sim-modem/api/modem/gps/status.go

package gps

import (
	"fmt"
	"strconv"
	"strings"
)

type Status struct {
	GotResponses         bool    `json:"gotResponses"`
	IsValidData          bool    `json:"isValidData"`
	FoundSatelitesCount  int     `json:"foundSatelitesCount"`
	ActiveSatelitesCount int     `json:"activeSatelitesCount"`
	Rms                  float32 `json:"rms"` // Root mean square
}

var StatusNil = Status{
	GotResponses:         false,
	IsValidData:          false,
	FoundSatelitesCount:  0,
	ActiveSatelitesCount: 0,
	Rms:                  0,
}

func (g *gps) GetStatus() (Status, error) {
	// Provides more information about signal and possible problems using NMEA reports

	// Collect reports
	reports, err := g.collectNmeaReports(nmeaFlagsAll) // Now minimum
	if err != nil {
		return StatusNil, fmt.Errorf("collect nmea reports: %w", err)
	}

	// Annalise
	st := Status{}

checkLoop:
	for _, s := range reports {
		// Check for NMEA format
		if len(s) < 1 || s[0] != '$' {
			continue checkLoop
		}
		st.GotResponses = true

		// g.logger.Println("NMEA check:", s)
		values := strings.Split(s, ",")
		if len(values[0]) != 6 {
			return StatusNil, fmt.Errorf("nmea invalid sentence: %s", s)
		}
		switch values[0][3:] { // Switch by content
		case "GSV": // Any satelites
			// g.logger.Println("check GSV")
			// Check len
			if len(values) < 17 {
				g.logger.Println("GSV too small values")
				continue checkLoop
			}

			// Decode
			// 0 - msg type
			// 1 - number of msgs
			// 2 - index of this msg
			// 3 - number of visible satelites
			// 4: - other data

			// Msg index
			index, err := strconv.Atoi(values[3])
			if err != nil {
				g.logger.Println("GSV too small values")
				continue checkLoop
			}
			_ = index
			// if index != 0 {
			// 	g.logger.Println("discard not first GSV msg")
			// 	continue checkLoop
			// }

			// Count
			satCount, err := strconv.Atoi(values[4])
			if err != nil {
				g.logger.Println("GSV too small values")
				continue checkLoop
			}
			st.FoundSatelitesCount = satCount
		case "GSA": // Active satelites
			// g.logger.Println("check GSA")

			// Check len
			if len(values) < 17 {
				g.logger.Println("GSV too small values")
				continue checkLoop
			}

			// Decode
			// 0 - msg type
			// 1 - mode of selecting format
			// 2 - mode of selected format
			// 3:15 - IDs of active satelites
			// 15: - other data

			// Counting active satelites
			count := 0
			for _, v := range values[3:15] {
				if _, err := strconv.Atoi(v); err == nil {
					count += 1
				}
			}
			st.ActiveSatelitesCount = max(st.ActiveSatelitesCount, count)
		case "RMC": // Minimum GPS data
			// g.logger.Println("check RMC")
			// Check len
			if len(values) < 12 {
				g.logger.Println("RMC too small values")
				continue checkLoop
			}

			// Decode
			// 0 - msg type
			// 1 - time
			// 2 - is data valid or not
			// 3: - other data

			// Is valid value
			if values[2] == "A" {
				st.IsValidData = true
			}
		case "GST":
			// g.logger.Println("check GST")
			// Check len
			if len(values) < 8 {
				g.logger.Println("GST too small values")
				continue checkLoop
			}

			// Decode
			// 0 - msg type
			// 1 - time
			// 2 - Root Mean Square
			// 3: - other data

			rms, err := strconv.ParseFloat(values[2], 32)
			if err != nil {
				g.logger.Println("RMS decode:", err.Error())
				continue checkLoop
			}
			st.Rms = float32(rms)
		}
	}

	return st, nil
}