Feature/erc777 #1159

contracts/drafts/ERC777/IERC777.sol

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+pragma solidity ^0.5.2;
+
+/**
+ * @title ERC777 token interface
+ * @dev See https://eips.ethereum.org/EIPS/eip-777
+ */
+interface IERC777 {
+    function authorizeOperator(address operator) external;
+
+    function revokeOperator(address operator) external;
+
+    function send(address to, uint256 amount, bytes calldata data) external;
+
+    function operatorSend(
+        address from,
+        address to,
+        uint256 amount,
+        bytes calldata data,
+        bytes calldata operatorData
+    ) external;
+
+    function burn(uint256 amount, bytes calldata data) external;
+
+    function operatorBurn(
+        address from,
+        uint256 amount,
+        bytes calldata data,
+        bytes calldata operatorData
+    ) external;
+
+    function name() external view returns (string memory);
+
+    function symbol() external view returns (string memory);
+
+    function totalSupply() external view returns (uint256);
+
+    function balanceOf(address owner) external view returns (uint256);
+
+    function granularity() external view returns (uint256);
+
+    function defaultOperators() external view returns (address[] memory);
+
+    function isOperatorFor(address operator, address tokenHolder) external view returns (bool);
+
+    event Sent(
+        address indexed operator,
+        address indexed from,
+        address indexed to,
+        uint256 amount,
+        bytes data,
+        bytes operatorData
+    );
+
+    event Minted(address indexed operator, address indexed to, uint256 amount, bytes data, bytes operatorData);
+
+    event Burned(address indexed operator, address indexed from, uint256 amount, bytes data, bytes operatorData);
+
+    event AuthorizedOperator(address indexed operator, address indexed tokenHolder);
+
+    event RevokedOperator(address indexed operator, address indexed tokenHolder);
+}

contracts/drafts/ERC777/IERC777Recipient.sol

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+pragma solidity ^0.5.2;
+
+/**
+ * @title ERC777 token recipient interface
+ * @dev See https://eips.ethereum.org/EIPS/eip-777
+ */
+interface IERC777Recipient {
+    function tokensReceived(
+        address operator,
+        address from,
+        address to,
+        uint amount,
+        bytes calldata userData,
+        bytes calldata operatorData
+    ) external;
+}

contracts/drafts/ERC777/IERC777Sender.sol

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+pragma solidity ^0.5.2;
+
+/**
+ * @title ERC777 token sender interface
+ * @dev See https://eips.ethereum.org/EIPS/eip-777
+ */
+interface IERC777Sender {
+    function tokensToSend(
+        address operator,
+        address from,
+        address to,
+        uint amount,
+        bytes calldata userData,
+        bytes calldata operatorData
+    ) external;
+}

contracts/mocks/ERC777Mock.sol

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+pragma solidity ^0.5.2;
+
+import "../drafts/ERC777/ERC777.sol";
+
+contract ERC777Mock is ERC777 {
+    constructor (
+        address initialHolder,
+        uint256 initialBalance,
+        string memory name,
+        string memory symbol,
+        uint256 granularity,
+        address[] memory defaultOperators
+    ) public ERC777(name, symbol, granularity, defaultOperators) {
+        _mint(msg.sender, initialHolder, initialBalance, "", "");
+    }
+}

contracts/mocks/ERC777ReceiverMock.sol

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+pragma solidity ^0.5.2;
+
+import "../drafts/ERC777/IERC777Recipient.sol";
+import "../drafts/IERC1820Registry.sol";
+
+/**
+ * @title ERC777TokensRecipientMock a contract that implements tokensReceived() hook
+ * @author Bertrand Masius <[email protected]>
+ * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-777.md
+ */
+contract ERC777ReceiverMock is IERC777Recipient {
+
+    IERC1820Registry private _erc1820 = IERC1820Registry(0x1820b744B33945482C17Dc37218C01D858EBc714);
+
+    event TokensReceived(
+        address indexed operator,
+        address indexed from,
+        address indexed to,
+        uint256 amount,
+        bytes data,
+        bytes operatorData
+    );
+
+    constructor(bool setInterface) public {
+        // register interface
+        if (setInterface) {
+            _erc1820.setInterfaceImplementer(
+                address(this),
+                keccak256("ERC777TokensRecipient"),
+                address(this)
+            );
+        }
+    }
+
+    /**
+     * @dev tokensReceived() hook
+     * @param operator address operator requesting the transfer
+     * @param from address token holder address
+     * @param to address recipient address
+     * @param amount uint256 amount of tokens to transfer
+     * @param userData bytes extra information provided by the token holder (if any)
+     * @param operatorData bytes extra information provided by the operator (if any)
+     */
+    function tokensReceived(
+        address operator,
+        address from,
+        address to,
+        uint256 amount,
+        bytes calldata userData,
+        bytes calldata operatorData
+    )
+    external
+    {
+        emit TokensReceived(
+            operator,
+            from,
+            to,
+            amount,
+            userData,
+            operatorData
+        );
+    }
+}

contracts/mocks/ERC777SenderMock.sol

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+pragma solidity ^0.5.2;
+
+import "../drafts/ERC777/IERC777.sol";
+import "../drafts/ERC777/IERC777Sender.sol";
+import "../drafts/IERC1820Registry.sol";
+import "../drafts/ERC1820Implementer.sol";
+
+contract ERC777SenderMock is IERC777Sender, ERC1820Implementer {
+    event TokensToSendCalled(
+        address operator,
+        address from,
+        address to,
+        uint256 amount,
+        bytes data,
+        bytes operatorData,
+        address token,
+        uint256 fromBalance,
+        uint256 toBalance
+    );
+
+    bool private _shouldRevert;
+    IERC1820Registry private _erc1820 = IERC1820Registry(0x1820b744B33945482C17Dc37218C01D858EBc714);
+
+    bytes32 constant private TOKENS_SENDER_INTERFACE_HASH = keccak256("ERC777TokensSender");
+
+    constructor(address account) public {
+        if (account != address(0)) {
+            _registerInterfaceForAddress(TOKENS_SENDER_INTERFACE_HASH, account);
+        } else {
+            address self = address(this);
+            _registerInterfaceForAddress(TOKENS_SENDER_INTERFACE_HASH, self);
+            _erc1820.setInterfaceImplementer(self, TOKENS_SENDER_INTERFACE_HASH, self);
+        }
+    }
+
+    function tokensToSend(
+        address operator,
+        address from,
+        address to,
+        uint amount,
+        bytes calldata userData,
+        bytes calldata operatorData
+    ) external {
+        if (_shouldRevert) {
+            revert();
+        }
+
+        IERC777 token = IERC777(msg.sender);
+
+        uint256 fromBalance = token.balanceOf(from);
+        // when called due to burn, to will be the zero address, which will have a balance of 0
+        uint256 toBalance = token.balanceOf(to);
+
+        emit TokensToSendCalled(
+            operator,
+            from,
+            to,
+            amount,
+            userData,
+            operatorData,
+            address(token),
+            fromBalance,
+            toBalance
+        );
+    }
+
+    function setShouldRevert(bool shouldRevert) public {
+        _shouldRevert = shouldRevert;
+    }
+
+    function send(IERC777 token, address to, uint256 amount, bytes memory data) public {
+        // This is 777's send function, not the Solidity send function
+        token.send(to, amount, data); // solhint-disable-line check-send-result
+    }
+
+    function burn(IERC777 token, uint256 amount, bytes memory data) public {
+        token.burn(amount, data);
+    }
+}
+