Course code parser

course_code.rb

# A parser for course code strings
#
# Course codes are unique identifiers used to identify particular classes instructed at an edicuational institution.
#
# There isn't any real standard for course codes, but the examples below demonstrate common formats for course codes
# in the places where this parser is used.
#
# The parser itself is generated using [Treetop](https://github.com/nathansobo/treetop), so look there if you're interested
# in the underlying framework that generates the CourseCodeParser class when we load up our parser grammar.
#
# Course Code format
# ------------------
# FINN 936  1      # Standard format, department code, followed by course number
#                  # and section number
# GRN  900P SE     # CPT format, department code followed by a course number,
#                  # followed by a 'F' or 'P' (full-time, part-time), followed
#                  # by an 2+ character suffix indicating the department running
#                  # that particular CPT section/courseterm
# GRN  900F SE   1 # Identical to the above, with the addition
#                  # of a section number
#
# @example Parsing a course code in the standard course code format
#   cc = CourseCodeParser.new.parse('CEN  948  1')
#   cc.course_code.text_value # => 'CEN  948'
#   cc.course_code.department_code.text_value # => 'CEN'
#   cc.course_code.course_number.text_value # => '948'
#   cc.section_number.text_value # => '1'
#
# @example Parsing a course code in the CPT format
#   cc = CourseCodeParser.new.parse('GRN  900F CE')
#   cc.course_code.text_value # => 'GRN  900F'
#   cc.course_code.department_code.text_value # => 'GRN'
#   cc.course_code.course_number.text_value # => '900F'
#   cc.cpt_division.text_value # => 'CE'
#
# @note This class is generated by the Treetop grammer file defined in
#   `course_code.treetop`
class CourseCodeParser; end

# The above line is a bit of a hack to let us get generated documentation for
# the dynamically defined class CourseCodeParser. To keep that hack from
# from breaking real, useful code, we undefine it here.
Object.send(:remove_const, :CourseCodeParser)

Treetop.load 'course_code.treetop'

course_code.treetop

grammar CourseCode
  rule root
    (course_code space section_number / course_code space cpt_division space section_number / course_code space cpt_division) {
      # For our purposes, the 'section' identifier of a course code may be
      # a section_number, a cpt_division, or a combination of the two.
      def section
        if respond_to?(:cpt_division) && respond_to?(:section_number)
          format('%s %s', cpt_division.text_value, section_number.text_value)
        elsif respond_to?(:cpt_division)
          cpt_division.text_value
        elsif respond_to?(:section_number)
          section_number.text_value
        end
      end
    }
  end

  rule section_number
    number 1..2
  end

  rule course_code
    department_code space course_number
  end

  rule cpt_division
    letter letter
  end

  rule course_number
    number 2..3 letter?
  end

  rule department_code
    letter 2..4
  end

  rule number
    [0-9]
  end

  rule letter
    [a-zA-Z]
  end

  rule space
    ("\\\n" / [ \t])*
  end
end