engine.rb

require "importmap/map"

# Use Rails.application.importmap to access the map
Rails::Application.send(:attr_accessor, :importmap)
Rails::Application.send(:attr_accessor, :importmaps)

module Importmap
  class Engine < ::Rails::Engine
    config.importmap = ActiveSupport::OrderedOptions.new
    config.importmap.paths = []
    config.importmap.sweep_cache = Rails.env.development? || Rails.env.test?
    config.importmap.cache_sweepers = []
    config.importmap.rescuable_asset_errors = []

    config.autoload_once_paths = %W( #{root}/app/helpers )

    initializer "importmap" do |app|
      app.importmap = Importmap::Map.new
      app.importmaps = ActiveSupport::OrderedOptions.new

      app.config.importmap.paths << app.root.join("config/importmap.rb")
      app.config.importmap.paths.each { |path| app.importmap.draw(path) }

      Dir.glob(app.root.join("config", "importmaps", "*.rb")).each do |path|
        app.importmaps[File.basename(path, ".rb")] = Importmap::Map.new.draw(path)
      end
    end

    initializer "importmap.reloader" do |app|
      unless app.config.cache_classes
        Importmap::Reloader.new.tap do |reloader|
          reloader.execute
          app.reloaders << reloader
          app.reloader.to_run { reloader.execute }
        end
      end
    end

    initializer "importmap.cache_sweeper" do |app|
      if app.config.importmap.sweep_cache && !app.config.cache_classes
        app.config.importmap.cache_sweepers << app.root.join("app/javascript")
        app.config.importmap.cache_sweepers << app.root.join("vendor/javascript")

        app.importmap.cache_sweeper(watches: app.config.importmap.cache_sweepers)
        app.importmaps.each_value { |map| map.cache_sweeper(watches: app.config.importmap.cache_sweepers) }

        ActiveSupport.on_load(:action_controller_base) do
          before_action do
            Rails.application.importmap.cache_sweeper.execute_if_updated
            Rails.application.importmaps.each_value { |map| map.cache_sweeper.execute_if_updated }
          end
        end
      end
    end

    initializer "importmap.assets" do |app|
      if app.config.respond_to?(:assets)
        app.config.assets.paths << Rails.root.join("app/javascript")
        app.config.assets.paths << Rails.root.join("vendor/javascript")
      end
    end

    initializer "importmap.helpers" do
      ActiveSupport.on_load(:action_controller_base) do
        helper Importmap::ImportmapTagsHelper
      end
    end

    initializer "importmap.rescuable_asset_errors" do |app|
      if defined?(Propshaft)
        app.config.importmap.rescuable_asset_errors << Propshaft::MissingAssetError
      end

      if defined?(Sprockets::Rails)
        app.config.importmap.rescuable_asset_errors << Sprockets::Rails::Helper::AssetNotFound
      end
    end
  end
end