// FILE: ./internal/sources/openweather/observation.go
package openweather

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"time"

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

// ObservationSource polls the OpenWeatherMap "Current weather" endpoint and emits a RAW observation Event.
//
// Refactor (mirrors NWS):
//   - Source responsibility: fetch bytes + emit a valid event envelope.
//   - Normalizer responsibility: decode JSON + map to canonical model.WeatherObservation.
//
// Typical URL shape (provided via config):
//
//	https://api.openweathermap.org/data/2.5/weather?lat=...&lon=...&appid=...&units=metric
//
// IMPORTANT UNIT POLICY (weatherfeeder convention):
// OpenWeather changes units based on the `units` query parameter but does NOT include the unit
// system in the response body. To keep normalization deterministic, this driver *requires*
// `units=metric`. If absent (or non-metric), the driver returns an error.
type ObservationSource struct {
	name      string
	url       string
	userAgent string
	client    *http.Client
}

func NewObservationSource(cfg config.SourceConfig) (*ObservationSource, error) {
	if strings.TrimSpace(cfg.Name) == "" {
		return nil, fmt.Errorf("openweather_observation: name is required")
	}
	if cfg.Params == nil {
		return nil, fmt.Errorf("openweather_observation %q: params are required (need params.url)", cfg.Name)
	}

	rawURL, ok := cfg.ParamString("url", "URL")
	if !ok {
		return nil, fmt.Errorf("openweather_observation %q: params.url is required", cfg.Name)
	}

	// Fail fast: enforce deterministic unit system.
	if err := requireMetricUnits(rawURL); err != nil {
		return nil, fmt.Errorf("openweather_observation %q: %w", cfg.Name, err)
	}

	ua := cfg.ParamStringDefault("weatherfeeder (openweather client)", "user_agent", "userAgent")

	return &ObservationSource{
		name:      cfg.Name,
		url:       rawURL,
		userAgent: ua,
		client: &http.Client{
			Timeout: 10 * time.Second,
		},
	}, nil
}

func (s *ObservationSource) Name() string { return s.name }

// Kind is used for routing/policy.
// We keep Kind canonical (observation) even for raw events; Schema differentiates raw vs canonical.
func (s *ObservationSource) Kind() event.Kind { return event.Kind("observation") }

// Poll fetches OpenWeather "current weather" and emits exactly one RAW Event.
// The RAW payload is json.RawMessage and Schema is standards.SchemaRawOpenWeatherCurrentV1.
func (s *ObservationSource) Poll(ctx context.Context) ([]event.Event, error) {
	// Re-check policy defensively (in case the URL is mutated after construction).
	if err := requireMetricUnits(s.url); err != nil {
		return nil, fmt.Errorf("openweather_observation %q: %w", s.name, err)
	}

	raw, meta, err := s.fetchRaw(ctx)
	if err != nil {
		return nil, err
	}

	eventID := buildEventID(s.name, meta)
	if strings.TrimSpace(eventID) == "" {
		// Extremely defensive fallback: should never happen, but keep the envelope valid.
		eventID = fmt.Sprintf("openweather:current:%s:%s", s.name, time.Now().UTC().Format(time.RFC3339Nano))
	}

	var effectiveAt *time.Time
	if !meta.ParsedTimestamp.IsZero() {
		t := meta.ParsedTimestamp.UTC()
		effectiveAt = &t
	}

	e := event.Event{
		ID:          eventID,
		Kind:        s.Kind(),
		Source:      s.name,
		EmittedAt:   time.Now().UTC(),
		EffectiveAt: effectiveAt,

		// RAW schema (normalizer matches on this).
		Schema: standards.SchemaRawOpenWeatherCurrentV1,

		// Raw JSON; normalizer will decode and map to canonical model.WeatherObservation.
		Payload: raw,
	}

	if err := e.Validate(); err != nil {
		return nil, err
	}

	return []event.Event{e}, nil
}

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

// openWeatherMeta is a *minimal* decode of the OpenWeather payload used only to build
// a stable Event.ID and a useful EffectiveAt for the envelope.
type openWeatherMeta struct {
	Dt int64 `json:"dt"` // unix seconds, UTC

	ID   int64  `json:"id"`   // city id (if present)
	Name string `json:"name"` // city name (optional)

	Coord struct {
		Lon float64 `json:"lon"`
		Lat float64 `json:"lat"`
	} `json:"coord"`

	// Convenience fields populated after decode.
	ParsedTimestamp time.Time `json:"-"`
}

func (s *ObservationSource) fetchRaw(ctx context.Context) (json.RawMessage, openWeatherMeta, error) {
	b, err := common.FetchBody(ctx, s.client, s.url, s.userAgent, "application/json")
	if err != nil {
		return nil, openWeatherMeta{}, fmt.Errorf("openweather_observation %q: %w", s.name, err)
	}

	raw := json.RawMessage(b)

	var meta openWeatherMeta
	if err := json.Unmarshal(b, &meta); err != nil {
		// If metadata decode fails, still return raw; envelope will fall back to computed ID.
		return raw, openWeatherMeta{}, nil
	}

	if meta.Dt > 0 {
		meta.ParsedTimestamp = time.Unix(meta.Dt, 0).UTC()
	}

	return raw, meta, nil
}

func buildEventID(sourceName string, meta openWeatherMeta) string {
	// Prefer provider city ID if present; otherwise fall back to lat/lon.
	locKey := ""
	if meta.ID != 0 {
		locKey = fmt.Sprintf("city:%d", meta.ID)
	} else if meta.Coord.Lat != 0 || meta.Coord.Lon != 0 {
		locKey = fmt.Sprintf("coord:%.5f,%.5f", meta.Coord.Lat, meta.Coord.Lon)
	} else {
		locKey = "loc:unknown"
	}

	ts := meta.ParsedTimestamp
	if ts.IsZero() {
		// We prefer stable IDs, but if the payload didn't decode, use "now" so we still emit.
		ts = time.Now().UTC()
	}

	// Example:
	// openweather:current:<configured-source-name>:city:12345:2026-01-14T17:00:00.123Z
	return fmt.Sprintf("openweather:current:%s:%s:%s", sourceName, locKey, ts.Format(time.RFC3339Nano))
}

// requireMetricUnits enforces weatherfeeder's OpenWeather unit policy.
//
// OpenWeather does not tell us the unit system in the response body. We therefore enforce that
// the request URL explicitly contains units=metric; otherwise normalization would be ambiguous.
func requireMetricUnits(rawURL string) error {
	u, err := url.Parse(strings.TrimSpace(rawURL))
	if err != nil {
		return fmt.Errorf("invalid url %q: %w", rawURL, err)
	}

	units := strings.ToLower(strings.TrimSpace(u.Query().Get("units")))
	if units != "metric" {
		// Treat missing units ("" -> standard) as non-compliant too.
		if units == "" {
			units = "(missing; defaults to standard)"
		}
		return fmt.Errorf("url must include units=metric (got units=%s)", units)
	}

	return nil
}