Add API to query district by GPS location

platform/district.go

@@ -0,0 +1,31 @@
+package platform
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/Gleipnir-Technology/nidus-sync/db"
+	"github.com/Gleipnir-Technology/nidus-sync/db/models"
+
+	"github.com/stephenafamo/bob/dialect/psql"
+	"github.com/stephenafamo/bob/dialect/psql/sm"
+)
+
+func DistrictForLocation(ctx context.Context, lng float64, lat float64) (*models.District, error) {
+	rows, err := models.Districts.Query(
+		sm.Where(
+			psql.F("ST_Contains", psql.Raw("geom_4326"), psql.F("ST_SetSRID", psql.F("ST_MakePoint", psql.Arg(lng), psql.Arg(lat)), psql.Arg(4326))),
+		),
+	).All(ctx, db.PGInstance.BobDB)
+	if err != nil {
+		return nil, fmt.Errorf("failed to query district: %w", err)
+	}
+	switch len(rows) {
+	case 0:
+		return nil, nil
+	case 1:
+		return rows[0], nil
+	default:
+		return nil, nil
+	}
+}