Switch the whitelist reference to use an interface

contracts/DecentralizedAutonomousTrust.sol

@@ -1,6 +1,6 @@
 pragma solidity 0.5.13;
 
-import "./Whitelist.sol";
+import "./interfaces/IWhitelist.sol";
 import "./math/BigDiv.sol";
 import "./math/Sqrt.sol";
 import "@openzeppelin/contracts-ethereum-package/contracts/token/ERC20/IERC20.sol";
@@ -105,7 +105,7 @@ contract DecentralizedAutonomousTrust
    */
 
   /// @notice The contract for transfer authorizations, if any.
-  Whitelist public whitelist;
+  IWhitelist public whitelist;
 
   /// @notice The total number of burned FAIR tokens, excluding tokens burned from a `Sell` action in the DAT.
   uint public burnedSupply;
@@ -419,7 +419,7 @@ contract DecentralizedAutonomousTrust
     require(msg.sender == control, "CONTROL_ONLY");
 
     // address(0) is okay
-    whitelist = Whitelist(_whitelistAddress);
+    whitelist = IWhitelist(_whitelistAddress);
 
     require(_control != address(0), "INVALID_ADDRESS");
     control = _control;

contracts/Whitelist.sol

@@ -1,12 +1,13 @@
 pragma solidity 0.5.13;
 
 
-import "./interfaces/ERC1404.sol";
+import "./interfaces/IWhitelist.sol";
 
 /**
- * @title ERC-1404 whitelist implementation which manages KYC approvals for the org.
+ * @title whitelist implementation which manages KYC approvals for the org.
+ * @dev modeled after ERC-1404
  */
-contract Whitelist is ERC1404
+contract Whitelist is IWhitelist
 {
   /**
    * Emits when an operator KYC approves (or revokes) a trader.
@@ -85,6 +86,8 @@ contract Whitelist is ERC1404
   /**
    * @notice Called by the DAT contract before a transfer occurs.
    * @dev This call will revert when the transfer is not authorized.
+   * This is a mutable call to allow additional data to be recorded,
+   * such as when the user aquired their tokens.
    */
   function authorizeTransfer(
     address _from,

contracts/interfaces/ERC1404.sol → contracts/interfaces/IWhitelist.sol

@@ -4,8 +4,9 @@ pragma solidity 0.5.13;
 /**
  * Source: https://raw.githubusercontent.com/simple-restricted-token/reference-implementation/master/contracts/token/ERC1404/ERC1404.sol
  * With ERC-20 APIs removed (will be implemented as a separate contract).
+ * And adding authorizeTransfer.
  */
-interface ERC1404
+interface IWhitelist
 {
   /**
    * @notice Detects if a transfer will be reverted and if so returns an appropriate reference code
@@ -32,4 +33,17 @@ interface ERC1404
     uint8 restrictionCode
   ) external pure
     returns (string memory);
+
+  /**
+   * @notice Called by the DAT contract before a transfer occurs.
+   * @dev This call will revert when the transfer is not authorized.
+   * This is a mutable call to allow additional data to be recorded,
+   * such as when the user aquired their tokens.
+   */
+  function authorizeTransfer(
+    address _from,
+    address _to,
+    uint _value,
+    bool _isSell
+  ) external;
 }