rafaelgonzalez/dice_box

module DiceBox
  # Representation of a dice
  class Dice
    # @!attribute [r] sides
    # @return [Array] the Array of Sides of the Dice
    attr_reader :sides

    # @!attribute [r] rolled_side
    # @return [Dice::Side] the last rolled Side
    attr_reader :rolled_side

    # @!attribute [r] rolled
    # @return [Integer] the result from the previous roll
    attr_reader :rolled
    alias_method :result, :rolled
    alias_method :rolled_value, :rolled

    # @param sides_number [Integer] the number of Sides this Dice should have
    def initialize(sides_number)
      @sides = build_sides(sides_number)
      @rolled_side = nil
      @rolled = nil
    end

    # Rolls multiple dices with the same number of sides
    # @param sides_number [Integer] the number of sides of the dices
    # @param amount [Integer] the number of dices rolled
    # @return [Integer] the total roll result
    def self.roll(sides_number, amount = 1)
      return 0 if amount.nil? || amount <= 0

      amount.times.map do
        Random.new.rand(1..sides_number)
      end.reduce(&:+)
    end

    # Rolls the dice
    # @note Sets #rolled_side to the rolled Side
    # @note Sets #rolled to the rolled Side's value
    # @return [Integer] the value of the rolled Side
    def roll
      @rolled_side = balanced? ? sides.sample : weighted_roll
      @rolled = rolled_side.value
    end

    # Returns the highest value the Dice can roll
    # @return [Integer] maximum roll value
    def maximum
      sides.map(&:value).max
    end
    alias_method :max, :maximum

    # Returns the lowest value the Dice can roll
    # @return [Integer] minimum roll value
    def minimum
      sides.map(&:value).min
    end
    alias_method :min, :minimum

    # Determines if all Sides of the Dice have the same weight
    # @return [Boolean]
    def fair?
      !crooked?
    end
    alias_method :balanced?, :fair?

    # Determines if at least one Side has a different weight than any
    # other Side of the Dice
    # @return [Boolean]
    def crooked?
      sides.map(&:weight).any? do |weight|
        weight != sides.first.weight
      end
    end
    alias_method :loaded?, :crooked?

    # The weight of the Dice, sum of all Sides weights
    # @return [Float] the weight of the Dice
    def weight
      sides.map(&:weight).reduce(&:+)
    end

    # Returns a Hash with all the possible values for this Dice,
    # with their respective probabilities.
    #
    # @return [Hash] the probabilities
    def probabilities
      hash = {}

      sides.map(&:value).each do |value|
        hash[value] = probability(value)
      end

      hash
    end

    # The probability to roll a given Side
    #
    # @param side [DiceBox::Dice::Side] the side
    # @return [Float] the probability
    #
    # @note If the Dice has the Side instance defined multiple times,
    #       this will influence the result, see example.
    #
    # @example A Dice with a Side defined multiple times.
    #   dice = DiceBox::Dice.new(3)
    #   side = DiceBox::Dice::Side.new(1)
    #   dice.sides[0] = dice.sides[1] = dice.sides[2] = side
    #   side.probability_for_side(side) # => 1.0
    def probability_for_side(side)
      equal_sides = sides.select { |s| s == side }

      equal_sides.map(&:weight).reduce(:+).to_f / weight.to_f
    end

    # The probability to roll a given value
    # @param value [Fixnum]
    # @return [Float] the probability
    def probability(value)
      probability_for_sides(:==, value)
    end

    # The probability to roll a value greater than the given value
    # @param value [Fixnum]
    # @return [Float] the probability
    def probability_greater_than(value)
      probability_for_sides(:>, value)
    end
    alias_method :probability_gt, :probability_greater_than

    # The probability to roll a value greater than or equal to the given value
    # @param value [Fixnum]
    # @return [Float] the probability
    def probability_greater_than_or_equal(value)
      probability_for_sides(:>=, value)
    end
    alias_method :probability_gtoe, :probability_greater_than_or_equal

    # The probability to roll a value lower than the given value
    # @param value [Fixnum]
    # @return [Float] the probability
    def probability_lower_than(value)
      probability_for_sides(:<, value)
    end
    alias_method :probability_lt, :probability_lower_than

    # The probability to roll a value lower than or equal to the given value
    # @param value [Fixnum]
    # @return [Float] the probability
    def probability_lower_than_or_equal(value)
      probability_for_sides(:<=, value)
    end
    alias_method :probability_ltoe, :probability_lower_than_or_equal

    private

    # Instantiates multiple Sides
    # @param sides_number [Integer] the number of Sides to instantiate
    # @return [Array] the Array of instantiated Sides
    def build_sides(sides_number)
      sides_number.times.map do |number|
        Side.new(number + 1)
      end
    end

    # Rolls the Dice taking Sides weights into account
    # @return [Side] the rolled Side
    def weighted_roll
      num = rand(0..weight)

      sides.each do |side|
        return side if side.weight > num
        num -= side.weight
      end
    end

    def probability_for_sides(operator, value)
      sides_list = sides.select { |s| s.value.public_send(operator, value) }

      if fair?
        fair_probability_for_sides(sides_list)
      else
        weighted_probability_for_sides(sides_list)
      end
    end

    def fair_probability_for_sides(sides_list)
      sides_list.size.to_f / sides.size.to_f
    end

    def weighted_probability_for_sides(sides_list)
      sides_list.map(&:weight).reduce(:+).to_f / weight.to_f
    end
  end
end