Add discard changes warning dialog to media-send module.

app/src/main/java/org/thoughtcrime/securesms/mediasend/v3/MediaSendV3Activity.kt

@@ -228,10 +228,7 @@ class MediaSendV3Activity :
                   .show(supportFragmentManager)
               }
 
-              is MediaSendFlowHudCommand.CloseScreen -> {
-                // TODO [media-send] warning dialog
-                finish()
-              }
+              is MediaSendFlowHudCommand.CloseScreen -> finish()
             }
           }
         )

feature/media-send/src/main/java/org/signal/mediasend/MediaSendFlowViewModel.kt

@@ -128,6 +128,7 @@ class MediaSendFlowViewModel(
   internal val usernameScannedDialog = DialogController<String>()
   internal val linkedDeviceScannedDialog = DialogController<Unit>()
   internal val saveToStorageDialog = DialogController<Unit>()
+  internal val discardMediaDialog = DialogController<Unit>()
   internal val addToGroupStoryDialog = DialogController<MediaRecipientId>()
 
   internal val writeStoragePermission = PermissionController(
@@ -260,6 +261,23 @@ class MediaSendFlowViewModel(
     }
   }
 
+  /**
+   * Leaves the flow at the user's request, confirming first if that would throw a selection away. Closing for reasons
+   * of our own emits [MediaSendFlowHudCommand.CloseScreen] directly instead.
+   */
+  internal fun onCloseRequested() {
+    if (state.value.selectedMedia.isEmpty()) {
+      sendHudCommand(MediaSendFlowHudCommand.CloseScreen)
+      return
+    }
+
+    viewModelScope.launch {
+      if (discardMediaDialog.show(Unit) == DialogResult.POSITIVE) {
+        sendHudCommand(MediaSendFlowHudCommand.CloseScreen)
+      }
+    }
+  }
+
   /**
    * Backs out of a select screen while nothing is selected, stepping over an editor that would have nothing to edit
    * and no toolbar to leave by. Decided here rather than when the selection empties, so that re-selecting something
@@ -269,7 +287,7 @@ class MediaSendFlowViewModel(
     val destination = backStack.dropLast(1).dropLastWhile { it == MediaSendRoute.Edit }
 
     if (destination.isEmpty()) {
-      sendHudCommand(MediaSendFlowHudCommand.CloseScreen)
+      onCloseRequested()
       return
     }
 
@@ -291,7 +309,7 @@ class MediaSendFlowViewModel(
 
   private fun onCameraXScreenEvent(event: CameraXScreenEvents) {
     when (event) {
-      CameraXScreenEvents.CameraCloseClicked -> sendHudCommand(MediaSendFlowHudCommand.CloseScreen)
+      CameraXScreenEvents.CameraCloseClicked -> onCloseRequested()
       CameraXScreenEvents.GalleryClicked -> backStack.goToFolders()
       is CameraXScreenEvents.ImageCaptured -> handleImageCaptured(event)
       is CameraXScreenEvents.VideoCaptured -> handleVideoCaptured(event)

feature/media-send/src/main/java/org/signal/mediasend/MediaSendNavigation.kt

@@ -1,6 +1,7 @@
 package org.signal.mediasend
 
 import android.annotation.SuppressLint
+import androidx.activity.compose.BackHandler
 import androidx.compose.animation.AnimatedVisibility
 import androidx.compose.animation.fadeIn
 import androidx.compose.animation.fadeOut
@@ -17,6 +18,7 @@ import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.res.stringResource
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.lifecycle.viewmodel.compose.viewModel
 import androidx.lifecycle.viewmodel.navigation3.rememberViewModelStoreNavEntryDecorator
@@ -29,6 +31,7 @@ import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.collectLatest
 import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.map
+import org.signal.core.ui.compose.DialogController
 import org.signal.core.ui.compose.Dialogs
 import org.signal.core.ui.compose.Snackbars
 import org.signal.core.ui.compose.showSnackbar
@@ -129,6 +132,13 @@ internal fun MediaSendNavigation(
       }
     }
 
+    // NavDisplay only consumes back while there is somewhere left to go back to. Composed after it to catch the press
+    // at the root, which would otherwise fall through to the activity and finish it.
+    BackHandler(enabled = viewModel.backStack.size == 1) {
+      viewModel.onCloseRequested()
+    }
+
+    DiscardMediaDialog(viewModel.discardMediaDialog)
     Snackbar(viewModel.snackbarEvents)
     Toast(viewModel.toastEvents)
     SendProgress(viewModel.state)
@@ -138,6 +148,26 @@ internal fun MediaSendNavigation(
 private val TOAST_DURATION = 3.seconds
 private val SEND_PROGRESS_DELAY = 300.milliseconds
 
+/**
+ * Dialog displayed when the user tries to close out of media send, to warn them that they'll discard media.
+ */
+@Composable
+private fun DiscardMediaDialog(
+  controller: DialogController<Unit>
+) {
+  controller.Content { _, onDismissRequest, onConfirm, _, onDeny ->
+    Dialogs.SimpleAlertDialog(
+      title = stringResource(R.string.MediaSendDialogs__discard_media),
+      body = stringResource(R.string.MediaSendDialogs__you_will_lose_any_media),
+      confirm = stringResource(R.string.MediaSendDialogs__discard),
+      dismiss = stringResource(android.R.string.cancel),
+      onConfirm = onConfirm,
+      onDeny = onDeny,
+      onDismissRequest = onDismissRequest
+    )
+  }
+}
+
 /**
  * Covers the whole flow while a send is in flight, so that the media on its way out cannot be edited or resent. Sends
  * that resolve immediately never show it.

feature/media-send/src/main/res/values/strings.xml

@@ -6,6 +6,10 @@
   <string name="MediaSendDialogs__youll_lose_any_changes">You\'ll lose any changes you\'ve made to this photo.</string>
   <!-- Confirmation button that discards the user\'s image edits. -->
   <string name="MediaSendDialogs__discard">Discard</string>
+  <!-- Dialog title shown when the user tries to close media send while media is selected. -->
+  <string name="MediaSendDialogs__discard_media">Discard media?</string>
+  <!-- Dialog body explaining that leaving media send will discard the selected media along with any edits. -->
+  <string name="MediaSendDialogs__you_will_lose_any_media">You will lose any media you captured and changes you made.</string>
   <!-- Dialog title asking to save the media being edited to the phone\'s storage -->
   <string name="MediaSendDialogs__save_to_phone">Save to phone?</string>
   <!-- Dialog message explaining that media will be saved to your phone and can potentially be accessed by other apps. -->