new sign transaction event

Essentials/src/main/java/com/earth2me/essentials/signs/SignBuy.java

@@ -3,6 +3,7 @@
 import com.earth2me.essentials.ChargeException;
 import com.earth2me.essentials.Trade;
 import com.earth2me.essentials.User;
+import net.ess3.api.events.SignTransactionEvent;
 import net.ess3.api.IEssentials;
 import net.ess3.api.MaxMoneyException;
 import org.bukkit.inventory.ItemStack;
@@ -45,6 +46,12 @@ protected boolean onSignInteract(final ISign sign, final User player, final Stri
         }
 
         charge.isAffordableFor(player);
+        final SignTransactionEvent signTransactionEvent = new SignTransactionEvent(sign, this, player, items.getItemStack(), SignTransactionEvent.TransactionType.BUY, charge.getMoney());
+
+        ess.getServer().getPluginManager().callEvent(signTransactionEvent);
+        if (signTransactionEvent.isCancelled()) {
+            return true;
+        }
         if (!items.pay(player)) {
             throw new ChargeException("inventoryFull");
         }

Essentials/src/main/java/com/earth2me/essentials/signs/SignSell.java

@@ -4,6 +4,7 @@
 import com.earth2me.essentials.Trade;
 import com.earth2me.essentials.Trade.OverflowType;
 import com.earth2me.essentials.User;
+import net.ess3.api.events.SignTransactionEvent;
 import net.ess3.api.IEssentials;
 import net.ess3.api.MaxMoneyException;
 import org.bukkit.inventory.ItemStack;
@@ -47,6 +48,13 @@ protected boolean onSignInteract(final ISign sign, final User player, final Stri
         }
 
         charge.isAffordableFor(player);
+
+        final SignTransactionEvent signTransactionEvent = new SignTransactionEvent(sign, this, player, charge.getItemStack(), SignTransactionEvent.TransactionType.SELL, money.getMoney());
+        ess.getServer().getPluginManager().callEvent(signTransactionEvent);
+        if (signTransactionEvent.isCancelled()) {
+            return false;
+        }
+
         money.pay(player, OverflowType.DROP);
         charge.charge(player);
         Trade.log("Sign", "Sell", "Interact", username, charge, username, money, sign.getBlock().getLocation(), player.getMoney(), ess);

Essentials/src/main/java/net/ess3/api/events/SignTransactionEvent.java

@@ -0,0 +1,79 @@
+package net.ess3.api.events;
+
+import com.earth2me.essentials.signs.EssentialsSign;
+import net.ess3.api.IUser;
+import org.bukkit.event.Cancellable;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
+import org.bukkit.event.HandlerList;
+
+import java.math.BigDecimal;
+
+/**
+ * Fired when a player either buys or sells from an Essentials sign
+ */
+public final class SignTransactionEvent extends SignInteractEvent implements Cancellable {
+    private static final HandlerList handlers = new HandlerList();
+    private final ItemStack itemStack;
+    private final TransactionType transactionType;
+    private final BigDecimal transactionValue;
+    private boolean isCancelled = false;
+
+    public SignTransactionEvent(EssentialsSign.ISign sign, EssentialsSign essSign, IUser user, ItemStack itemStack, TransactionType transactionType, BigDecimal transactionValue) {
+        super(sign, essSign, user);
+        this.itemStack = itemStack;
+        this.transactionType = transactionType;
+        this.transactionValue = transactionValue;
+    }
+
+    @Override
+    public boolean isCancelled() {
+        return this.isCancelled;
+    }
+
+    @Override
+    public void setCancelled(boolean cancelled) {
+        this.isCancelled = cancelled;
+    }
+
+    /**
+     * Gets the ItemStack that is about to be bought or sold in this transition.
+     * @return The ItemStack being bought or sold.
+     */
+    public @NotNull ItemStack getItemStack() {
+        return itemStack.clone();
+    }
+
+    /**
+     * Gets the type of transaction, either buy or sell.
+     * @return The transaction type.
+     */
+    public @NotNull TransactionType getTransactionType() {
+        return transactionType;
+    }
+
+    /**
+     * Gets the value of the item being bought or sold.
+     * @return The item's value.
+     */
+    public BigDecimal getTransactionValue() {
+        return transactionValue;
+    }
+
+    /**
+    * The type of transaction for this sign transaction.
+    */
+    public enum TransactionType {
+        BUY,
+        SELL
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+}