'application/json'
      request.body = JSON.generate(payload)

      response = Net::HTTP.start(ENDPOINT.hostname, ENDPOINT.port, use_ssl: true, read_timeout: 15) do |http|
        http.request(request)
      end

      unless response.is_a?(Net::HTTPSuccess)
        raise "emails.sh returned #{response.code}: #{response.body}"
      end

      JSON.parse(response.body)
    end

    private

    def html_part(message)
      return message.html_part.body.decoded if message.html_part
      message.content_type&.start_with?('text/html') ? message.body.decoded : nil
    end

    def text_part(message)
      return message.text_part.body.decoded if message.text_part
      message.mime_type == 'text/plain' ? message.body.decoded : nil
    end
  end
end

require Rails.root.join('lib/emailssh/delivery_method')

ActionMailer::Base.add_delivery_method(
  :emailssh,
  Emailssh::DeliveryMethod,
  api_key: Rails.application.credentials.dig(:emailssh, :api_key) || ENV['EMAILSSH_API_KEY']
)

class UserMailer < ApplicationMailer
  default from: 'Acme <hello@acme.com>'

  def welcome(user)
    @user = user
    @login_url = login_url

    mail(to: @user.email, subject: 'Welcome to Acme')
  end
end

# Call it from the controller. deliver_later hands it to Active Job so the HTTP
# request to emails.sh does not happen inside the user's request.
#   UserMailer.welcome(user).deliver_later