module SPARQL; module Algebra
  class Operator

    ##
    # The SPARQL UPDATE `deleteWhere` operator.
    #
    # The DELETE WHERE operation is a shortcut form for the DELETE/INSERT operation where bindings matched by the WHERE clause are used to define the triples in a graph that will be deleted.
    #
    # @example
    #   (deleteWhere ((triple :a foaf:knows ?b))
    #
    # @see http://www.w3.org/TR/sparql11-update/#deleteWhere
    class DeleteWhere < Operator::Unary
      include SPARQL::Algebra::Update

      NAME = [:deleteWhere]

      ##
      # Query the operand, and delete all statements created by binding each solution to the patterns
      #
      # @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 = {})
        # Operands are an array of patterns and Queries (when named).
        # Create a new query made up all patterns
        patterns = operand.inject([]) do |memo, op|
          if op.respond_to?(:statements)
            memo += op.statements.to_a
          else
            memo << op
          end
          memo
        end
        query = RDF::Query.new(*patterns)
        debug(options) {"DeleteWhere query #{query.to_sse}"}
        query.execute(queryable, options.merge(depth: options[:depth].to_i + 1)) do |solution|
          debug(options) {"DeleteWhere solution #{solution.to_sse}"}
          query.each_statement do |pattern|
            pattern = pattern.dup.bind(solution)
            debug(options) {"DeleteWhere statement #{statement.to_sse}"}
            queryable.delete(RDF::Statement.from(pattern)) if pattern.bound? || pattern.constant?
          end
        end
        queryable
      end
    end # DeleteWhere
  end # Operator
end; end # SPARQL::Algebra