Add filter for enterprises within a radius

app/assets/javascripts/darkswarm/filters/distance_within_km.js.coffee

@@ -0,0 +1,5 @@
+Darkswarm.filter 'distanceWithinKm', ->
+  (enterprises, range) ->
+    enterprises ||= []
+    enterprises.filter (enterprise) ->
+      enterprise.distance / 1000 <= range

spec/javascripts/unit/darkswarm/filters/distance_within_km_spec.js.coffee

@@ -0,0 +1,17 @@
+describe "filtering enterprises to those within a certain radius", ->
+  filter = null
+  enterprises = [
+    {distance: 25000}
+    {distance: 75000}
+  ]
+
+  beforeEach ->
+    module 'Darkswarm'
+    inject ($filter) ->
+      filter = $filter('distanceWithinKm')
+
+  it "filters to those enterprises within a distance", ->
+    expect(filter(enterprises, 50)).toEqual [enterprises[0]]
+
+  it "returns empty array when enterprises array is null", ->
+    expect(filter(null, 50)).toEqual []