Parser for file made up of sections

Question

I'm parsing a file made up of various sections. I have a current_section variable that tracks which portion of the file I'm currently processing and the following check_for_next_section method that returns either the next section based on the contents of the current line or current_section if there are no matches based on the contents of the current line.

This method is getting flagged by rubocop for both 'perceived complexity' and 'cyclomatic complexity'. How can I reduce these?

SECTION_HEADERS = { 
 hawaii_1: '"[2] For Hawaii, the following Postal Codes are Zone 44 for Ground', 
 hawaii_2: '"For Hawaii, the following Postal Codes are Zone 46 for Ground', 
 alaska_1: '"[3] For Alaska, the following Postal Codes are Zone 44 for Ground', 
 alaska_2: '"For Alaska, the following Postal Codes are Zone 46 for Ground' 
}.freeze 
 
def check_for_next_section(line, current_section) 
 return :zones if current_section == :preamble && line.starts_with?('Dest. ZIP') 
 return :hawaii_1 if current_section == :zones && !line.blank? && line.starts_with?(SECTION_HEADERS[:hawaii_1])
 return :hawaii_2 if current_section == :hawaii_1 && line.starts_with?(SECTION_HEADERS[:hawaii_2]) 
 return :alaska_1 if current_section == :hawaii_2 && line.starts_with?(SECTION_HEADERS[:alaska_1]) 
 return :alaska_2 if current_section == :alaska_1 && line.starts_with?(SECTION_HEADERS[:alaska_2]) 
 
 current_section 
end

Answer 1

If complexity is getting to high for a method it's usually a good idea to split out helper methods. If you end up to pass in the same parameters to each of these methods, it could also be a good idea to extract a class.

Some solution could be

def check_for_next_section(line, current_section)
 ZoneCheck.new(line, current_section).run
end
class ZoneCheck
 SECTION_HEADERS = {
 hawaii_1: '"[2] For Hawaii, the following Postal Codes are Zone 44 for Ground',
 hawaii_2: '"For Hawaii, the following Postal Codes are Zone 46 for Ground',
 alaska_1: '"[3] For Alaska, the following Postal Codes are Zone 44 for Ground',
 alaska_2: '"For Alaska, the following Postal Codes are Zone 46 for Ground'
 }.freeze
 def initialize(line, current_section)
 @line = line
 @current_section = current_section
 end
 def run
 if zones?
 :zones
 elsif hawaii_1?
 :hawaii_1
 elsif hawaii_2?
 :hawaii_2
 elsif alaska_1?
 :alaska_1
 elsif alaska_2?
 :alaska_2
 else
 current_section
 end 
 end
 private
 attr_reader :line, :current_section
 def zones?
 current_section == :preamble &&
 line.starts_with?('Dest. ZIP')
 end
 def hawaii_1?
 current_section == :zones &&
 !line.blank? &&
 line.starts_with?(SECTION_HEADERS[:hawaii_1])
 end
 def hawaii_2?
 current_section == :hawaii_1 &&
 line.starts_with?(SECTION_HEADERS[:hawaii_2])
 end
 def alaska_1?
 current_section == :hawaii_2 &&
 line.starts_with?(SECTION_HEADERS[:alaska_1])
 end
 def alaska_2?
 current_section == :alaska_1 &&
 line.starts_with?(SECTION_HEADERS[:alaska_2])
 end
end

Answer 2

I do not understand why !line.blank? is needed. Assuming it is not you could create a second constant:

NEXT_SECTION = {
 { current: :preamble, line_start: 'Dest.' } => :zones 
 { current: :zones, line_start: SECTION_HEADERS[:hawaii_1] } => :hawaii_1
 { current: :hawaii_1, line_start: SECTION_HEADERS[:hawaii_2] } => :hawaii_2,
 { current: :hawaii_2, line_start: SECTION_HEADERS[:alaska_1] } => :alaska_1,
 { current: :alaska_1, line_start: SECTION_HEADERS[:alaska_2] } => :alaska_2
}.freeze

and write your method as follows.

def next_section(current_section, line)
 h, next_section = NEXT_SECTION.find do |h, next_section|
 h == { current: current_section, line_start: line[0, h[:line_start].size] }
 end
 h.nil? ? current_section : next_section
end