query max amount of datapoints

storage/weather-data.go

@@ -2,6 +2,7 @@ package storage
 
 import (
 	"errors"
+	"math"
 	"math/rand"
 	"time"
 
@@ -128,6 +129,16 @@ func GetOnlyQueriedFields(dataPoints []*WeatherData, query *WeatherQuery) []*Wea
 	for _, data := range dataPoints {
 		data.OnlyQueriedValues(query)
 	}
+
+	if query.MaxDataPoints >= 0 && len(dataPoints) > query.MaxDataPoints {
+		var result = make([]*WeatherData, query.MaxDataPoints)
+		division := float64(len(dataPoints)) / float64(query.MaxDataPoints)
+		for i := 0; i < query.MaxDataPoints; i++ {
+			result[i] = dataPoints[int(math.Round(float64(i)*division))]
+		}
+		return result
+	}
+
 	return dataPoints
 }
 

storage/weather-query.go

@@ -10,15 +10,17 @@ import (
 )
 
 type WeatherQuery struct {
-	Start    time.Time
-	End      time.Time
-	SensorId uuid.UUID
-	Values   map[SensorValueType]bool
+	Start         time.Time
+	End           time.Time
+	SensorId      uuid.UUID
+	MaxDataPoints int
+	Values        map[SensorValueType]bool
 }
 
 //NewWeatherQuery creates a new empty WeatherQuery
 func NewWeatherQuery() *WeatherQuery {
 	query := new(WeatherQuery)
+	query.MaxDataPoints = -1
 	query.Values = make(map[SensorValueType]bool)
 	return query
 }
@@ -38,6 +40,7 @@ func ParseFromUrlQuery(query url.Values) (*WeatherQuery, error) {
 
 	start := query.Get("start")
 	end := query.Get("end")
+	max := query.Get("maxDataPoints")
 
 	if len(start) != 0 {
 		if tval, err := time.Parse(time.RFC3339, start); err == nil {
@@ -57,6 +60,15 @@ func ParseFromUrlQuery(query url.Values) (*WeatherQuery, error) {
 		}
 	}
 
+	if len(max) != 0 {
+		if tval, err := strconv.Atoi(max); err == nil {
+			result.MaxDataPoints = tval
+		} else if err != nil {
+			fmt.Println(err)
+			return nil, err
+		}
+	}
+
 	for k, v := range query {
 		if k == "start" || k == "end" {
 			continue