Use Rails app root to join paths

Without that it is not always ensured that the path is
the hosts apps root path.

lib/generators/alchemy/install/install_generator.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
-require "rails"
+require "rails/generators"
 
 module Alchemy
   module Generators
@@ -14,41 +14,41 @@ class InstallGenerator < ::Rails::Generators::Base
       source_root File.expand_path("files", __dir__)
 
       def copy_config
-        copy_file "#{config_path}/config.yml", "config/alchemy/config.yml"
+        copy_file "#{gem_config_path}/config.yml", app_config_path.join("alchemy", "config.yml")
       end
 
       def copy_yml_files
         %w(elements page_layouts menus).each do |file|
-          template "#{__dir__}/templates/#{file}.yml.tt", "config/alchemy/#{file}.yml"
+          template "#{__dir__}/templates/#{file}.yml.tt", app_config_path.join("alchemy", "#{file}.yml")
         end
       end
 
       def install_assets
-        copy_file "all.js", "vendor/assets/javascripts/alchemy/admin/all.js"
-        copy_file "all.css", "vendor/assets/stylesheets/alchemy/admin/all.css"
+        copy_file "all.js", app_vendor_assets_path.join("javascripts", "alchemy", "admin", "all.js")
+        copy_file "all.css", app_vendor_assets_path.join("stylesheets", "alchemy", "admin", "all.css")
       end
 
       def copy_demo_views
         return if @options[:skip_demo_files]
 
-        copy_file "application.html.erb", "app/views/layouts/application.html.erb"
-        copy_file "article.scss", "app/assets/stylesheets/alchemy/elements/article.scss"
+        copy_file "application.html.erb", app_views_path.join("layouts", "application.html.erb")
+        copy_file "article.scss", app_assets_path.join("stylesheets", "alchemy", "elements", "article.scss")
 
         stylesheet_require = " *= require_tree ./alchemy/elements\n"
-        if File.exist?("app/assets/stylesheets/application.css")
-          insert_into_file "app/assets/stylesheets/application.css", stylesheet_require,
+        if File.exist?(app_assets_path.join("stylesheets", "application.css"))
+          insert_into_file app_assets_path.join("stylesheets", "application.css"), stylesheet_require,
             before: " */"
         else
-          create_file "app/assets/stylesheets/application.css", "/*\n#{stylesheet_require} */\n"
+          create_file app_assets_path.join("stylesheets", "application.css"), "/*\n#{stylesheet_require} */\n"
         end
 
-        copy_file "_article.html.erb", "app/views/alchemy/elements/_article.html.erb"
-        copy_file "_standard.html.erb", "app/views/alchemy/page_layouts/_standard.html.erb"
-        copy_file "alchemy.en.yml", "config/locales/alchemy.en.yml"
+        copy_file "_article.html.erb", app_views_path.join("alchemy", "elements", "_article.html.erb")
+        copy_file "_standard.html.erb", app_views_path.join("alchemy", "page_layouts", "_standard.html.erb")
+        copy_file "alchemy.en.yml", app_config_path.join("locales", "alchemy.en.yml")
       end
 
       def copy_dragonfly_config
-        template "#{__dir__}/templates/dragonfly.rb.tt", "config/initializers/dragonfly.rb"
+        template "#{__dir__}/templates/dragonfly.rb.tt", app_config_path.join("initializers", "dragonfly.rb")
       end
 
       def install_gutentag_migrations
@@ -57,8 +57,28 @@ def install_gutentag_migrations
 
       private
 
-      def config_path
-        @_config_path ||= File.expand_path("../../../../../config/alchemy", __dir__)
+      def gem_config_path
+        @_config_path ||= File.expand_path("../../../../config/alchemy", __dir__)
+      end
+
+      def app_config_path
+        @_app_config_path ||= app_root.join("config")
+      end
+
+      def app_views_path
+        @_app_views_path ||= app_root.join("app", "views")
+      end
+
+      def app_assets_path
+        @_app_assets_path ||= app_root.join("app", "assets")
+      end
+
+      def app_vendor_assets_path
+        @_app_vendor_assets_path ||= app_root.join("vendor", "assets")
+      end
+
+      def app_root
+        @_app_root ||= Rails.root
       end
     end
   end