// FILE: internal/sources/nws/alerts.go
package nws

import (
	"context"
	"encoding/json"
	"strings"
	"time"

	"gitea.maximumdirect.net/ejr/feedkit/config"
	"gitea.maximumdirect.net/ejr/feedkit/event"
	nwscommon "gitea.maximumdirect.net/ejr/weatherfeeder/internal/providers/nws"
	"gitea.maximumdirect.net/ejr/weatherfeeder/internal/sources/common"
	"gitea.maximumdirect.net/ejr/weatherfeeder/internal/standards"
)

// AlertsSource polls an NWS alerts endpoint and emits a RAW alerts Event.
//
// It intentionally emits the *entire* upstream payload as json.RawMessage and only decodes
// minimal metadata for Event.EffectiveAt and Event.ID.
//
// Output schema:
//   - standards.SchemaRawNWSAlertsV1
type AlertsSource struct {
	http *common.HTTPSource
}

func NewAlertsSource(cfg config.SourceConfig) (*AlertsSource, error) {
	const driver = "nws_alerts"

	// NWS alerts responses are GeoJSON-ish; allow fallback to plain JSON as well.
	hs, err := common.NewHTTPSource(driver, cfg, "application/geo+json, application/json")
	if err != nil {
		return nil, err
	}

	return &AlertsSource{http: hs}, nil
}

func (s *AlertsSource) Name() string { return s.http.Name }

// Kind is used for routing/policy.
func (s *AlertsSource) Kind() event.Kind { return event.Kind("alert") }

func (s *AlertsSource) Poll(ctx context.Context) ([]event.Event, error) {
	raw, meta, err := s.fetchRaw(ctx)
	if err != nil {
		return nil, err
	}

	// EffectiveAt policy for alerts:
	// Prefer the collection-level "updated" timestamp (best dedupe signal).
	// If missing, fall back to the most recent per-alert timestamp we can parse.
	var effectiveAt *time.Time
	switch {
	case !meta.ParsedUpdated.IsZero():
		t := meta.ParsedUpdated.UTC()
		effectiveAt = &t
	case !meta.ParsedLatestFeatureTime.IsZero():
		t := meta.ParsedLatestFeatureTime.UTC()
		effectiveAt = &t
	}

	emittedAt := time.Now().UTC()

	// NWS alerts collections do not provide a stable per-snapshot ID.
	// Use Source:EffectiveAt (or Source:EmittedAt fallback) for dedupe friendliness.
	eventID := common.ChooseEventID("", s.http.Name, effectiveAt, emittedAt)

	return common.SingleRawEvent(
		s.Kind(),
		s.http.Name,
		standards.SchemaRawNWSAlertsV1,
		eventID,
		emittedAt,
		effectiveAt,
		raw,
	)
}

// ---- RAW fetch + minimal metadata decode ----

// alertsMeta is a minimal view of the NWS /alerts FeatureCollection.
// We only decode fields used to set EffectiveAt deterministically.
type alertsMeta struct {
	Updated  string `json:"updated"`
	Features []struct {
		Properties struct {
			Sent      string `json:"sent"`
			Effective string `json:"effective"`
			Expires   string `json:"expires"`
			Ends      string `json:"ends"`
		} `json:"properties"`
	} `json:"features"`

	ParsedUpdated           time.Time `json:"-"`
	ParsedLatestFeatureTime time.Time `json:"-"`
}

func (s *AlertsSource) fetchRaw(ctx context.Context) (json.RawMessage, alertsMeta, error) {
	raw, err := s.http.FetchJSON(ctx)
	if err != nil {
		return nil, alertsMeta{}, err
	}

	var meta alertsMeta
	if err := json.Unmarshal(raw, &meta); err != nil {
		// If metadata decode fails, still return raw; Poll will fall back to Source:EmittedAt.
		return raw, alertsMeta{}, nil
	}

	// Top-level updated (preferred).
	if us := strings.TrimSpace(meta.Updated); us != "" {
		if t, err := nwscommon.ParseTime(us); err == nil {
			meta.ParsedUpdated = t.UTC()
		}
	}

	// If Updated is missing/unparseable, compute a best-effort "latest" feature timestamp.
	// We prefer Sent/Effective, and fall back to Expires/Ends if needed.
	var latest time.Time
	for _, f := range meta.Features {
		candidates := []string{
			f.Properties.Sent,
			f.Properties.Effective,
			f.Properties.Expires,
			f.Properties.Ends,
		}
		for _, s := range candidates {
			ts := strings.TrimSpace(s)
			if ts == "" {
				continue
			}
			t, err := nwscommon.ParseTime(ts)
			if err != nil {
				continue
			}
			t = t.UTC()
			if latest.IsZero() || t.After(latest) {
				latest = t
			}
		}
	}
	meta.ParsedLatestFeatureTime = latest

	return raw, meta, nil
}