feat(config): enable/disable prefix matching numerals feature via con…

…fig flag (pelias#1596)

sanitizer/_tokenizer.js

@@ -1,4 +1,33 @@
 const _ = require('lodash');
+const config = require('pelias-config').generate();
+
+// optionally disable prefix matching numerals
+const feature = {
+  prefix_match_numerals: config.get('api.feature.prefix_match_numerals', true)
+};
+
+// only in the event that the final token is a numeral, this function
+// decides whether that numeric token should be considered complete or not.
+const shouldMarkNumericFinalTokenAsComplete = (clean) => {
+
+  // this feature may optionally be disabled via config
+  // in this situation the numeric suffix is always considered complete
+  if (feature.prefix_match_numerals === false) { return true; }
+
+  // inspect request layers
+  const layers = _.get(clean, 'layers', []);
+
+  // user has not explicitely specified any layers.
+  // this will include addresses, so disable for the same reasons as below.
+  if (!_.isArray(layers) || _.isEmpty(layers)) { return true; }
+
+  // user has explicitely requested the address layer.
+  // avoid prefix matching house number numerals.
+  if (layers.includes('address')) { return true; }
+
+  // default behaviour is to allow prefix matching numerals
+  return false;
+};
 
 /**
   simplified version of the elaticsearch tokenizer, used in order to
@@ -46,13 +75,10 @@ function _sanitize( raw, clean ){
     }
   }
 
-  // if requesting the address layer AND final character is a numeral then consider
-  // all tokens as complete in order to avoid prefix matching numerals.
-  const layers = _.get(clean, 'layers', []);
-  if (!_.isArray(layers) || _.isEmpty(layers) || layers.includes('address')) {
-    if (/[0-9]$/.test(text)) {
-      parserConsumedAllTokens = true;
-    }
+  // if the final character is a numeral then consider all tokens
+  // as complete in order to avoid prefix matching numerals.
+  if (/[0-9]$/.test(text) && shouldMarkNumericFinalTokenAsComplete(clean)) {
+    parserConsumedAllTokens = true;
   }
 
   // always set 'clean.tokens*' arrays for consistency and to avoid upstream errors.