feat(dedupe): Handle Geonames records with overridden parents

Background
==========

In pelias/geonames#93 we added some special case
logic to the Geonames importer that ensures Geonames records in the
`locality` and `localadmin` layer have themselves as parents in that
layer.

Before this change, they would have a Who's on First parent, but these
parents didn't always line up perfectly. Sometimes it would lead to
broken labels, and as I recall it could also break search queries that
rely on locality/localadmin names.

Hierarchy checks
================

This special logic causes problems with our hierarchy checks, which
expect records that can be considered duplicates to share all parents
higher than the _lower_ record.

So for example, if a locality and localadmin are to be considered
duplicates, the hierarchy must be the same from the country layer down
to localadmin.

Geonames localadmins
====================

Geonames seems to have a penchant for having both a `locality` _and_ a
`localadmin` record for a given city, even when the local administrative
divisions don't really support such nuance.

These records often have a name following the format 'City of X', which
makes them very disruptive and confusing when shown in a list of
results.

Deduplication
=============

Our deduplication code can handle minor name differences like 'City of'
after #1371, but can't handle the
hierarchy differences that generally occur with these records.

Generally, there will be one of two scenarios:
- A WOF locality record for the city can't deduplicate with the Geonames
  localadmin because the WOF record is parented by a WOF localadmin
- A WOF locality record for the city can't deduplicate with the Geonames
  localadmin beause the WOF record has no localadmin parent at all

Concordances (from #1606) generally
don't help either, since ther often isn't a localadmin in WOF to even
have a concordance to the Geonames localadmin.

Adding a hierarchy exception
============================

This PR works by skipping the hierarchy checks for any layer
where a Geonames record has itself as a parent. This means that assuming
all the other layers are the same, the names are compatible, etc,
deduplication is still possible.

Impact
======

Of the 314 cities in our
[`top_us_cities`](https://github.com/pelias/fuzzy-tests/blob/master/test_cases/top_us_cities.json)
fuzzy tests, most of them (125) had a 'City of X' record
somewhere in the results when querying via the autocomplete endpoint.

With this PR, there are only 15 cases.

Potential regressions
=====================

Theoretically, this could allow records that aren't actually duplicates
to be deduped, but they would have to have a similar name and likely
share at least a `county`, so it feels like the chance for error is
limited.

That said, there are no regressions in our acceptance tests, and quite a
few improvements.

helper/diffPlaces.js

@@ -46,6 +46,26 @@ function isUsState(item) {
   return item.parent.country_a[0] === 'USA' && item.layer === 'region';
 }
 
+// Geonames records in the locality and localadmin layer are parented by themselves
+// This breaks our other hierarchy logic, so check for this special case
+function isGeonamesWithSelfParent(item, placeType) {
+  if (item.source !== 'geonames') { return false; }
+  if (item.layer !== placeType) { return false; }
+
+  if (!item.parent) { return false; }
+
+  // get the relevant parent id(s) for the placeType in question
+  const parent_records = item.parent[`${placeType}_id`] || [];
+
+  // check if the parent ids at this layer match this Geonames record
+  // we have special cased Geonames parents in many cases
+  // handle both array and scalar values
+  if (item.source_id === parent_records) { return true; }
+  if (parent_records.includes(item.source_id)) { return true; }
+
+  return false;
+}
+
 /**
  * Compare the parent properties if they exist.
  * Returns false if the objects are the same, else true.
@@ -108,6 +128,11 @@ function isParentHierarchyDifferent(item1, item2){
     // skip layers that are more granular than $maxRank
     if (rank > maxRank){ return false; }
 
+    // Special case Geonames records that are parented by themselves and would otherwise break these checks
+    if (isGeonamesWithSelfParent(item1, placeType) || isGeonamesWithSelfParent(item2, placeType)) {
+      return false;
+    }
+
     // ensure the parent ids are the same for all placetypes
     return isPropertyDifferent( parent1, parent2, `${placeType}_id` );
   });

test/unit/helper/diffPlaces.js

@@ -790,6 +790,40 @@ module.exports.tests.geonames = function (test, common) {
   });
 };
 
+module.exports.tests.geonames_self_parent = function (test, common) {
+  test('geonames records that parent themselves should not break hierarchy checks', function(t) {
+    const gn_record = {
+      source: 'geonames',
+      layer: 'localadmin',
+      source_id: '7163824',
+      name: {
+        default: 'City of New York'
+      },
+      parent: {
+        country_id: ['85633793'], // USA, WOF
+        region_id: ['85688543'], // NY, WOF
+        localadmin_id: ['7163824'] // New York County, Geonames
+      }
+    };
+    const wof_record = {
+      source: 'whosonfirst',
+      layer: 'locality',
+      source_id: '85977539',
+      name: {
+        default: 'New York'
+      },
+      parent: {
+        country_id: ['85633793'], // USA, WOF
+        region_id: ['85688543'], // NY, WOF
+        //localadmin_id: null // no localadmin is set for NYC in WOF
+      }
+    };
+
+    t.false(isDifferent(gn_record, wof_record), 'should be the same based on hierarchy');
+    t.end();
+  });
+};
+
 module.exports.all = function (tape, common) {
 
   function test(name, testFunction) {