class Rails::Generators::Db::System::ChangeGenerator

def self.default_generator_root
  path = File.expand_path(File.join(base_name, "app"), base_root)
  path if File.exist?(path)
end

def all_database_gems
  DATABASES.map { |database| gem_for_database(database) }
end

def all_database_gems_regex
  all_database_gem_names = all_database_gems.map(&:first)
  /(\b#{all_database_gem_names.join('\b|\b')}\b)/
end

def edit_database_config
  template("config/databases/#{options[:database]}.yml", "config/database.yml")
end

def edit_gemfile
  name, version = gem_for_database
  gsub_file("Gemfile", all_database_gems_regex, name)
  gsub_file("Gemfile", gem_entry_regex_for(name), gem_entry_for(name, *version))
end

def gem_entry_for(*gem_name_and_version)
  gem_name_and_version.map! { |segment| "\"#{segment}\"" }
  "gem #{gem_name_and_version.join(", ")}"
end

def gem_entry_regex_for(gem_name)
  /^gem.*\b#{gem_name}\b.*/
end

def initialize(*)
  super
  unless DATABASES.include?(options[:to])
    raise Error, "Invalid value for --to option. Supported preconfigurations are: #{DATABASES.join(", ")}."
  end
  opt = options.dup
  opt[:database] ||= opt[:to]
  self.options = opt.freeze
end