Added GetExtents method

datastore/README.md

@@ -240,6 +240,24 @@ $ grpcurl -d '{"standard_names": ["wind_speed", "air_temperature"], "interval":
 ...
 ```
 
+### Getting the time- and geo extent of all observations currently in the storage
+
+```text
+$ grpcurl -plaintext -proto protobuf/datastore.proto 127.0.0.1:50050 datastore.Datastore.GetExtents
+{
+  "timeExtent": {
+    "start": "2022-12-31T00:00:00Z",
+    "end": "2022-12-31T23:50:00Z"
+  },
+  "geoExtent": {
+    "xMin": -68.2758333,
+    "yMin": 12.13,
+    "xMax": 7.1493220605216,
+    "yMax": 55.399166666667
+  }
+}
+```
+
 ## Testing the datastore service with a Python client
 
 ### Compiling the protobuf file

datastore/dsimpl/getextents.go

@@ -0,0 +1,20 @@
+package dsimpl
+
+import (
+	"context"
+	"fmt"
+
+	"datastore/datastore"
+)
+
+func (svcInfo *ServiceInfo) GetExtents(
+	ctx context.Context, request *datastore.GetExtentsRequest) (
+	*datastore.GetExtentsResponse, error) {
+
+	response, err := svcInfo.Sbe.GetExtents(request)
+	if err != nil {
+		return nil, fmt.Errorf("svcInfo.Sbe.GetExtents() failed: %v", err)
+	}
+
+	return response, nil
+}

datastore/protobuf/datastore.proto

@@ -22,6 +22,7 @@ option go_package = "./datastore";
 service Datastore {
   rpc PutObservations(PutObsRequest) returns (PutObsResponse);
   rpc GetObservations(GetObsRequest) returns (GetObsResponse);
+  rpc GetExtents(GetExtentsRequest) returns (GetExtentsResponse);
 }
 
 //---------------------------------------------------------------------------
@@ -35,6 +36,13 @@ message Polygon { // horizontal area; three or more points
   repeated Point points = 1;
 }
 
+message BoundingBox {
+  double xMin = 1;
+  double yMin = 2;
+  double xMax = 3;
+  double yMax = 4;
+}
+
 message TimeInterval {
   google.protobuf.Timestamp start = 1;
   google.protobuf.Timestamp end = 2;
@@ -127,9 +135,21 @@ message GetObsRequest {
   // TODO: add search filters for other metadata
 }
 
-
 message GetObsResponse {
   int32 status = 1;
   string error = 2; // any error description (empty on success)
   repeated Metadata2 observations = 3;
 }
+
+//---------------------------------------------------------------------------
+
+message GetExtentsRequest {
+  // currently no args
+}
+
+message GetExtentsResponse {
+  int32 status = 1;
+  string error = 2; // any error description (empty on success)
+  TimeInterval time_extent = 3;
+  BoundingBox geo_extent = 4;
+}

datastore/storagebackend/postgresql/getextents.go

@@ -0,0 +1,71 @@
+package postgresql
+
+import (
+	"database/sql"
+	"datastore/datastore"
+	"fmt"
+	"time"
+
+	_ "github.com/lib/pq"
+	"google.golang.org/protobuf/types/known/timestamppb"
+)
+
+// getTimeExtent gets the current time extent of all observations in the storage.
+func getTimeExtent(db *sql.DB) (*datastore.TimeInterval, error) {
+	query := "SELECT min(obstime_instant), max(obstime_instant) FROM observation"
+	row := db.QueryRow(query)
+
+	var start, end time.Time
+
+	err := row.Scan(&start, &end)
+	if err != nil {
+		return nil, fmt.Errorf("row.Scan() failed: %v", err)
+	}
+
+	return &datastore.TimeInterval{
+		Start: timestamppb.New(start),
+		End:   timestamppb.New(end),
+	}, nil
+}
+
+// getGeoExtent gets the current geo extent of all observations in the storage.
+func getGeoExtent(db *sql.DB) (*datastore.BoundingBox, error) {
+	query := `
+		SELECT ST_XMin(ext), ST_YMin(ext), ST_XMax(ext), ST_YMax(ext)
+		FROM (SELECT ST_Extent(point::geometry) AS ext FROM geo_point) t
+	`
+	row := db.QueryRow(query)
+
+	var xmin, ymin, xmax, ymax float64
+
+	err := row.Scan(&xmin, &ymin, &xmax, &ymax)
+	if err != nil {
+		return nil, fmt.Errorf("row.Scan() failed: %v", err)
+	}
+
+	return &datastore.BoundingBox{
+		XMin: xmin,
+		YMin: ymin,
+		XMax: xmax,
+		YMax: ymax,
+	}, nil
+}
+
+// GetExtents ... (see documentation in StorageBackend interface)
+func (sbe *PostgreSQL) GetExtents(request *datastore.GetExtentsRequest) (
+	*datastore.GetExtentsResponse, error) {
+
+	var err error
+
+	timeExtent, err := getTimeExtent(sbe.Db)
+	if err != nil {
+		return nil, fmt.Errorf("getTimeExtent() failed: %v", err)
+	}
+
+	geoExtent, err := getGeoExtent(sbe.Db)
+	if err != nil {
+		return nil, fmt.Errorf("getGeoExtent() failed: %v", err)
+	}
+
+	return &datastore.GetExtentsResponse{TimeExtent: timeExtent, GeoExtent: geoExtent}, nil
+}

datastore/storagebackend/storagebackend.go

@@ -17,4 +17,8 @@ type StorageBackend interface {
 	// GetObservations retrieves observations from the storage.
 	// Returns nil upon success, otherwise error.
 	GetObservations(*datastore.GetObsRequest) (*datastore.GetObsResponse, error)
+
+	// GetExtents gets the time- and geo extents of all currently stored observations.
+	// Returns nil upon success, otherwise error.
+	GetExtents(*datastore.GetExtentsRequest) (*datastore.GetExtentsResponse, error)
 }