1 files changed, 46 insertions, 0 deletions
diff --git a/src/main/kotlin/me/bush/illnamethislater/CancelState.kt b/src/main/kotlin/me/bush/illnamethislater/CancelState.kt
new file mode 100644
index 0000000..270d88f
--- /dev/null
+++ b/src/main/kotlin/me/bush/illnamethislater/CancelState.kt
@@ -0,0 +1,46 @@
+package me.bush.illnamethislater
+
+import sun.misc.Unsafe
+import kotlin.reflect.KClass
+import kotlin.reflect.KMutableProperty1
+import kotlin.reflect.full.declaredMembers
+import kotlin.reflect.full.isSubclassOf
+import kotlin.reflect.jvm.javaField
+import kotlin.reflect.typeOf
+
+/**
+ * @author bush
+ * @since 1.0.0
+ */
+internal fun interface CancelledState {
+
+    /**
+     * Will either return false, cast [event] to [Event] and return [Event.cancelled], or use
+     * [Unsafe.getBoolean] to get the value of the "cancelled" field of an external event.
+     *
+     * @author bush
+     * @since 1.0.0
+     */
+    fun isCancelled(event: Any): Boolean
+
+    companion object {
+        private val UNSAFE = Unsafe::class.declaredMembers.single { it.name == "theUnsafe" }.handleCall() as Unsafe
+
+        // This is really just for interoperability with forge events, but ig it would work with anything
+        private val CANCELLED_NAMES = arrayOf("canceled", "cancelled")
+        private val NOT_CANCELLABLE by lazy { CancelledState { false } }
+        private val OFFSETS = hashMapOf<KClass<*>, Long>()
+
+        fun cancelStateOf(type: KClass<*>, bus: EventBus): CancelledState {
+            if (type.isSubclassOf(Event::class)) return CancelledState { (it as Event).cancelled }
+            if (!bus.externalSupport) return NOT_CANCELLABLE
+            type.allMembers.filter { it.name in CANCELLED_NAMES && it.returnType == typeOf<Boolean>() }
+                .filterIsInstance<KMutableProperty1<*, *>>().toList().let {
+                    if (it.isEmpty()) return NOT_CANCELLABLE
+                    if (it.size != 1) bus.logger.warn("Multiple possible cancel fields found for event type $type")
+                    OFFSETS[type] = UNSAFE.objectFieldOffset(it[0].javaField)
+                    return CancelledState { UNSAFE.getBoolean(it, OFFSETS[type]!!) }
+                }
+        }
+    }
+}