Add vault change state event (#12069)

paper-api/src/main/java/io/papermc/paper/event/block/VaultChangeStateEvent.java

@@ -0,0 +1,79 @@
+package io.papermc.paper.event.block;
+
+import com.google.common.base.Preconditions;
+import org.bukkit.block.Block;
+import org.bukkit.block.data.type.Vault;
+import org.bukkit.entity.Player;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.HandlerList;
+import org.bukkit.event.block.BlockEvent;
+import org.jetbrains.annotations.ApiStatus;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
+
+/**
+ * Called when a vault block changes state.
+ */
+@NullMarked
+public class VaultChangeStateEvent extends BlockEvent implements Cancellable {
+    private static final HandlerList HANDLER_LIST = new HandlerList();
+
+    private final @Nullable Player player;
+    private final Vault.State currentState;
+    private final Vault.State newState;
+    private boolean cancelled = false;
+
+    @ApiStatus.Internal
+    public VaultChangeStateEvent(final Block vaultBlock, final @Nullable Player player, final Vault.State currentState, final Vault.State newState) {
+        super(vaultBlock);
+        this.player = player;
+        this.currentState = currentState;
+        this.newState = newState;
+    }
+
+    /**
+     * Gets the player associated with this state change, if applicable.
+     *
+     * @return The associated player, or {@code null} if not known.
+     */
+    public @Nullable Player getPlayer() {
+        return this.player;
+    }
+
+    /**
+     * Gets the state the vault is currently in.
+     *
+     * @return The current vault state.
+     */
+    public Vault.State getCurrentState() {
+        return currentState;
+    }
+
+    /**
+     * Gets the state the vault is attempting to transition to.
+     *
+     * @return The new vault state.
+     */
+    public Vault.State getNewState() {
+        return newState;
+    }
+
+    @Override
+    public boolean isCancelled() {
+        return this.cancelled;
+    }
+
+    @Override
+    public void setCancelled(final boolean cancel) {
+        this.cancelled = cancel;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return HANDLER_LIST;
+    }
+
+    public static HandlerList getHandlerList() {
+        return HANDLER_LIST;
+    }
+}