fast-lookup.rb

require "active_support/all"

Resource = Struct.new(:absolute_path)

paths = [
 Resource.new("/bread/crumbs/three"),
 Resource.new("/bread"),
 Resource.new("/bread/crumbs"),
 Resource.new("/bread/crumbs/one"),
 Resource.new("/bread/crumbs/two"),
 Resource.new("/pages/two"),
 Resource.new("/pages/three")
]

class FastAbsoluteLookup
  def initialize(paths)
    @paths = paths
  end

  def find(path:)
    sections = path.split("/")
    finder = sections.slice(1..-2)
    smart_index.dig("/", *finder, :resources)&.find { |r| r.absolute_path == path }
  end

  private

  def smart_index
    @smart_index ||= begin
      r = {}

      @paths.each do |input|
        path_sections = input.absolute_path.split("/")
        relevant_path_segements = ["/", *path_sections.slice(1..-2)]

        insert_resource_on_segement = relevant_path_segements.last

        # Instantiate the hash for each section
        relevant_path_segements.size.times do |index|
          instantiation_segements = relevant_path_segements.slice(0..index)
          if instantiation_segements.one?
            r[instantiation_segements.last] ||= {
              resources: []
            }
          else
            h = r.dig(*instantiation_segements.slice(0..-2))

            h[instantiation_segements.last] ||= {
              resources: []
            }
          end
        end

        r.dig(*relevant_path_segements)[:resources] << input
      end

      r.with_indifferent_access
    end
  end
end

lookup = FastAbsoluteLookup.new(paths)

pp lookup.find(path: "/bread/crumbs/two")
pp lookup.find(path: "/bread/crumbs")
pp lookup.find(path: "/bread")
pp lookup.find(path: "/blarg/target") # should be nil