tabletop-companion/app/services/dice_roller.rb

# frozen_string_literal: true

require "dice"

class DiceRoller
  attr_reader :dice
  attr_reader :result

  def initialize(roll_command, stat: nil)
    @roll_command = roll_command
    @stat = stat&.value
    @dice = []
  end

  def roll
    roll_command = parse_roll_command_references(roll_command)
    Dice.roll(roll_command)
  end

  def valid?
    return if @roll_command.blank?

    # No repeated math operators
    return false if @roll_command.match?(/[+\-*\/]{2,}/)

    # No leading or trailing math operators
    return false if @roll_command.match?(/\A[+\-*\/]/) || @roll_command.match?(/[+\-*\/]\z/)

    @roll_command.match?(
      /
      \A(
        (\d*d\d*) |
        ([+\-*\/]) |
        (\d+) |
        (self)
      )*\z/xi,
    )
  end

  private

    def roll_delimiters
      [ "+", "-", "*", "/" ]
    end

    def roll_dice(command)
      parts = command.downcase.split("d").compact_blank
      die_type = parts.last
      dice_number = parts.length > 1 ? parts.first.to_i : 1

      result = 0
      dice_number.times do
        roll = rand(1..die_type.to_i)
        result += roll
        dice << [ die_type, result ]
      end
      result
    end

    def parse_roll_command_references(roll_command)
      roll_command = @roll_command.include?("self") ? @roll_command.gsub("self", @stat.to_s) : @roll_command

      roll_command.split(Regexp.union(roll_delimiters)).each do |part|
        next if part.match?(/\A\d*\z/)
        next if part.match?(/\A\d*d\d*\z/)

        value = CharacterSheetFeature.find_by(slug: part).featurable.value
        raise "#{part} not found" if value.blank?
        roll_command.gsub!(part, value.to_s)
      end
      roll_command
    end
end