require "../util.cr"
require "./thue.cr"
require "./rule.cr"

class Thue::Parser
  def initialize(code_io : IO)
    @raw_code = code_io.gets_to_end
    code_io.close # just in case
  end

  def parse
    rules = [] of Rule
    line_iterator = @raw_code.lines.each

    line_iterator.each do |line|
      case line
      when "", "::="
        # stops iteration of lines to be picked up by string builder
        break

      # returned match objects are provably not_nil, safe
      when .matches?(R_INPUT_RULE)
        m = line.match(R_INPUT_RULE).not_nil!
        rules << InputRule.new(m[1])

      when .matches?(R_OUTPUT_RULE)
        m = line.match(R_OUTPUT_RULE).not_nil!
        rules << OutputRule.new(m[1], m[2])

      when .matches?(R_NORMAL_RULE)
        m = line.match(R_NORMAL_RULE).not_nil!
        rules << NormalRule.new(m[1], m[2])

      else
        raise Util::ParserError.new("No separator between code and initial state near '#{line}'")
      end
    end

    state = String.build do |str|
      # resumes from where rule parser left off
      line_iterator.each do |line|
        str << line
        str << '\n'
      end
    end

    {rules, state}
  end
end