# frozen_string_literal: true

require 'singleton'
require_relative 'duck_fiber'
require_relative 'nullary_relation'

module MiniKraken
  module Core
    # A nullary relation that always returns a failure outcome.
    class Fail < NullaryRelation
      include Singleton

      # Constructor. Initialize the relation's name & freeze it...
      def initialize
        super('fail')
      end

      # Returns a Fiber-like object (a DuckFiber).
      # When that object receives the message resume, it will
      # signal a failure to the provided context.
      # @param _actuals [Array] MUST be empty array for nullary relation.
      # @param ctx [Core::Context] Runtime context
      # @return [Core::DuckFiber]
      def solver_for(_actuals, ctx)
        DuckFiber.new(-> { ctx.failed! })
      end
    end # class
  end # module
end # module