Add 'approve' functionality to ERC875

ERCTokenImplementation.sol

@@ -17,20 +17,23 @@ contract ERC
 pragma solidity ^0.4.17;
 contract Token is ERC
 {
-    uint totalTickets;
+    uint totalTokens;
     mapping(address => uint256[]) inventory;
-    uint16 ticketIndex = 0; //to track mapping in tickets
+    // Owner of account approves the transfer of specific indices by another account
+    mapping(address => mapping (address => uint256[])) allowed;
+    uint16 tokenIndex = 0; 
     uint expiryTimeStamp;
     address owner;   // the address that calls selfdestruct() and takes fees
     address admin;
     uint transferFee;
     uint numOfTransfers = 0;
     string public name;
     string public symbol;
-    uint8 public constant decimals = 0; //no decimals as tickets cannot be split
+    uint8 public constant decimals = 0; //no decimals as tokens cannot be split
 
     event Transfer(address indexed _from, address indexed _to, uint256[] tokenIndices);
     event TransferFrom(address indexed _from, address indexed _to, uint _value);
+    event Approval(address indexed owner, address indexed _approved, uint indexed tokenCount);
 
     modifier adminOnly()
     {
@@ -48,8 +51,8 @@ contract Token is ERC
         string eventSymbol,
         address adminAddr) public
     {
-        totalTickets = numberOfTokens.length;
-        //assign some tickets to event admin
+        totalTokens = numberOfTokens.length;
+        //assign some tokens to event admin
         expiryTimeStamp = expiry;
         owner = msg.sender;
         admin = adminAddr;
@@ -82,11 +85,11 @@ contract Token is ERC
         address seller = ecrecover(message, v, r, s);
 
         for(uint i = 0; i < tokenIndices.length; i++)
-        { // transfer each individual tickets in the ask order
+        { // transfer each individual tokenss in the ask order
             uint index = uint(tokenIndices[i]);
-            require((inventory[seller][index] > 0)); // 0 means ticket sold.
+            require((inventory[seller][index] > 0)); // 0 means token sold.
             inventory[msg.sender].push(inventory[seller][index]);
-            inventory[seller][index] = 0; // 0 means ticket sold.
+            inventory[seller][index] = 0; // 0 means token sold.
         }
         seller.transfer(msg.value);
     }
@@ -177,20 +180,46 @@ contract Token is ERC
         }
     }
 
-    function transferFrom(address _from, address _to, uint256[] tokenIndices)
-        adminOnly public
+    function transferFrom(address _from, address _to, uint256[] tokenIndices) public
     {
         bool isadmin = msg.sender == admin;
         for(uint i = 0; i < tokenIndices.length; i++)
         {
             require(inventory[_from][i] != 0 || isadmin);
+            require(allowed[_from][msg.sender][i] == tokenIndices[i] || isadmin);
             //pushes each element with ordering
             uint index = uint(tokenIndices[i]);
             inventory[_to].push(inventory[msg.sender][index]);
             inventory[_from][index] = 0;
+            delete allowed[_from][msg.sender][i];
         }
     }
 
+    // Function can be used by external smart contract to ensure it is allowed to move NFTs
+    function checkAllowed(address owner, address proxy) public view returns (uint16[])
+    {
+        return allowed[owner][proxy];
+    }
+
+    // This function approves specific NTFs to be available for use in an external contract
+    // See transferFromContract() above.
+    function approve(address _approved, uint256[] tokenIndices) public
+    {
+        // allow caller to cancel approval - each approval call resets previous approval
+        // putting 0 indices resets approval
+        delete allowed[msg.sender][_approved];
+
+        for(uint i = 0; i < tokenIndices.length; i++)
+        {
+            uint index = uint(tokenIndices[i]);
+            //check token ownership, abort function and revert changes if any problems
+            if(inventory[msg.sender][index] == 0) revert("No token at index");
+        }
+        //Confirmed that msg.sender owns these tokens; can now allow external contract to move them
+        allowed[msg.sender][_approved] = tokenIndices;
+        emit Approval(msg.sender, _approved, tokenIndices.length);
+    }
+
     function endContract() public
     {
         if(msg.sender == owner)