embedded-bt-rssi-monitor/main.go

package main

import (
	"fmt"
	"log"
	"net/http"
	"os"
	"time"

	"tinygo.org/x/bluetooth"
)

type MonitoredDevice struct {
	MacAddress  string
	RssiHistory []int16   // RSSI readings over time.  The latest is always last element: RssiHistory[len(RssiHistory)-1]
	LastPing    time.Time // Last time device was scanned
}

const (
	rssiHistoryLength = 3
	pingTimeout       = time.Second * 60
	// rssiThreshold        int16 = -80 // anything lower doesn't count

	rssiThresholdLower   int16 = -82
	rssiThresholdUpper   int16 = -72
	terminalDashboardURL       = "http://localhost:8080/set?screen="
)

var (
	adapter          = bluetooth.DefaultAdapter
	monitoredDevices []MonitoredDevice
)

// Application Startup
func init() {
	log.Printf("embedded-bt-rssi-monitor init")

	// Load application configuration from environment variables
	/*
		envVars := make(map[string]string)
		envVars["required"] = os.Getenv("required")
		// Validate that all required environment variables are set
		for key, value := range envVars {
			if value == "" {
				log.Fatalf("shell environment variable %s is not set", key)
			}
		}
	*/

	monitoredDevices = make([]MonitoredDevice, 0)

	for i := 0; true; i++ {
		macAddress := os.Getenv(fmt.Sprintf("btmacaddress_%d", i))
		if macAddress == "" {
			break
		}

		fmt.Println("Watching MAC Address: ", macAddress)

		monitoredDevice := MonitoredDevice{MacAddress: macAddress}
		monitoredDevices = append(monitoredDevices, monitoredDevice)
	}
}

func main() {
	// Enable BLE interface.
	must("enable BLE stack", adapter.Enable())

	go evaluator()

	// Start scanning.
	println("scanning...")
	err := adapter.Scan(scanHandler)
	must("start scan", err)
}

func must(action string, err error) {
	if err != nil {
		panic("failed to " + action + ": " + err.Error())
	}
}

// Runs against every device returned in a scan result
func scanHandler(adapter *bluetooth.Adapter, device bluetooth.ScanResult) {
	// First filter out devices that we don't care about
	for i := range monitoredDevices {
		if monitoredDevices[i].MacAddress == device.Address.String() {
			log.Println(device.LocalName(), device.Address, device.RSSI)
			monitoredDevices[i].LastPing = time.Now()
			monitoredDevices[i].RssiHistory = append(monitoredDevices[i].RssiHistory, device.RSSI)
			if len(monitoredDevices[i].RssiHistory) > rssiHistoryLength { // keep up to rssiHistoryLength, and then begin popping out the first element
				monitoredDevices[i].RssiHistory = monitoredDevices[i].RssiHistory[1:]
			}
			break
		}
	}
}

// Reads the MonitoredDevices and takes an action
// meant to run in a goroutine
func evaluator() {

	var screenOff bool

	for {
		time.Sleep(time.Second * 20)

		bestSignal := rssiThresholdLower

		for i := range monitoredDevices {
			if time.Now().After(monitoredDevices[i].LastPing.Add(pingTimeout)) {
				continue // ignore device
			}

			averageRssi := getAverage(monitoredDevices[i].RssiHistory)

			if averageRssi > bestSignal {
				bestSignal = averageRssi
			}
		}

		if bestSignal > rssiThresholdUpper {
			if screenOff {
				screenOff = false
				log.Printf("setting screen to: budget")
				_, err := http.Get(fmt.Sprintf("%sbudget", terminalDashboardURL))
				if err != nil {
					log.Printf("failed to set budget screen: %v", err)
				}
			}
		} else if bestSignal <= rssiThresholdLower {
			if !screenOff {
				screenOff = true
				log.Printf("setting screen to: off")
				_, err := http.Get(fmt.Sprintf("%soff", terminalDashboardURL))
				if err != nil {
					log.Printf("failed to set off screen: %v", err)
				}
			}
		}
	}
}

func getAverage(nums []int16) int16 {
	var sum int16
	for _, num := range nums {
		sum += num
	}

	return sum / int16(len(nums))
}