module GamesDice

  # specifies when and how a ComplexDie should be re-rolled
  class RerollRule

    # allowed reasons for making a reroll
    TYPES = {
      :reroll_add => '+',
      :reroll_new_die => '*',
      :reroll_new_keeper => '*',
      :reroll_subtract => '-',
      :reroll_replace => '|',
      :reroll_use_best => '/',
      :reroll_use_worst => '\\',
    }

    # trigger_op, trigger_value, type and limit set the attributes of the same name
    #  rule = GamesDice::RerollRule.new( 10, :<=, :reroll_add ) # an 'exploding' die
    def initialize trigger_value, trigger_op, type, limit=nil

      if ! trigger_value.respond_to?( trigger_op )
        raise ArgumentError, "trigger_value #{trigger_value.inspect} cannot respond to trigger_op #{trigger_value.inspect}"
      end

      unless TYPES.has_key?(type)
        raise ArgumentError, "Unrecognised reason for a re-roll #{type}"
      end

      @trigger_value = trigger_value
      @trigger_op = trigger_op
      @type = type
      @limit = limit ? Integer(limit) : 1000
      @limit = 1 if @type == :reroll_subtract
    end

    # a valid symbol for a method, which will be called against #trigger_value with the current
    # die result as a param. It should return true or false
    attr_reader :trigger_op

    # an Integer value or Range that will cause the reroll to occur. #trigger_op is called against it
    attr_reader :trigger_value

    # a symbol, should be one of the following:
    #   :reroll_add - add result of reroll to running total, and ignore :reroll_subtract for this die
    #   :reroll_new_die - roll a new die of the same type
    #   :reroll_new_keeper - roll a new die of the same type, and keep the result
    #   :reroll_subtract - subtract result of reroll from running total, and reverse sense of any further :reroll_add results
    #   :reroll_replace - use the new value in place of existing value for the die
    #   :reroll_use_best - use the new value if it is higher than the erxisting value
    #   :reroll_use_worst - use the new value if it is higher than the existing value
    attr_reader :type

    # maximum number of times this rule should be applied to a single die. If type is:reroll_subtract,
    # this value is always 1. A default value of 100 is used if not set in the constructor
    attr_reader :limit

    # runs the rule against a test value, returning truth value from calling the trigger_op method
    def applies? test_value
      @trigger_value.send( @trigger_op, test_value ) ? true : false
    end

  end # class RerollRule

end # module GamesDice