# Copyright (c) 2020 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 at its middle. The target's preexisting tags
          # are unaffected beyond any merging of overlapping tags.
          class Center < Contrast::Agent::Assess::Policy::Propagator::Base
            class << self
              def propagate propagation_node, preshift, target
                sources = propagation_node.sources
                source1 = find_source(sources[0], preshift)

                if source1.length == target.length
                  target.cs__copy_from(source1, 0, propagation_node.untags)
                  target.cs__properties.cleanup_tags
                  return
                end

                # find original in the target, copy tags to the new position in target
                original_start_index = target[0..target.length / 2 + 1].rindex(source1)
                original_start_index ||= 1
                target.cs__copy_from(source1, original_start_index, propagation_node.untags)

                return unless sources[1]

                original_end_index = original_start_index + source1.length - 1
                handle_incoming_tags(target, propagation_node, sources[1], preshift, original_start_index, original_end_index)
              end

              private

              # If the input passed in to wrap around the existing object has
              # tags, we have to prepend and append those tags to the centered
              # value.
              # @param target [Object] the thing to apply tags to.
              # @param propagation_node [Contrast::Agent::Assess::Policy::PropagationNode]
              #   the node that indicates how this propagation should be
              #   handled.
              # @param source_location [String] the marker to indicate where in
              #   the preshift the source is located.
              # @param preshift [Contrast::Agent::Assess::Preshift] the state
              #   of the call before the method was executed.
              # @param start_index [Integer] where the centered object starts.
              # @param end_index [Integer] where the centered object ends.
              def handle_incoming_tags target, propagation_node, source_location, preshift, start_index, end_index
                source = find_source(source_location, preshift)
                iterate_tags(target, propagation_node, source, 0, start_index)
                iterate_tags(target, propagation_node, source, end_index, target.length)
              end

              def iterate_tags target, propagation_node, source, start, stop
                while start < stop
                  target.cs__copy_from(source, start, propagation_node.untags)
                  start += source.length
                  next unless start > stop

                  target.cs__properties.tags_at(start - source.length).each do |tag|
                    tag.update_end(stop)
                  end
                end
              end
            end
          end
        end
      end
    end
  end
end