module SPARQL; module Algebra
  class Operator

    ##
    # The SPARQL UPDATE `with` operator.
    #
    # The WITH clause provides a convenience for when an operation primarily refers to a single graph.
    #
    # @example
    #   (with :g1
    #     (bgp (triple ?s ?p ?o))
    #     (insert ((triple ?s ?p "z"))))
    #
    # @see http://www.w3.org/TR/sparql11-update/#deleteInsert
    class With < Operator
      include SPARQL::Algebra::Update

      NAME = :with

      ##
      # Executes this upate on the given `writable` graph or repository.
      #
      # Effectively filters results by setting a default `__graph_name__` variable so that it is used when binding to perform update operations on the appropriate triples.
      #
      # @param  [RDF::Queryable] queryable
      #   the graph or repository to write
      # @param  [Hash{Symbol => Object}] options
      #   any additional keyword options
      # @option options [Boolean] debug
      #   Query execution debugging
      # @return [RDF::Queryable]
      #   Returns queryable.
      # @raise [IOError]
      #   If `from` does not exist, unless the `silent` operator is present
      # @see    http://www.w3.org/TR/sparql11-update/
      def execute(queryable, options = {})
        debug(options) {"With: #{operand.to_sse}"}
        # Bound variable
        name = operands.shift

        unless queryable.has_graph?(name)
          debug(options) {"=> default data source #{name}"}
          load_opts = {debug: options.fetch(:debug, nil), base_uri: name}
          debug(options) {"=> load #{name}"}
          queryable.load(name.to_s, load_opts)
        end

        # Set name for RDF::Graph descendants having no graph_name to the name variable
        each_descendant do |op|
          case op
          when RDF::Query, RDF::Query::Pattern
            unless op.graph_name
              debug(options) {"set graph_name on #{op.to_sse}"}
              op.graph_name = RDF::Query::Variable.new(:__graph_name__, name)
            end
          end
        end
        query = operands.shift

        # Restrict query portion to this graph
        queryable.query(query, options.merge(depth: options[:depth].to_i + 1)) do |solution|
          debug(options) {"(solution)=>#{solution.inspect}"}

          # Execute each operand with queryable and solution
          operands.each do |op|
            op.execute(queryable, solution, options.merge(depth: options[:depth].to_i + 1))
          end
        end
      end
    end # With
  end # Operator
end; end # SPARQL::Algebra