weatherfeeder/internal/normalizers/nws/helpers.go

// FILE: internal/normalizers/nws/helpers.go
package nws

import (
	"strconv"
	"strings"
	"unicode"

	normcommon "gitea.maximumdirect.net/ejr/weatherfeeder/internal/normalizers/common"
	"gitea.maximumdirect.net/ejr/weatherfeeder/model"
)

// centroidLatLon returns a best-effort centroid (lat, lon) from a GeoJSON polygon.
// If geometry is missing or malformed, returns (nil, nil).
func centroidLatLon(coords [][][]float64) (lat *float64, lon *float64) {
	if len(coords) == 0 || len(coords[0]) == 0 {
		return nil, nil
	}

	var sumLon, sumLat float64
	var n float64

	for _, pt := range coords[0] {
		if len(pt) < 2 {
			continue
		}
		sumLon += pt[0]
		sumLat += pt[1]
		n++
	}

	if n == 0 {
		return nil, nil
	}

	avgLon := sumLon / n
	avgLat := sumLat / n

	return &avgLat, &avgLon
}

func tempCFromNWS(v *float64, unit string) *float64 {
	if v == nil {
		return nil
	}

	u := strings.ToUpper(strings.TrimSpace(unit))
	switch u {
	case "F":
		c := normcommon.TempCFromF(*v)
		return &c
	case "C":
		c := *v
		return &c
	default:
		// Unknown unit; be conservative.
		return nil
	}
}

// wmoFromNWSForecast infers a canonical WMO code for a forecast period.
//
// Strategy:
//  1. Try to infer from shortForecast using the cross-provider fallback.
//  2. Special-case mixed rain+snow using temperature when available (since our WMO table
//     does not include a “mixed precip” code).
//  3. Fall back to an icon token (e.g., "rain", "snow", "ovc", "bkn", "sct", ...).
func wmoFromNWSForecast(shortForecast, iconURL string, tempC *float64) model.WMOCode {
	sf := strings.TrimSpace(shortForecast)
	s := strings.ToLower(sf)

	// Mixed precip heuristic: choose rain vs snow based on temperature.
	if strings.Contains(s, "rain") && strings.Contains(s, "snow") {
		if tempC != nil && *tempC <= 0.0 {
			return 73 // Snow
		}
		return 63 // Rain
	}

	if code := normcommon.WMOFromTextDescription(sf); code != model.WMOUnknown {
		return code
	}

	// Icon fallback: token is usually the last path segment (before any comma/query).
	if token := nwsIconToken(iconURL); token != "" {
		// Try the general text fallback first (works for "rain", "snow", etc.).
		if code := normcommon.WMOFromTextDescription(token); code != model.WMOUnknown {
			return code
		}

		// Sky-condition icon tokens are common; map conservatively.
		switch token {
		case "ovc", "bkn", "cloudy", "ovcast":
			return 3
		case "sct", "bkn-sct":
			return 2
		case "few":
			return 1
		case "skc", "clr", "clear":
			return 0
		}
	}

	return model.WMOUnknown
}

func nwsIconToken(iconURL string) string {
	u := strings.TrimSpace(iconURL)
	if u == "" {
		return ""
	}

	// Drop query string.
	base := strings.SplitN(u, "?", 2)[0]

	// Take last path segment.
	parts := strings.Split(base, "/")
	if len(parts) == 0 {
		return ""
	}
	last := parts[len(parts)-1]
	if last == "" && len(parts) > 1 {
		last = parts[len(parts)-2]
	}

	// Some icons look like "rain,30" or "snow,20".
	last = strings.SplitN(last, ",", 2)[0]
	last = strings.ToLower(strings.TrimSpace(last))

	return last
}

// parseNWSWindSpeedKmh parses NWS wind speed strings like:
//   - "9 mph"
//   - "10 to 15 mph"
//
// and converts to km/h.
//
// Policy: if a range is present, we use the midpoint (best effort).
func parseNWSWindSpeedKmh(s string) *float64 {
	raw := strings.ToLower(strings.TrimSpace(s))
	if raw == "" {
		return nil
	}

	nums := extractFloats(raw)
	if len(nums) == 0 {
		return nil
	}

	val := nums[0]
	if len(nums) >= 2 && (strings.Contains(raw, " to ") || strings.Contains(raw, "-")) {
		val = (nums[0] + nums[1]) / 2.0
	}

	switch {
	case strings.Contains(raw, "mph"):
		k := normcommon.SpeedKmhFromMph(val)
		return &k

	case strings.Contains(raw, "km/h") || strings.Contains(raw, "kph"):
		k := val
		return &k

	case strings.Contains(raw, "kt") || strings.Contains(raw, "kts") || strings.Contains(raw, "knot"):
		// 1 knot = 1.852 km/h
		k := val * 1.852
		return &k

	default:
		// Unknown unit; be conservative.
		return nil
	}
}

// parseNWSWindDirectionDegrees maps compass directions to degrees.
// Returns nil if direction is empty/unknown.
func parseNWSWindDirectionDegrees(dir string) *float64 {
	d := strings.ToUpper(strings.TrimSpace(dir))
	if d == "" {
		return nil
	}

	// 16-wind compass.
	m := map[string]float64{
		"N":   0,
		"NNE": 22.5,
		"NE":  45,
		"ENE": 67.5,
		"E":   90,
		"ESE": 112.5,
		"SE":  135,
		"SSE": 157.5,
		"S":   180,
		"SSW": 202.5,
		"SW":  225,
		"WSW": 247.5,
		"W":   270,
		"WNW": 292.5,
		"NW":  315,
		"NNW": 337.5,
	}

	if deg, ok := m[d]; ok {
		return &deg
	}
	return nil
}

func extractFloats(s string) []float64 {
	var out []float64
	var buf strings.Builder

	flush := func() {
		if buf.Len() == 0 {
			return
		}
		v, err := strconv.ParseFloat(buf.String(), 64)
		if err == nil {
			out = append(out, v)
		}
		buf.Reset()
	}

	for _, r := range s {
		if unicode.IsDigit(r) || r == '.' {
			buf.WriteRune(r)
			continue
		}
		flush()
	}
	flush()

	return out
}