// SPDX-License-Identifier: MIT

pragma solidity 0.6.11;

import "./Interfaces/IZUSDToken.sol";
import "./Dependencies/SafeMath.sol";
import "./Dependencies/Ownable.sol";
import "./Dependencies/CheckContract.sol";
import "./Dependencies/console.sol";
import "./ZUSDTokenStorage.sol";

/**
 *
 * Based upon OpenZeppelin's ERC20 contract:
 * https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol
 *
 * and their EIP2612 (ERC20Permit / ERC712) functionality:
 * https://github.com/OpenZeppelin/openzeppelin-contracts/blob/53516bc555a454862470e7860a9b5254db4d00f5/contracts/token/ERC20/ERC20Permit.sol
 *
 *
 * --- Functionality added specific to the ZUSDToken ---
 *
 * 1) Transfer protection: blacklist of addresses that are invalid recipients (i.e. core Zero contracts) in external
 * transfer() and transferFrom() calls. The purpose is to protect users from losing tokens by mistakenly sending ZUSD directly to a Zero
 * core contract, when they should rather call the right function.
 *
 * 2) sendToPool() and returnFromPool(): functions callable only Zero core contracts, which move ZUSD tokens between Zero <-> user.
 */

contract ZUSDToken is ZUSDTokenStorage, CheckContract, IZUSDToken, Ownable {
    using SafeMath for uint256;
    // --- Events ---
    event TroveManagerAddressChanged(address _troveManagerAddress);
    event StabilityPoolAddressChanged(address _newStabilityPoolAddress);
    event BorrowerOperationsAddressChanged(address _newBorrowerOperationsAddress);

    function initialize(
        address _troveManagerAddress,
        address _stabilityPoolAddress,
        address _borrowerOperationsAddress
    ) public virtual initializer onlyOwner {
        _initialize(_troveManagerAddress, _stabilityPoolAddress, _borrowerOperationsAddress);
    }

    function _initialize(
        address _troveManagerAddress,
        address _stabilityPoolAddress,
        address _borrowerOperationsAddress
    ) internal {
        checkContract(_troveManagerAddress);
        checkContract(_stabilityPoolAddress);
        checkContract(_borrowerOperationsAddress);

        troveManagerAddress = _troveManagerAddress;
        emit TroveManagerAddressChanged(_troveManagerAddress);

        stabilityPoolAddress = _stabilityPoolAddress;
        emit StabilityPoolAddressChanged(_stabilityPoolAddress);

        borrowerOperationsAddress = _borrowerOperationsAddress;
        emit BorrowerOperationsAddressChanged(_borrowerOperationsAddress);

        bytes32 hashedName = keccak256(bytes(_NAME));
        bytes32 hashedVersion = keccak256(bytes(_VERSION));

        _HASHED_NAME = hashedName;
        _HASHED_VERSION = hashedVersion;
        _CACHED_CHAIN_ID = _chainID();
        _CACHED_DOMAIN_SEPARATOR = _buildDomainSeparator(_TYPE_HASH, hashedName, hashedVersion);
    }

    // --- Functions for intra-Zero calls ---

    function mint(address _account, uint256 _amount) external override {
        _requireCallerIsBorrowerOperations();
        _mint(_account, _amount);
    }

    function burn(address _account, uint256 _amount) external override {
        _requireCallerIsBOorTroveMorSP();
        _burn(_account, _amount);
    }

    function sendToPool(
        address _sender,
        address _poolAddress,
        uint256 _amount
    ) external override {
        _requireCallerIsStabilityPool();
        _transfer(_sender, _poolAddress, _amount);
    }

    function returnFromPool(
        address _poolAddress,
        address _receiver,
        uint256 _amount
    ) external override {
        _requireCallerIsTroveMorSP();
        _transfer(_poolAddress, _receiver, _amount);
    }

    // --- External functions ---

    function totalSupply() external view override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) external view override returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount) external override returns (bool) {
        _requireValidRecipient(recipient);
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    function allowance(address owner, address spender) external view override returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount) external override returns (bool) {
        _approve(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external override returns (bool) {
        _requireValidRecipient(recipient);
        _transfer(sender, recipient, amount);
        _approve(
            sender,
            msg.sender,
            _allowances[sender][msg.sender].sub(amount, "ERC20: transfer amount exceeds allowance")
        );
        return true;
    }

    function increaseAllowance(address spender, uint256 addedValue)
        external
        override
        returns (bool)
    {
        _approve(msg.sender, spender, _allowances[msg.sender][spender].add(addedValue));
        return true;
    }

    function decreaseAllowance(address spender, uint256 subtractedValue)
        external
        override
        returns (bool)
    {
        _approve(
            msg.sender,
            spender,
            _allowances[msg.sender][spender].sub(
                subtractedValue,
                "ERC20: decreased allowance below zero"
            )
        );
        return true;
    }

    // --- EIP 2612 Functionality ---

    function domainSeparator() public view override returns (bytes32) {
        if (_chainID() == _CACHED_CHAIN_ID) {
            return _CACHED_DOMAIN_SEPARATOR;
        } else {
            return _buildDomainSeparator(_TYPE_HASH, _HASHED_NAME, _HASHED_VERSION);
        }
    }

    function permit(
        address owner,
        address spender,
        uint256 amount,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external override {
        require(deadline >= now, "ZUSD: expired deadline");
        bytes32 digest = keccak256(
            abi.encodePacked(
                "\x19\x01",
                domainSeparator(),
                keccak256(
                    abi.encode(
                        _PERMIT_TYPEHASH,
                        owner,
                        spender,
                        amount,
                        _nonces[owner]++,
                        deadline
                    )
                )
            )
        );
        address recoveredAddress = ecrecover(digest, v, r, s);
        require(recoveredAddress == owner, "ZUSD: invalid signature");
        _approve(owner, spender, amount);
    }

    function nonces(address owner) external view override returns (uint256) {
        // FOR EIP 2612
        return _nonces[owner];
    }

    // --- Internal operations ---

    function _chainID() private pure returns (uint256 chainID) {
        assembly {
            chainID := chainid()
        }
    }

    function _buildDomainSeparator(
        bytes32 typeHash,
        bytes32 name,
        bytes32 version
    ) private view returns (bytes32) {
        return keccak256(abi.encode(typeHash, name, version, _chainID(), address(this)));
    }

    // --- Internal operations ---
    // Warning: sanity checks (for sender and recipient) should have been done before calling these internal functions

    function _transfer(
        address sender,
        address recipient,
        uint256 amount
    ) internal {
        assert(sender != address(0));
        assert(recipient != address(0));

        _balances[sender] = _balances[sender].sub(
            amount,
            "ERC20: transfer amount exceeds balance"
        );
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    function _mint(address account, uint256 amount) internal {
        assert(account != address(0));

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    function _burn(address account, uint256 amount) internal {
        assert(account != address(0));

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal {
        assert(owner != address(0));
        assert(spender != address(0));

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    // --- 'require' functions ---

    function _requireValidRecipient(address _recipient) internal view {
        require(
            _recipient != address(0) && _recipient != address(this),
            "ZUSD: Cannot transfer tokens directly to the ZUSD token contract or the zero address"
        );
    }

    function _requireCallerIsBorrowerOperations() internal view {
        require(
            msg.sender == borrowerOperationsAddress,
            "ZUSDToken: Caller is not BorrowerOperations"
        );
    }

    function _requireCallerIsBOorTroveMorSP() internal view {
        require(
            msg.sender == borrowerOperationsAddress ||
                msg.sender == troveManagerAddress ||
                msg.sender == stabilityPoolAddress,
            "ZUSD: Caller is neither BorrowerOperations nor TroveManager nor StabilityPool"
        );
    }

    function _requireCallerIsStabilityPool() internal view {
        require(msg.sender == stabilityPoolAddress, "ZUSD: Caller is not the StabilityPool");
    }

    function _requireCallerIsTroveMorSP() internal view {
        require(
            msg.sender == troveManagerAddress || msg.sender == stabilityPoolAddress,
            "ZUSD: Caller is neither TroveManager nor StabilityPool"
        );
    }

    // --- Optional functions ---

    function name() external view override returns (string memory) {
        return _NAME;
    }

    function symbol() external view override returns (string memory) {
        return _SYMBOL;
    }

    function decimals() external view override returns (uint8) {
        return _DECIMALS;
    }

    function version() external view override returns (string memory) {
        return _VERSION;
    }

    function permitTypeHash() external view override returns (bytes32) {
        return _PERMIT_TYPEHASH;
    }
}