require 'dry/core/constants'
require 'dry/monads/registry'

module Dry
  # Common, idiomatic monads for Ruby
  #
  # @api public
  module Monads
    # @private
    def self.included(base)
      if all_loaded?
        base.include(*constructors)
      else
        raise "Load all monads first with require 'dry/monads/all'"
      end
    end

    # Build a module with cherry-picked monads.
    # It saves a bit of typing when you add multiple
    # monads to one class. Not loaded monads get loaded automatically.
    #
    # @example
    #   require 'dry/monads'
    #
    #   class CreateUser
    #     include Dry::Monads[:result, :do]
    #
    #     def initialize(repo, send_email)
    #       @repo = repo
    #       @send_email = send_email
    #     end
    #
    #     def call(name)
    #       if @repo.user_exist?(name)
    #         Failure(:user_exists)
    #       else
    #         user = yield @repo.add_user(name)
    #         yield @send_email.(user)
    #         Success(user)
    #       end
    #     end
    #   end
    #
    # @param [Array<Symbol>] monads
    # @return [Module]
    # @api public
    def self.[](*monads)
      monads.sort!
      @mixins.fetch_or_store(monads.hash) do
        monads.each { |m| load_monad(m) }
        mixins = monads.map { |m| registry.fetch(m) }
        ::Module.new { include(*mixins) }.freeze
      end
    end
  end
end