Moved formula code/validation to separate module

app/models/quantity.rb

@@ -1,6 +1,5 @@
 class Quantity < ActiveRecord::Base
-  require 'ripper'
-  QUANTITY_TTYPES = [:on_ident, :on_tstring_content, :on_const]
+  include BodyTracking::Formula
 
   enum domain: {
     diet: 0,
@@ -16,41 +15,7 @@ class Quantity < ActiveRecord::Base
   validate if: -> { parent.present? } do
     errors.add(:parent, :parent_domain_mismatch) unless domain == parent.domain
   end
-  validate if: -> { formula.present? } do
-    # 1st: check if formula is valid Ruby code
-    tokenized_length = Ripper.tokenize(formula).join.length
-    unless tokenized_length == formula.length
-      errors.add(:formula, :invalid_formula, {part: formula[0...tokenized_length]})
-    end
-
-    # 2nd: check if formula contains only allowed token types
-    identifiers = []
-    Ripper.lex(formula).each do |location, ttype, token|
-      case
-      when QUANTITY_TTYPES.include?(ttype)
-        identifiers << token
-      when [:on_sp, :on_int, :on_rational, :on_float, :on_tstring_beg, :on_tstring_end,
-        :on_lparen, :on_rparen].include?(ttype)
-      when :on_op == ttype && '+-*/'.include?(token)
-      else
-        errors.add(:formula, :disallowed_token,
-                   {token: token, ttype: ttype, location: location})
-      end
-    end
-
-    # 3rd: check for disallowed function calls (they are not detected by Ripper.lex)
-    # FIXME: this is unreliable (?) detection of function calls, should be replaced
-    # with parsing Ripper.sexp if necessary
-    function = Ripper.slice(formula, 'ident [sp]* lparen')
-    errors.add(:formula, :disallowed_function_call, {function: function}) if function
-
-    # 4th: check if identifiers used in formula correspond to existing quantities
-    identifiers.uniq!
-    quantities = self.project.quantities.where(name: identifiers).pluck(:name)
-    if quantities.length != identifiers.length
-      errors.add(:formula, :unknown_quantity, {quantities: identifiers - quantities})
-    end
-  end
+  validates :formula, formula: true
 
   after_initialize do
     if new_record?
@@ -64,14 +29,14 @@ class Quantity < ActiveRecord::Base
 
   def formula_quantities
     q_names = Ripper.lex(formula).map do |*, ttype, token|
-      token if QUANTITY_TTYPES.include?(ttype)
+      token if BodyTracking::Formula::QUANTITY_TTYPES.include?(ttype)
     end.compact
     self.project.quantities.where(name: q_names).to_a
   end
 
   def calculate(inputs)
     paramed_formula = Ripper.lex(formula).map do |*, ttype, token|
-      QUANTITY_TTYPES.include?(ttype) ? "params['#{token}']" : token
+      BodyTracking::Formula::QUANTITY_TTYPES.include?(ttype) ? "params['#{token}']" : token
     end.join
     inputs.map { |i, values| [i, get_binding(values).eval(paramed_formula)] }
   end