feat(find): add option to preCache all features

Fixes #78

README.md

@@ -12,6 +12,7 @@ The most up-to-date and accurate node.js geographical timezone lookup package.
 ```javascript
     var geoTz = require('geo-tz')
 
+    geoTz.preCache()  // optionally load all features into memory
     geoTz(47.650499, -122.350070)  // ['America/Los_Angeles']
     geoTz(43.839319, 87.526148)  // ['Asia/Shanghai', 'Asia/Urumqi']
 ```
@@ -26,7 +27,11 @@ Returns the timezone names found at `lat`, `lon`.  The timezone names will be th
 
 This library does an exact geographic lookup which has tradeoffs.  It is perhaps a little bit slower that other libraries, has a larger installation size on disk and cannot be used in the browser.  However, the results are more accurate than other libraries that compromise by approximating the lookup of the data.
 
-The data is indexed for fast analysis with automatic caching (with time expiration) of subregions of geographic data for when a precise lookup is needed.
+The data is indexed for fast analysis with automatic caching with time expiration (or optional an unexpiring cache of the whole world) of subregions of geographic data for when a precise lookup is needed.
+
+### geoTz.preCache()
+
+Loads all geographic features into memory in an unexpiring cache.  This has tradeoffs.  More memory will be consumed and it will take a little longer before the program is ready to start looking up features, but future lookups will be a lot faster - especially for areas which haven't had a lookup in a while.
 
 ## An Important Note About Maintenance
 

lib/find.js

@@ -9,7 +9,30 @@ var point = require('@turf/helpers').point
 
 var tzData = require('../data/index.json')
 
-const featureCache = new Cache()
+let featureCache = new Cache()
+
+/**
+ * A function that will load all features into an unexpiring cache
+ */
+var preCache = function () {
+  const _eternalCache = {}
+  featureCache = {
+    get: (quadPos) => _eternalCache[quadPos]
+  }
+
+  // shoutout to github user @magwo for an initial version of this recursive function
+  var preloadFeaturesRecursive = function (curTzData, quadPos) {
+    if (curTzData === 'f') {
+      var geoJson = loadFeatures(quadPos)
+      _eternalCache[quadPos] = geoJson
+    } else if (typeof curTzData === 'object') {
+      Object.getOwnPropertyNames(curTzData).forEach(function (value) {
+        preloadFeaturesRecursive(curTzData[value], quadPos + value)
+      })
+    }
+  }
+  preloadFeaturesRecursive(tzData.lookup, '')
+}
 
 var loadFeatures = function (quadPos) {
   // exact boundaries saved in file
@@ -169,3 +192,4 @@ var getTimezone = function (lat, lon) {
 }
 
 module.exports = getTimezone
+module.exports.preCache = preCache

tests/find.test.js

@@ -51,7 +51,7 @@ describe('find tests', function () {
     var europeBottomRight = [39.8602076, 34.9127951]
     var count = 2000
 
-    it('should find timezone of ' + count + ' random european positions', function () {
+    var findRandomPositions = function () {
       var timingStr = 'find tz of ' + count + ' random european positions'
       console.time(timingStr)
       for (var i = 0; i < count; i++) {
@@ -61,6 +61,19 @@ describe('find tests', function () {
         )
       }
       console.timeEnd(timingStr)
-    })
+    }
+
+    it(
+      'should find timezone of ' + count + ' random european positions with on-demand caching',
+      findRandomPositions
+    )
+
+    it(
+      'should find timezone of ' + count + ' random european positions with precache',
+      function () {
+        geoTz.preCache()
+        findRandomPositions()
+      }
+    )
   })
 })