Exclusive stake gyser (#258)

* updated deps

* exclusive stake geyser

* fixed incorrect check

contracts/ExclusiveGeyser.sol

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-3.0-only
+pragma solidity 0.7.6;
+pragma abicoder v2;
+
+import {IUniversalVault} from "./UniversalVault.sol";
+import {Geyser} from "./Geyser.sol";
+
+/// @title ExclusiveGeyser
+/// @notice A special extension of GeyserV2 which allows staking in,
+///         at most one distribution program in any given time, for a given staking token.
+/// @dev Security contact: [email protected]
+contract ExclusiveGeyser is Geyser {
+    /// @inheritdoc Geyser
+    function stake(
+        address vault,
+        uint256 amount,
+        bytes calldata permission
+    ) public override {
+        // verify that vault has NOT locked staking token in other programs
+        _enforceExclusiveStake(IUniversalVault(vault));
+
+        // continue with regular stake
+        super.stake(vault, amount, permission);
+    }
+
+    function _enforceExclusiveStake(IUniversalVault vault) private view {
+        address stakingToken = super.getGeyserData().stakingToken;
+        uint256 lockCount = vault.getLockSetCount();
+        for (uint256 i = 0; i < lockCount; i++) {
+            IUniversalVault.LockData memory lock = vault.getLockAt(i);
+            if(lock.token == stakingToken){
+                require(lock.delegate == address(this), "ExclusiveGeyser: expected exclusive stake");
+            }
+        }
+    }
+}

contracts/Geyser.sol

@@ -317,7 +317,7 @@ contract Geyser is IGeyser, Powered, OwnableUpgradeable {
 
     /* geyser getters */
 
-    function getGeyserData() external view override returns (GeyserData memory geyser) {
+    function getGeyserData() public view override returns (GeyserData memory geyser) {
         return _geyser;
     }
 
@@ -788,7 +788,7 @@ contract Geyser is IGeyser, Powered, OwnableUpgradeable {
         address vault,
         uint256 amount,
         bytes calldata permission
-    ) external override onlyOnline {
+    ) public virtual override onlyOnline {
         // verify vault is valid
         require(isValidVault(vault), "Geyser: vault is not registered");