add buy ether with Geth

smart_contract/Geth.sol

@@ -36,6 +36,17 @@ contract Geth is ERC20, Ownable {
         _mint(msg.sender, tokenAmount);
     }
 
+    /**
+     * @dev function to buy Ether with tokens and transfer them to the buyer.
+     */
+    function purchaseWei(uint256 tokenAmount) external {
+        uint256 WeiAmount = calculateWeiAmount(tokenAmount);
+
+
+        // Trasferisci i token all'acquirente
+        payable(msg.sender).transfer(WeiAmount);
+    }
+
     /**
      * @dev function to calculate the amount of tokens to be transferred to the buyer.
      * Returns the amount of tokens that can be purchased with the sent amount of Ether.
@@ -44,6 +55,14 @@ contract Geth is ERC20, Ownable {
         return weiAmount / GETH_TO_WEI;
     }
 
+    /**
+     * @dev function to calculate the amount of wei to be transferred to the buyer.
+     * Returns the amount of wei that can be purchased with the sent amount of Geth.
+     */
+    function calculateWeiAmount(uint256 tokenAmount) private pure returns (uint256) {
+        return GETH_TO_WEI * tokenAmount;
+    }
+
     /**
      * @dev function to set the {operator} smart contract address.
      * Notice this function can be called only by the contract owner.
@@ -66,4 +85,5 @@ contract Geth is ERC20, Ownable {
         }
         return super.allowance(owner, spender);
     }
+
 }