First part of extracting parts out of MiBandSupport

Extract Activity Data fetching into distinct 'operation' class.

Fix a few small things wrt transaction-local GattCallbacks along the way.

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/AbstractBTLEDeviceSupport.java

@@ -132,7 +132,7 @@ public abstract class AbstractBTLEDeviceSupport extends AbstractDeviceSupport im
      * @return the characteristic for the given UUID or <code>null</code>
      * @see #addSupportedService(UUID)
      */
-    protected BluetoothGattCharacteristic getCharacteristic(UUID uuid) {
+    public BluetoothGattCharacteristic getCharacteristic(UUID uuid) {
         if (mAvailableCharacteristics == null) {
             return null;
         }

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/BtLEQueue.java

@@ -61,7 +61,7 @@ public final class BtLEQueue {
             while (!mDisposed && !mCrashed) {
                 try {
                     Transaction transaction = mTransactions.take();
-                    internalGattCallback.setTransactionGattCallback(null);
+                    internalGattCallback.reset();
 
                     if (!isConnected()) {
                         // TODO: request connection and initialization from the outside and wait until finished
@@ -114,7 +114,6 @@ public final class BtLEQueue {
                 } finally {
                     mWaitForActionResultLatch = null;
                     mWaitCharacteristic = null;
-                    internalGattCallback.reset();
                 }
             }
             LOG.info("Queue Dispatch Thread terminated.");
@@ -185,6 +184,7 @@ public final class BtLEQueue {
     }
 
     private void handleDisconnected(int status) {
+        internalGattCallback.reset();
         mTransactions.clear();
         mAbortTransaction = true;
         if (mWaitForActionResultLatch != null) {

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/miband/MiBandSupport.java

@@ -3,7 +3,6 @@ package nodomain.freeyourgadget.gadgetbridge.service.devices.miband;
 import android.bluetooth.BluetoothGatt;
 import android.bluetooth.BluetoothGattCharacteristic;
 import android.content.SharedPreferences;
-import android.database.sqlite.SQLiteDatabase;
 import android.net.Uri;
 import android.preference.PreferenceManager;
 import android.widget.Toast;
@@ -12,19 +11,14 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
-import java.text.DateFormat;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Calendar;
 import java.util.GregorianCalendar;
 import java.util.UUID;
-import java.util.concurrent.TimeUnit;
 
-import nodomain.freeyourgadget.gadgetbridge.GBApplication;
 import nodomain.freeyourgadget.gadgetbridge.R;
-import nodomain.freeyourgadget.gadgetbridge.database.DBHandler;
 import nodomain.freeyourgadget.gadgetbridge.deviceevents.GBDeviceEventVersionInfo;
-import nodomain.freeyourgadget.gadgetbridge.devices.SampleProvider;
 import nodomain.freeyourgadget.gadgetbridge.devices.miband.MiBandConst;
 import nodomain.freeyourgadget.gadgetbridge.devices.miband.MiBandCoordinator;
 import nodomain.freeyourgadget.gadgetbridge.devices.miband.MiBandFWHelper;
@@ -37,11 +31,10 @@ import nodomain.freeyourgadget.gadgetbridge.service.btle.AbstractBTLEDeviceSuppo
 import nodomain.freeyourgadget.gadgetbridge.service.btle.BtLEAction;
 import nodomain.freeyourgadget.gadgetbridge.service.btle.TransactionBuilder;
 import nodomain.freeyourgadget.gadgetbridge.service.btle.actions.AbortTransactionAction;
-import nodomain.freeyourgadget.gadgetbridge.service.btle.actions.SetDeviceBusyAction;
 import nodomain.freeyourgadget.gadgetbridge.service.btle.actions.SetDeviceStateAction;
 import nodomain.freeyourgadget.gadgetbridge.service.btle.actions.SetProgressAction;
+import nodomain.freeyourgadget.gadgetbridge.service.devices.miband.operations.FetchActivityOperation;
 import nodomain.freeyourgadget.gadgetbridge.util.CheckSums;
-import nodomain.freeyourgadget.gadgetbridge.util.DateTimeUtils;
 import nodomain.freeyourgadget.gadgetbridge.util.GB;
 
 import static nodomain.freeyourgadget.gadgetbridge.devices.miband.MiBandConst.DEFAULT_VALUE_FLASH_COLOUR;
@@ -68,29 +61,10 @@ import static nodomain.freeyourgadget.gadgetbridge.devices.miband.MiBandConst.ge
 
 public class MiBandSupport extends AbstractBTLEDeviceSupport {
 
-    //temporary buffer, size is a multiple of 60 because we want to store complete minutes (1 minute = 3 bytes)
-    private static final int activityDataHolderSize = 3 * 60 * 4; // 8h
-
-    private static class ActivityStruct {
-        public byte[] activityDataHolder = new byte[activityDataHolderSize];
-        //index of the buffer above
-        public int activityDataHolderProgress = 0;
-        //number of bytes we will get in a single data transfer, used as counter
-        public int activityDataRemainingBytes = 0;
-        //same as above, but remains untouched for the ack message
-        public int activityDataUntilNextHeader = 0;
-        //timestamp of the single data transfer, incremented to store each minute's data
-        public GregorianCalendar activityDataTimestampProgress = null;
-        //same as above, but remains untouched for the ack message
-        public GregorianCalendar activityDataTimestampToAck = null;
-    }
-
     private static final Logger LOG = LoggerFactory.getLogger(MiBandSupport.class);
     private volatile boolean telephoneRinging;
     private volatile boolean isLocatingDevice;
 
-    private ActivityStruct activityStruct;
-
     private DeviceInfo mDeviceInfo;
 
     private boolean firmwareInfoSent = false;
@@ -234,7 +208,6 @@ public class MiBandSupport extends AbstractBTLEDeviceSupport {
     private static final byte[] startVibrate = new byte[]{MiBandService.COMMAND_SEND_NOTIFICATION, 1};
     private static final byte[] stopVibrate = new byte[]{MiBandService.COMMAND_STOP_MOTOR_VIBRATE};
     private static final byte[] reboot = new byte[]{MiBandService.COMMAND_REBOOT};
-    private static final byte[] fetch = new byte[]{MiBandService.COMMAND_FETCH_DATA};
 
     private byte[] getNotification(long vibrateDuration, int vibrateTimes, int flashTimes, int flashColour, int originalColour, long flashDuration) {
         byte[] vibrate = new byte[]{MiBandService.COMMAND_SEND_NOTIFICATION, (byte) 1};
@@ -546,11 +519,7 @@ public class MiBandSupport extends AbstractBTLEDeviceSupport {
     @Override
     public void onFetchActivityData() {
         try {
-            TransactionBuilder builder = performInitialized("fetch activity data");
-//            builder.write(getCharacteristic(MiBandService.UUID_CHARACTERISTIC_LE_PARAMS), getLowLatency());
-            builder.add(new SetDeviceBusyAction(getDevice(), getContext().getString(R.string.busy_task_fetch_activity_data), getContext()));
-            builder.write(getCharacteristic(MiBandService.UUID_CHARACTERISTIC_CONTROL_POINT), fetch);
-            builder.queue(getQueue());
+            new FetchActivityOperation(this).perform();
         } catch (IOException ex) {
             LOG.error("Unable to fetch MI activity data", ex);
         }
@@ -646,9 +615,7 @@ public class MiBandSupport extends AbstractBTLEDeviceSupport {
         super.onCharacteristicChanged(gatt, characteristic);
 
         UUID characteristicUUID = characteristic.getUuid();
-        if (MiBandService.UUID_CHARACTERISTIC_ACTIVITY_DATA.equals(characteristicUUID)) {
-            handleActivityNotif(characteristic.getValue());
-        } else if (MiBandService.UUID_CHARACTERISTIC_BATTERY.equals(characteristicUUID)) {
+        if (MiBandService.UUID_CHARACTERISTIC_BATTERY.equals(characteristicUUID)) {
             handleBatteryInfo(characteristic.getValue(), BluetoothGatt.GATT_SUCCESS);
         } else if (MiBandService.UUID_CHARACTERISTIC_NOTIFICATION.equals(characteristicUUID)) {
             handleNotificationNotif(characteristic.getValue());
@@ -792,151 +759,6 @@ public class MiBandSupport extends AbstractBTLEDeviceSupport {
         builder.write(characteristic, alarmMessage);
     }
 
-    /**
-     * Method to handle the incoming activity data.
-     * There are two kind of messages we currently know:
-     * - the first one is 11 bytes long and contains metadata (how many bytes to expect, when the data starts, etc.)
-     * - the second one is 20 bytes long and contains the actual activity data
-     *
-     * The first message type is parsed by this method, for every other length of the value param, bufferActivityData is called.
-     * @see #bufferActivityData(byte[])
-     *
-     *
-     * @param value
-     */
-    private void handleActivityNotif(byte[] value) {
-        boolean firstChunk = activityStruct == null;
-        if (firstChunk) {
-            activityStruct = new ActivityStruct();
-        }
-
-        if (value.length == 11) {
-            // byte 0 is the data type: 1 means that each minute is represented by a triplet of bytes
-            int dataType = value[0];
-            // byte 1 to 6 represent a timestamp
-            GregorianCalendar timestamp = parseTimestamp(value, 1);
-
-            // counter of all data held by the band
-            int totalDataToRead = (value[7] & 0xff) | ((value[8] & 0xff) << 8);
-            totalDataToRead *= (dataType == 1) ? 3 : 1;
-
-
-            // counter of this data block
-            int dataUntilNextHeader = (value[9] & 0xff) | ((value[10] & 0xff) << 8);
-            dataUntilNextHeader *= (dataType == 1) ? 3 : 1;
-
-            // there is a total of totalDataToRead that will come in chunks (3 bytes per minute if dataType == 1),
-            // these chunks are usually 20 bytes long and grouped in blocks
-            // after dataUntilNextHeader bytes we will get a new packet of 11 bytes that should be parsed
-            // as we just did
-
-            if (firstChunk && dataUntilNextHeader != 0) {
-                GB.toast(getContext().getString(R.string.user_feedback_miband_activity_data_transfer,
-                        DateTimeUtils.formatDurationHoursMinutes((totalDataToRead / 3), TimeUnit.MINUTES),
-                        DateFormat.getDateTimeInstance().format(timestamp.getTime())), Toast.LENGTH_LONG, GB.INFO);
-            }
-            LOG.info("total data to read: " + totalDataToRead + " len: " + (totalDataToRead / 3) + " minute(s)");
-            LOG.info("data to read until next header: " + dataUntilNextHeader + " len: " + (dataUntilNextHeader / 3) + " minute(s)");
-            LOG.info("TIMESTAMP: " + DateFormat.getDateTimeInstance().format(timestamp.getTime()).toString() + " magic byte: " + dataUntilNextHeader);
-
-            activityStruct.activityDataRemainingBytes = activityStruct.activityDataUntilNextHeader = dataUntilNextHeader;
-            activityStruct.activityDataTimestampToAck = (GregorianCalendar) timestamp.clone();
-            activityStruct.activityDataTimestampProgress = timestamp;
-
-        } else {
-            bufferActivityData(value);
-        }
-        LOG.debug("activity data: length: " + value.length + ", remaining bytes: " + activityStruct.activityDataRemainingBytes);
-
-        if (activityStruct.activityDataRemainingBytes == 0) {
-            sendAckDataTransfer(activityStruct.activityDataTimestampToAck, activityStruct.activityDataUntilNextHeader);
-        }
-    }
-
-    private GregorianCalendar parseTimestamp(byte[] value, int offset) {
-        GregorianCalendar timestamp = new GregorianCalendar(
-                value[offset] + 2000,
-                value[offset + 1],
-                value[offset + 2],
-                value[offset + 3],
-                value[offset + 4],
-                value[offset + 5]);
-        return timestamp;
-    }
-
-    /**
-     * Method to store temporarily the activity data values got from the Mi Band.
-     *
-     * Since we expect chunks of 20 bytes each, we do not store the received bytes it the length is different.
-     *
-     * @param value
-     */
-    private void bufferActivityData(byte[] value) {
-
-        if (activityStruct.activityDataRemainingBytes >= value.length) {
-            //I don't like this clause, but until we figure out why we get different data sometimes this should work
-            if (value.length == 20 || value.length == activityStruct.activityDataRemainingBytes) {
-                System.arraycopy(value, 0, activityStruct.activityDataHolder, activityStruct.activityDataHolderProgress, value.length);
-                activityStruct.activityDataHolderProgress += value.length;
-                activityStruct.activityDataRemainingBytes -= value.length;
-
-                if (this.activityDataHolderSize == activityStruct.activityDataHolderProgress) {
-                    flushActivityDataHolder();
-                }
-            } else {
-                // the length of the chunk is not what we expect. We need to make sense of this data
-                LOG.warn("GOT UNEXPECTED ACTIVITY DATA WITH LENGTH: " + value.length + ", EXPECTED LENGTH: " + activityStruct.activityDataRemainingBytes);
-                for (byte b : value) {
-                    LOG.warn("DATA: " + String.format("0x%8x", b));
-                }
-            }
-        } else {
-            LOG.error("error buffering activity data: remaining bytes: " + activityStruct.activityDataRemainingBytes + ", received: " + value.length);
-        }
-    }
-
-    /**
-     * empty the local buffer for activity data, arrange the values received in groups of three and
-     * store them in the DB
-     */
-    private void flushActivityDataHolder() {
-        if (activityStruct == null) {
-            LOG.debug("nothing to flush, struct is already null");
-            return;
-        }
-        LOG.debug("flushing activity data holder");
-        byte category, intensity, steps;
-
-        DBHandler dbHandler = null;
-        try {
-            dbHandler = GBApplication.acquireDB();
-            try (SQLiteDatabase db = dbHandler.getWritableDatabase()) { // explicitly keep the db open while looping over the samples
-                for (int i = 0; i < activityStruct.activityDataHolderProgress; i += 3) { //TODO: check if multiple of 3, if not something is wrong
-                    category = activityStruct.activityDataHolder[i];
-                    intensity = activityStruct.activityDataHolder[i + 1];
-                    steps = activityStruct.activityDataHolder[i + 2];
-
-                    dbHandler.addGBActivitySample(
-                            (int) (activityStruct.activityDataTimestampProgress.getTimeInMillis() / 1000),
-                            SampleProvider.PROVIDER_MIBAND,
-                            (short) (intensity & 0xff),
-                            (short) (steps & 0xff),
-                            category);
-                    activityStruct.activityDataTimestampProgress.add(Calendar.MINUTE, 1);
-                }
-            } finally {
-                activityStruct.activityDataHolderProgress = 0;
-            }
-        } catch (Exception ex) {
-            GB.toast(getContext(), ex.getMessage(), Toast.LENGTH_LONG, GB.ERROR);
-        } finally {
-            if (dbHandler != null) {
-                dbHandler.release();
-            }
-        }
-    }
-
-
     private void handleControlPointResult(byte[] value, int status) {
         if (status != BluetoothGatt.GATT_SUCCESS) {
             LOG.warn("Could not write to the control point.");
@@ -952,56 +774,6 @@ public class MiBandSupport extends AbstractBTLEDeviceSupport {
         }
     }
 
-    private void unsetBusy() {
-        getDevice().unsetBusyTask();
-        getDevice().sendDeviceUpdateIntent(getContext());
-    }
-
-    /**
-     * Acknowledge the transfer of activity data to the Mi Band.
-     *
-     * After receiving data from the band, it has to be acknowledged. This way the Mi Band will delete
-     * the data it has on record.
-     *
-     * @param time
-     * @param bytesTransferred
-     */
-    private void sendAckDataTransfer(Calendar time, int bytesTransferred) {
-        byte[] ack = new byte[]{
-                MiBandService.COMMAND_CONFIRM_ACTIVITY_DATA_TRANSFER_COMPLETE,
-                (byte) (time.get(Calendar.YEAR) - 2000),
-                (byte) time.get(Calendar.MONTH),
-                (byte) time.get(Calendar.DATE),
-                (byte) time.get(Calendar.HOUR_OF_DAY),
-                (byte) time.get(Calendar.MINUTE),
-                (byte) time.get(Calendar.SECOND),
-                (byte) (bytesTransferred & 0xff),
-                (byte) (0xff & (bytesTransferred >> 8))
-        };
-        try {
-            TransactionBuilder builder = performInitialized("send acknowledge");
-            builder.write(getCharacteristic(MiBandService.UUID_CHARACTERISTIC_CONTROL_POINT), ack);
-            builder.queue(getQueue());
-
-            // flush to the DB after sending the ACK
-            flushActivityDataHolder();
-
-            //The last data chunk sent by the miband has always length 0.
-            //When we ack this chunk, the transfer is done.
-            if (getDevice().isBusy() && bytesTransferred == 0) {
-                handleActivityFetchFinish();
-            }
-        } catch (IOException ex) {
-            LOG.error("Unable to send ack to MI", ex);
-        }
-    }
-
-    private void handleActivityFetchFinish() {
-        LOG.info("Fetching activity data has finished.");
-        activityStruct = null;
-        unsetBusy();
-    }
-
     private void handleBatteryInfo(byte[] value, int status) {
         if (status == BluetoothGatt.GATT_SUCCESS) {
             BatteryInfo info = new BatteryInfo(value);
@@ -1145,4 +917,10 @@ public class MiBandSupport extends AbstractBTLEDeviceSupport {
         }
         return true;
     }
+
+    // overridden to make visible to operations
+    @Override
+    public TransactionBuilder performInitialized(String taskName) throws IOException {
+        return super.performInitialized(taskName);
+    }
 }

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/miband/operations/AbstractMiBandOperation.java

@@ -0,0 +1,115 @@
+package nodomain.freeyourgadget.gadgetbridge.service.devices.miband.operations;
+
+import android.bluetooth.BluetoothGatt;
+import android.bluetooth.BluetoothGattCharacteristic;
+import android.bluetooth.BluetoothGattDescriptor;
+import android.content.Context;
+
+import java.io.IOException;
+import java.util.UUID;
+
+import nodomain.freeyourgadget.gadgetbridge.impl.GBDevice;
+import nodomain.freeyourgadget.gadgetbridge.service.btle.BtLEQueue;
+import nodomain.freeyourgadget.gadgetbridge.service.btle.GattCallback;
+import nodomain.freeyourgadget.gadgetbridge.service.btle.TransactionBuilder;
+import nodomain.freeyourgadget.gadgetbridge.service.devices.miband.MiBandSupport;
+
+/**
+ * Abstract base class for a MiBandOperation, i.e. an operation that does more than
+ * just sending a few bytes to the band. It typically involves exchanging many messages
+ * between the mobile and the band.
+ *
+ * One operation may execute multiple @{link Transaction transactions} with each
+ * multiple @{link BTLEAction actions}.
+ *
+ * This class implements GattCallback so that subclasses may override those methods
+ * to handle those events.
+ * Note: by default all Gatt events are forwarded to MiBandSupport, subclasses may override
+ * this behavior.
+ */
+public abstract class AbstractMiBandOperation implements GattCallback, MiBandOperation {
+    private final MiBandSupport mSupport;
+
+    protected AbstractMiBandOperation(MiBandSupport support) {
+        mSupport = support;
+    }
+
+    /**
+     * Delegates to MiBandSupport and additionally sets this instance as the Gatt
+     * callback for the transaction.
+     * @param taskName
+     * @return
+     * @throws IOException
+     */
+    public TransactionBuilder performInitialized(String taskName) throws IOException {
+        TransactionBuilder builder = mSupport.performInitialized(taskName);
+        builder.setGattCallback(this);
+        return builder;
+    }
+
+    protected Context getContext() {
+        return mSupport.getContext();
+    }
+
+    protected GBDevice getDevice() {
+        return mSupport.getDevice();
+    }
+
+    protected BluetoothGattCharacteristic getCharacteristic(UUID uuid) {
+        return mSupport.getCharacteristic(uuid);
+    }
+
+    protected BtLEQueue getQueue() {
+        return mSupport.getQueue();
+    }
+
+    protected void unsetBusy() {
+        getDevice().unsetBusyTask();
+        getDevice().sendDeviceUpdateIntent(getContext());
+    }
+
+    public MiBandSupport getSupport() {
+        return mSupport;
+    }
+
+    // All Gatt callbacks delegated to MiBandSupport
+    @Override
+    public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
+        mSupport.onConnectionStateChange(gatt, status, newState);
+    }
+
+    @Override
+    public void onServicesDiscovered(BluetoothGatt gatt) {
+        mSupport.onServicesDiscovered(gatt);
+    }
+
+    @Override
+    public void onCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
+        mSupport.onCharacteristicRead(gatt, characteristic, status);
+    }
+
+    @Override
+    public void onCharacteristicWrite(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
+        mSupport.onCharacteristicWrite(gatt, characteristic, status);
+    }
+
+    @Override
+    public void onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) {
+        mSupport.onCharacteristicChanged(gatt, characteristic);
+    }
+
+    @Override
+    public void onDescriptorRead(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status) {
+        mSupport.onDescriptorRead(gatt, descriptor, status);
+    }
+
+    @Override
+    public void onDescriptorWrite(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status) {
+        mSupport.onDescriptorWrite(gatt, descriptor, status);
+    }
+
+    @Override
+    public void onReadRemoteRssi(BluetoothGatt gatt, int rssi, int status) {
+        mSupport.onReadRemoteRssi(gatt, rssi, status);
+    }
+}

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/miband/operations/FetchActivityOperation.java

@@ -0,0 +1,265 @@
+package nodomain.freeyourgadget.gadgetbridge.service.devices.miband.operations;
+
+import android.bluetooth.BluetoothGatt;
+import android.bluetooth.BluetoothGattCharacteristic;
+import android.database.sqlite.SQLiteDatabase;
+import android.widget.Toast;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.text.DateFormat;
+import java.util.Calendar;
+import java.util.GregorianCalendar;
+import java.util.UUID;
+import java.util.concurrent.TimeUnit;
+
+import nodomain.freeyourgadget.gadgetbridge.GBApplication;
+import nodomain.freeyourgadget.gadgetbridge.R;
+import nodomain.freeyourgadget.gadgetbridge.database.DBHandler;
+import nodomain.freeyourgadget.gadgetbridge.devices.SampleProvider;
+import nodomain.freeyourgadget.gadgetbridge.devices.miband.MiBandService;
+import nodomain.freeyourgadget.gadgetbridge.service.btle.TransactionBuilder;
+import nodomain.freeyourgadget.gadgetbridge.service.btle.actions.SetDeviceBusyAction;
+import nodomain.freeyourgadget.gadgetbridge.service.devices.miband.MiBandSupport;
+import nodomain.freeyourgadget.gadgetbridge.util.DateTimeUtils;
+import nodomain.freeyourgadget.gadgetbridge.util.GB;
+
+public class FetchActivityOperation extends AbstractMiBandOperation {
+    private static final Logger LOG = LoggerFactory.getLogger(FetchActivityOperation.class);
+    private static final byte[] fetch = new byte[]{MiBandService.COMMAND_FETCH_DATA};
+
+    //temporary buffer, size is a multiple of 60 because we want to store complete minutes (1 minute = 3 bytes)
+    private static final int activityDataHolderSize = 3 * 60 * 4; // 8h
+
+    private static class ActivityStruct {
+        public byte[] activityDataHolder = new byte[activityDataHolderSize];
+        //index of the buffer above
+        public int activityDataHolderProgress = 0;
+        //number of bytes we will get in a single data transfer, used as counter
+        public int activityDataRemainingBytes = 0;
+        //same as above, but remains untouched for the ack message
+        public int activityDataUntilNextHeader = 0;
+        //timestamp of the single data transfer, incremented to store each minute's data
+        public GregorianCalendar activityDataTimestampProgress = null;
+        //same as above, but remains untouched for the ack message
+        public GregorianCalendar activityDataTimestampToAck = null;
+    }
+
+    private ActivityStruct activityStruct;
+
+    public FetchActivityOperation(MiBandSupport support) {
+        super(support);
+    }
+
+    @Override
+    public void perform() throws IOException {
+        TransactionBuilder builder = performInitialized("fetch activity data");
+//            builder.write(getCharacteristic(MiBandService.UUID_CHARACTERISTIC_LE_PARAMS), getLowLatency());
+        builder.add(new SetDeviceBusyAction(getDevice(), getContext().getString(R.string.busy_task_fetch_activity_data), getContext()));
+        builder.write(getCharacteristic(MiBandService.UUID_CHARACTERISTIC_CONTROL_POINT), fetch);
+        builder.queue(getQueue());
+    }
+
+
+    @Override
+    public void onCharacteristicChanged(BluetoothGatt gatt,
+                                        BluetoothGattCharacteristic characteristic) {
+        UUID characteristicUUID = characteristic.getUuid();
+        if (MiBandService.UUID_CHARACTERISTIC_ACTIVITY_DATA.equals(characteristicUUID)) {
+            handleActivityNotif(characteristic.getValue());
+        } else {
+            super.onCharacteristicChanged(gatt, characteristic);
+        }
+    }
+
+    private void handleActivityFetchFinish() {
+        LOG.info("Fetching activity data has finished.");
+        activityStruct = null;
+        unsetBusy();
+    }
+
+    /**
+     * Method to handle the incoming activity data.
+     * There are two kind of messages we currently know:
+     * - the first one is 11 bytes long and contains metadata (how many bytes to expect, when the data starts, etc.)
+     * - the second one is 20 bytes long and contains the actual activity data
+     *
+     * The first message type is parsed by this method, for every other length of the value param, bufferActivityData is called.
+     * @see #bufferActivityData(byte[])
+     *
+     *
+     * @param value
+     */
+    private void handleActivityNotif(byte[] value) {
+        boolean firstChunk = activityStruct == null;
+        if (firstChunk) {
+            activityStruct = new ActivityStruct();
+        }
+
+        if (value.length == 11) {
+            // byte 0 is the data type: 1 means that each minute is represented by a triplet of bytes
+            int dataType = value[0];
+            // byte 1 to 6 represent a timestamp
+            GregorianCalendar timestamp = parseTimestamp(value, 1);
+
+            // counter of all data held by the band
+            int totalDataToRead = (value[7] & 0xff) | ((value[8] & 0xff) << 8);
+            totalDataToRead *= (dataType == 1) ? 3 : 1;
+
+
+            // counter of this data block
+            int dataUntilNextHeader = (value[9] & 0xff) | ((value[10] & 0xff) << 8);
+            dataUntilNextHeader *= (dataType == 1) ? 3 : 1;
+
+            // there is a total of totalDataToRead that will come in chunks (3 bytes per minute if dataType == 1),
+            // these chunks are usually 20 bytes long and grouped in blocks
+            // after dataUntilNextHeader bytes we will get a new packet of 11 bytes that should be parsed
+            // as we just did
+
+            if (firstChunk && dataUntilNextHeader != 0) {
+                GB.toast(getContext().getString(R.string.user_feedback_miband_activity_data_transfer,
+                        DateTimeUtils.formatDurationHoursMinutes((totalDataToRead / 3), TimeUnit.MINUTES),
+                        DateFormat.getDateTimeInstance().format(timestamp.getTime())), Toast.LENGTH_LONG, GB.INFO);
+            }
+            LOG.info("total data to read: " + totalDataToRead + " len: " + (totalDataToRead / 3) + " minute(s)");
+            LOG.info("data to read until next header: " + dataUntilNextHeader + " len: " + (dataUntilNextHeader / 3) + " minute(s)");
+            LOG.info("TIMESTAMP: " + DateFormat.getDateTimeInstance().format(timestamp.getTime()).toString() + " magic byte: " + dataUntilNextHeader);
+
+            activityStruct.activityDataRemainingBytes = activityStruct.activityDataUntilNextHeader = dataUntilNextHeader;
+            activityStruct.activityDataTimestampToAck = (GregorianCalendar) timestamp.clone();
+            activityStruct.activityDataTimestampProgress = timestamp;
+
+        } else {
+            bufferActivityData(value);
+        }
+        LOG.debug("activity data: length: " + value.length + ", remaining bytes: " + activityStruct.activityDataRemainingBytes);
+
+        if (activityStruct.activityDataRemainingBytes == 0) {
+            sendAckDataTransfer(activityStruct.activityDataTimestampToAck, activityStruct.activityDataUntilNextHeader);
+        }
+    }
+
+    /**
+     * Method to store temporarily the activity data values got from the Mi Band.
+     *
+     * Since we expect chunks of 20 bytes each, we do not store the received bytes it the length is different.
+     *
+     * @param value
+     */
+    private void bufferActivityData(byte[] value) {
+
+        if (activityStruct.activityDataRemainingBytes >= value.length) {
+            //I don't like this clause, but until we figure out why we get different data sometimes this should work
+            if (value.length == 20 || value.length == activityStruct.activityDataRemainingBytes) {
+                System.arraycopy(value, 0, activityStruct.activityDataHolder, activityStruct.activityDataHolderProgress, value.length);
+                activityStruct.activityDataHolderProgress += value.length;
+                activityStruct.activityDataRemainingBytes -= value.length;
+
+                if (this.activityDataHolderSize == activityStruct.activityDataHolderProgress) {
+                    flushActivityDataHolder();
+                }
+            } else {
+                // the length of the chunk is not what we expect. We need to make sense of this data
+                LOG.warn("GOT UNEXPECTED ACTIVITY DATA WITH LENGTH: " + value.length + ", EXPECTED LENGTH: " + activityStruct.activityDataRemainingBytes);
+                for (byte b : value) {
+                    LOG.warn("DATA: " + String.format("0x%8x", b));
+                }
+            }
+        } else {
+            LOG.error("error buffering activity data: remaining bytes: " + activityStruct.activityDataRemainingBytes + ", received: " + value.length);
+        }
+    }
+
+    /**
+     * empty the local buffer for activity data, arrange the values received in groups of three and
+     * store them in the DB
+     */
+    private void flushActivityDataHolder() {
+        if (activityStruct == null) {
+            LOG.debug("nothing to flush, struct is already null");
+            return;
+        }
+        LOG.debug("flushing activity data holder");
+        byte category, intensity, steps;
+
+        DBHandler dbHandler = null;
+        try {
+            dbHandler = GBApplication.acquireDB();
+            try (SQLiteDatabase db = dbHandler.getWritableDatabase()) { // explicitly keep the db open while looping over the samples
+                for (int i = 0; i < activityStruct.activityDataHolderProgress; i += 3) { //TODO: check if multiple of 3, if not something is wrong
+                    category = activityStruct.activityDataHolder[i];
+                    intensity = activityStruct.activityDataHolder[i + 1];
+                    steps = activityStruct.activityDataHolder[i + 2];
+
+                    dbHandler.addGBActivitySample(
+                            (int) (activityStruct.activityDataTimestampProgress.getTimeInMillis() / 1000),
+                            SampleProvider.PROVIDER_MIBAND,
+                            (short) (intensity & 0xff),
+                            (short) (steps & 0xff),
+                            category);
+                    activityStruct.activityDataTimestampProgress.add(Calendar.MINUTE, 1);
+                }
+            } finally {
+                activityStruct.activityDataHolderProgress = 0;
+            }
+        } catch (Exception ex) {
+            GB.toast(getContext(), ex.getMessage(), Toast.LENGTH_LONG, GB.ERROR);
+        } finally {
+            if (dbHandler != null) {
+                dbHandler.release();
+            }
+        }
+    }
+
+    /**
+     * Acknowledge the transfer of activity data to the Mi Band.
+     *
+     * After receiving data from the band, it has to be acknowledged. This way the Mi Band will delete
+     * the data it has on record.
+     *
+     * @param time
+     * @param bytesTransferred
+     */
+    private void sendAckDataTransfer(Calendar time, int bytesTransferred) {
+        byte[] ack = new byte[]{
+                MiBandService.COMMAND_CONFIRM_ACTIVITY_DATA_TRANSFER_COMPLETE,
+                (byte) (time.get(Calendar.YEAR) - 2000),
+                (byte) time.get(Calendar.MONTH),
+                (byte) time.get(Calendar.DATE),
+                (byte) time.get(Calendar.HOUR_OF_DAY),
+                (byte) time.get(Calendar.MINUTE),
+                (byte) time.get(Calendar.SECOND),
+                (byte) (bytesTransferred & 0xff),
+                (byte) (0xff & (bytesTransferred >> 8))
+        };
+        try {
+            TransactionBuilder builder = performInitialized("send acknowledge");
+            builder.write(getCharacteristic(MiBandService.UUID_CHARACTERISTIC_CONTROL_POINT), ack);
+            builder.queue(getQueue());
+
+            // flush to the DB after sending the ACK
+            flushActivityDataHolder();
+
+            //The last data chunk sent by the miband has always length 0.
+            //When we ack this chunk, the transfer is done.
+            if (getDevice().isBusy() && bytesTransferred == 0) {
+                handleActivityFetchFinish();
+            }
+        } catch (IOException ex) {
+            LOG.error("Unable to send ack to MI", ex);
+        }
+    }
+
+    private GregorianCalendar parseTimestamp(byte[] value, int offset) {
+        GregorianCalendar timestamp = new GregorianCalendar(
+                value[offset] + 2000,
+                value[offset + 1],
+                value[offset + 2],
+                value[offset + 3],
+                value[offset + 4],
+                value[offset + 5]);
+        return timestamp;
+    }
+}

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/miband/operations/MiBandOperation.java

@@ -0,0 +1,9 @@
+package nodomain.freeyourgadget.gadgetbridge.service.devices.miband.operations;
+
+import java.io.IOException;
+
+import nodomain.freeyourgadget.gadgetbridge.service.devices.miband.MiBandSupport;
+
+public interface MiBandOperation {
+    public void perform() throws IOException;
+}