require 'parslet'
require 'ap'

module Dice
  class Bag < Parslet::Parser
    rule(:count)              { match('[0-9]').repeat(1).as(:count) }
    rule(:sides)              { str('d') >> match('[0-9]').repeat(1).as(:sides) }
    rule(:explode)            { str('e') >> match('[0-9]').repeat(1).as(:explode) }
    rule(:reroll)             { str('r') >> match('[0-9]').repeat(1).as(:reroll) }
    rule(:modifier_operator)  { match('[+|-]').as(:modifier_operator) }
    rule(:modifier)           { modifier_operator >> match('[0-9]').repeat(1).as(:modifier) }
    rule(:die)                { (count >> sides >> ( reroll | explode ).maybe >> ( reroll | explode ).maybe >> modifier.maybe).as(:die) }
    root(:die)
  end
end

class Trans < Parslet::Transform
  rule(:count => simple(:c)) { Integer(c) }
end

parser = Dice::Bag.new.parse('1d20')
ap parser
# {
#     :die => {
#         :count => "1",
#         :sides => "20"
#     }
# }

ap Trans.new.apply(parser)
#{
#    :die => {
#        :count => "1",
#        :sides => "20"
#    }
#}