parser.rb

require 'csv'
require 'zlib'

# Mandatory: Create a single output file containing the date sent, the sender and the subject for each of the messages

class EmailParser

  def initialize(filepath)
    @filepath = filepath
  end

  def flush_to_file ary
    CSV.open("output.csv", "a") do |csv|
      csv << [ary[0], ary[1], ary[2]]
    end
  end
  
  def parse_msg
    if @filepath.to_s.strip.length == 0
      raise ArgumentError, "Missing argument.  Include a filepath to process."
    end

    Zlib::GzipReader.open(@filepath) do |file|
      msg_fields = []
      dateFlag, fromFlag, subjectFlag = false
      
      file.each_line do |line|
        case line
        when /Date: /
          unless dateFlag == true
            msg_fields[0] = line
            dateFlag = true
          end
        when /From:/
          msg_fields[1] = line unless fromFlag == true
          fromFlag = true
        when /Subject:/
          msg_fields[2] = line unless subjectFlag == true
          subjectFlag = true
        end

        if msg_fields.count == 3
          #puts msg_fields.inspect
          #flush_to_file msg_fields
          msg_fields.clear
          dateFlag, fromFlag, subjectFlag = false
        end
      end
    end
  end
  
end

parser = EmailParser.new(ARGV[0]).parse_msg