module ViewModel::MigratableView

def realize_paths!
  @migration_paths.clear
  graph = RGL::DirectedAdjacencyGraph.new
  # Add a vertex for the current version, in case no edges reach it
  graph.add_vertex(self.schema_version)
  # Add edges backwards, as we care about paths from the latest version
  @migration_classes.each_key do |from, to|
    graph.add_edge(to, from)
  end
  paths = graph.dijkstra_shortest_paths(Hash.new { 1 }, self.schema_version)
  paths.each do |target_version, path|
    next if path.nil? || path.length == 1
    # Store the path forwards rather than backwards
    path_migration_classes = path.reverse.each_cons(2).map do |from, to|
      @migration_classes.fetch([from, to])
    end
    key = [target_version, schema_version]
    @migration_paths[key] = path_migration_classes.map(&:new)
  end
  @realized_paths = true
end