Fix left click on air being ignored and right click on block being handled twice

worldedit-core/src/main/java/com/sk89q/worldedit/extension/platform/AbstractPlatform.java

@@ -55,4 +55,9 @@ public abstract class AbstractPlatform implements Platform {
         return null;
     }
 
+    @Override
+    public long getTickCount() {
+        return System.nanoTime() / 50_000_000;
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/extension/platform/Platform.java

@@ -216,6 +216,14 @@ public interface Platform extends Keyed {
      */
     Set<SideEffect> getSupportedSideEffects();
 
+    /**
+     * Get the number of ticks since the server started.
+     * On some platforms this value may be an approximation based on the JVM run time.
+     *
+     * @return The number of ticks since the server started.
+     */
+    long getTickCount();
+
     //FAWE start
 
     /**

worldedit-core/src/main/java/com/sk89q/worldedit/internal/event/InteractionDebouncer.java

@@ -0,0 +1,69 @@
+/*
+ * WorldEdit, a Minecraft world manipulation toolkit
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldEdit team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldedit.internal.event;
+
+import com.sk89q.worldedit.extension.platform.Platform;
+import com.sk89q.worldedit.util.Identifiable;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+import java.util.UUID;
+
+public class InteractionDebouncer {
+    private final Platform platform;
+    private final Map<UUID, Interaction> lastInteractions = new HashMap<>();
+
+    public InteractionDebouncer(Platform platform) {
+        this.platform = platform;
+    }
+
+    public void clearInteraction(Identifiable player) {
+        lastInteractions.remove(player.getUniqueId());
+    }
+
+    public void setLastInteraction(Identifiable player, boolean result) {
+        lastInteractions.put(player.getUniqueId(), new Interaction(platform.getTickCount(), result));
+    }
+
+    public Optional<Boolean> getDuplicateInteractionResult(Identifiable player) {
+        Interaction last = lastInteractions.get(player.getUniqueId());
+        if (last == null) {
+            return Optional.empty();
+        }
+
+        long now = platform.getTickCount();
+        if (now - last.tick <= 1) {
+            return Optional.of(last.result);
+        }
+
+        return Optional.empty();
+    }
+
+    private static class Interaction {
+        public final long tick;
+        public final boolean result;
+
+        public Interaction(long tick, boolean result) {
+            this.tick = tick;
+            this.result = result;
+        }
+    }
+}