feat: add price per base unit

app/helpers/group_orders_helper.rb

@@ -53,4 +53,12 @@ module GroupOrdersHelper
       return 'missing-many'
     end
   end
+
+  def price_per_base_unit(article:, price:)
+    quantity_unit = QuantityUnit.parse(article.unit)
+    return nil unless quantity_unit.present?
+
+    scaled_price, base_unit = quantity_unit.scale_price_to_base_unit(price)
+    "#{number_to_currency(scaled_price)}/#{base_unit}"
+  end
 end

app/lib/quantity_unit.rb

@@ -0,0 +1,59 @@
+class QuantityUnit
+  def initialize(quantity, unit)
+    @quantity = quantity
+    @unit = unit
+  end
+
+  def self.parse(number_with_unit)
+    # remove whitespace
+    number_with_unit = number_with_unit.gsub(/\s+/, '')
+    # to lowercase
+    number_with_unit = number_with_unit.downcase
+    # remove numerical part
+    number = number_with_unit.gsub(/[^0-9.,]/, '')
+    # remove unit part
+    unit = number_with_unit.gsub(/[^a-zA-Z]/, '')
+    # convert comma to dot
+    number = number.gsub(',', '.')
+    # convert to float
+    number = number.to_f
+
+    return nil unless unit.in?(%w[g kg l ml])
+
+    QuantityUnit.new(number, unit)
+  end
+
+  def scale_price_to_base_unit(price)
+    return nil unless price.is_a?(Numeric)
+
+    factor = if @unit == 'kg' || @unit == 'l'
+      1
+    elsif @unit == 'g' || @unit == 'ml'
+      1000
+    end
+
+    scaled_price = price / @quantity * factor
+    scaled_price.round(2)
+
+    base_unit = if @unit == 'kg' || @unit == 'g'
+      'kg'
+    elsif @unit == 'l' || @unit == 'ml'
+      'L'
+    end
+
+    [scaled_price, base_unit]
+  end
+
+
+  def to_s
+    "#{@quantity} #{@unit}"
+  end
+
+  def quantity
+    @quantity
+  end
+
+  def unit
+    @unit
+  end
+end