rulebook_rewrite.rb

module RuleBook
  def RuleBook.add_rules(object, instance_or_class, rules)
    instance_or_class = instance_or_class.to_s.downcase.strip.to_sym
    raise(ArgumentError, "'instance_or_class' must equal :instance or :class") unless [:instance, :class].include?(instance_or_class)
    raise(ArgumentError, "'rules' must be a Hash") unless rules.is_a?(Hash)

    unless object.instance_variable_get(:@_rulebook_initiated) # Class instance variable. Not class variable. Not instance variable. Is confusing.
      object.instance_variable_set(:@_rulebook_initiated, true)
      object.instance_variable_set(:@_rulebook, {:instance=>{}, :class=>{}}) # @_rulebook is actually two rulebooks, instance and class
    end

    case instance_or_class
      when :instance then object.instance_eval { include RuleBook::InstanceMethods }
      when :class then object.instance_eval { extend RuleBook::ClassMethods }
    end

    object.instance_variable_get(:@_rulebook)[instance_or_class].merge!(rules)
  end

  def RuleBook.find_and_call_rule_if_exists(object, instance_or_class, method, *args, &blk)
    instance_or_class = instance_or_class.to_s.downcase.strip.to_sym
    raise(ArgumentError, "'instance_or_class' must equal :instance or :class") unless [:instance, :class].include?(instance_or_class)
    where_to_find_rulebook = instance_or_class == :instance ? object.class : object
    rulebook = where_to_find_rulebook.instance_variable_get(:@_rulebook)[instance_or_class]
    matching_rules = rulebook.find_all{ |a| regex = a.first; !!regex.match(method.to_s) }

    unless matching_rules.empty?
      last_result = nil

      matching_rules.each do |regex, method_assigned_to_rule|
        match = regex.match(method)
        last_result = object.send(method_assigned_to_rule, *match.captures, *args)
      end

      last_result
    else
      raise(NoMethodError, "method '#{method}' does not exist.")
    end
  end

  module InstanceMethods
    def method_missing(method, *args, &blk)
      RuleBook.find_and_call_rule_if_exists(self, :instance, method, *args, &blk)
    end
  end

  module ClassMethods
    def method_missing(method, *args, &blk)
      RuleBook.find_and_call_rule_if_exists(self, :class, method, *args, &blk)
    end
  end
end

class Module
  def instance_rule(rules)
    RuleBook.add_rules(self, :instance, rules)
  end
  def class_rule(rules)
    RuleBook.add_rules(self, :class, rules)
  end
end