use ruby-units for unit parsing (closes foodcoops/foodsoft#200)

Conflicts:
	Gemfile
	Gemfile.lock

Gemfile

@@ -39,6 +39,7 @@ gem "rails-settings-cached", "0.3.1"
 gem 'resque'
 gem 'whenever', require: false # For defining cronjobs, see config/schedule.rb
 gem 'protected_attributes'
+gem 'ruby-units'
 
 # we use the git version of acts_as_versioned, and need to include it in this Gemfile
 gem 'acts_as_versioned', git: 'git://github.com/technoweenie/acts_as_versioned.git'

Gemfile.lock

@@ -281,6 +281,7 @@ GEM
     rspec-rerun (0.1.3)
       rspec (>= 2.11.0)
     ruby-prof (0.14.2)
+    ruby-units (1.4.4)
     rubyzip (1.1.0)
     sass (3.2.14)
     sass-rails (4.0.1)
@@ -421,6 +422,7 @@ DEPENDENCIES
   rspec-rails
   rspec-rerun
   ruby-prof
+  ruby-units
   sass-rails (~> 4.0.0)
   select2-rails
   selenium-webdriver

app/models/article.rb

@@ -117,6 +117,7 @@ class Article < ActiveRecord::Base
   # returns nil if units are eqal
   def convert_units
     if unit != shared_article.unit
+      # legacy, used by foodcoops in Germany
       if shared_article.unit == "KI" and unit == "ST" # 'KI' means a box, with a different amount of items in it
         # try to match the size out of its name, e.g. "banana 10-12 St" => 10
         new_unit_quantity = /[0-9\-\s]+(St)/.match(shared_article.name).to_s.to_i
@@ -126,13 +127,13 @@ class Article < ActiveRecord::Base
         else
           false
         end
-      else # get factors for fc and supplier
-        fc_unit_factor = FoodsoftConfig[:units][self.unit]
-        supplier_unit_factor = FoodsoftConfig[:units][self.shared_article.unit]
-        if fc_unit_factor and supplier_unit_factor
-          convertion_factor = fc_unit_factor / supplier_unit_factor
-          new_price = BigDecimal((convertion_factor * shared_article.price).to_s).round(2)
-          new_unit_quantity = ( 1 / convertion_factor) * shared_article.unit_quantity
+      else # use ruby-units to convert
+        fc_unit = (::Unit.new(unit) rescue nil)
+        supplier_unit = (::Unit.new(shared_article.unit) rescue nil)
+        if fc_unit and supplier_unit and fc_unit =~ supplier_unit
+          conversion_factor = (fc_unit.convert_to(supplier_unit.units) / supplier_unit).scalar
+          new_price = shared_article.price * conversion_factor
+          new_unit_quantity = shared_article.unit_quantity / conversion_factor
           [new_price, new_unit_quantity]
         else
           false

config/app_config.yml.SAMPLE

@@ -91,22 +91,6 @@ default: &defaults
     encoding: utf8
     socket: /opt/lampp/var/mysql/mysql.sock
 
-  # auto-units-conversion
-  # this is used for automatic article-synchronization to handle different units
-  # e.g. when foodcoop-unit should be 500g and supplier-unit is 1kg
-  units:
-    KG: 1
-    1kg: 1
-    500g: 0.5
-    400g: 0.4
-    300g: 0.3
-    250g: 0.25
-    200g: 0.2
-    150g: 0.15
-    125g: 0.125
-    100g: 0.1
-    50g: 0.05
-
 development:
   <<: *defaults
 

config/initializers/ruby_units.rb

@@ -0,0 +1,37 @@
+# add some more units
+
+if defined? RubyUnits
+  RubyUnits::Unit.redefine!('liter') do |unit|
+    unit.aliases   += %w{ltr}
+  end
+
+  RubyUnits::Unit.redefine!('kilogram') do |unit|
+    unit.aliases   += %w{KG}
+  end
+
+  RubyUnits::Unit.redefine!('gram') do |unit|
+    unit.aliases   += %w{gr}
+  end
+
+  RubyUnits::Unit.define('piece') do |unit|
+    unit.definition = RubyUnits::Unit.new('1 each')
+    unit.aliases    = %w{pc pcs piece pieces}   # locale: en
+    unit.aliases   += %w{st stuk stuks}         # locale: nl
+    unit.kind       = :counting
+  end
+
+  # we use pc for piece, not parsec
+  RubyUnits::Unit.redefine!('parsec') do |unit|
+    unit.aliases = unit.aliases.reject {|u| u=='pc'}
+    unit.display_name = 'parsec'
+  end
+
+  # workaround for ruby-units' require mathn warning: "zero and implicit precision is deprecated."
+  # default precision of 8 which same as all database definitions in db/migrate/20131213002332_*.rb
+  class Rational
+    alias orig_to_d to_d
+    def to_d(precision=8)
+      orig_to_d(precision)
+    end
+  end
+end