Add redis support for distributed caching

vendor/github.com/alicebob/miniredis/v2/geo.go

@@ -0,0 +1,46 @@
+package miniredis
+
+import (
+	"math"
+
+	"github.com/alicebob/miniredis/v2/geohash"
+)
+
+func toGeohash(long, lat float64) uint64 {
+	return geohash.EncodeIntWithPrecision(lat, long, 52)
+}
+
+func fromGeohash(score uint64) (float64, float64) {
+	lat, long := geohash.DecodeIntWithPrecision(score, 52)
+	return long, lat
+}
+
+// haversin(θ) function
+func hsin(theta float64) float64 {
+	return math.Pow(math.Sin(theta/2), 2)
+}
+
+// distance function returns the distance (in meters) between two points of
+// a given longitude and latitude relatively accurately (using a spherical
+// approximation of the Earth) through the Haversin Distance Formula for
+// great arc distance on a sphere with accuracy for small distances
+// point coordinates are supplied in degrees and converted into rad. in the func
+// distance returned is meters
+// http://en.wikipedia.org/wiki/Haversine_formula
+// Source: https://gist.github.com/cdipaolo/d3f8db3848278b49db68
+func distance(lat1, lon1, lat2, lon2 float64) float64 {
+	// convert to radians
+	// must cast radius as float to multiply later
+	var la1, lo1, la2, lo2 float64
+	la1 = lat1 * math.Pi / 180
+	lo1 = lon1 * math.Pi / 180
+	la2 = lat2 * math.Pi / 180
+	lo2 = lon2 * math.Pi / 180
+
+	earth := 6372797.560856 // Earth radius in METERS, according to src/geohash_helper.c
+
+	// calculate
+	h := hsin(la2-la1) + math.Cos(la1)*math.Cos(la2)*hsin(lo2-lo1)
+
+	return 2 * earth * math.Asin(math.Sqrt(h))
+}