add additional dialog to prevent accidentally dismissing the caption dialog (#4999)

as discussed in https://github.com/tuskyapp/Tusky/pull/4942

Suggestions for a better text welcome.

app/src/main/java/com/keylesspalace/tusky/components/compose/dialog/CaptionDialog.kt

@@ -25,6 +25,7 @@ import android.text.InputFilter
 import android.view.View
 import android.view.WindowManager
 import android.widget.LinearLayout
+import androidx.appcompat.app.AlertDialog
 import androidx.core.os.bundleOf
 import androidx.fragment.app.DialogFragment
 import com.bumptech.glide.Glide
@@ -139,6 +140,19 @@ class CaptionDialog : DialogFragment() {
             )
             window?.setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_ADJUST_RESIZE)
         }
+        (dialog as AlertDialog?)?.getButton(AlertDialog.BUTTON_NEGATIVE)?.setOnClickListener {
+            if (arguments?.getString(EXISTING_DESCRIPTION_ARG).orEmpty() != binding.imageDescriptionText.text.toString()) {
+                MaterialAlertDialogBuilder(requireContext())
+                    .setMessage(R.string.confirm_dismiss_caption)
+                    .setPositiveButton(R.string.yes) { _, _ ->
+                        dialog?.dismiss()
+                    }
+                    .setNegativeButton(R.string.no, null)
+                    .show()
+            } else {
+                dialog?.dismiss()
+            }
+        }
     }
 
     override fun onSaveInstanceState(outState: Bundle) {

app/src/main/res/values/strings.xml

@@ -912,4 +912,8 @@
     <string name="notification_info_private_mention">Private mention</string>
     <string name="notification_info_mention">Mention</string>
     <string name="notification_info_private_reply">Private reply</string>
+
+    <string name="yes">Yes</string>
+    <string name="no">No</string>
+    <string name="confirm_dismiss_caption">Discard caption changes?</string>
 </resources>