feat(dedupe): Check Geonames<->WOF concordances

These concordances can be trusted over any other signals and really help
us remove lots of bad Geonames data.

helper/diffPlaces.js

@@ -4,6 +4,7 @@ const unicode = require('./unicode');
 const placeTypes = require('./placeTypes');
 const canonicalLayers = require('../helper/type_mapping').getCanonicalLayers();
 const field = require('../helper/fieldValue');
+const codec = require('pelias-model').codec;
 
 // only consider these layers as synonymous for deduplication purposes.
 // when performing inter-layer deduping, layers coming earlier in this list take
@@ -169,11 +170,43 @@ function isAddressDifferent(item1, item2){
   return false;
 }
 
+function isGeonamesConcordanceSame(item1, item2) {
+  let wof_record;
+  let gn_record;
+
+  if (item1.source === 'geonames' && item2.source === 'whosonfirst') {
+    gn_record = item1;
+    wof_record = item2;
+  } else if (item2.source === 'geonames' && item1.source === 'whosonfirst') {
+    gn_record = item2;
+    wof_record = item1;
+  } else {
+    // could not match to one geonames and one wof concordance, so this check does not apply
+    return false;
+  }
+
+  const concordances = _.get(wof_record, 'addendum.concordances');
+
+  if (concordances) {
+    const json = codec.decode(concordances);
+    const concordance_id = json['gn:id'];
+
+    if (concordance_id && typeof concordance_id === 'number' && concordance_id.toString() === gn_record.source_id) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
 /**
  * Compare the two records and return true if they differ and false if same.
  * Optionally provide $requestLanguage (req.clean.lang.iso6393) to improve name deduplication.
  */
 function isDifferent(item1, item2, requestLanguage){
+  // records that share a geonames concordance are the same, regardless of any other checks
+  if( isGeonamesConcordanceSame( item1, item2 ) ){ return false; }
+
   if( isLayerDifferent( item1, item2 ) ){ return true; }
   if( isParentHierarchyDifferent( item1, item2 ) ){ return true; }
   if( isNameDifferent( item1, item2, requestLanguage ) ){ return true; }

test/unit/helper/diffPlaces.js

@@ -561,6 +561,31 @@ module.exports.tests.normalizeString = function (test, common) {
   });
 };
 
+module.exports.tests.geonames = function (test, common) {
+  test('geonames record with concordance is the same, regardless of anything else', function(t) {
+    const gn_record = {
+      source: 'geonames',
+      source_id: '123',
+      name: {
+        'default': 'One name'
+      }
+    };
+    const wof_record = {
+      source: 'whosonfirst',
+      source_id: '345',
+      name: {
+        default: 'Different name'
+      },
+      addendum: {
+        concordances: '{ "gn:id": 123 }'
+      }
+    };
+
+    t.false(isDifferent(gn_record, wof_record), 'should be the same based on concordance');
+    t.end();
+  });
+};
+
 module.exports.all = function (tape, common) {
 
   function test(name, testFunction) {