Unit conversion and parsing

app/controllers/ingredients_controller.rb

@@ -66,6 +66,13 @@ class IngredientsController < ApplicationController
     @ingredients = Ingredient.where("name LIKE ?", query).order(:name)
   end
 
+  def convert
+    quantity = params[:quantity]
+    unit = params[:unit]
+    factor = params[:factor]
+    output_unit = params[:output_unit]
+  end
+
   private
     # Use callbacks to share common setup or constraints between actions.
     def set_ingredient

app/models/unit_conversion.rb

@@ -1,6 +1,9 @@
 module UnitConversion
 
-  UNIT_PARSING_REGEX = /^(?<value>(?:-?[0-9]+)?(?:\.?[0-9]*)?)\s*(?<unit>[a-z\/.\-()0-9]+)$/
+  DECIMAL_REGEX = /(?:-?[0-9]+)?\.[0-9]+/
+  RATIONAL_REGEX = /-?(?:[0-9]+|(?:[0-9] )?[0-9]+\/[0-9]+)/
+  UNIT_REGEX = /[\[\]a-zA-Z][\[\]a-zA-Z\/.\-()0-9]*/
+  UNIT_PARSING_REGEX = /^(?<value>#{DECIMAL_REGEX}|#{RATIONAL_REGEX})\s+(?<unit>#{UNIT_REGEX})$/
 
   UNIT_ALIASES = {
       cup: %w(cups c),
@@ -31,7 +34,8 @@ module UnitConversion
 
       if match && match[:value].present? && match[:unit].present?
         begin
-          Unitwise(match[:value].to_f, match[:unit])
+          value = get_value(match[:value])
+          Unitwise(value, normalize_unit_names(match[:unit]))
         rescue Unitwise::ExpressionError => err
           raise UnknownUnitError, err.message
         end
@@ -45,13 +49,55 @@ module UnitConversion
     end
 
     def normalize_unit_names(unit_description)
-      result = unit_description.dup
-
-      result = result.downcase.gsub(/[a-z]+/) do |match|
+      unit_description.downcase.gsub(/[a-z]+/) do |match|
         UNIT_ALIAS_MAP[match] || match
       end
+    end
 
-      result
+    def get_value(str)
+      if str =~ /^#{RATIONAL_REGEX}$/
+        parts = str.split(' ')
+        if parts.length == 2
+          whole = parts.first.to_r
+          fractional = parts.last.to_r
+          (whole.abs + fractional) * (whole < 0 ? -1.to_r : 1.to_r)
+        else
+          str.to_r
+        end
+      elsif str =~ /^#{DECIMAL_REGEX}$/
+        str.to_d
+      else
+        raise UnparseableUnitError, "str (#{str}) is not a valid number"
+      end
+    end
+
+    def convert(quantity, factor, input_unit, output_unit)
+
+      value = get_value(quantity)
+      factor = get_value(factor)
+
+      if value.is_a?(BigDecimal) && factor.is_a?(Rational)
+        factor = factor.to_d(10)
+      end
+
+      input_unit = normalize_unit_names(input_unit)
+      output_unit = normalize_unit_names(output_unit)
+
+      original = Unitwise(value, input_unit)
+      scaled = original * factor
+
+      converted = scaled.convert_to output_unit
+
+      if value.is_a? Rational
+        rational_val = converted.value.to_r.rationalize(0.001)
+        if rational_val.denominator == 1
+          rational_val.to_i.to_s
+        else
+          rational_val.to_s
+        end
+      else
+        "%g" % ("%.3f" % converted.value)
+      end
     end
 
   end

spec/models/unit_conversion_spec.rb

@@ -0,0 +1,157 @@
+require 'rails_helper'
+
+RSpec.describe UnitConversion do
+
+  describe '.get_value' do
+    it 'returns rationals' do
+      expect(UnitConversion.get_value('1/2')).to eq Rational(1, 2)
+      expect(UnitConversion.get_value('1 1/2')).to eq Rational(3, 2)
+      expect(UnitConversion.get_value('-1/2')).to eq Rational(-1, 2)
+      expect(UnitConversion.get_value('-1 1/2')).to eq Rational(-3, 2)
+    end
+
+    it 'returns decimals' do
+      expect(UnitConversion.get_value('-1')).to eq -1.to_d
+      expect(UnitConversion.get_value('1.0')).to eq 1.to_d
+      expect(UnitConversion.get_value('5.56')).to eq "5.56".to_d
+    end
+  end
+
+  describe '.convert' do
+    it 'scales decimal numbers' do
+      expect(UnitConversion.convert('1', '2', 'cup', 'cup')).to eq '2'
+      expect(UnitConversion.convert('1.5', '2', 'cup', 'cup')).to eq '3'
+      expect(UnitConversion.convert('4', '.5', 'cup', 'cup')).to eq '2'
+      expect(UnitConversion.convert('4', '1/2', 'cup', 'cup')).to eq '2'
+    end
+
+    it 'scales rational numbers' do
+      expect(UnitConversion.convert('1/2', '2', 'cup', 'cup')).to eq '1'
+      expect(UnitConversion.convert('1 1/2', '2', 'cup', 'cup')).to eq '3'
+      expect(UnitConversion.convert('4', '.5', 'cup', 'cup')).to eq '2'
+      expect(UnitConversion.convert('4', '1/2', 'cup', 'cup')).to eq '2'
+      expect(UnitConversion.convert('2', '1/3', 'cup', 'cup')).to eq '2/3'
+    end
+
+    it 'converts units' do
+      expect(UnitConversion.convert('1/2', '1', 'cup', 'tbsp')).to eq '8'
+      expect(UnitConversion.convert('8', '1', 'tablespoon', 'cup')).to eq '1/2'
+      expect(UnitConversion.convert('1', '1', 'tablespoon', 'cup')).to eq '1/16'
+      expect(UnitConversion.convert('2.0', '1', 'tablespoon', 'cup')).to eq '0.125'
+    end
+
+    it 'converts and scales' do
+      expect(UnitConversion.convert('1/2', '2', 'cup', 'tbsp')).to eq '16'
+      expect(UnitConversion.convert('2.0', '1 1/2', 'tablespoon', 'cup')).to eq '0.188'
+      expect(UnitConversion.convert('2', '1 1/2', 'tablespoon', 'cup')).to eq '3/16'
+    end
+  end
+
+  describe '.parse' do
+    it 'correctly parses strings to Units' do
+      data = {
+          '4 c' => Unitwise(4, 'cup'),
+          '5.5 oz' => Unitwise(5.5, 'ounce'),
+          '-4 tbsp' => Unitwise(-4, 'tablespoon'),
+          '223 g/c' => Unitwise(223, 'gram/cup'),
+          '1/3 c' => Unitwise("1/3".to_r, 'cup'),
+          '-5/16 g' => Unitwise("-5/16".to_r, 'gram')
+      }
+
+      data.each do |input, output|
+        expect(UnitConversion.parse(input)).to eq output
+      end
+    end
+
+    it 'raises UnknownUnitError with bad units' do
+      data = [
+          '5 cats',
+          '33 gulps/thinking',
+          '9.2 meeters/s2',
+          '5/8 floor'
+      ]
+
+      data.each do |input|
+        expect { UnitConversion.parse(input) }.to raise_error(UnitConversion::UnknownUnitError), "'#{input}' didn't raise"
+      end
+    end
+
+    it 'raises UnparseableUnitError on malformed string' do
+      data = [
+          '55',
+          '55.5',
+          '-55',
+          '-55.55',
+          '5.5/2 cups',
+          '2/3.0 cups',
+          'ounce',
+          '-.4 cups',
+          'gallons 6',
+          '5,5 tsp'
+      ]
+
+      data.each do |input|
+        expect { UnitConversion.parse(input) }.to raise_error(UnitConversion::UnparseableUnitError), "'#{input}' didn't raise"
+      end
+    end
+  end
+
+  describe '.density?' do
+    it 'returns true for any mass over volume unit' do
+      data = [
+          Unitwise(1, 'gram/cup'),
+          Unitwise(1, 'pound/gallon'),
+          Unitwise(1, 'ounce/tablespoon'),
+          Unitwise(1, 'ounce/centimeter3')
+      ]
+
+      data.each do |input|
+        expect(UnitConversion.density?(input)).to be_truthy
+      end
+    end
+
+    it 'returns false for any non density unit' do
+      data = [
+          Unitwise(1, 'cup'),
+          Unitwise(1, 'gram'),
+          Unitwise(1, 'gram/hour'),
+          Unitwise(1, 'centimeter3/ounce')
+      ]
+
+      data.each do |input|
+        expect(UnitConversion.density?(input)).to be_falsey
+      end
+    end
+  end
+
+  describe '.normalize_unit_name' do
+
+    it 'converts simple units' do
+      data = {
+          'c' => 'cup',
+          'cups' => 'cup',
+          'pints' => 'pint',
+          'g' => 'gram',
+          'grams' => 'gram'
+      }
+
+      data.each do |input, output|
+        expect(UnitConversion.normalize_unit_names(input)).to eq output
+      end
+    end
+
+    it 'converts mixed units' do
+      data = {
+          'oz/c' => 'ounce/cup',
+          'kg/cups' => 'kilogram/cup',
+          'pints/junk' => 'pint/junk'
+      }
+
+      data.each do |input, output|
+        expect(UnitConversion.normalize_unit_names(input)).to eq output
+      end
+    end
+
+  end
+
+end