Add PreTransactionEvent

Essentials/src/main/java/com/earth2me/essentials/User.java

@@ -22,6 +22,7 @@
 import net.ess3.api.events.MuteStatusChangeEvent;
 import net.ess3.api.events.UserBalanceUpdateEvent;
 import net.ess3.provider.PlayerLocaleProvider;
+import net.essentialsx.api.v2.events.PreTransactionEvent;
 import net.essentialsx.api.v2.events.TransactionEvent;
 import net.essentialsx.api.v2.services.mail.MailSender;
 import net.kyori.adventure.text.Component;
@@ -270,11 +271,19 @@ public void payUser(final User reciever, final BigDecimal value, final UserBalan
         }
 
         if (canAfford(value)) {
-            setMoney(getMoney().subtract(value), cause);
-            reciever.setMoney(reciever.getMoney().add(value), cause);
-            sendTl("moneySentTo", AdventureUtil.parsed(NumberUtil.displayCurrency(value, ess)), reciever.getDisplayName());
-            reciever.sendTl("moneyRecievedFrom", AdventureUtil.parsed(NumberUtil.displayCurrency(value, ess)), getDisplayName());
-            final TransactionEvent transactionEvent = new TransactionEvent(this.getSource(), reciever, value);
+            // Call an event for pre-transaction
+            final PreTransactionEvent preTransactionEvent = new PreTransactionEvent(this.getSource(), reciever, value);
+            ess.getServer().getPluginManager().callEvent(preTransactionEvent);
+            if (preTransactionEvent.isCancelled()) {
+                return;
+            }
+            final BigDecimal transactionAmount = preTransactionEvent.getAmount();
+
+            setMoney(getMoney().subtract(transactionAmount), cause);
+            reciever.setMoney(reciever.getMoney().add(transactionAmount), cause);
+            sendTl("moneySentTo", AdventureUtil.parsed(NumberUtil.displayCurrency(transactionAmount, ess)), reciever.getDisplayName());
+            reciever.sendTl("moneyRecievedFrom", AdventureUtil.parsed(NumberUtil.displayCurrency(transactionAmount, ess)), getDisplayName());
+            final TransactionEvent transactionEvent = new TransactionEvent(this.getSource(), reciever, transactionAmount);
             ess.getServer().getPluginManager().callEvent(transactionEvent);
         } else {
             throw new ChargeException("notEnoughMoney", AdventureUtil.parsed(NumberUtil.displayCurrency(value, ess)));

Essentials/src/main/java/net/essentialsx/api/v2/events/PreTransactionEvent.java

@@ -0,0 +1,59 @@
+package net.essentialsx.api.v2.events;
+
+import com.earth2me.essentials.CommandSource;
+import com.google.common.base.Preconditions;
+import net.ess3.api.IUser;
+import org.bukkit.Bukkit;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.HandlerList;
+
+import java.math.BigDecimal;
+
+/**
+ * Fired when a transaction (e.g. /pay) is about to be handled.
+ */
+public class PreTransactionEvent extends TransactionEvent implements Cancellable {
+    private static final HandlerList handlers = new HandlerList();
+
+    private boolean cancelled;
+
+    public PreTransactionEvent(final CommandSource requester, final IUser target, final BigDecimal amount) {
+        super(!Bukkit.isPrimaryThread(), requester, target, amount);
+    }
+
+    /**
+     * Sets the amount to be subtracted from the requester's balance.
+     * <p>
+     * Note: Changing this amount will not verify the requester actually has enough balance to complete the transaction.
+     * @param decimal the new amount
+     */
+    public void setAmount(final BigDecimal decimal) {
+        Preconditions.checkNotNull(decimal, "decimal cannot be null");
+        Preconditions.checkArgument(decimal.compareTo(BigDecimal.ZERO) >= 0, "decimal cannot be negative");
+
+        this.amount = decimal;
+    }
+
+    @Override
+    public boolean isCancelled() {
+        return cancelled;
+    }
+
+    /**
+     * If this event should be cancelled. If cancelled, no messages will be displayed to the users involved.
+     * @param cancelled whether this event should be cancelled
+     */
+    @Override
+    public void setCancelled(boolean cancelled) {
+        this.cancelled = cancelled;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+}

Essentials/src/main/java/net/essentialsx/api/v2/events/TransactionEvent.java

@@ -16,15 +16,19 @@ public class TransactionEvent extends Event {
 
     private final CommandSource requester;
     private final IUser target;
-    private final BigDecimal amount;
+    protected BigDecimal amount;
 
-    public TransactionEvent(CommandSource requester, IUser target, BigDecimal amount) {
-        super(!Bukkit.isPrimaryThread());
+    protected TransactionEvent(boolean async, CommandSource requester, IUser target, BigDecimal amount) {
+        super(async);
         this.requester = requester;
         this.target = target;
         this.amount = amount;
     }
 
+    public TransactionEvent(CommandSource requester, IUser target, BigDecimal amount) {
+        this(!Bukkit.isPrimaryThread(), requester, target, amount);
+    }
+
     /**
      * @return the user who initiated the transaction
      */