README.md

1. don't use self.method name, just put it in class << self
2. don't use get_property, use the property name directly get_ and set_ is considered noise in ruby
3. always add () in function definition with parameters
4. you should always specify your rescued excpetion class
5. there are a lot of cryptic lines with implicit logic like flatten[1]
6. be consistent with methods names "_by(id)"

drug_info.rb

class Info
  class << self
    def category_by(id)
      cat_id = read_file('drug_category').keep_if { |c| c[0] == id }.flatten[1]
      categories = read_file('category')
      cat = categories.select { |c| c[0] == cat_id }
      parent_id = cat.flatten[1]
      parent_cat = categories.select { |c| c[0] == parent_id }
      parent_cat.flatten[2].empty? ? cat.flatten[2].to_s : "#{cat.flatten[2]} (#{parent_cat.flatten[2]})"
    rescue StandardError => error
      puts error
    end

    def company_by(id)
      read_file('companies').keep_if { |c| c[0] == id }.flatten[1]
    end

    def active_ingredients(id)
      ais = read_file('drug_ai')
      active_ingredient = ais.select { |a| a[1] == id }
      active_ingredient.each_with_object([]) do |ac, ing|
        concentration = ac[2]
        name = read_file('ai').select { |n| n[0] == ac[0] }.flatten
        unit = read_file('drug_ai_unit').select { |u| u[0] == ac[3] }.flatten
        ing << "#{name[1].capitalize} #{concentration} #{unit[1].downcase}"
      end
    end

    def form_by(id)
      read_file('form').select { |f| f[0] == id }.flatten[1]
    end

    def read_file(file)
      file_name = file.end_with?('.csv') ? file : file + '.csv'
      CSV.read(file_name, col_sep: '|').tap(&:shift)
    end
  end
end