From 906609696ba9474feaea2fb501e669f69f8cbdba Mon Sep 17 00:00:00 2001
From: TfT_02 <tft_02@hotmail.com>
Date: Sun, 15 Jun 2014 01:47:31 +0200
Subject: [PATCH] Workaround a CB bug by tracking piston events

There is a bug in Craftbukkit that causes piston events to fire
multiple times. We need to keep track of the extend and retract events
to see which piston events should be processed.
---
 .../nossr50/listeners/BlockListener.java      |  8 +++++++
 src/main/java/com/gmail/nossr50/mcMMO.java    |  1 +
 .../com/gmail/nossr50/util/EventUtils.java    | 23 +++++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/src/main/java/com/gmail/nossr50/listeners/BlockListener.java b/src/main/java/com/gmail/nossr50/listeners/BlockListener.java
index 9802de1b5..8503f521c 100644
--- a/src/main/java/com/gmail/nossr50/listeners/BlockListener.java
+++ b/src/main/java/com/gmail/nossr50/listeners/BlockListener.java
@@ -63,6 +63,10 @@ public class BlockListener implements Listener {
      */
     @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
     public void onBlockPistonExtend(BlockPistonExtendEvent event) {
+        if (!EventUtils.shouldProcessEvent(event.getBlock(), true)) {
+            return;
+        }
+
         List<Block> blocks = event.getBlocks();
         BlockFace direction = event.getDirection();
         Block futureEmptyBlock = event.getBlock().getRelative(direction); // Block that would be air after piston is finished
@@ -93,6 +97,10 @@ public class BlockListener implements Listener {
      */
     @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
     public void onBlockPistonRetract(BlockPistonRetractEvent event) {
+        if (!EventUtils.shouldProcessEvent(event.getBlock(), false)) {
+            return;
+        }
+
         if (!event.isSticky()) {
             return;
         }
diff --git a/src/main/java/com/gmail/nossr50/mcMMO.java b/src/main/java/com/gmail/nossr50/mcMMO.java
index 8e88cf21b..5f0e7a071 100644
--- a/src/main/java/com/gmail/nossr50/mcMMO.java
+++ b/src/main/java/com/gmail/nossr50/mcMMO.java
@@ -112,6 +112,7 @@ public class mcMMO extends JavaPlugin {
     public final static String disarmedItemKey     = "mcMMO: Disarmed Item";
     public final static String playerDataKey       = "mcMMO: Player Data";
     public final static String greenThumbDataKey   = "mcMMO: Green Thumb";
+    public final static String pistonDataKey       = "mcMMO: Piston State";
 
     public static FixedMetadataValue metadataValue;
 
diff --git a/src/main/java/com/gmail/nossr50/util/EventUtils.java b/src/main/java/com/gmail/nossr50/util/EventUtils.java
index 97ed41201..535214f79 100644
--- a/src/main/java/com/gmail/nossr50/util/EventUtils.java
+++ b/src/main/java/com/gmail/nossr50/util/EventUtils.java
@@ -8,6 +8,7 @@ import org.bukkit.entity.Fish;
 import org.bukkit.entity.Player;
 import org.bukkit.event.player.PlayerFishEvent;
 import org.bukkit.inventory.ItemStack;
+import org.bukkit.metadata.FixedMetadataValue;
 import org.bukkit.plugin.PluginManager;
 
 import com.gmail.nossr50.mcMMO;
@@ -194,4 +195,26 @@ public class EventUtils {
 
         return event;
     }
+
+    /**
+     * There is a bug in CraftBukkit that causes piston events to
+     * fire multiple times. Check this method to see if the piston event
+     * should be processed.
+     *
+     * @param block      Block object of the piston block
+     * @param isExtendEvent should be true when called from BlockPistonExtendEvent
+     *
+     * @return true if the PistonEvent should be processed, false otherwise
+     */
+    public static boolean shouldProcessEvent(Block block, boolean isExtendEvent) {
+        String pistonAction = isExtendEvent ? "EXTEND" : "RETRACT";
+        String lastAction = block.hasMetadata(mcMMO.pistonDataKey) ? block.getMetadata(mcMMO.pistonDataKey).get(0).asString() : "";
+
+        if (!lastAction.equals(pistonAction)) {
+            block.setMetadata(mcMMO.pistonDataKey, new FixedMetadataValue(mcMMO.p, pistonAction));
+            return true;
+        }
+
+        return false;
+    }
 }