module HashPersistent
  class Store
    attr_reader :key_value_store, :key_prefix, :cached_to
    
    def initialize(key_value_store, key_prefix)
      raise ArgumentError unless key_value_store.respond_to?(:has_key?) and key_prefix.respond_to?(:to_s)
      @key_value_store = key_value_store
      @key_prefix = key_prefix
      yield self if block_given?
    end
    
    def cached_to=(cache)
      raise ArgumentError unless cache.is_a?(HashPersistent::Store) if cache
      @cached_to = cache
    end
    
    def save(object)
      store_this = object.dup
      store_this.store = nil if store_this.respond_to?(:store)
      @key_value_store[@key_prefix + store_this.key] = store_this

      @cached_to.save(object) if @cached_to

      object.store = self if object.respond_to?(:store)
      self
    end

    def delete(object)
      @key_value_store.delete(@key_prefix + object.key)
      @cached_to.delete(object) if @cached_to

      object.store = self if object.respond_to?(:store)
      self
    end

    def find(key)
      if @cached_to
        found = @cached_to.find(key)
        unless found
          found = @key_value_store[@key_prefix + key]
          @cached_to.save(found) if found
        end
      else
        found = @key_value_store[@key_prefix + key]
      end
      return nil unless found

      object = found.dup
      object.store = self if object.respond_to?(:store)

      object
    end

    def create(key, class_to_create, *args, &block)
      object = class_to_create.new(*args, &block)
      object.key = key
      object.store = self if object.respond_to?(:store)
      object
    end
    
    def find_or_create(key, class_to_create, *args, &block)
      #TODO: Lock?
      save(create(key, class_to_create, *args, &block)) unless find(key)
      find(key)
    end
  end
end