{ lib, ... }:
let
  inherit (lib)
    filterAttrs
    groupBy
    mapAttrs
    unique
    ;

  serviceNamesByUid = entries:
    mapAttrs (_uid: uidEntries: unique (map (entry: entry.entry) uidEntries)) (
      groupBy (entry: toString entry.value) entries
    );

  duplicateUids = entries:
    filterAttrs (_uid: serviceNames: builtins.length serviceNames > 1) (serviceNamesByUid entries);

in
{
  # Next stable UID: 20003
  replicate = true;

  type = lib.types.ints.positive;

  validate = entries: [
    {
      assertion = duplicateUids entries == { };
      message = "Stable UID allocations must be unique.";
    }
  ];
}