package fusion

import (
	"context"
	"database/sql"
	"encoding/binary"
	"fmt"
	"log"
	"math"
	"sort"
	"strings"
	"time"

	"weatherstation/internal/database"
)

const (
	providerOpenMeteo = "open-meteo"
	providerCaiyun    = "caiyun"
	providerImdroid   = "imdroid"
	outputProvider    = "imdroid_mix"
)

var defaultTriad = database.Triad{OpenMeteo: 0.4, Caiyun: 0.3, Imdroid: 0.3}

// RunForIssued runs fusion for all stations at the given issued (hour bucket, CST).
// It persists weights into forecast_weights_current and fused rows into forecast_hourly.
func RunForIssued(ctx context.Context, issued time.Time) error {
	db := database.GetDB()
	stations, err := loadStations(ctx, db)
	if err != nil {
		return err
	}
	for _, st := range stations {
		if err := runForStation(ctx, db, st, issued); err != nil {
			log.Printf("fusion: station=%s issued=%s error=%v", st.ID, issued.Format(time.RFC3339), err)
		}
	}
	return nil
}

type stationInfo struct {
	ID    string
	Alias string
	Lat   sql.NullFloat64
	Lon   sql.NullFloat64
	Z     sql.NullInt64
	Y     sql.NullInt64
	X     sql.NullInt64
}

func loadStations(ctx context.Context, db *sql.DB) ([]stationInfo, error) {
	rows, err := db.QueryContext(ctx, `
        SELECT station_id,
               COALESCE(NULLIF(station_alias,''), station_id) AS alias,
               latitude, longitude, z, y, x
        FROM stations
        WHERE latitude IS NOT NULL AND longitude IS NOT NULL
        ORDER BY station_id`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var list []stationInfo
	for rows.Next() {
		var s stationInfo
		if err := rows.Scan(&s.ID, &s.Alias, &s.Lat, &s.Lon, &s.Z, &s.Y, &s.X); err != nil {
			return nil, err
		}
		list = append(list, s)
	}
	return list, nil
}

type providerMatrix struct {
	Provider string
	Samples  []forecastSample
}

type forecastSample struct {
	Rain      float64
	Temp      float64
	Humidity  float64
	WindSpeed float64
	WindGust  float64
	WindDir   float64
	Prob      float64
	Pressure  float64
	UV        float64
}

func runForStation(ctx context.Context, db *sql.DB, st stationInfo, issued time.Time) error {
	// Log header
	log.Printf("")
	log.Printf("issue %s station=%s", issued.Format("2006-01-02 15:04:05"), st.ID)

	// Presence at issued
	present := presentProviders(db, st.ID, issued)
	presOrdered := orderByProvidersAll(present)
	added, removed := diffPresence(db, st.ID, present)
	if len(added) > 0 || len(removed) > 0 {
		log.Printf("sources %v added=%v removed=%v", presOrdered, added, removed)
	}

	// Load previous triad snapshot or default
	triad, _, ok, _ := database.GetWeightsCurrent(ctx, st.ID)
	if !ok {
		triad = defaultTriad
	}

	// Apply missing/new rules
	triad = applyMissingTransfer(triad, present)
	triad = applyNewAllocation(triad, present)

	// Learning (I-1 vs (I-2)+1)
	learnStart := issued.Add(-time.Hour)
	learnEnd := issued
	actual, actualOK, err := fetchActualHourlyRain(db, st.ID, learnStart, learnEnd)
	if err != nil {
		log.Printf("fusion: actual error station=%s issued=%s err=%v", st.ID, issued.Format(time.RFC3339), err)
	} else if actualOK {
		prevIssue := issued.Add(-2 * time.Hour)
		preds, names := lead1PredsAt(db, st.ID, prevIssue, presOrdered)
		log.Printf("在 [%s,%s) ，该小时本站实况雨量累计为:%.3f，预报源在 issue=%s 发布的 +1h %s-%s 预报值是 %s",
			learnStart.Format("15:04"), learnEnd.Format("15:04"), actual,
			prevIssue.Format("15:04"), learnStart.Format("15:04"), learnEnd.Format("15:04"),
			formatFloatSlice(preds))
		triad = learnTriad(triad, names, preds, actual)
	}

	// Build matrix samples for issued (providers present only)
	matrix := buildMatrix(db, st.ID, issued, presOrdered)

	// Effective weights (ordered by presOrdered)
	effBefore := triadToSlice(triad, presOrdered)
	eff := effBefore // learning already applied
	log.Printf("学习前权重 %s ，本轮使用权重 %s", toNamed(effBefore, presOrdered), toNamed(eff, presOrdered))

	// Fuse with mask
	fused := fuseForecastsWith(matrix, eff)
	preMask := []float64{fused[0].Rain, fused[1].Rain, fused[2].Rain}
	maskApplied := false
	// Mask requires radar context
	if hasMaskCtx(st) {
		rep, err := checkRadarMask(db, buildMaskContext(st), issued)
		if err == nil && rep.Scanned {
			// per-hour apply: if hits==0 then zero rain
			for h := 0; h < 3; h++ {
				if rep.HitsByHour[h] == 0 {
					fused[h].Rain = 0
					maskApplied = true
				}
			}
			log.Printf("mask t=%s wind=%.1fm/s %.0f° tiles=%d hits=[%d,%d,%d] applied=%v",
				issued.Format("2006-01-02 15:04:05"), rep.WindSpeed, rep.WindDir, rep.Tiles,
				rep.HitsByHour[0], rep.HitsByHour[1], rep.HitsByHour[2], maskApplied)
		}
	}
	postMask := []float64{fused[0].Rain, fused[1].Rain, fused[2].Rain}
	log.Printf("预报 %s , mask=%v , 融合的结果 %s", formatFloatSlice(preMask), maskApplied, formatFloatSlice(postMask))

	// Persist fused rows
	if err := upsertFused(ctx, db, st.ID, issued, fused); err != nil {
		return err
	}
	// Persist triad snapshot for next hour
	if err := database.UpsertWeightsCurrent(ctx, st.ID, triad, issued); err != nil {
		return err
	}
	return nil
}

func formatFloatSlice(vs []float64) string {
	parts := make([]string, len(vs))
	for i, v := range vs {
		parts[i] = fmt.Sprintf("%.2f", v)
	}
	return "[" + strings.Join(parts, ",") + "]"
}

func toNamed(ws []float64, names []string) string {
	parts := make([]string, len(ws))
	for i := range ws {
		parts[i] = fmt.Sprintf("%s=%.2f", names[i], ws[i])
	}
	return strings.Join(parts, ", ")
}

func triadToSlice(t database.Triad, names []string) []float64 {
	out := make([]float64, len(names))
	for i, n := range names {
		switch n {
		case providerOpenMeteo:
			out[i] = t.OpenMeteo
		case providerCaiyun:
			out[i] = t.Caiyun
		case providerImdroid:
			out[i] = t.Imdroid
		}
	}
	return out
}

func sliceToTriad(vals []float64, names []string) database.Triad {
	t := database.Triad{}
	for i, n := range names {
		switch n {
		case providerOpenMeteo:
			t.OpenMeteo = vals[i]
		case providerCaiyun:
			t.Caiyun = vals[i]
		case providerImdroid:
			t.Imdroid = vals[i]
		}
	}
	return t
}

func presentProviders(db *sql.DB, stationID string, issued time.Time) map[string]bool {
	out := map[string]bool{}
	// Check providers within [issued, issued+1h)
	for _, p := range []string{providerOpenMeteo, providerCaiyun, providerImdroid} {
		var cnt int
		_ = db.QueryRow(`SELECT COUNT(*) FROM forecast_hourly WHERE station_id=$1 AND provider=$2 AND issued_at >= $3 AND issued_at < $3 + interval '1 hour'`, stationID, p, issued).Scan(&cnt)
		if cnt > 0 {
			out[p] = true
		}
	}
	return out
}

func orderByProvidersAll(present map[string]bool) []string {
	base := []string{providerOpenMeteo, providerCaiyun, providerImdroid}
	out := make([]string, 0, len(present))
	for _, p := range base {
		if present[p] {
			out = append(out, p)
		}
	}
	return out
}

func diffPresence(db *sql.DB, stationID string, present map[string]bool) (added, removed []string) {
	// Use last hour presence from forecast_hourly as proxy
	prev := map[string]bool{}
	// naive: if provider had any row at issued-1h bucket, consider present
	// We don't know issued here; caller logs only.
	// Return stable order using base sequence.
	base := []string{providerOpenMeteo, providerCaiyun, providerImdroid}
	for _, p := range base {
		if present[p] && !prev[p] {
			added = append(added, p)
		}
		if !present[p] && prev[p] {
			removed = append(removed, p)
		}
	}
	return added, removed
}

func applyMissingTransfer(t database.Triad, present map[string]bool) database.Triad {
	// Sum of missing weights
	missing := 0.0
	if !present[providerOpenMeteo] {
		missing += t.OpenMeteo
		t.OpenMeteo = 0
	}
	if !present[providerCaiyun] {
		missing += t.Caiyun
		t.Caiyun = 0
	}
	if !present[providerImdroid] {
		missing += t.Imdroid
		t.Imdroid = 0
	}
	if missing == 0 {
		return t
	}
	// Give to current max among present
	maxP := ""
	maxW := -1.0
	for p, ok := range present {
		if !ok {
			continue
		}
		w := 0.0
		switch p {
		case providerOpenMeteo:
			w = t.OpenMeteo
		case providerCaiyun:
			w = t.Caiyun
		case providerImdroid:
			w = t.Imdroid
		}
		if w > maxW {
			maxW = w
			maxP = p
		}
	}
	switch maxP {
	case providerOpenMeteo:
		t.OpenMeteo += missing
	case providerCaiyun:
		t.Caiyun += missing
	case providerImdroid:
		t.Imdroid += missing
	}
	return t
}

func applyNewAllocation(t database.Triad, present map[string]bool) database.Triad {
	// allocate 0.2 from current max to any newly present which currently has 0
	for _, p := range []string{providerOpenMeteo, providerCaiyun, providerImdroid} {
		// we don't track prior presence; heuristic: if present and weight==0 allocate
		if present[p] && getW(t, p) <= 0 {
			// find current max (excluding p)
			type pair struct {
				name string
				w    float64
			}
			arr := []pair{{providerOpenMeteo, t.OpenMeteo}, {providerCaiyun, t.Caiyun}, {providerImdroid, t.Imdroid}}
			sort.Slice(arr, func(i, j int) bool { return arr[i].w > arr[j].w })
			src := arr[0]
			if src.name == p && len(arr) > 1 {
				src = arr[1]
			}
			delta := 0.2
			if src.w < delta {
				delta = src.w
			}
			t = setW(t, src.name, src.w-delta)
			t = setW(t, p, getW(t, p)+delta)
		}
	}
	return t
}

func getW(t database.Triad, p string) float64 {
	switch p {
	case providerOpenMeteo:
		return t.OpenMeteo
	case providerCaiyun:
		return t.Caiyun
	case providerImdroid:
		return t.Imdroid
	}
	return 0
}
func setW(t database.Triad, p string, v float64) database.Triad {
	switch p {
	case providerOpenMeteo:
		t.OpenMeteo = v
	case providerCaiyun:
		t.Caiyun = v
	case providerImdroid:
		t.Imdroid = v
	}
	return t
}

func learnTriad(t database.Triad, names []string, preds []float64, actual float64) database.Triad {
	if len(names) != len(preds) || len(names) == 0 {
		return t
	}
	// find best/worst among names by absolute error
	best, worst := 0, 0
	for i := range preds {
		if math.Abs(preds[i]-actual) < math.Abs(preds[best]-actual) {
			best = i
		}
		if math.Abs(preds[i]-actual) > math.Abs(preds[worst]-actual) {
			worst = i
		}
	}
	// log absolute errors
	parts := make([]string, 0, len(names))
	for i := range names {
		parts = append(parts, fmt.Sprintf("%s |%.2f-%.3f|=%.3f", names[i], preds[i], actual, math.Abs(preds[i]-actual)))
	}
	log.Printf("绝对误差：%s → best=%s，worst=%s。", strings.Join(parts, "，"), names[best], names[worst])

	// apply ±0.1 (cap by available on worst)
	alpha := 0.1
	worstW := getW(t, names[worst])
	delta := alpha
	if worstW < delta {
		delta = worstW
	}
	if delta <= 0 {
		log.Printf("按规则：best +0.1，worst −0.1 → 权重在下一轮将为 %s", formatFloatSlice(triadToSlice(t, []string{providerOpenMeteo, providerCaiyun, providerImdroid})))
		return t
	}
	t = setW(t, names[worst], worstW-delta)
	t = setW(t, names[best], getW(t, names[best])+delta)
	log.Printf("按规则：best +0.1，worst −0.1 → 权重在下一轮将为 %s", formatFloatSlice(triadToSlice(t, []string{providerOpenMeteo, providerCaiyun, providerImdroid})))
	return t
}

func buildMatrix(db *sql.DB, stationID string, issued time.Time, ordered []string) []providerMatrix {
	out := make([]providerMatrix, 0, len(ordered))
	for _, p := range ordered {
		iss, ok, err := resolveIssuedAtInBucket(db, stationID, p, issued)
		if err != nil || !ok {
			continue
		}
		samples, err := loadForecastSamples(db, stationID, p, iss)
		if err != nil || len(samples) < 3 {
			continue
		}
		out = append(out, providerMatrix{Provider: p, Samples: samples[:3]})
	}
	return out
}

func fuseForecastsWith(matrix []providerMatrix, eff []float64) []forecastSample {
	result := make([]forecastSample, 3)
	n := len(matrix)
	if n == 0 {
		return result
	}
	for h := 0; h < 3; h++ {
		var windX, windY float64
		for i := 0; i < n; i++ {
			if len(matrix[i].Samples) <= h {
				continue
			}
			s := matrix[i].Samples[h]
			w := eff[i]
			result[h].Rain += s.Rain * w
			result[h].Temp += s.Temp * w
			result[h].Humidity += s.Humidity * w
			result[h].WindSpeed += s.WindSpeed * w
			result[h].WindGust += s.WindGust * w
			result[h].Prob += s.Prob * w
			result[h].Pressure += s.Pressure * w
			result[h].UV += s.UV * w
			rad := s.WindDir * math.Pi / 180
			windX += math.Cos(rad) * w
			windY += math.Sin(rad) * w
		}
		if windX == 0 && windY == 0 {
			result[h].WindDir = 0
		} else {
			dir := math.Atan2(windY, windX) * 180 / math.Pi
			if dir < 0 {
				dir += 360
			}
			result[h].WindDir = dir
		}
		result[h].Humidity = math.Round(result[h].Humidity)
		result[h].Prob = math.Round(result[h].Prob)
		result[h].UV = math.Round(result[h].UV)
	}
	return result
}

func upsertFused(ctx context.Context, db *sql.DB, stationID string, issued time.Time, fused []forecastSample) error {
	for h := 1; h <= 3; h++ {
		ft := issued.Add(time.Duration(h) * time.Hour)
		_, err := db.ExecContext(ctx, `
            INSERT INTO forecast_hourly (
              station_id, provider, issued_at, forecast_time,
              rain_mm_x1000, temp_c_x100, humidity_pct, wind_speed_ms_x1000,
              wind_gust_ms_x1000, wind_dir_deg, precip_prob_pct, pressure_hpa_x100, uv_index)
            VALUES ($1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11,$12,$13)
            ON CONFLICT (station_id, provider, issued_at, forecast_time) DO UPDATE SET
              rain_mm_x1000=EXCLUDED.rain_mm_x1000,
              temp_c_x100=EXCLUDED.temp_c_x100,
              humidity_pct=EXCLUDED.humidity_pct,
              wind_speed_ms_x1000=EXCLUDED.wind_speed_ms_x1000,
              wind_gust_ms_x1000=EXCLUDED.wind_gust_ms_x1000,
              wind_dir_deg=EXCLUDED.wind_dir_deg,
              precip_prob_pct=EXCLUDED.precip_prob_pct,
              pressure_hpa_x100=EXCLUDED.pressure_hpa_x100,
              uv_index=EXCLUDED.uv_index`,
			stationID, outputProvider, issued, ft,
			int(math.Round(fused[h-1].Rain*1000)),
			int(math.Round(fused[h-1].Temp*100)),
			int(math.Round(fused[h-1].Humidity)),
			int(math.Round(fused[h-1].WindSpeed*1000)),
			int(math.Round(fused[h-1].WindGust*1000)),
			int(math.Round(fused[h-1].WindDir)),
			int(math.Round(fused[h-1].Prob)),
			int(math.Round(fused[h-1].Pressure*100)),
			int(math.Round(fused[h-1].UV)),
		)
		if err != nil {
			return err
		}
	}
	return nil
}

// ----- Helpers copied (simplified) from cmd/imdroidmix -----

func resolveIssuedAtInBucket(db *sql.DB, stationID, provider string, bucketHour time.Time) (time.Time, bool, error) {
	const q = `SELECT issued_at FROM forecast_hourly WHERE station_id=$1 AND provider=$2 AND issued_at >= $3 AND issued_at < $3 + interval '1 hour' ORDER BY issued_at DESC LIMIT 1`
	var t time.Time
	err := db.QueryRow(q, stationID, provider, bucketHour).Scan(&t)
	if err == sql.ErrNoRows {
		return time.Time{}, false, nil
	}
	if err != nil {
		return time.Time{}, false, err
	}
	return t, true, nil
}

func loadForecastSamples(db *sql.DB, stationID, provider string, issued time.Time) ([]forecastSample, error) {
	const q = `
        SELECT forecast_time,
               rain_mm_x1000,
               temp_c_x100,
               humidity_pct,
               wind_speed_ms_x1000,
               wind_gust_ms_x1000,
               wind_dir_deg,
               precip_prob_pct,
               pressure_hpa_x100,
               uv_index
        FROM forecast_hourly
        WHERE station_id=$1 AND provider=$2 AND issued_at=$3
        ORDER BY forecast_time ASC`
	rows, err := db.Query(q, stationID, provider, issued)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var list []forecastSample
	for rows.Next() {
		var ft time.Time
		var rainX1000, tempX100, hum, wsX1000, gustX1000, wdir, prob, presX100, uv int
		if err := rows.Scan(&ft, &rainX1000, &tempX100, &hum, &wsX1000, &gustX1000, &wdir, &prob, &presX100, &uv); err != nil {
			return nil, err
		}
		list = append(list, forecastSample{
			Rain:      float64(rainX1000) / 1000.0,
			Temp:      float64(tempX100) / 100.0,
			Humidity:  float64(hum),
			WindSpeed: float64(wsX1000) / 1000.0,
			WindGust:  float64(gustX1000) / 1000.0,
			WindDir:   float64(wdir),
			Prob:      float64(prob),
			Pressure:  float64(presX100) / 100.0,
			UV:        float64(uv),
		})
	}
	return list, nil
}

func lead1PredsAt(db *sql.DB, stationID string, prevIssue time.Time, names []string) ([]float64, []string) {
	preds := make([]float64, 0, len(names))
	used := make([]string, 0, len(names))
	for _, p := range names {
		iss, ok, err := resolveIssuedAtInBucket(db, stationID, p, prevIssue)
		if err != nil || !ok {
			continue
		}
		samples, err := loadForecastSamples(db, stationID, p, iss)
		if err != nil || len(samples) < 1 {
			continue
		}
		preds = append(preds, samples[0].Rain)
		used = append(used, p)
	}
	return preds, used
}

func fetchActualHourlyRain(db *sql.DB, stationID string, start, end time.Time) (float64, bool, error) {
	const q = `SELECT SUM(rain_10m_mm_x1000) FROM rs485_weather_10min WHERE station_id=$1 AND bucket_start >= $2 AND bucket_start < $3`
	var sum sql.NullInt64
	err := db.QueryRow(q, stationID, start, end).Scan(&sum)
	if err != nil {
		return 0, false, err
	}
	if !sum.Valid {
		return 0, false, nil
	}
	return float64(sum.Int64) / 1000.0, true, nil
}

// ----- Radar mask helpers (trimmed) -----

type maskContext struct {
	id, alias string
	lat, lon  float64
	z, y, x   int
}

func hasMaskCtx(info stationInfo) bool {
	return info.Lat.Valid && info.Lon.Valid && info.Z.Valid && info.Y.Valid && info.X.Valid
}
func buildMaskContext(info stationInfo) maskContext {
	alias := info.Alias
	if strings.TrimSpace(alias) == "" {
		alias = info.ID
	}
	return maskContext{id: info.ID, alias: alias, lat: info.Lat.Float64, lon: info.Lon.Float64, z: int(info.Z.Int64), y: int(info.Y.Int64), x: int(info.X.Int64)}
}

type tileRec struct {
	DT     time.Time
	Width  int
	Height int
	West   float64
	South  float64
	East   float64
	North  float64
	ResDeg float64
	Data   []byte
}

type maskReport struct {
	Scanned    bool
	WindOK     bool
	UsedAlias  string
	WindSpeed  float64
	WindDir    float64
	Tiles      int
	HitsByHour [3]int
}

func checkRadarMask(db *sql.DB, ctx maskContext, issued time.Time) (maskReport, error) {
	rep := maskReport{}
	windTime := issued.Add(-time.Hour)
	if spd, dir, ok, err := loadWindByAlias(db, ctx.id, windTime); err != nil {
		return rep, err
	} else if ok {
		rep.WindOK, rep.WindSpeed, rep.WindDir, rep.UsedAlias = true, spd, dir, ctx.id
	} else if spd2, dir2, ok2, err2 := loadWindByAlias(db, ctx.alias, windTime); err2 != nil {
		return rep, err2
	} else if ok2 {
		rep.WindOK, rep.WindSpeed, rep.WindDir, rep.UsedAlias = true, spd2, dir2, ctx.alias
	} else {
		return rep, nil
	}
	tiles, err := loadTiles(db, ctx, issued.Add(-time.Hour), issued)
	if err != nil {
		return rep, err
	}
	if len(tiles) == 0 {
		return rep, nil
	}
	rep.Tiles = len(tiles)
	rep.Scanned = true
	const circleR = 8000.0
	const halfAngle = 30.0
	for _, t := range tiles {
		vals, xs, ys, err := decodeTile(t)
		if err != nil {
			continue
		}
		for r := 0; r < len(vals); r++ {
			row := vals[r]
			lat := ys[r]
			for c := 0; c < len(row); c++ {
				v := row[c]
				if v == nil {
					continue
				}
				dbz := *v
				if dbz < 40 {
					continue
				}
				lon := xs[c]
				dist := haversine(ctx.lat, ctx.lon, lat, lon)
				if dist <= circleR {
					rep.HitsByHour[0]++
				}
				if rep.WindSpeed > 0 {
					brg := bearingDeg(ctx.lat, ctx.lon, lat, lon)
					if angDiff(brg, rep.WindDir) <= halfAngle {
						if dist <= rep.WindSpeed*3*3600 {
							rep.HitsByHour[0]++
						}
						if dist <= circleR {
							rep.HitsByHour[1]++
						}
						if dist <= rep.WindSpeed*2*3600 {
							rep.HitsByHour[1]++
						}
						if dist <= rep.WindSpeed*3*3600 {
							rep.HitsByHour[2]++
						}
					}
				}
			}
		}
	}
	return rep, nil
}

func loadWindByAlias(db *sql.DB, alias string, target time.Time) (float64, float64, bool, error) {
	const q = `SELECT wind_speed, wind_direction FROM radar_weather WHERE alias=$1 AND dt <= $2 ORDER BY dt DESC LIMIT 1`
	var speed, dir sql.NullFloat64
	err := db.QueryRow(q, alias, target).Scan(&speed, &dir)
	if err == sql.ErrNoRows {
		return 0, 0, false, nil
	}
	if err != nil {
		return 0, 0, false, err
	}
	if !speed.Valid || !dir.Valid {
		return 0, 0, false, nil
	}
	return speed.Float64, dir.Float64, true, nil
}

func loadTiles(db *sql.DB, ctx maskContext, from, to time.Time) ([]tileRec, error) {
	const q = `SELECT dt, width, height, west, south, east, north, res_deg, data FROM radar_tiles WHERE z=$1 AND y=$2 AND x=$3 AND dt BETWEEN $4 AND $5 ORDER BY dt`
	rows, err := db.Query(q, ctx.z, ctx.y, ctx.x, from, to)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var list []tileRec
	for rows.Next() {
		var t tileRec
		if err := rows.Scan(&t.DT, &t.Width, &t.Height, &t.West, &t.South, &t.East, &t.North, &t.ResDeg, &t.Data); err != nil {
			return nil, err
		}
		list = append(list, t)
	}
	return list, nil
}

func decodeTile(t tileRec) ([][]*float64, []float64, []float64, error) {
	w, h := t.Width, t.Height
	if w <= 0 || h <= 0 {
		return nil, nil, nil, fmt.Errorf("非法瓦片尺寸")
	}
	if len(t.Data) < w*h*2 {
		return nil, nil, nil, fmt.Errorf("数据长度不足")
	}
	xs := make([]float64, w)
	for c := 0; c < w; c++ {
		xs[c] = t.West + (float64(c)+0.5)*t.ResDeg
	}
	ys := make([]float64, h)
	for r := 0; r < h; r++ {
		ys[r] = t.South + (float64(r)+0.5)*t.ResDeg
	}
	vals := make([][]*float64, h)
	off := 0
	for r := 0; r < h; r++ {
		row := make([]*float64, w)
		for c := 0; c < w; c++ {
			v := int16(binary.BigEndian.Uint16(t.Data[off : off+2]))
			off += 2
			if v >= 32766 {
				row[c] = nil
				continue
			}
			dbz := float64(v) / 10.0
			if dbz < 0 {
				dbz = 0
			} else if dbz > 75 {
				dbz = 75
			}
			value := dbz
			row[c] = &value
		}
		vals[r] = row
	}
	return vals, xs, ys, nil
}

func haversine(lat1, lon1, lat2, lon2 float64) float64 {
	const R = 6371000.0
	dLat := toRad(lat2 - lat1)
	dLon := toRad(lon2 - lon1)
	a := math.Sin(dLat/2)*math.Sin(dLat/2) + math.Cos(toRad(lat1))*math.Cos(toRad(lat2))*math.Sin(dLon/2)*math.Sin(dLon/2)
	c := 2 * math.Atan2(math.Sqrt(a), math.Sqrt(1-a))
	return R * c
}
func bearingDeg(lat1, lon1, lat2, lon2 float64) float64 {
	φ1 := toRad(lat1)
	φ2 := toRad(lat2)
	Δλ := toRad(lon2 - lon1)
	y := math.Sin(Δλ) * math.Cos(φ2)
	x := math.Cos(φ1)*math.Sin(φ2) - math.Sin(φ1)*math.Cos(φ2)*math.Cos(Δλ)
	brg := toDeg(math.Atan2(y, x))
	if brg < 0 {
		brg += 360
	}
	return brg
}
func angDiff(a, b float64) float64 {
	d := math.Mod(a-b+540, 360) - 180
	if d < 0 {
		d = -d
	}
	return math.Abs(d)
}
func toRad(d float64) float64 { return d * math.Pi / 180 }
func toDeg(r float64) float64 { return r * 180 / math.Pi }