Add support for drag + drop in the media send flow.

app/src/main/java/org/thoughtcrime/securesms/mediasend/v2/MediaSelectionViewModel.kt

@@ -22,6 +22,7 @@ import org.thoughtcrime.securesms.recipients.RecipientId
 import org.thoughtcrime.securesms.scribbles.ImageEditorFragment
 import org.thoughtcrime.securesms.util.Util
 import org.thoughtcrime.securesms.util.livedata.Store
+import java.util.Collections
 
 /**
  * ViewModel which maintains the list of selected media and other shared values.
@@ -62,6 +63,8 @@ class MediaSelectionViewModel(
     }
   }
 
+  private var lastMediaDrag: Pair<Int, Int> = Pair(0, 0)
+
   init {
     val recipientId = destination.getRecipientId()
     if (recipientId != null) {
@@ -123,6 +126,52 @@ class MediaSelectionViewModel(
     )
   }
 
+  fun swapMedia(originalStart: Int, end: Int): Boolean {
+    var start: Int = originalStart
+
+    if (lastMediaDrag.first == start && lastMediaDrag.second == end) {
+      return true
+    } else if (lastMediaDrag.first == start) {
+      start = lastMediaDrag.second
+    }
+
+    val snapshot = store.state
+
+    if (end >= snapshot.selectedMedia.size || end < 0 || start >= snapshot.selectedMedia.size || start < 0) {
+      return false
+    }
+
+    lastMediaDrag = Pair(originalStart, end)
+
+    val newMediaList = snapshot.selectedMedia.toMutableList()
+
+    if (start < end) {
+      for (i in start until end) {
+        Collections.swap(newMediaList, i, i + 1)
+      }
+    } else {
+      for (i in start downTo end + 1) {
+        Collections.swap(newMediaList, i, i - 1)
+      }
+    }
+
+    store.update {
+      it.copy(
+        selectedMedia = newMediaList
+      )
+    }
+
+    return true
+  }
+
+  fun isValidMediaDragPosition(position: Int): Boolean {
+    return position >= 0 && position < store.state.selectedMedia.size
+  }
+
+  fun onMediaDragFinished() {
+    lastMediaDrag = Pair(0, 0)
+  }
+
   fun removeMedia(media: Media) {
     val snapshot = store.state
     val newMediaList = snapshot.selectedMedia - media

app/src/main/java/org/thoughtcrime/securesms/mediasend/v2/gallery/MediaGalleryFragment.kt

@@ -9,6 +9,7 @@ import androidx.fragment.app.viewModels
 import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.Transformations
 import androidx.recyclerview.widget.GridLayoutManager
+import androidx.recyclerview.widget.ItemTouchHelper
 import androidx.recyclerview.widget.RecyclerView
 import org.thoughtcrime.securesms.R
 import org.thoughtcrime.securesms.components.recyclerview.GridDividerDecoration
@@ -39,6 +40,8 @@ class MediaGalleryFragment : Fragment(R.layout.v2_media_gallery_fragment) {
   private lateinit var bottomBarGroup: View
   private lateinit var selectedRecycler: RecyclerView
 
+  private var selectedMediaTouchHelper: ItemTouchHelper? = null
+
   private val galleryAdapter = MappingAdapter()
   private val selectedAdapter = MappingAdapter()
 
@@ -88,6 +91,7 @@ class MediaGalleryFragment : Fragment(R.layout.v2_media_gallery_fragment) {
       callbacks.onSelectedMediaClicked(media)
     }
     selectedRecycler.adapter = selectedAdapter
+    selectedMediaTouchHelper?.attachToRecyclerView(selectedRecycler)
 
     MediaGallerySelectableItem.registerAdapter(
       mappingAdapter = galleryAdapter,
@@ -153,6 +157,10 @@ class MediaGalleryFragment : Fragment(R.layout.v2_media_gallery_fragment) {
     viewStateLiveData.value = state
   }
 
+  fun bindSelectedMediaItemDragHelper(helper: ItemTouchHelper) {
+    selectedMediaTouchHelper = helper
+  }
+
   data class ViewState(
     val selectedMedia: List<Media> = listOf()
   )

app/src/main/java/org/thoughtcrime/securesms/mediasend/v2/gallery/MediaSelectionGalleryFragment.kt

@@ -5,11 +5,13 @@ import android.view.View
 import androidx.activity.OnBackPressedCallback
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.viewModels
+import androidx.recyclerview.widget.ItemTouchHelper
 import org.thoughtcrime.securesms.R
 import org.thoughtcrime.securesms.mediasend.Media
 import org.thoughtcrime.securesms.mediasend.v2.MediaSelectionNavigator
 import org.thoughtcrime.securesms.mediasend.v2.MediaSelectionNavigator.Companion.requestPermissionsForCamera
 import org.thoughtcrime.securesms.mediasend.v2.MediaSelectionViewModel
+import org.thoughtcrime.securesms.mediasend.v2.review.MediaSelectionItemTouchHelper
 import org.thoughtcrime.securesms.permissions.Permissions
 
 private const val MEDIA_GALLERY_TAG = "MEDIA_GALLERY"
@@ -29,6 +31,8 @@ class MediaSelectionGalleryFragment : Fragment(R.layout.fragment_container), Med
   override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
     mediaGalleryFragment = ensureMediaGalleryFragment()
 
+    mediaGalleryFragment.bindSelectedMediaItemDragHelper(ItemTouchHelper(MediaSelectionItemTouchHelper(sharedViewModel)))
+
     sharedViewModel.state.observe(viewLifecycleOwner) { state ->
       mediaGalleryFragment.onViewStateUpdated(MediaGalleryFragment.ViewState(state.selectedMedia))
     }

app/src/main/java/org/thoughtcrime/securesms/mediasend/v2/review/MediaReviewFragment.kt

@@ -15,6 +15,7 @@ import androidx.core.graphics.drawable.DrawableCompat
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.setFragmentResultListener
 import androidx.fragment.app.viewModels
+import androidx.recyclerview.widget.ItemTouchHelper
 import androidx.recyclerview.widget.RecyclerView
 import androidx.viewpager2.widget.ViewPager2
 import io.reactivex.rxjava3.disposables.CompositeDisposable
@@ -181,6 +182,7 @@ class MediaReviewFragment : Fragment(R.layout.v2_media_review_fragment) {
       }
     }
     selectionRecycler.adapter = selectionAdapter
+    ItemTouchHelper(MediaSelectionItemTouchHelper(sharedViewModel)).attachToRecyclerView(selectionRecycler)
 
     sharedViewModel.state.observe(viewLifecycleOwner) { state ->
       pagerAdapter.submitMedia(state.selectedMedia)

app/src/main/java/org/thoughtcrime/securesms/mediasend/v2/review/MediaSelectionItemTouchHelper.java

@@ -0,0 +1,54 @@
+package org.thoughtcrime.securesms.mediasend.v2.review;
+
+import androidx.annotation.NonNull;
+import androidx.recyclerview.widget.ItemTouchHelper;
+import androidx.recyclerview.widget.RecyclerView;
+
+import org.thoughtcrime.securesms.mediasend.v2.MediaSelectionViewModel;
+
+/**
+ * A touch helper for handling drag + drop on the media rail in the media send flow.
+ */
+public class MediaSelectionItemTouchHelper extends ItemTouchHelper.Callback {
+
+  private final MediaSelectionViewModel viewModel;
+
+  public MediaSelectionItemTouchHelper(MediaSelectionViewModel viewModel) {
+    this.viewModel = viewModel;
+  }
+
+  @Override
+  public boolean isLongPressDragEnabled() {
+    return true;
+  }
+
+  @Override
+  public boolean isItemViewSwipeEnabled() {
+    return false;
+  }
+
+  @Override
+  public int getMovementFlags(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
+    if (viewModel.isValidMediaDragPosition(viewHolder.getAdapterPosition())) {
+      int dragFlags = ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
+      return makeMovementFlags(dragFlags, 0);
+    } else {
+      return 0;
+    }
+  }
+
+  @Override
+  public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
+    return viewModel.swapMedia(viewHolder.getAdapterPosition(), target.getAdapterPosition());
+  }
+
+  @Override
+  public void clearView(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
+    super.clearView(recyclerView, viewHolder);
+    viewModel.onMediaDragFinished();
+  }
+
+  @Override
+  public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
+  }
+}

app/src/main/java/org/thoughtcrime/securesms/recipients/Recipient.java

@@ -1,5 +1,7 @@
 package org.thoughtcrime.securesms.recipients;
 
+import static org.thoughtcrime.securesms.database.RecipientDatabase.InsightsBannerTier;
+
 import android.content.Context;
 import android.graphics.drawable.Drawable;
 import android.net.Uri;
@@ -32,7 +34,6 @@ import org.thoughtcrime.securesms.database.RecipientDatabase.MentionSetting;
 import org.thoughtcrime.securesms.database.RecipientDatabase.RegisteredState;
 import org.thoughtcrime.securesms.database.RecipientDatabase.UnidentifiedAccessMode;
 import org.thoughtcrime.securesms.database.RecipientDatabase.VibrateState;
-import org.thoughtcrime.securesms.database.model.databaseprotos.ChatColor;
 import org.thoughtcrime.securesms.database.model.databaseprotos.RecipientExtras;
 import org.thoughtcrime.securesms.dependencies.ApplicationDependencies;
 import org.thoughtcrime.securesms.groups.GroupId;
@@ -59,12 +60,9 @@ import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
 import java.util.UUID;
 import java.util.stream.Collectors;
 
-import static org.thoughtcrime.securesms.database.RecipientDatabase.InsightsBannerTier;
-
 public class Recipient {
 
   private static final String TAG = Log.tag(Recipient.class);

app/src/main/res/layout/v2_media_review_fragment.xml

@@ -55,12 +55,13 @@
             android:id="@+id/selection_recycler"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
-            android:layout_marginStart="8dp"
-            android:layout_marginEnd="16dp"
+            android:paddingStart="8dp"
+            android:paddingEnd="8dp"
             android:layout_marginBottom="2dp"
             android:alpha="0"
             android:orientation="horizontal"
             android:visibility="gone"
+            android:clipToPadding="false"
             app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
             app:layout_constraintBottom_toTopOf="@id/controls_shade"
             tools:alpha="1"