DeviceScan.kt

fun startScan() {
        scanFilters = buildScanFilters()
        scanSettings = buildScanSettings()
        if (!adapter.isMultipleAdvertisementSupported) {
            _viewState.value = DeviceScanViewState.AdvertisementNotSupported
            return
        }

        if (scanCallback == null) {
            scanner = adapter.bluetoothLeScanner
            _viewState.value = DeviceScanViewState.ActiveScan
            Handler().postDelayed({ stopScanning() }, SCAN_PERIOD)
            scanCallback = DeviceScanCallback()
            scanner?.startScan(scanFilters, scanSettings, scanCallback)
        } 
}

private fun buildScanFilters(): List<ScanFilter> {
        val builder = ScanFilter.Builder()
        builder.setServiceUuid(ParcelUuid(SERVICE_UUID))
        val filter = builder.build()
        return listOf(filter)
}

private fun buildScanSettings(): ScanSettings {
        return ScanSettings.Builder()
            .setScanMode(ScanSettings.SCAN_MODE_LOW_POWER)
            .build()
}

private inner class DeviceScanCallback : ScanCallback() {
        override fun onBatchScanResults(results: List<ScanResult>) {
            super.onBatchScanResults(results)
            for (item in results) {
                item.device?.let { device ->
                    scanResults[device.address] = device
                }
            }
            Log.i(TAG, scanResults.toString())
            _viewState.value = DeviceScanViewState.ScanResults(scanResults)
        }

        override fun onScanResult(
            callbackType: Int,
            result: ScanResult
        ) {
            super.onScanResult(callbackType, result)
            result.device?.let { device ->
                scanResults[device.address] = device
            }
            Log.i(TAG, scanResults.toString())
            _viewState.value = DeviceScanViewState.ScanResults(scanResults)
        }

        override fun onScanFailed(errorCode: Int) {
            super.onScanFailed(errorCode)
            val errorMessage = "Scan failed: $errorCode"
            _viewState.value = DeviceScanViewState.Error(errorMessage)
        }
    }