[wallet] Add HasUnusedKeys() helper

Author: John Newbery

src/wallet/wallet.cpp

@@ -3611,6 +3611,11 @@ void CReserveKey::ReturnKey()
     vchPubKey = CPubKey();
 }
 
+bool CWallet::HasUnusedKeys(int min_keys) const
+{
+    return setExternalKeyPool.size() >= min_keys && (setInternalKeyPool.size() >= min_keys || !CanSupportFeature(FEATURE_HD_SPLIT));
+}
+
 void CWallet::GetScriptForMining(std::shared_ptr<CReserveScript> &script)
 {
     std::shared_ptr<CReserveKey> rKey = std::make_shared<CReserveKey>(this);

src/wallet/wallet.h

@@ -813,7 +813,7 @@ class CWallet : public CCryptoKeyStore, public CValidationInterface
     const CWalletTx* GetWalletTx(const uint256& hash) const;
 
     //! check whether we are allowed to upgrade (or already support) to the named feature
-    bool CanSupportFeature(enum WalletFeature wf) { AssertLockHeld(cs_wallet); return nWalletMaxVersion >= wf; }
+    bool CanSupportFeature(enum WalletFeature wf) const { AssertLockHeld(cs_wallet); return nWalletMaxVersion >= wf; }
 
     /**
      * populate vCoins with vector of available COutputs.
@@ -978,6 +978,8 @@ class CWallet : public CCryptoKeyStore, public CValidationInterface
     bool GetKeyFromPool(CPubKey &key, bool internal = false);
     int64_t GetOldestKeyPoolTime();
     const std::map<CKeyID, int64_t>& GetAllReserveKeys() const { return m_pool_key_to_index; }
+    /** Does the wallet have at least min_keys in the keypool? */
+    bool HasUnusedKeys(int min_keys) const;
 
     std::set< std::set<CTxDestination> > GetAddressGroupings();
     std::map<CTxDestination, CAmount> GetAddressBalances();