WIP

app/lib/admin/metrics/dimension/email_domains_dimension.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+class Admin::Metrics::Dimension::EmailDomainsDimension < Admin::Metrics::Dimension::BaseDimension
+  def key
+    'email_domains'
+  end
+
+  protected
+
+  def perform_query
+    sql = <<-SQL.squish
+      SELECT split_part(email, '@', 2) AS domain, count(*) AS value
+      FROM users
+      WHERE created_at BETWEEN $1 AND $2
+      GROUP BY split_part(email, '@', 2)
+      ORDER BY count(*) DESC
+      LIMIT $3
+    SQL
+
+    rows = ActiveRecord::Base.connection.select_all(sql, nil, [[nil, @start_at], [nil, @end_at], [nil, @limit]])
+
+    rows.map { |row| { key: row['domain'], human_key: row['domain'], value: row['value'].to_s } }
+  end
+end