feat: Districts table and geojson stub

internal/repository/postgres/district.go

@@ -0,0 +1,65 @@
+package postgres
+
+import (
+	"context"
+
+	"gis/internal/domain"
+
+	"github.com/google/uuid"
+)
+
+// ListAllObservations returns every observation for a dataset ordered by
+// (kato_code, date). Unlike ListObservations it is unpaginated: it backs GeoJSON
+// assembly, where all of a dataset's observations are needed at once.
+func (r *DatasetRepository) ListAllObservations(ctx context.Context, datasetID uuid.UUID) ([]domain.Observation, error) {
+	rows, err := r.pool.Query(ctx,
+		`SELECT `+observationColumns+`
+		 FROM dataset_observations
+		 WHERE dataset_id = $1
+		 ORDER BY kato_code, date`,
+		datasetID)
+	if err != nil {
+		return nil, mapError(err)
+	}
+	defer rows.Close()
+
+	out := make([]domain.Observation, 0)
+	for rows.Next() {
+		o, err := scanObservation(rows)
+		if err != nil {
+			return nil, mapError(err)
+		}
+		out = append(out, o)
+	}
+	return out, mapError(rows.Err())
+}
+
+// DistrictGeometriesByKato returns the districts whose KATO codes are in katos,
+// keyed by KATO, with each boundary serialized as a GeoJSON geometry object in
+// EPSG:4326. KATO codes with no matching district are simply absent from the
+// result map.
+func (r *DatasetRepository) DistrictGeometriesByKato(ctx context.Context, katos []string) (map[string]domain.District, error) {
+	out := make(map[string]domain.District)
+	if len(katos) == 0 {
+		return out, nil
+	}
+
+	rows, err := r.pool.Query(ctx,
+		`SELECT kato, name, ST_AsGeoJSON(coordinates)::jsonb
+		 FROM districts
+		 WHERE kato = ANY($1)`,
+		katos)
+	if err != nil {
+		return nil, mapError(err)
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var d domain.District
+		if err := rows.Scan(&d.Kato, &d.Name, &d.Geometry); err != nil {
+			return nil, mapError(err)
+		}
+		out[d.Kato] = d
+	}
+	return out, mapError(rows.Err())
+}