feat: add lazy install generator

README.md

@@ -146,20 +146,18 @@ puts result.issues.to_a.map(&:message)
 
 ## Rails Usage
 
-For an app that uses Crawlscope through rake tasks, load the task entrypoint
-only when a Crawlscope task is requested. In the application's `Rakefile`,
-before `require_relative "config/application"`:
+Run the install generator after adding the gem:
 
-```ruby
-list_tasks = Rake.application.options.show_tasks || ARGV.any? { |argument| ["-T", "--tasks"].include?(argument) }
-require "crawlscope/tasks" if list_tasks || ARGV.any? { |argument| argument.start_with?("crawlscope:") }
+```bash
+bin/rails generate crawlscope:install
 ```
 
-This preserves `bin/rails --tasks` and the `crawlscope:*` tasks without loading
-Crawlscope during normal Rails boot. Runtime callers should explicitly
-`require "crawlscope"` immediately before configuring or using the gem.
+The generator creates `config/initializers/crawlscope.rb` with an idempotent
+`CrawlscopeConfiguration.apply` loader and adds conditional `crawlscope/tasks`
+loading to the application's `Rakefile`. This preserves `bin/rails --tasks` and
+the `crawlscope:*` tasks without loading Crawlscope during normal Rails boot.
 
-In an initializer:
+Customize the `Crawlscope.configure` block inside the generated initializer:
 
 ```ruby
 Crawlscope.configure do |config|
@@ -170,6 +168,17 @@ Crawlscope.configure do |config|
 end
 ```
 
+Runtime callers must apply the generated configuration before using
+Crawlscope:
+
+```ruby
+CrawlscopeConfiguration.apply
+Crawlscope.configuration.audit
+```
+
+Rake tasks apply it automatically because `crawlscope/tasks` loads the gem
+before Rails evaluates the initializer.
+
 Then run:
 
 ```bash

lib/crawlscope.rb

@@ -27,6 +27,7 @@ def reset!
 end
 
 Crawlscope.instance_variable_set(:@loader, Zeitwerk::Loader.for_gem)
+Crawlscope.loader.ignore("#{__dir__}/generators")
 Crawlscope.loader.ignore("#{__dir__}/tasks")
 Crawlscope.loader.ignore("#{__dir__}/crawlscope/railtie.rb")
 Crawlscope.loader.ignore("#{__dir__}/crawlscope/tasks.rb")

lib/generators/crawlscope/install_generator.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+require "rails/generators"
+
+module Crawlscope
+  module Generators
+    class InstallGenerator < Rails::Generators::Base
+      source_root File.expand_path("templates", __dir__)
+
+      desc "Create a lazy-safe Crawlscope initializer and task loader"
+
+      def create_initializer
+        template "initializer.rb.tt", "config/initializers/crawlscope.rb"
+      end
+
+      def configure_rakefile
+        rakefile = File.join(destination_root, "Rakefile")
+        return unless File.exist?(rakefile)
+        return if File.read(rakefile).include?('require "crawlscope/tasks"')
+
+        inject_into_file "Rakefile", rakefile_setup, before: /^require_relative ["']config\/application["']/
+      end
+
+      private
+
+      def rakefile_setup
+        <<~RUBY
+          crawlscope_tasks_requested = Rake.application.options.show_tasks ||
+            ARGV.any? { |argument| ["-T", "--tasks"].include?(argument) }
+          require "crawlscope/tasks" if crawlscope_tasks_requested ||
+            ARGV.any? { |argument| argument.start_with?("crawlscope:") }
+
+        RUBY
+      end
+    end
+  end
+end

lib/generators/crawlscope/templates/initializer.rb.tt

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module CrawlscopeConfiguration
+  MUTEX = Mutex.new
+
+  def self.apply
+    return if @applied
+
+    MUTEX.synchronize do
+      return if @applied
+
+      require "crawlscope"
+
+      Crawlscope.configure do |config|
+        config.base_url = -> { ENV.fetch("CRAWLSCOPE_BASE_URL", "http://localhost:3000") }
+        config.sitemap_path = lambda {
+          ENV.fetch("SITEMAP", Rails.public_path.join("sitemap.xml").to_s)
+        }
+        config.site_name = ENV.fetch("CRAWLSCOPE_SITE_NAME", "Application")
+      end
+
+      @applied = true
+    end
+  end
+end
+
+CrawlscopeConfiguration.apply if defined?(Crawlscope)

test/crawlscope/install_generator_test.rb

@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "generators/crawlscope/install_generator"
+require "open3"
+require "rbconfig"
+
+class CrawlscopeInstallGeneratorTest < Minitest::Test
+  def test_generates_lazy_initializer_and_task_loader
+    Dir.mktmpdir do |destination|
+      File.write(File.join(destination, "Rakefile"), <<~RUBY)
+        require_relative "config/application"
+        Rails.application.load_tasks
+      RUBY
+
+      Crawlscope::Generators::InstallGenerator.start([], destination_root: destination)
+
+      initializer = File.join(destination, "config/initializers/crawlscope.rb")
+      rakefile = File.read(File.join(destination, "Rakefile"))
+
+      assert File.exist?(initializer)
+      assert_includes File.read(initializer), "module CrawlscopeConfiguration"
+      assert_includes File.read(initializer), "CrawlscopeConfiguration.apply if defined?(Crawlscope)"
+      assert_includes rakefile, 'require "crawlscope/tasks"'
+      assert_operator rakefile.index('require "crawlscope/tasks"'), :<, rakefile.index('require_relative "config/application"')
+
+      _stdout, stderr, status = Open3.capture3(RbConfig.ruby, initializer)
+      assert status.success?, stderr
+
+      script = <<~RUBY
+        require "pathname"
+
+        module Rails
+          def self.public_path
+            Pathname.new("public")
+          end
+        end
+
+        require "crawlscope"
+        load ARGV.fetch(0)
+
+        configuration = Crawlscope.configuration
+        CrawlscopeConfiguration.apply
+        abort "configuration replaced" unless Crawlscope.configuration.equal?(configuration)
+        abort "base URL missing" unless configuration.base_url == "http://localhost:3000"
+        abort "sitemap missing" unless configuration.sitemap_path == "public/sitemap.xml"
+      RUBY
+      _stdout, stderr, status = Open3.capture3(
+        RbConfig.ruby,
+        "-I#{File.expand_path("../../lib", __dir__)}",
+        "-e",
+        script,
+        initializer
+      )
+      assert status.success?, stderr
+    end
+  end
+end