class ActionView::Digestor

def compute_and_store_digest(cache_key, options) # called under @@digest_monitor lock
  klass = if options[:partial] || options[:name].include?("/_")
    # Prevent re-entry or else recursive templates will blow the stack.
    # There is no need to worry about other threads seeing the +false+ value,
    # as they will then have to wait for this thread to let go of the @@digest_monitor lock.
    pre_stored = @@cache.put_if_absent(cache_key, false).nil? # put_if_absent returns nil on insertion
    PartialDigestor
  else
    Digestor
  end
  digest = klass.new(options).digest
  # Store the actual digest if config.cache_template_loading is true
  @@cache[cache_key] = stored_digest = digest if ActionView::Resolver.caching?
  digest
ensure
  # something went wrong or ActionView::Resolver.caching? is false, make sure not to corrupt the @@cache
  @@cache.delete_pair(cache_key, false) if pre_stored && !stored_digest
end

def dependencies
  DependencyTracker.find_dependencies(name, template)
rescue ActionView::MissingTemplate
  logger.try :error, "  '#{name}' file doesn't exist, so no dependencies"
  []
end

def dependency_digest
  template_digests = dependencies.collect do |template_name|
    Digestor.digest(name: template_name, finder: finder, partial: true)
  end
  (template_digests + injected_dependencies).join("-")
end

def digest(options)
  options.assert_valid_keys(:name, :finder, :dependencies, :partial)
  cache_key = ([ options[:name], options[:finder].details_key.hash ].compact + Array.wrap(options[:dependencies])).join('.')
  # this is a correctly done double-checked locking idiom
  # (ThreadSafe::Cache's lookups have volatile semantics)
  @@cache[cache_key] || @@digest_monitor.synchronize do
    @@cache.fetch(cache_key) do # re-check under lock
      compute_and_store_digest(cache_key, options)
    end
  end
end

def digest
  Digest::MD5.hexdigest("#{source}-#{dependency_digest}").tap do |digest|
    logger.try :debug, "  Cache digest for #{template.inspect}: #{digest}"
  end
rescue ActionView::MissingTemplate
  logger.try :error, "  Couldn't find template for digesting: #{name}"
  ''
end

def initialize(options)
  @name, @finder = options.values_at(:name, :finder)
  @options = options.except(:name, :finder)
end

def injected_dependencies
  Array.wrap(options[:dependencies])
end

def logger
  ActionView::Base.logger
end

def logical_name
  name.gsub(%r|/_|, "/")
end

def nested_dependencies
  dependencies.collect do |dependency|
    dependencies = PartialDigestor.new(name: dependency, finder: finder).nested_dependencies
    dependencies.any? ? { dependency => dependencies } : dependency
  end
end

def partial?
  false
end

def source
  template.source
end

def template
  @template ||= finder.disable_cache { finder.find(logical_name, [], partial?) }
end