Add SimpleGUI interface and listener for inventory events

Introduces the SimpleGUI interface for custom inventory GUIs and a corresponding SimpleGUIListener to handle inventory click, close, and drag events. Registers the listener in KPlugin to enable event handling for SimpleGUI implementations.

Author: CoasterFreakDE

src/main/kotlin/cc/modlabs/kpaper/inventory/simple/SimpleGUI.kt

@@ -0,0 +1,17 @@
+package cc.modlabs.kpaper.inventory.simple
+
+import org.bukkit.event.inventory.InventoryClickEvent
+import org.bukkit.event.inventory.InventoryCloseEvent
+import org.bukkit.event.inventory.InventoryDragEvent
+import org.bukkit.inventory.InventoryHolder
+
+interface SimpleGUI : InventoryHolder {
+
+    fun open(): Unit = Unit
+
+    fun handle(event: InventoryClickEvent): Unit = Unit
+
+    fun onClose(event: InventoryCloseEvent): Unit = Unit
+
+    fun onDrag(event: InventoryDragEvent): Unit = Unit
+}

src/main/kotlin/cc/modlabs/kpaper/inventory/simple/SimpleGUIListener.kt

@@ -0,0 +1,38 @@
+package cc.modlabs.kpaper.inventory.simple
+
+import org.bukkit.event.EventHandler
+import org.bukkit.event.Listener
+import org.bukkit.event.inventory.InventoryClickEvent
+import org.bukkit.event.inventory.InventoryCloseEvent
+import org.bukkit.event.inventory.InventoryDragEvent
+
+internal class SimpleGUIListener : Listener {
+
+    @EventHandler
+    fun onInventoryClick(event: InventoryClickEvent) {
+        val inventory = event.clickedInventory ?: return
+        val holder =  inventory.getHolder(false)
+        if (holder is SimpleGUI) {
+            holder.handle(event)
+        }
+    }
+
+    @EventHandler
+    fun onInventoryClose(event: InventoryCloseEvent) {
+        val inventory = event.inventory
+        val holder =  inventory.getHolder(false)
+        if (holder is SimpleGUI) {
+            holder.onClose(event)
+        }
+    }
+
+    @EventHandler
+    fun onInventoryDrag(event: InventoryDragEvent) {
+        val inventory = event.inventory
+        val holder =  inventory.getHolder(false)
+        if (holder is SimpleGUI) {
+            holder.onDrag(event)
+        }
+    }
+
+}

src/main/kotlin/cc/modlabs/kpaper/main/KPlugin.kt

@@ -3,6 +3,7 @@
 import cc.modlabs.kpaper.event.CustomEventListener
 import cc.modlabs.kpaper.inventory._internal.AnvilListener
 import cc.modlabs.kpaper.inventory._internal.ItemClickListener
+import cc.modlabs.kpaper.inventory.simple.SimpleGUIListener
 import org.bukkit.Bukkit
 import org.bukkit.plugin.java.JavaPlugin
 
@@ -54,6 +55,7 @@ abstract class KPlugin : JavaPlugin() {
         if (isFeatureEnabled(Feature.CUSTOM_EVENTS)) {
             CustomEventListener.load()
         }
+        Bukkit.getPluginManager().registerEvents(SimpleGUIListener(), this)
 
         startup()
     }