class JekyllIncludeCache::Tag

def self.digest_cache
  @digest_cache ||= {}
end

def digest(path_hash, params_hash)
  md5 = Digest::MD5.new
  md5.update path_hash.to_s
  md5.update params_hash.to_s
  md5.hexdigest
end

def key(path, params)
  path_hash   = path.hash
  params_hash = quick_hash(params)
  self.class.digest_cache[path_hash] ||= {}
  self.class.digest_cache[path_hash][params_hash] ||= digest(path_hash, params_hash)
end

def path(context)
  site   = context.registers[:site]
  file   = render_variable(context) || @file
  locate_include_file(context, file, site.safe)
end

def quick_hash(params)
  return params.hash unless params
  md5 = Digest::MD5.new
  params.sort.each do |_, value|
    # Using the fact that Jekyll documents don't change during a build.
    # Instead of calculating the hash of an entire document (expensive!)
    # we just use its object id.
    if value.is_a? Jekyll::Drops::Drop
      md5.update value.object_id.to_s
    else
      md5.update value.hash.to_s
    end
  end
  md5.hexdigest
end

def render(context)
  path   = path(context)
  params = parse_params(context) if @params
  key = key(path, params)
  return unless path
  if JekyllIncludeCache.cache.key?(key)
    Jekyll.logger.debug "Include cache hit:", path
    JekyllIncludeCache.cache[key]
  else
    Jekyll.logger.debug "Include cache miss:", path
    JekyllIncludeCache.cache[key] = super
  end
end