Send email confirmation when BTC payment is confirmed

app/jobs/btcpay_check_donation_job.rb

@@ -4,15 +4,19 @@ class BtcpayCheckDonationJob < ApplicationJob
   def perform(donation)
     return if donation.completed?
 
-    invoice = BtcpayManager::FetchInvoice.call(invoice_id: donation.btcpay_invoice_id)
+    invoice = BtcpayManager::FetchInvoice.call(
+      invoice_id: donation.btcpay_invoice_id
+    )
 
     case invoice["status"]
     when "Settled"
-      # TODO use time from actual payment confirmation
       donation.paid_at = DateTime.now
       donation.payment_status = "settled"
       donation.save!
-      # TODO send email
+
+      NotificationMailer.with(user: donation.user)
+                        .bitcoin_donation_confirmed
+                        .deliver_later
     when "Processing"
       re_enqueue_job(donation)
     end

app/mailers/notification_mailer.rb

@@ -23,4 +23,11 @@ class NotificationMailer < ApplicationMailer
     @subject = "New invitations added to your account"
     mail to: @user.email, subject: @subject
   end
+
+  def bitcoin_donation_confirmed
+    @user = params[:user]
+    @donation = params[:donation]
+    @subject = "Donation confirmed"
+    mail to: @user.email, subject: @subject
+  end
 end

app/views/notification_mailer/bitcoin_donation_confirmed.text.erb

@@ -0,0 +1,11 @@
+Hi <%= @user.display_name.presence || @user.cn %>,
+
+Your bitcoin donation has been confirmed successfully. <3
+
+Thank you so much for helping us with keeping the lights on, as well as with continually improving our services for you!
+
+You can find all of your past financial contributions on this page:
+
+<%= contributions_donations_url %>
+
+Have a nice day!