SPIGOT-4570: Add FluidLevelChangeEvent

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/block/data/Levelled.java

@@ -9,6 +9,8 @@ package org.bukkit.block.data;
  * to "falling" fluids. All falling fluids have the same behaviour, but the
  * level corresponds to that of the block above them, equal to
  * <code>this.level - 8</code>
+ * <b>Note that counterintuitively, an adjusted level of 1 is the highest level,
+ * whilst 7 is the lowest.</b>
  * <br>
  * May not be higher than {@link #getMaximumLevel()}.
  */

paper-api/src/main/java/org/bukkit/event/block/FluidLevelChangeEvent.java

@@ -0,0 +1,70 @@
+package org.bukkit.event.block;
+
+import com.google.common.base.Preconditions;
+import org.bukkit.Warning;
+import org.bukkit.block.Block;
+import org.bukkit.block.data.BlockData;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.HandlerList;
+
+/**
+ * Called when the fluid level of a block changes due to changes in adjacent
+ * blocks.
+ *
+ * @deprecated draft API
+ */
+@Deprecated
+@Warning(false)
+public class FluidLevelChangeEvent extends BlockEvent implements Cancellable {
+
+    private static final HandlerList handlers = new HandlerList();
+    private boolean cancelled;
+    //
+    private BlockData newData;
+
+    public FluidLevelChangeEvent(Block theBlock, BlockData newData) {
+        super(theBlock);
+        this.newData = newData;
+    }
+
+    /**
+     * Gets the new data of the changed block.
+     *
+     * @return new data
+     */
+    public BlockData getNewData() {
+        return newData;
+    }
+
+    /**
+     * Sets the new data of the changed block. Must be of the same Material as
+     * the old one.
+     *
+     * @param newData the new data
+     */
+    public void setNewData(BlockData newData) {
+        Preconditions.checkArgument(newData != null, "newData null");
+        Preconditions.checkArgument(this.newData.getMaterial().equals(newData.getMaterial()), "Cannot change fluid type");
+
+        this.newData = newData;
+    }
+
+    @Override
+    public boolean isCancelled() {
+        return cancelled;
+    }
+
+    @Override
+    public void setCancelled(boolean cancelled) {
+        this.cancelled = cancelled;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+}