Beginnings of filter_query_param hook for modifying where clauses before the query in ActiveRecord

filter_query_param.rb

ActiveRecord::QueryMethods.class_eval do 
  # this is code from the original file, with the .map do |x| ... added to build_where
  # ideally, we would alias original_where where and work with the relation.where_values, but 
  # I haven't yet been successful in that attempt.
  def where(opts, *rest)
    return self if opts.blank?

    relation = clone
    relation.where_values += 
      build_where(opts, rest) # begin the added code (next line)
      .map do |condition|                            # is this a valid solution to the shared @@query_filters problem?
        ActiveRecord::Base.query_filters.select{|qf| qf[:table_name] == table.name }.each do |query_filter| 
          # I'm not really sure what we're trying to do here. Should we drop the 
          # requirement to pass the param name to the filter_query_param method and just
          # send the whole condition to the filter_method? 
          # 
          # If not, what are we sending as input to the filter_method? 
          
          condition.gsub!(/\b#{query_filter[:param]}\b/, query_filter[:filter_method].call(query_filter[:param]))
        end
        condition
      end
    # end the added code
    relation
  end
end

ActiveRecord::Base.class_eval do
  # this means all our models are sharing the same @@query_filters. That won't work.
  @@query_filters = []
  def self.query_filters
    @@query_filters
  end
    
  def self.filter_query_param(param, filter_method_name) # we can figure out the &block later
    @@query_filters << {:param=>param, :filter_method=>method(filter_method_name), :table_name=>self.table_name}
                                                                                   # is this a valid solution to the shared @@query_filters problem?
  end
end

class Blah < ActiveRecord::Base
  # I don't like having to call filter_query_param after defining the filter_methods
  # But if we wait until later to turn it into a method, it's not defined.
  # How can we work around that?
  def self.lower(match)
    "lower(#{match})"
  end
  
  filter_query_param(:title, :lower)
end