Added NBTData support

src/main/kotlin/net/axay/kspigot/annotations/KSpigotAnnotations.kt

@@ -16,4 +16,16 @@ annotation class UnsafeImplementation
  * unstable and should be checked every time
  * with a version change.
  */
-annotation class NMS_1_16_1
+annotation class NMS_1_16_1
+
+/**
+ * This element uses [net.minecraft.server]
+ * in some way. Because of that, it is
+ * unstable and should be checked every time
+ * with a version change.
+ *
+ * This element uses some part of NMS
+ * which is more likely to stay the same
+ * over a long period of time.
+ */
+annotation class NMS_General

src/main/kotlin/net/axay/kspigot/nbt/NBTData.kt

@@ -0,0 +1,79 @@
+package net.axay.kspigot.nbt
+
+import net.axay.kspigot.annotations.NMS_General
+import net.minecraft.server.v1_16_R1.*
+
+@NMS_General
+class NBTData {
+
+    val nbtTagCompound: NBTTagCompound
+
+    constructor(nbtTagCompound: NBTTagCompound?) {
+        this.nbtTagCompound = nbtTagCompound ?: NBTTagCompound()
+    }
+
+    constructor(nbtString: String) : this(MojangsonParser.parse(nbtString))
+
+    fun serialize() = nbtTagCompound.toString()
+
+    /**
+     * This method gets the value
+     * at the given [key]. The returned type
+     * must be specified.
+     * The returned value is null, if it
+     * was not possible to find any value at
+     * the specified location, or if the type
+     * is not the one which was specified.
+     */
+    operator fun <T> get(key: String): T? {
+        val value = nbtTagCompound.get(key)
+        return if (value != null) {
+            val loadedValue = when (value) {
+                is NBTTagCompound -> NBTData(value)
+                is NBTTagByte -> value.asByte()
+                is NBTTagByteArray -> value.bytes
+                is NBTTagDouble -> value.asDouble()
+                is NBTTagFloat -> value.asFloat()
+                is NBTTagInt -> value.asInt()
+                is NBTTagIntArray -> value.ints
+                is NBTTagList -> value
+                is NBTTagLong -> value.asLong()
+                is NBTTagLongArray -> value.longs
+                is NBTTagShort -> value.asShort()
+                is NBTTagString -> value.asString()
+                else -> null
+            }
+            return loadedValue as? T
+        } else null
+    }
+
+    /**
+     * This method sets some [value]
+     * at the position of the given [key].
+     */
+    operator fun <T> set(key: String, value: T): Boolean {
+        when (value) {
+            is NBTData -> nbtTagCompound.set(key, value.nbtTagCompound)
+            is Byte -> nbtTagCompound.setByte(key, value)
+            is ByteArray -> nbtTagCompound.setByteArray(key, value)
+            is Double -> nbtTagCompound.setDouble(key, value)
+            is Float -> nbtTagCompound.setFloat(key, value)
+            is Int -> nbtTagCompound.setInt(key, value)
+            is IntArray -> nbtTagCompound.setIntArray(key, value)
+            is List<*> -> nbtTagCompound.set(key, value as NBTList<*>)
+            is Long -> nbtTagCompound.setLong(key, value)
+            is LongArray -> nbtTagCompound.set(key, NBTTagLongArray(value))
+            is Short -> nbtTagCompound.setShort(key, value)
+            is String -> nbtTagCompound.setString(key, value)
+            else -> return false
+        }
+        return true
+    }
+
+    companion object {
+
+        fun deserialize(nbtString: String) = NBTData(nbtString)
+
+    }
+
+}

src/main/kotlin/net/axay/kspigot/nbt/NBTDataLoader.kt

@@ -0,0 +1,18 @@
+package net.axay.kspigot.nbt
+
+import net.axay.kspigot.annotations.NMS_General
+import net.minecraft.server.v1_16_R1.NBTTagCompound
+import org.bukkit.craftbukkit.v1_16_R1.entity.CraftEntity
+import org.bukkit.craftbukkit.v1_16_R1.inventory.CraftItemStack
+import org.bukkit.entity.Entity
+import org.bukkit.inventory.ItemStack
+
+@NMS_General
+val Entity.nbtData: NBTData get() {
+    val nbtTagCompound = NBTTagCompound()
+    (this as CraftEntity).handle.load(nbtTagCompound)
+    return NBTData(nbtTagCompound)
+}
+
+@NMS_General
+val ItemStack.nbtData: NBTData get() = NBTData(CraftItemStack.asNMSCopy(this).tag)