module RailsConnector

# This module provides advances auto-invalidating caching mechanism for storing obj data.
#
# To keep it up-to-date it's caches and changes should be updated periodically
# It's changes should be updated every time a new workspace data has been fetched.
# It's caches should be updated every time a new obj data has been fetched.
module ContentStateCaching
  class << self
    # How deep should a content state chain be inspected. Default depth is 20.
    attr_accessor :cache_lookup_depth

    # At which lookup depth to copy a hit found in an ancestor content state
    # to the current content state's cache. Default depth is 5.
    attr_accessor :cache_replication_depth

    # Creates a new content state for given workspace with given ancetor and returns it.
    def store_content_state(workspace_data)
      ContentState.create(content_state_id: workspace_data.to_content_state_id,
          changes: workspace_data.changes,
          from_content_state_id: workspace_data.from_content_state_id)
    end

    # Fetches last known content state id for a given workspace id.
    # Returns nil if there is no content state for that workspace.
    def find_content_state_id(workspace_id)
      CmsCacheStorage.read_workspace_content_state_id(workspace_id)
    end

    # Stores current content state id for workspace with given id.
    def store_content_state_id(workspace_id, content_state_id)
      CmsCacheStorage.write_workspace_content_state_id(workspace_id, content_state_id)
    end

    # Updates caches with data from given workspace.
    # Should be called every time a new OBJ data has been fetched.
    def store_obj_data(workspace_data, index, key, data)
      content_state = workspace_data.content_state
      content_state.save_obj_data(index, key, data) if content_state
    end

    # Fetches up-to-date obj data for given workspace, index and key.
    # Returns nil if no up-to-date data found.
    def find_obj_data(workspace_data, index, key)
      return unless current_content_state = workspace_data.content_state
      if index == 'permalink'
        current_content_state.find_obj_data(index, key)
      else
        visitor = ContentStateVisitor.new(current_content_state)
        cache_lookup_depth.times do |depth|
          return unless content_state = visitor.visit_next
          if hit = content_state.find_obj_data(index, key)
            visitor.visited_except_current.each { |cs| return if cs.has_changes_for?(index, key, hit) }
            current_content_state.save_obj_data(index, key, hit) if depth >= cache_replication_depth
            return hit
          end
        end
        nil
      end
    end
  end

  self.cache_replication_depth = 5
  self.cache_lookup_depth = 20
end

end