# Copyright (c) 2022 Contrast Security, Inc. See https://www.contrastsecurity.com/enduser-terms-0317a for more details.
# frozen_string_literal: true

module Contrast
  module Agent
    module Assess
      module Policy
        module Propagator
          # Propagation that results in all the tags of the source being
          # applied to the target. In those cases where overflow occurred,
          # the overflow is tagged the same as the character which preceded it.
          # The target's preexisting tags are shifted to account for this.
          class Next < Contrast::Agent::Assess::Policy::Propagator::Base
            class << self
              # String has some silly methods like next. Basically, this flips a
              # character in a predictable manner
              def propagate propagation_node, preshift, target
                return unless (properties = Contrast::Agent::Assess::Tracker.properties!(target))

                source = find_source(propagation_node.sources[0], preshift)
                properties.copy_from(source, target, 0, propagation_node.untags)

                # this means the char that was shifted overflowed and created new
                # chars (i.e 'z' "wraps" to create 'aa' )
                unless target.length == source.length
                  properties.copy_from(source, target, 0, propagation_node.untags)

                  first_difference = (0...source.length).find { |i| source[i] != target[i] } || source.length

                  properties.tags_at(first_difference).each do |tag|
                    tag.shift_end(target.length - source.length)
                  end
                end

                properties.cleanup_tags
              end
            end
          end
        end
      end
    end
  end
end