refactor: remove init() and package-level rootCmd, add error logging

- Move flag registration from init() to main()
- Make rootCmd a local variable in main() instead of a package variable
- Log errors from hciconfig down/up reset commands
- Log errors from BLE power characteristic writes

cmd/bridge/bluetooth.go

@@ -72,7 +72,9 @@ func ExposeBluetooth(events <-chan Event) {
 		binary.LittleEndian.PutUint16(payload[4:], uint16(completedRevs))
 		binary.LittleEndian.PutUint16(payload[6:], uint16(lastCompletedRev))
 
-		powerChar.Write(payload)
+		if _, err := powerChar.Write(payload); err != nil {
+			logPrintf("bt: failed to write power characteristic: %v\n", err)
+		}
 		logPrintf("bt: watts: %d  rpm: %.0f  completedRevs: %.0f  lastRevTime: %.0f processingTime: %v\n",
 			watts, rpm, completedRevs, lastCompletedRev, time.Now().Sub(now))
 	}

cmd/bridge/cli.go

@@ -66,8 +66,12 @@ This allows these trainers to be used with modern devices that don't support ANT
 			logMsgf("product: 0x%04x/%d", productID, productID)
 			logMsgf("device: 0x%03x/%d", deviceNumber, deviceNumber)
 
-			exec.Command("hciconfig", "hci0", "down").Run()
-			exec.Command("hciconfig", "hci0", "up").Run()
+			if err := exec.Command("hciconfig", "hci0", "down").Run(); err != nil {
+				logPrintf("hciconfig down failed: %v\n", err)
+			}
+			if err := exec.Command("hciconfig", "hci0", "up").Run(); err != nil {
+				logPrintf("hciconfig up failed: %v\n", err)
+			}
 
 			events := make(chan Event)
 			go ListenForTrainer(uint16(c.vendorID), uint16(c.productID), c.deviceNumber, events)