sources: standardize Event.ID on Source:EffectiveAt; simplify raw event helper

- Adopt an opinionated Event.ID policy across sources:
  - use upstream-provided ID when available
  - otherwise derive a stable ID from Source:EffectiveAt (RFC3339Nano, UTC)
  - fall back to Source:EmittedAt when EffectiveAt is unavailable
- Add common/id helper to centralize ID selection logic and keep sources consistent
- Simplify common event construction by collapsing SingleRawEventAt/SingleRawEvent
  into a single explicit SingleRawEvent helper (emittedAt passed in)
- Update NWS/Open-Meteo/OpenWeather observation sources to:
  - compute EffectiveAt first
  - generate IDs via the shared helper
  - build envelopes via the unified SingleRawEvent helper
- Improve determinism and dedupe-friendliness without changing schemas or payloads

internal/sources/openmeteo/observation.go

@@ -4,8 +4,6 @@ package openmeteo
 import (
 	"context"
 	"encoding/json"
-	"fmt"
-	"strings"
 	"time"
 
 	"gitea.maximumdirect.net/ejr/feedkit/config"
@@ -23,8 +21,6 @@ type ObservationSource struct {
 func NewObservationSource(cfg config.SourceConfig) (*ObservationSource, error) {
 	const driver = "openmeteo_observation"
 
-	// We require params.user_agent for uniformity across sources (even though Open-Meteo
-	// itself does not strictly require a special User-Agent).
 	hs, err := common.NewHTTPSource(driver, cfg, "application/json")
 	if err != nil {
 		return nil, err
@@ -37,30 +33,27 @@ func (s *ObservationSource) Name() string { return s.http.Name }
 
 func (s *ObservationSource) Kind() event.Kind { return event.Kind("observation") }
 
-// Poll fetches Open-Meteo "current" and emits exactly one RAW Event.
 func (s *ObservationSource) Poll(ctx context.Context) ([]event.Event, error) {
 	raw, meta, err := s.fetchRaw(ctx)
 	if err != nil {
 		return nil, err
 	}
 
-	eventID := buildEventID(s.http.Name, meta)
-	if strings.TrimSpace(eventID) == "" {
-		// Extremely defensive fallback: keep the envelope valid no matter what.
-		eventID = fmt.Sprintf("openmeteo:current:%s:%s", s.http.Name, time.Now().UTC().Format(time.RFC3339Nano))
-	}
-
 	var effectiveAt *time.Time
 	if !meta.ParsedTimestamp.IsZero() {
 		t := meta.ParsedTimestamp.UTC()
 		effectiveAt = &t
 	}
 
+	emittedAt := time.Now().UTC()
+	eventID := common.ChooseEventID("", s.http.Name, effectiveAt, emittedAt)
+
 	return common.SingleRawEvent(
 		s.Kind(),
 		s.http.Name,
 		standards.SchemaRawOpenMeteoCurrentV1,
 		eventID,
+		emittedAt,
 		effectiveAt,
 		raw,
 	)
@@ -69,10 +62,8 @@ func (s *ObservationSource) Poll(ctx context.Context) ([]event.Event, error) {
 // ---- RAW fetch + minimal metadata decode ----
 
 type openMeteoMeta struct {
-	Latitude         float64 `json:"latitude"`
-	Longitude        float64 `json:"longitude"`
-	Timezone         string  `json:"timezone"`
-	UTCOffsetSeconds int     `json:"utc_offset_seconds"`
+	Timezone         string `json:"timezone"`
+	UTCOffsetSeconds int    `json:"utc_offset_seconds"`
 
 	Current struct {
 		Time string `json:"time"`
@@ -89,31 +80,13 @@ func (s *ObservationSource) fetchRaw(ctx context.Context) (json.RawMessage, open
 
 	var meta openMeteoMeta
 	if err := json.Unmarshal(raw, &meta); err != nil {
-		// If metadata decode fails, still return raw; envelope will fall back to computed ID without EffectiveAt.
+		// If metadata decode fails, still return raw; envelope will omit EffectiveAt.
 		return raw, openMeteoMeta{}, nil
 	}
 
-	// Best effort: compute a stable EffectiveAt + event ID component.
-	// If parsing fails, we simply omit EffectiveAt and fall back to time.Now() in buildEventID.
 	if t, err := openmeteo.ParseTime(meta.Current.Time, meta.Timezone, meta.UTCOffsetSeconds); err == nil {
 		meta.ParsedTimestamp = t.UTC()
 	}
 
 	return raw, meta, nil
 }
-
-func buildEventID(sourceName string, meta openMeteoMeta) string {
-	locKey := ""
-	if meta.Latitude != 0 || meta.Longitude != 0 {
-		locKey = fmt.Sprintf("coord:%.5f,%.5f", meta.Latitude, meta.Longitude)
-	} else {
-		locKey = "loc:unknown"
-	}
-
-	ts := meta.ParsedTimestamp
-	if ts.IsZero() {
-		ts = time.Now().UTC()
-	}
-
-	return fmt.Sprintf("openmeteo:current:%s:%s:%s", sourceName, locKey, ts.Format(time.RFC3339Nano))
-}