module Scrivito

# This class represents a single instance of a content state.
# Basically a content state has three important characteristics: cache with obj datas,
# changes representing changed objs and ways they has been changed and an ancestor content state.
class ContentState < Struct.new(:content_state_id, :changes, :changes_index, :from_content_state_id)
  class << self
    private :new

    # Creates a new content state with given changes and ancestor (optional).
    def create(attributes)
      new(attributes).tap do |content_state|
        content_state.index_changes!
        CmsDataCache.write_content_state(content_state.content_state_id, content_state.to_hash)
      end
    end

    # Finds a previously saved content state.
    # Returns nil if not found.
    def find(content_state_id)
      if content_state_data = CmsDataCache.read_content_state(content_state_id)
        new(content_state_data)
      end
    end

    # Fetches an existing workspace.
    # If not found creates a new one and returns it.
    def find_or_create(content_state_id)
      find(content_state_id) || create(content_state_id: content_state_id)
    end
  end

  def initialize(attributes)
    super(*attributes.symbolize_keys.values_at(:content_state_id, :changes, :changes_index,
        :from_content_state_id))
  end

  # Stores arbitrary data in cache.
  # Cache key is build from given index and key.
  def save_obj_data(index, key, data)
    CmsDataCache.write_obj_data(content_state_id, index, key, data)
  end

  # Fetches previously stored arbitrary data from cache.
  # Returns nil if nothing found.
  # Cache key is build from given index and key.
  def find_obj_data(index, key)
    CmsDataCache.read_obj_data(content_state_id, index, key)
  end

  # Fetches and caches the ancestor.
  # Returns nil if there is no ancestor.
  def from_content_state
    @from_content_state ||= self.class.find(from_content_state_id)
  end

  # Determines whether given data is still up-to-date for given index and key.
  def has_changes_for?(index, key, data)
    case index
    when 'id'
      id_index.include?(key)
    when 'path'
      path_index.include?(key) || data.first && id_index.include?(data.first['_id'].first)
    when 'ppath'
      ppath_index.include?(key) || data.find { |d| id_index.include?(d['_id'].first) }
    end
  end

  # Computes for a given changes feed a set of access-efficient indexes.
  def index_changes!
    id_index, path_index, ppath_index = Set.new, Set.new, Set.new
    if changes.present?
      changes.each do |hash|
        id_index.add(hash['id'])
        if path = hash['modified_path']
          path_index.add(path)
          ppath_index.add(ParentPath.of(path)) if path != '/'
        end
      end
    end
    self.changes = nil
    self.changes_index = {'id' => id_index, 'path' => path_index, 'ppath' => ppath_index}
  end

  # Returns a hash representation of a content state for serialization purpose.
  def to_hash
    {
      content_state_id: content_state_id,
      changes_index: changes_index,
      from_content_state_id: from_content_state_id
    }
  end

  private

  def id_index
    @id_index ||= changes_index['id']
  end

  def path_index
    @path_index ||= changes_index['path']
  end

  def ppath_index
    @ppath_index ||= changes_index['ppath']
  end
end

end