Wallet: Add a Wallet.waitForBalance() method.

core/src/main/java/com/google/bitcoin/core/Wallet.java

@@ -19,6 +19,7 @@ package com.google.bitcoin.core;
 import com.google.bitcoin.crypto.KeyCrypterScrypt;
 import com.google.common.collect.ArrayListMultimap;
 import com.google.common.collect.Multimap;
+import com.google.common.util.concurrent.SettableFuture;
 import org.bitcoinj.wallet.Protos.Wallet.EncryptionType;
 import org.spongycastle.crypto.params.KeyParameter;
 
@@ -2807,6 +2808,45 @@ public class Wallet implements Serializable, BlockChainListener {
         setCoinSelector(Wallet.AllowUnconfirmedCoinSelector.get());
     }
 
+    /**
+     * Returns a future that will complete when the balance of the given type is equal or larger to the given value.
+     * If the wallet already has a large enough balance the future is returned in a pre-completed state. Note that this
+     * method is not blocking, if you want to <i>actually</i> wait immediately, you have to call .get() on the result.
+     */
+    public ListenableFuture<BigInteger> waitForBalance(final BigInteger value, final BalanceType type) {
+        final SettableFuture<BigInteger> future = SettableFuture.create();
+        final BigInteger current = getBalance(type);
+        if (current.compareTo(value) >= 0) {
+            // Already have enough.
+            future.set(current);
+            return future;
+        }
+        addEventListener(new AbstractWalletEventListener() {
+            private boolean done = false;
+
+            @Override
+            public void onTransactionConfidenceChanged(Wallet wallet, Transaction tx) {
+                check();
+            }
+
+            private void check() {
+                final BigInteger newBalance = getBalance(type);
+                if (!done && newBalance.compareTo(value) >= 0) {
+                    // Have enough now.
+                    done = true;
+                    removeEventListener(this);
+                    future.set(newBalance);
+                }
+            }
+
+            @Override
+            public void onCoinsReceived(Wallet w, Transaction t, BigInteger b1, BigInteger b2) {
+                check();
+            }
+        });
+        return future;
+    }
+
     /////////////////////////////////////////////////////////////////////////////////////////////////////////////////
     //
     // Boilerplate for running event listeners - unlocks the wallet, runs, re-locks.

core/src/test/java/com/google/bitcoin/core/WalletTest.java

@@ -22,6 +22,7 @@ import com.google.bitcoin.crypto.KeyCrypter;
 import com.google.bitcoin.crypto.KeyCrypterException;
 import com.google.bitcoin.crypto.KeyCrypterScrypt;
 import com.google.common.collect.Lists;
+import com.google.common.util.concurrent.ListenableFuture;
 import com.google.protobuf.ByteString;
 
 import org.bitcoinj.wallet.Protos;
@@ -175,9 +176,15 @@ public class WalletTest extends TestWithWallet {
 
     private void receiveAPendingTransaction(Wallet wallet, Address toAddress) throws Exception {
         BigInteger v1 = Utils.toNanoCoins(1, 0);
+        final ListenableFuture<BigInteger> availFuture = wallet.waitForBalance(v1, Wallet.BalanceType.AVAILABLE);
+        final ListenableFuture<BigInteger> estimatedFuture = wallet.waitForBalance(v1, Wallet.BalanceType.ESTIMATED);
+        assertFalse(availFuture.isDone());
+        assertFalse(estimatedFuture.isDone());
         Transaction t1 = sendMoneyToWallet(wallet, v1, toAddress, null);
         assertEquals(BigInteger.ZERO, wallet.getBalance());
         assertEquals(v1, wallet.getBalance(Wallet.BalanceType.ESTIMATED));
+        assertFalse(availFuture.isDone());
+        assertTrue(estimatedFuture.isDone());
         assertEquals(1, wallet.getPoolSize(Pool.PENDING));
         assertEquals(0, wallet.getPoolSize(WalletTransaction.Pool.UNSPENT));
         sendMoneyToWallet(wallet, t1, AbstractBlockChain.NewBlockType.BEST_CHAIN);
@@ -185,6 +192,8 @@ public class WalletTest extends TestWithWallet {
         assertEquals("Incorrect confirmed tx PENDING pool size", 0, wallet.getPoolSize(WalletTransaction.Pool.PENDING));
         assertEquals("Incorrect confirmed tx UNSPENT pool size", 1, wallet.getPoolSize(WalletTransaction.Pool.UNSPENT));
         assertEquals("Incorrect confirmed tx ALL pool size", 1, wallet.getPoolSize(WalletTransaction.Pool.ALL));
+        assertTrue(availFuture.isDone());
+        assertTrue(estimatedFuture.isDone());
     }
 
     private void basicSanityChecks(Wallet wallet, Transaction t, Address fromAddress, Address destination) throws ScriptException {