Add SPC provider parsing helpers

internal/providers/spc/geojson.go

@@ -0,0 +1,105 @@
+package spc
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// GeoJSONFeatureCollection is the minimal SPC outlook FeatureCollection shape
+// needed by weatherfeeder.
+type GeoJSONFeatureCollection struct {
+	Type     string           `json:"type"`
+	Features []GeoJSONFeature `json:"features"`
+}
+
+// GeoJSONFeature preserves typed SPC properties and compact raw geometry.
+type GeoJSONFeature struct {
+	Type       string            `json:"type"`
+	Properties GeoJSONProperties `json:"properties"`
+	Geometry   json.RawMessage   `json:"geometry"`
+}
+
+// GeoJSONProperties contains the SPC fields used by canonical mapping.
+type GeoJSONProperties struct {
+	ValidISO   string `json:"VALID_ISO"`
+	ExpireISO  string `json:"EXPIRE_ISO"`
+	IssueISO   string `json:"ISSUE_ISO"`
+	Forecaster string `json:"FORECASTER"`
+	Label      string `json:"LABEL"`
+	Label2     string `json:"LABEL2"`
+	DN         *int   `json:"DN"`
+}
+
+// DecodeGeoJSON decodes an SPC GeoJSON outlook product and compacts feature
+// geometry JSON for stable downstream storage.
+func DecodeGeoJSON(raw []byte) (GeoJSONFeatureCollection, error) {
+	var collection GeoJSONFeatureCollection
+	if err := json.Unmarshal(raw, &collection); err != nil {
+		return GeoJSONFeatureCollection{}, fmt.Errorf("decode geojson: %w", err)
+	}
+	for i := range collection.Features {
+		geom, err := compactJSON(collection.Features[i].Geometry)
+		if err != nil {
+			return GeoJSONFeatureCollection{}, fmt.Errorf("features[%d].geometry: %w", i, err)
+		}
+		collection.Features[i].Geometry = geom
+	}
+	return collection, nil
+}
+
+func (p *GeoJSONProperties) UnmarshalJSON(raw []byte) error {
+	type alias GeoJSONProperties
+	var aux struct {
+		alias
+		DN any `json:"DN"`
+	}
+	if err := json.Unmarshal(raw, &aux); err != nil {
+		return err
+	}
+	*p = GeoJSONProperties(aux.alias)
+	dn, err := parseSeverityRank(aux.DN)
+	if err != nil {
+		return err
+	}
+	p.DN = dn
+	return nil
+}
+
+func parseSeverityRank(value any) (*int, error) {
+	switch v := value.(type) {
+	case nil:
+		return nil, nil
+	case float64:
+		rank := int(v)
+		if float64(rank) != v {
+			return nil, fmt.Errorf("DN must be an integer, got %v", v)
+		}
+		return &rank, nil
+	case string:
+		v = strings.TrimSpace(v)
+		if v == "" {
+			return nil, nil
+		}
+		rank, err := strconv.Atoi(v)
+		if err != nil {
+			return nil, fmt.Errorf("DN must be an integer, got %q", v)
+		}
+		return &rank, nil
+	default:
+		return nil, fmt.Errorf("DN must be an integer or string, got %T", value)
+	}
+}
+
+func compactJSON(raw json.RawMessage) (json.RawMessage, error) {
+	if len(raw) == 0 {
+		return nil, fmt.Errorf("missing")
+	}
+	var buf bytes.Buffer
+	if err := json.Compact(&buf, raw); err != nil {
+		return nil, err
+	}
+	return json.RawMessage(buf.Bytes()), nil
+}