// FILE: ./internal/sources/common/id.go
package common

import (
	"fmt"
	"strings"
	"time"
)

// ChooseEventID applies weatherfeeder's opinionated Event.ID policy:
//
//   - If upstream provides an ID, use it (trimmed).
//   - Otherwise, ID is "<Source>:<EffectiveAt>" when available.
//   - If EffectiveAt is unavailable, fall back to "<Source>:<EmittedAt>".
//
// Timestamps are encoded as RFC3339Nano in UTC.
func ChooseEventID(upstreamID, sourceName string, effectiveAt *time.Time, emittedAt time.Time) string {
	if id := strings.TrimSpace(upstreamID); id != "" {
		return id
	}

	src := strings.TrimSpace(sourceName)
	if src == "" {
		src = "UNKNOWN_SOURCE"
	}

	// Prefer EffectiveAt for dedupe friendliness.
	if effectiveAt != nil && !effectiveAt.IsZero() {
		return fmt.Sprintf("%s:%s", src, effectiveAt.UTC().Format(time.RFC3339Nano))
	}

	// Fall back to EmittedAt (still stable within a poll invocation).
	t := emittedAt.UTC()
	if t.IsZero() {
		t = time.Now().UTC()
	}

	return fmt.Sprintf("%s:%s", src, t.Format(time.RFC3339Nano))
}