Add support for chipsea / OKOK 2.0 scales

For now only handles weight, impedance is read, but not used for
anything, algorithms not known.

The scale does not indicate whether it is sending the weight in kg or in
lbs, always assuming kg.

android_app/app/src/main/java/com/health/openscale/core/bluetooth/BluetoothFactory.java

@@ -116,6 +116,9 @@ public static BluetoothCommunication createDeviceDriver(Context context, String
         if (deviceName.startsWith("Shape200") || deviceName.startsWith("Shape100") || deviceName.startsWith("Shape50") || deviceName.startsWith("Style100")) {
             return new BluetoothSoehnle(context);
         }
+        if (deviceName.equals("ADV")) {
+            return new BluetoothOKOK(context);
+        }
         return null;
     }
 }

android_app/app/src/main/java/com/health/openscale/core/bluetooth/BluetoothOKOK.java

@@ -0,0 +1,95 @@
+package com.health.openscale.core.bluetooth;
+
+import android.bluetooth.le.ScanResult;
+import android.content.Context;
+import android.bluetooth.le.ScanFilter;
+import android.os.Handler;
+import android.os.Looper;
+import android.util.SparseArray;
+
+import com.health.openscale.core.datatypes.ScaleMeasurement;
+import com.welie.blessed.BluetoothCentral;
+import com.welie.blessed.BluetoothCentralCallback;
+import com.welie.blessed.BluetoothPeripheral;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.LinkedList;
+import java.util.List;
+
+import timber.log.Timber;
+
+public class BluetoothOKOK extends BluetoothCommunication {
+    private static final int MANUFACTURER_DATA_ID = 0x20ca; // 16-bit little endian "header" 0xca 0x20
+    private static final int IDX_FINAL = 6;
+    private static final int IDX_WEIGHT_MSB = 8;
+    private static final int IDX_WEIGHT_LSB = 9;
+    private static final int IDX_IMPEDANCE_MSB = 10;
+    private static final int IDX_IMPEDANCE_LSB = 11;
+    private static final int IDX_CHECKSUM = 12;
+
+    private BluetoothCentral central;
+    private final BluetoothCentralCallback btCallback = new BluetoothCentralCallback() {
+        @Override
+        public void onDiscoveredPeripheral(@NotNull BluetoothPeripheral peripheral, @NotNull ScanResult scanResult) {
+            SparseArray<byte[]> manufacturerSpecificData = scanResult.getScanRecord().getManufacturerSpecificData();
+            byte[] data = scanResult.getScanRecord().getManufacturerSpecificData(MANUFACTURER_DATA_ID);
+            byte checksum = 0x20; // Version field is part of the checksum, but not in array
+            if (data == null || data.length != 19)
+                return;
+            if (data[IDX_FINAL] == 0)
+                return;
+            for (int i = 0; i < IDX_CHECKSUM; i++)
+                checksum ^= data[i];
+            if (data[IDX_CHECKSUM] != checksum) {
+                Timber.d("Checksum error, got %x, expected %x", data[12] & 0xff, checksum & 0xff);
+                return;
+            }
+            int weight = data[IDX_WEIGHT_MSB] & 0xff;
+            weight = weight << 8 | (data[IDX_WEIGHT_LSB] & 0xff);
+            int impedance = data[IDX_IMPEDANCE_MSB] & 0xff;
+            impedance = impedance << 8 | (data[IDX_IMPEDANCE_LSB] & 0xff);
+            Timber.d("Got weight: %f and impedance %f", weight / 10f, impedance / 10f);
+            ScaleMeasurement entry = new ScaleMeasurement();
+            entry.setWeight(weight / 10.0f);
+            addScaleMeasurement(entry);
+            disconnect();
+        }
+    };
+
+    public BluetoothOKOK(Context context)
+    {
+        super(context);
+        central = new BluetoothCentral(context, btCallback, new Handler(Looper.getMainLooper()));
+    }
+
+    @Override
+    public String driverName() {
+        return "OKOK";
+    }
+
+    @Override
+    public void connect(String macAddress) {
+        Timber.d("Mac address: %s", macAddress);
+        List<ScanFilter> filters = new LinkedList<ScanFilter>();
+        ScanFilter.Builder b = new ScanFilter.Builder();
+        b.setDeviceAddress(macAddress);
+        b.setDeviceName("ADV");
+        b.setManufacturerData(MANUFACTURER_DATA_ID, null, null);
+        filters.add(b.build());
+        central.scanForPeripheralsUsingFilters(filters);
+    }
+
+    @Override
+    public void disconnect() {
+        if (central != null)
+            central.stopScan();
+        central = null;
+        super.disconnect();
+    }
+
+    @Override
+    protected boolean onNextStep(int stepNr) {
+        return false;
+    }
+}