Completed most of auto-migration UI

app/src/main/java/exh/util/DeferredField.kt

@@ -0,0 +1,46 @@
+package exh.util
+
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+
+/**
+ * Field that can be initialized later. Users can suspend while waiting for the field to initialize.
+ *
+ * @author nulldev
+ */
+class DeferredField<T> {
+    @Volatile
+    private var content: T? = null
+
+    @Volatile
+    var initialized = false
+        private set
+
+    private val mutex = Mutex(true)
+
+    /**
+     * Initialize the field
+     */
+    fun initialize(content: T) {
+        // Fast-path new listeners
+        this.content = content
+        initialized = true
+
+        // Notify current listeners
+        mutex.unlock()
+    }
+
+    /**
+     * Will only suspend if !initialized.
+     */
+    suspend fun get(): T {
+        // Check if field is initialized and return immediately if it is
+        if(initialized) return content as T
+
+        // Wait for field to initialize
+        mutex.withLock {}
+
+        // Field is initialized, return value
+        return content!!
+    }
+}