Add Userlist as an additional provider (#5)

* Add Userlist as an additional provider

* Please standardrb

---------

Co-authored-by: eelco <[email protected]>

Author: benedikt

README.md

@@ -161,6 +161,7 @@ Courrier supports these transactional email providers:
 - [Postmark](https://postmarkapp.com)
 - [SendGrid](https://sendgrid.com)
 - [SparkPost](https://sparkpost.com)
+- [Userlist](https://userlist.com)
 
 ⚠️ Some providers still need manual verification of their implementation. If you're using one of these providers, please help verify the implementation by sharing your experience in [this GitHub issue](https://github.com/Rails-Designer/courrier/issues/4). 🙏
 

lib/courrier/email/provider.rb

@@ -10,6 +10,7 @@
 require "courrier/email/providers/preview"
 require "courrier/email/providers/sendgrid"
 require "courrier/email/providers/sparkpost"
+require "courrier/email/providers/userlist"
 
 module Courrier
   class Email
@@ -43,7 +44,8 @@ def deliver
         postmark: Courrier::Email::Providers::Postmark,
         preview: Courrier::Email::Providers::Preview,
         sendgrid: Courrier::Email::Providers::Sendgrid,
-        sparkpost: Courrier::Email::Providers::Sparkpost
+        sparkpost: Courrier::Email::Providers::Sparkpost,
+        userlist: Courrier::Email::Providers::Userlist
       }.freeze
 
       def configuration_missing_in_production?

lib/courrier/email/providers/userlist.rb

@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+module Courrier
+  class Email
+    module Providers
+      class Userlist < Base
+        ENDPOINT_URL = "https://push.userlist.com/messages"
+
+        def body
+          {
+            "from" => @options.from,
+            "to" => @options.to,
+            "subject" => @options.subject,
+            "body" => body_document
+          }.compact.merge(provider_options)
+        end
+
+        private
+
+        def headers
+          {
+            "Authorization" => "Push #{@api_key}"
+          }
+        end
+
+        def body_document
+          if @options.html && @options.text
+            multipart_document
+          elsif @options.html
+            html_document
+          elsif @options.text
+            text_document
+          end
+        end
+
+        def text_document
+          {
+            "type" => "text",
+            "content" => @options.text
+          }
+        end
+
+        def html_document
+          {
+            "type" => "html",
+            "content" => @options.html
+          }
+        end
+
+        def multipart_document
+          {
+            "type" => "multipart",
+            "content" => [
+              html_document,
+              text_document
+            ]
+          }
+        end
+
+        def provider_options
+          {"theme" => nil}.merge(@provider_options)
+        end
+      end
+    end
+  end
+end