add domain block model and checks

app/models/federails/moderation/domain_block.rb

@@ -0,0 +1,9 @@
+module Federails::Moderation
+  class DomainBlock < ApplicationRecord
+    validates :domain, presence: true, uniqueness: true, "federails/moderation/domain_name": true
+
+    def self.blocked?(query)
+      self.exists?(domain: [ query, PublicSuffix.parse(query).domain ])
+    end
+  end
+end

app/validators/federails/moderation/domain_name_validator.rb

@@ -0,0 +1,9 @@
+require "public_suffix"
+
+module Federails::Moderation
+  class DomainNameValidator < ActiveModel::EachValidator
+    def validate_each(record, attribute, value)
+      record.errors.add attribute, :invalid unless PublicSuffix.valid?(value, default_rule: nil)
+    end
+  end
+end

db/migrate/20241128115659_create_federails_moderation_domain_blocks.rb

@@ -0,0 +1,8 @@
+class CreateFederailsModerationDomainBlocks < ActiveRecord::Migration[8.0]
+  def change
+    create_table :federails_moderation_domain_blocks do |t|
+      t.string "domain", null: false, index: { unique: true }
+      t.timestamps
+    end
+  end
+end

federails-moderation.gemspec

@@ -24,4 +24,5 @@ Gem::Specification.new do |spec|
   end
   spec.add_dependency "rails", ">= 7.2.2"
   spec.add_dependency "federails", "~> 0.3"
+  spec.add_dependency "public_suffix", "~> 6.0"
 end

spec/models/domain_block_spec.rb

@@ -0,0 +1,45 @@
+RSpec.describe Federails::Moderation::DomainBlock do
+  [
+    "example.com",
+    "my.website.co.uk",
+    "Bücher.de",
+    "кц.рф",
+    "互联网中心.中国",
+    "☃.com"
+  ].each do |test|
+    it "is valid if domain name is #{test.inspect}" do
+      block = described_class.new(domain: test)
+      expect(block).to be_valid
+    end
+  end
+
+  [
+    nil,
+    "",
+    "example.invalid",
+    ".example.com"
+  ].each do |test|
+    it "is invalid if domain name is #{test.inspect}" do
+      block = described_class.new(domain: test)
+      expect(block).not_to be_valid
+    end
+  end
+
+  context "with a blocked domain" do
+    before do
+      described_class.create(domain: "blocked.com")
+    end
+
+    it "blocks the domain" do
+      expect(described_class.blocked?("blocked.com")).to be true
+    end
+
+    it "blocks subdomains" do
+      expect(described_class.blocked?("www.blocked.com")).to be true
+    end
+
+    it "allows other domains" do
+      expect(described_class.blocked?("example.com")).to be false
+    end
+  end
+end