require 'monitor'

class Module
  def cache_method *methods
    DeclarativeCache.cache_method self, *methods
  end
  
  def cache_method_with_params *methods
    DeclarativeCache.cache_method_with_params self, *methods
  end  
end

class Object
  def clear_cache_method
    instance_variables.each do |iv|
      remove_instance_variable iv if iv =~ /^@cached_/
    end
  end
end

module DeclarativeCache    
  DISABLED = false

  warn "CASHE DISABLED" if DISABLED
  unless DISABLED    
    class << self
                
      def cache_method klass, *methods
        methods.each do |method|
          klass.class_eval do
            als = "cached_#{escape_method(method)}"
            iv_check = "@#{als}_check"
            iv = "@#{als}"
          
            raise "Can't cache the #{method} twice!" if instance_methods.include?(als)
            
            alias_method als, method
            
            define_method method do |*args|
              raise "You tried to use cache without params for method with params (use 'cache_method_with_params' instead)!" unless args.empty?
              unless cached = instance_variable_get(iv)
                unless check = instance_variable_get(iv_check)
                  cached = send als
                  instance_variable_set iv, cached
                  instance_variable_set iv_check, true
                end
              end
              cached
            end
          end
        end
      end
      
      def cache_method_with_params klass, *methods        
        methods.each do |method|  
          klass.class_eval do      
            als = "cached_#{escape_method(method)}"
            iv = "@#{als}"
            
            raise "Can't cache the '#{method}' twice!" if instance_methods.include?(als)
            
            alias_method als, method
                    
            define_method method do |*args| 
              unless results = instance_variable_get(iv)
                results = Hash.new(NotDefined)
                instance_variable_set iv, results
              end
              
              result = results[args]
                        
              if result.equal? NotDefined 
                result = send als, *args
                results[args] = result
              end
            
              result
            end
          end
        end
      end
      
    end
  end
end