Use region flag for forecast

Not sure why, but when initially implementing the forecast support I
made it take region as a query parameter instead of grabbing the ones we
were already given from the region flag.

This commit makes the behaviour consistent.

data.go

@@ -121,23 +121,16 @@ func fetchFromURL(date time.Time, region string) ([]byte, error) {
 // forecastHandler returns JSON in a format compatible with the Grafana JSON-API
 // plugin. This allows you to display the forecast as Prometheus doesn't do values
 // in the future
-func forecastHandler(loc *time.Location) func(w http.ResponseWriter, r *http.Request) {
+func forecastHandler(loc *time.Location, regions []string) func(w http.ResponseWriter, r *http.Request) {
 	return func(w http.ResponseWriter, r *http.Request) {
-		query := r.URL.Query()
-		var regs []string
-		if regions, ok := query["region"]; ok {
-			regs = regions
-		} else {
-			regs = []string{"SN1", "SN2", "SN3", "SN4"}
-		}
 		type point struct {
 			Time   time.Time `json:"time"`
 			Region string    `json:"region"`
 			Value  float64   `json:"value"`
 		}
 		res := []point{}
 
-		for _, reg := range regs {
+		for _, reg := range regions {
 			now := time.Now().In(loc)
 			data, err := fetch(now, reg)
 			if err != nil {

main.go

@@ -88,7 +88,7 @@ func main() {
 		mux := http.NewServeMux()
 		mux.Handle("/metrics", promhttp.HandlerFor(p, promhttp.HandlerOpts{}))
 		mux.Handle("/prices", promhttp.InstrumentMetricHandler(p, promhttp.HandlerFor(c, promhttp.HandlerOpts{})))
-		mux.Handle("/forecast", promhttp.InstrumentMetricHandler(p, http.HandlerFunc(forecastHandler(loc))))
+		mux.Handle("/forecast", promhttp.InstrumentMetricHandler(p, http.HandlerFunc(forecastHandler(loc, regions))))
 		h := &http.Server{
 			Handler: mux,
 		}