Add location service (#29)

* Add location service

* Update README.md

location/domain/domain.go

@@ -0,0 +1,104 @@
+package domain
+
+import (
+	"sync"
+
+	geo "github.com/hailocab/go-geoindex"
+	"github.com/micro/micro/v3/service/errors"
+	common "github.com/micro/services/location/proto"
+)
+
+var (
+	mtx          sync.RWMutex
+	defaultIndex = geo.NewPointsIndex(geo.Km(0.5))
+)
+
+type Entity struct {
+	ID        string
+	Type      string
+	Latitude  float64
+	Longitude float64
+	Timestamp int64
+}
+
+func (e *Entity) Id() string {
+	return e.ID
+}
+
+func (e *Entity) Lat() float64 {
+	return e.Latitude
+}
+
+func (e *Entity) Lon() float64 {
+	return e.Longitude
+}
+
+func (e *Entity) ToProto() *common.Entity {
+	return &common.Entity{
+		Id:   e.ID,
+		Type: e.Type,
+		Location: &common.Point{
+			Latitude:  e.Latitude,
+			Longitude: e.Longitude,
+			Timestamp: e.Timestamp,
+		},
+	}
+}
+
+func ProtoToEntity(e *common.Entity) *Entity {
+	return &Entity{
+		ID:        e.Id,
+		Type:      e.Type,
+		Latitude:  e.Location.Latitude,
+		Longitude: e.Location.Longitude,
+		Timestamp: e.Location.Timestamp,
+	}
+}
+
+func Read(id string) (*Entity, error) {
+	mtx.RLock()
+	defer mtx.RUnlock()
+
+	p := defaultIndex.Get(id)
+	if p == nil {
+		return nil, errors.NotFound("location.read", "Not found")
+	}
+
+	entity, ok := p.(*Entity)
+	if !ok {
+		return nil, errors.InternalServerError("location.read", "Error reading entity")
+	}
+
+	return entity, nil
+}
+
+func Save(e *Entity) {
+	mtx.Lock()
+	defaultIndex.Add(e)
+	mtx.Unlock()
+}
+
+func Search(typ string, entity *Entity, radius float64, numEntities int) []*Entity {
+	mtx.RLock()
+	defer mtx.RUnlock()
+
+	points := defaultIndex.KNearest(entity, numEntities, geo.Meters(radius), func(p geo.Point) bool {
+		e, ok := p.(*Entity)
+		if !ok || e.Type != typ {
+			return false
+		}
+		return true
+	})
+
+	var entities []*Entity
+
+	for _, point := range points {
+		e, ok := point.(*Entity)
+		if !ok {
+			continue
+		}
+		entities = append(entities, e)
+	}
+
+	return entities
+}