1 files changed, 54 insertions, 0 deletions
diff --git a/src/main/kotlin/me/bush/illnamethislater/CancelledState.kt b/src/main/kotlin/me/bush/illnamethislater/CancelledState.kt
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+++ b/src/main/kotlin/me/bush/illnamethislater/CancelledState.kt
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+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
+
+/**
+ * A simple SAM interface for determining if an event (or any class) is cancellable.
+ *
+ * @author bush
+ * @since 1.0.0
+ */
+internal fun interface CancelledState {
+
+    /**
+     * Returns whether [event] is cancelled or not. [event] should only ever be of the type
+     * that was passed to [CancelledState.of], or this will cause an error.
+     */
+    fun isCancelled(event: Any): Boolean
+
+    // Maybe move this to eventbus or util? todo
+    // Make CancelledState a class? todo
+    companion object {
+        private val UNSAFE = Unsafe::class.declaredMembers.single { it.name == "theUnsafe" }.handleCall() as Unsafe
+        private val CANCELLED_NAMES = arrayOf("canceled", "cancelled")
+        private val NOT_CANCELLABLE = CancelledState { false }
+        private val OFFSETS = hashMapOf<KClass<*>, Long>()
+
+        /**
+         * Creates a [CancelledState] object for events of class [type].
+         */
+        // TODO: 3/31/2022 static/singleton fields
+        fun of(type: KClass<*>, config: Config): CancelledState {
+            // Default impl for our event class
+            if (type.isSubclassOf(Event::class)) return CancelledState { (it as Event).cancelled }
+            // If compat is disabled
+            if (!config.thirdPartyCompatibility) return NOT_CANCELLABLE
+            // Find a field named "cancelled" or "canceled"
+            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) config.logger.warn("Multiple possible cancel fields found for event type $type")
+                    OFFSETS[type] = UNSAFE.objectFieldOffset(it[0].javaField)
+                    // This is not using reflection, and it is the same speed as direct access.
+                    // If you are familiar with C, this is essentially the same idea as pointers.
+                    return CancelledState { event -> UNSAFE.getBoolean(event, OFFSETS[type]!!) }
+                }
+        }
+    }
+}