feat: android debounce backup state events to react native

Also fixes the numeric representation of backup state timestamps. Apparently doubles are ok, but integers not. Before this fix the RN side would get wrong timestamp like `"lastQueued": -86628891`

lib/android/src/main/java/com/reactnativeldk/Helpers.kt

@@ -1,4 +1,6 @@
 package com.reactnativeldk
+import android.os.Handler
+import android.os.Looper
 import com.facebook.react.bridge.*
 import org.json.JSONObject
 import org.ldk.enums.Currency
@@ -8,6 +10,7 @@ import java.io.File
 import java.io.FileOutputStream
 import java.net.URL
 import java.nio.channels.Channels
+import java.util.Date
 
 fun handleResolve(promise: Promise, res: LdkCallbackResponses) {
     if (res != LdkCallbackResponses.log_write_success) {
@@ -204,6 +207,22 @@ fun WritableMap.putHexString(key: String, bytes: ByteArray?) {
     }
 }
 
+/**
+ * Adds a Date object into the map.
+ * If the date is not null, it is converted to a double representing the unix timestamp.
+ * If it's null, a null value is added to the map.
+ *
+ * @param key The key under which the date will be stored in the map.
+ * @param date The date to be stored in the map. Can be null.
+ */
+fun WritableMap.putDateOrNull(key: String, date: Date?) {
+    if (date != null) {
+        putDouble(key, date.time.toDouble())
+    } else {
+        putNull(key)
+    }
+}
+
 fun WritableArray.pushHexString(bytes: ByteArray) {
     pushString(bytes.hexEncodedString())
 }
@@ -502,4 +521,24 @@ fun mergeObj(obj1: JSONObject, obj2: HashMap<String, Any>): HashMap<String, Any>
     }
 
     return newObj
-}
+}
+
+object UiThreadDebouncer {
+    private val pending = hashMapOf<String, Runnable>()
+    private val handler = Handler(Looper.getMainLooper())
+
+    /**
+     * Used to debounce an [action] function call to be executed after a delay on the main thread
+     *
+     * @param interval The delay in milliseconds after which the action will be executed. Default value is 250ms.
+     * @param key The unique identifier for the action to be debounced. If an action with the same key is already pending, it will be cancelled.
+     * @param action The function to be executed after the interval.
+     */
+    fun debounce(interval: Long = 250, key: String, action: () -> Unit) {
+        pending[key]?.let { handler.removeCallbacks(it) }
+        val runnable = Runnable(action)
+        pending[key] = runnable
+
+        handler.postDelayed(runnable, interval)
+    }
+}

lib/android/src/main/java/com/reactnativeldk/classes/BackupClient.kt

@@ -1,10 +1,13 @@
 package com.reactnativeldk.classes
+
 import com.facebook.react.bridge.Arguments
 import com.facebook.react.bridge.WritableMap
+import com.reactnativeldk.UiThreadDebouncer
 import com.reactnativeldk.EventTypes
 import com.reactnativeldk.LdkEventEmitter
 import com.reactnativeldk.hexEncodedString
 import com.reactnativeldk.hexa
+import com.reactnativeldk.putDateOrNull
 import org.json.JSONObject
 import org.ldk.structs.Result_StrSecp256k1ErrorZ.Result_StrSecp256k1ErrorZ_OK
 import org.ldk.structs.UtilMethods
@@ -61,17 +64,9 @@ data class BackupFileState(
     val encoded: WritableMap
         get() {
             val body = Arguments.createMap()
-            body.putInt("lastQueued", lastQueued.time.toInt())
-            if (lastPersisted != null) {
-                body.putInt("lastPersisted", lastPersisted!!.time.toInt())
-            } else {
-                body.putNull("lastPersisted")
-            }
-            if (lastFailed != null) {
-                body.putInt("lastFailed", lastFailed!!.time.toInt())
-            } else {
-                body.putNull("lastFailed")
-            }
+            body.putDouble("lastQueued", lastQueued.time.toDouble())
+            body.putDateOrNull("lastPersisted", lastPersisted)
+            body.putDateOrNull("lastFailed", lastFailed)
             if (lastErrorMessage != null) {
                 body.putString("lastErrorMessage", lastErrorMessage)
             } else {
@@ -592,10 +587,9 @@ class BackupClient {
                 body.putMap(key, state.encoded)
             }
 
-            LdkEventEmitter.send(
-                EventTypes.backup_state_update,
-                body
-            )
+            UiThreadDebouncer.debounce(interval = 250, key = "backupStateUpdate") {
+                LdkEventEmitter.send(EventTypes.backup_state_update, body)
+            }
 
             backupStateLock.unlock()
         }