Change farmhash to an optional dependency and add fall back to string…

…-hash (#91)

package.json

@@ -35,7 +35,6 @@
     "@turf/centroid": "^6.0.0",
     "alasql": "^0.4.0",
     "classybrew": "0.0.3",
-    "farmhash": "^2.0.5",
     "flora-sql-parser": "^0.7.5",
     "highland": "^3.0.0-beta.3",
     "lodash": "^4.17.4",
@@ -44,6 +43,7 @@
     "proj4": "^2.3.17",
     "simple-statistics": "^6.0.0",
     "srs": "^1.2.0",
+    "string-hash": "^1.1.3",
     "terraformer": "^1.0.7"
   },
   "devDependencies": {
@@ -52,5 +52,8 @@
     "standard": "^11.0.0",
     "tap-spec": "^5.0.0",
     "tape": "^4.6.3"
+  },
+  "optionalDependencies": {
+    "farmhash": "^2.1.0"
   }
 }

src/sql.js

@@ -1,5 +1,4 @@
 const Terraformer = require('terraformer')
-const farmhash = require('farmhash')
 const transformArray = require('./geometry/transform-array')
 const convertToEsri = require('./geometry/convert-to-esri')
 const convertFromEsri = require('./geometry/convert-from-esri')
@@ -10,6 +9,14 @@ const _ = require('lodash')
 const projectCoordinates = require('./geometry/project-coordinates')
 const reducePrecision = require('./geometry/reduce-precision')
 
+// Try to require farmhash, as it is an optional depenecy we can fall back to JavaScript only hashing library
+let hashFunction
+try {
+  hashFunction = require('farmhash').hash32
+} catch (e) {
+  hashFunction = require('string-hash')
+}
+
 sql.MAXSQLCACHESIZE = 0
 
 sql.fn.ST_Within = function (feature = {}, filterGeom = {}) {
@@ -151,7 +158,7 @@ function esriFy (properties, geometry, dateFields, requiresObjectId, idField) {
  */
 function createIntHash (inputStr) {
   // Hash to 32 bit unsigned integer
-  const hash = farmhash.hash32(inputStr)
+  const hash = hashFunction(inputStr)
   // Normalize to range of postive values of signed integer
   return Math.round((hash / 4294967295) * (2147483647))
 }

test/to-esri.js

@@ -97,7 +97,19 @@ test('adding an object id', t => {
   }
   const fixture = _.cloneDeep(geojson)
   const result = Winnow.query(fixture, options)
-  t.equal(result.features[0].attributes.OBJECTID, 239375164)
+
+  // A different hash can be returned depending on the library used
+  let hash
+  try {
+    // If requiring farmhash is successful we use that hash
+    require('farmhash')
+    hash = 239375164
+  } catch (e) {
+    // Else use the string-hash number
+    hash = 1729830217
+  }
+
+  t.equal(result.features[0].attributes.OBJECTID, hash)
   t.end()
 })