Add custom item features

(Not tested)

lib/src/main/kotlin/foundation/esoteric/minecraft/plugins/library/item/CustomItem.kt

@@ -0,0 +1,55 @@
+package foundation.esoteric.minecraft.plugins.library.item
+
+import org.bukkit.Bukkit
+import org.bukkit.Material
+import org.bukkit.entity.Player
+import org.bukkit.event.Listener
+import org.bukkit.inventory.ItemStack
+import org.bukkit.inventory.meta.ItemMeta
+import org.bukkit.persistence.PersistentDataType
+
+abstract class CustomItem(private val plugin: CustomItemPlugin, private val itemId: String, private val material: Material) : Listener {
+    init {
+        Bukkit.getPluginManager().registerEvents(this, plugin)
+
+        plugin.customItemManager.addCustomItem(itemId, this)
+    }
+
+    protected abstract fun generateCustomItem(baseCustomItem: ItemStack?, player: Player?): ItemStack
+
+    fun getCustomItem(player: Player?): ItemStack {
+        val item = ItemStack(material)
+        item.editMeta { meta: ItemMeta ->
+            meta.persistentDataContainer.set(
+                plugin.customItemManager.customItemIdKey,
+                PersistentDataType.STRING,
+                itemId
+            )
+        }
+        return generateCustomItem(item, player)
+    }
+
+    fun isItem(itemStack: ItemStack?): Boolean {
+        if (itemStack == null) {
+            return false
+        }
+
+        if (!itemStack.hasItemMeta()) {
+            return false
+        }
+
+        val dataContainerItemIdValue =
+            itemStack.itemMeta.persistentDataContainer.get(plugin.customItemManager.customItemIdKey, PersistentDataType.STRING)
+                ?: return false
+
+        return try {
+            itemId === dataContainerItemIdValue
+        } catch (exception: IllegalArgumentException) {
+            false
+        }
+    }
+
+    fun give(player: Player) {
+        player.inventory.addItem(getCustomItem(player))
+    }
+}

lib/src/main/kotlin/foundation/esoteric/minecraft/plugins/library/item/CustomItemManager.kt

@@ -0,0 +1,28 @@
+package foundation.esoteric.minecraft.plugins.library.item
+
+import org.bukkit.NamespacedKey
+import org.bukkit.entity.Player
+import org.bukkit.plugin.java.JavaPlugin
+
+class CustomItemManager(private val plugin: JavaPlugin) {
+
+    private val customItemMap: MutableMap<String, CustomItem> = HashMap()
+
+    val customItemIdKey: NamespacedKey = NamespacedKey(plugin, "custom_item_id")
+
+    fun getPlugin(): JavaPlugin {
+        return plugin
+    }
+
+    fun addCustomItem(itemId: String, customItem: CustomItem) {
+        customItemMap[itemId] = customItem
+    }
+
+    fun getAbstractCustomItem(itemId: String): CustomItem? {
+        return customItemMap[itemId]
+    }
+
+    fun giveCustomItem(itemId: String, player: Player?) {
+        customItemMap[itemId]!!.give(player!!)
+    }
+}

lib/src/main/kotlin/foundation/esoteric/minecraft/plugins/library/item/CustomItemPlugin.kt

@@ -0,0 +1,7 @@
+package foundation.esoteric.minecraft.plugins.library.item
+
+import org.bukkit.plugin.Plugin
+
+interface CustomItemPlugin : Plugin {
+    val customItemManager: CustomItemManager
+}