pragma solidity ^0.5.7;
// Copyright BigchainDB GmbH and Ocean Protocol contributors
// SPDX-License-Identifier: (Apache-2.0 AND CC-BY-4.0)
// Code is Apache-2.0 and docs are CC-BY-4.0

import './BToken.sol';
import './BMath.sol';

/**
* @title BPool
*  
* @dev Used by the (Ocean version) BFactory contract as a bytecode reference to
*      deploy new BPools.
*
* This contract is is nearly identical to the BPool.sol contract at [1]
*  The only difference is the "Proxy contract functionality" section 
*  given below. We'd inherit from BPool if we could, for simplicity.
*  But we can't, because the proxy section needs to access private
*  variables declared in BPool, and Solidity disallows this. Therefore
*  the best we can do for now is clearly demarcate the proxy section. 
*
*  [1] https://github.com/balancer-labs/balancer-core/contracts/.
*/
contract BPool is BToken, BMath {

    struct Record {
        bool bound;   // is token bound to pool
        uint index;   // private
        uint denorm;  // denormalized weight
        uint balance;
    }

    event LOG_SWAP(
        address indexed caller,
        address indexed tokenIn,
        address indexed tokenOut,
        uint256         tokenAmountIn,
        uint256         tokenAmountOut
    );

    event LOG_JOIN(
        address indexed caller,
        address indexed tokenIn,
        uint256         tokenAmountIn
    );

    event LOG_EXIT(
        address indexed caller,
        address indexed tokenOut,
        uint256         tokenAmountOut
    );

    event LOG_CALL(
        bytes4  indexed sig,
        address indexed caller,
        bytes           data
    ) anonymous;

    modifier _logs_() {
        emit LOG_CALL(msg.sig, msg.sender, msg.data);
        _;
    }

    modifier _lock_() {
        require(
            !_mutex, 
            'ERR_REENTRY'
        );
        _mutex = true;
        _;
        _mutex = false;
    }

    modifier _viewlock_() {
        require(!_mutex, 'ERR_REENTRY');
        _;
    }
    
    bool private _mutex;

    address private _factory;    // BFactory address to push token exitFee to
    address private _controller; // has CONTROL role
    bool private _publicSwap; // true if PUBLIC can call SWAP functions

    // `setSwapFee` and `finalize` require CONTROL
    // `finalize` sets `PUBLIC can SWAP`, `PUBLIC can JOIN`
    uint private _swapFee;
    bool private _finalized;

    address[] private _tokens;
    mapping(address=>Record) private  _records;
    uint private _totalWeight;

    //-----------------------------------------------------------------------
    //Proxy contract functionality: begin
    bool private initialized = false; 
    modifier onlyNotInitialized() {
        require(
            !initialized, 
            'ERR_ALREADY_INITIALIZED'
        );
        _;
    }
    function isInitialized() external view returns(bool) {
        return initialized;
    }
    
    // Called prior to contract deployment
    constructor() public {
        _initialize(msg.sender, msg.sender, MIN_FEE, false, false);
    }
    
    // Called prior to contract initialization (e.g creating new BPool instance)
    // Calls private _initialize function. Only if contract is not initialized.
    function initialize(
        address controller, 
        address factory, 
        uint swapFee,
        bool publicSwap,
        bool finalized
    )
        external
        onlyNotInitialized
        returns(bool)
    {
        require(
            controller != address(0),
            'ERR_INVALID_CONTROLLER_ADDRESS'
        );
        require(
            factory != address(0),
            'ERR_INVALID_FACTORY_ADDRESS'
        );
        require(swapFee >= MIN_FEE, 'ERR_MIN_FEE');
        require(swapFee <= MAX_FEE, 'ERR_MAX_FEE');
        return _initialize(controller, factory, swapFee, publicSwap, finalized);
    }
	
    // Private function called on contract initialization.
    function _initialize(
        address controller, 
        address factory, 
        uint swapFee,
        bool publicSwap, 
        bool finalized
    )
        private
        returns(bool)
    {
        _controller = controller;
        _factory = factory;
        _swapFee = swapFee;
        _publicSwap = publicSwap;
        _finalized = finalized;
	
        initialized = true;
        return initialized;
    }

    function setup(
        address dataTokenAaddress, 
        uint256 dataTokenAmount,
        uint256 dataTokenWeight,
        address baseTokenAddress, 
        uint256 baseTokenAmount,
        uint256 baseTokenWeight,
        uint256 swapFee
    )
        external
        _logs_
    {
        require(
            dataTokenAaddress != address(0),
            'ERR_INVALID_DATATOKEN_ADDRESS'
        );
        require(
            baseTokenAddress != address(0),
            'ERR_INVALID_BASETOKEN_ADDRESS'
        );
        // other inputs will be validated prior
        // calling the below functions
        // bind data token
        bind(
            dataTokenAaddress,
            dataTokenAmount,
            dataTokenWeight
        );
        emit LOG_JOIN(msg.sender, dataTokenAaddress, dataTokenAmount);
        // bind base token
        bind(
            baseTokenAddress,
            baseTokenAmount,
            baseTokenWeight
        );
        emit LOG_JOIN(msg.sender, baseTokenAddress, baseTokenAmount);
        setSwapFee(swapFee);
        // finalize
        finalize();
    }
    
    //Proxy contract functionality: end
    //-----------------------------------------------------------------------

    function isPublicSwap()
        external view
        returns (bool)
    {
        return _publicSwap;
    }

    function isFinalized()
        external view
        returns (bool)
    {
        return _finalized;
    }

    function isBound(address t)
        external view
        returns (bool)
    {
        return _records[t].bound;
    }

    function getNumTokens()
        external view
        returns (uint) 
    {
        return _tokens.length;
    }

    function getCurrentTokens()
        external view _viewlock_
        returns (address[] memory tokens)
    {
        return _tokens;
    }

    function getFinalTokens()
        external view
        _viewlock_
        returns (address[] memory tokens)
    {
        require(_finalized, 'ERR_NOT_FINALIZED');
        return _tokens;
    }

    function getDenormalizedWeight(address token)
        external view
        _viewlock_
        returns (uint)
    {

        require(_records[token].bound, 'ERR_NOT_BOUND');
        return _records[token].denorm;
    }

    function getTotalDenormalizedWeight()
        external view
        _viewlock_
        returns (uint)
    {
        return _totalWeight;
    }

    function getNormalizedWeight(address token)
        external view
        _viewlock_
        returns (uint)
    {

        require(_records[token].bound, 'ERR_NOT_BOUND');
        uint denorm = _records[token].denorm;
        return bdiv(denorm, _totalWeight);
    }

    function getBalance(address token)
        external view
        _viewlock_
        returns (uint)
    {

        require(_records[token].bound, 'ERR_NOT_BOUND');
        return _records[token].balance;
    }

    function getSwapFee()
        external view
        _viewlock_
        returns (uint)
    {
        return _swapFee;
    }

    function getController()
        external view
        _viewlock_
        returns (address)
    {
        return _controller;
    }

    function setSwapFee(uint swapFee)
        public
        _logs_
        _lock_
    { 
        require(!_finalized, 'ERR_IS_FINALIZED');
        require(msg.sender == _controller, 'ERR_NOT_CONTROLLER');
        require(swapFee >= MIN_FEE, 'ERR_MIN_FEE');
        require(swapFee <= MAX_FEE, 'ERR_MAX_FEE');
        _swapFee = swapFee;
    }

    function setController(address manager)
        external
        _logs_
        _lock_
    {
        require(
            manager != address(0),
            'ERR_INVALID_MANAGER_ADDRESS'
        );
        require(msg.sender == _controller, 'ERR_NOT_CONTROLLER');
        _controller = manager;
    }
	
    function setPublicSwap(bool public_)
        public
        _logs_
        _lock_
    {
        require(!_finalized, 'ERR_IS_FINALIZED');
        require(msg.sender == _controller, 'ERR_NOT_CONTROLLER');
        _publicSwap = public_;
    }

    function finalize()
        public
        _logs_
        _lock_
    {
        require(msg.sender == _controller, 'ERR_NOT_CONTROLLER');
        require(!_finalized, 'ERR_IS_FINALIZED');
        require(_tokens.length >= MIN_BOUND_TOKENS, 'ERR_MIN_TOKENS');

        _finalized = true;
        _publicSwap = true;

        _mintPoolShare(INIT_POOL_SUPPLY);
        _pushPoolShare(msg.sender, INIT_POOL_SUPPLY);
    }


    function bind(address token, uint balance, uint denorm)
        public
        _logs_
        // _lock_  Bind does not lock because it jumps to `rebind`, which does
    {
        require(msg.sender == _controller, 'ERR_NOT_CONTROLLER');
        require(!_records[token].bound, 'ERR_IS_BOUND');
        require(!_finalized, 'ERR_IS_FINALIZED');

        require(_tokens.length < MAX_BOUND_TOKENS, 'ERR_MAX_TOKENS');

        _records[token] = Record({
            bound: true,
            index: _tokens.length,
            denorm: 0,
            // balance and denorm will be validated
            balance: 0   // and set by `rebind`
        });
        _tokens.push(token);
        rebind(token, balance, denorm);
    }

    function rebind(address token, uint balance, uint denorm)
        public
        _logs_
        _lock_
    {

        require(msg.sender == _controller, 'ERR_NOT_CONTROLLER');
        require(_records[token].bound, 'ERR_NOT_BOUND');
        require(!_finalized, 'ERR_IS_FINALIZED');

        require(denorm >= MIN_WEIGHT, 'ERR_MIN_WEIGHT');
        require(denorm <= MAX_WEIGHT, 'ERR_MAX_WEIGHT');
        require(balance >= MIN_BALANCE, 'ERR_MIN_BALANCE');

        // Adjust the denorm and totalWeight
        uint oldWeight = _records[token].denorm;
        if (denorm > oldWeight) {
            _totalWeight = badd(_totalWeight, bsub(denorm, oldWeight));
            require(_totalWeight <= MAX_TOTAL_WEIGHT, 'ERR_MAX_TOTAL_WEIGHT');
        } else if (denorm < oldWeight) {
            _totalWeight = bsub(_totalWeight, bsub(oldWeight, denorm));
        }        
        _records[token].denorm = denorm;

        // Adjust the balance record and actual token balance
        uint oldBalance = _records[token].balance;
        _records[token].balance = balance;
        if (balance > oldBalance) {
            _pullUnderlying(token, msg.sender, bsub(balance, oldBalance));
        } else if (balance < oldBalance) {
            // In this case liquidity is being withdrawn, so charge EXIT_FEE
            uint tokenBalanceWithdrawn = bsub(oldBalance, balance);
            uint tokenExitFee = bmul(tokenBalanceWithdrawn, EXIT_FEE);
            _pushUnderlying(token, msg.sender, bsub(tokenBalanceWithdrawn, tokenExitFee));
            _pushUnderlying(token, _factory, tokenExitFee);
        }
    }

    function unbind(address token)
        external
        _logs_
        _lock_
    {

        require(msg.sender == _controller, 'ERR_NOT_CONTROLLER');
        require(_records[token].bound, 'ERR_NOT_BOUND');
        require(!_finalized, 'ERR_IS_FINALIZED');

        uint tokenBalance = _records[token].balance;
        uint tokenExitFee = bmul(tokenBalance, EXIT_FEE);

        _totalWeight = bsub(_totalWeight, _records[token].denorm);

        // Swap the token-to-unbind with the last token,
        // then delete the last token
        uint index = _records[token].index;
        uint last = _tokens.length - 1;
        _tokens[index] = _tokens[last];
        _records[_tokens[index]].index = index;
        _tokens.pop();
        _records[token] = Record({
            bound: false,
            index: 0,
            denorm: 0,
            balance: 0
        });

        _pushUnderlying(token, msg.sender, bsub(tokenBalance, tokenExitFee));
        _pushUnderlying(token, _factory, tokenExitFee);
    }

    // Absorb any tokens that have been sent to this contract into the pool
    function gulp(address token)
        external
        _logs_
        _lock_
    {
        require(_records[token].bound, 'ERR_NOT_BOUND');
        _records[token].balance = IERC20(token).balanceOf(address(this));
    }

    function getSpotPrice(address tokenIn, address tokenOut)
        external view
        _viewlock_
        returns (uint spotPrice)
    {
        require(_records[tokenIn].bound, 'ERR_NOT_BOUND');
        require(_records[tokenOut].bound, 'ERR_NOT_BOUND');
        Record storage inRecord = _records[tokenIn];
        Record storage outRecord = _records[tokenOut];
        return calcSpotPrice(
            inRecord.balance, 
            inRecord.denorm, 
            outRecord.balance, 
            outRecord.denorm, 
            _swapFee
        );
    }

    function getSpotPriceSansFee(address tokenIn, address tokenOut)
        external view
        _viewlock_
        returns (uint spotPrice)
    {
        require(_records[tokenIn].bound, 'ERR_NOT_BOUND');
        require(_records[tokenOut].bound, 'ERR_NOT_BOUND');
        Record storage inRecord = _records[tokenIn];
        Record storage outRecord = _records[tokenOut];
        return calcSpotPrice(
            inRecord.balance, 
            inRecord.denorm, 
            outRecord.balance, 
            outRecord.denorm, 
            0
        );
    }

    function joinPool(uint poolAmountOut, uint[] calldata maxAmountsIn)
        external
        _logs_
        _lock_
    {
        require(_finalized, 'ERR_NOT_FINALIZED');

        uint poolTotal = totalSupply();
        uint ratio = bdiv(poolAmountOut, poolTotal);
        require(ratio != 0, 'ERR_MATH_APPROX');

        for (uint i = 0; i < _tokens.length; i++) {
            address t = _tokens[i];
            uint bal = _records[t].balance;
            uint tokenAmountIn = bmul(ratio, bal);
            require(tokenAmountIn != 0, 'ERR_MATH_APPROX');
            require(tokenAmountIn <= maxAmountsIn[i], 'ERR_LIMIT_IN');
            _records[t].balance = badd(_records[t].balance, tokenAmountIn);
            emit LOG_JOIN(msg.sender, t, tokenAmountIn);
            _pullUnderlying(t, msg.sender, tokenAmountIn);
        }
        _mintPoolShare(poolAmountOut);
        _pushPoolShare(msg.sender, poolAmountOut);
    }

    function exitPool(uint poolAmountIn, uint[] calldata minAmountsOut)
        external
        _logs_
        _lock_
    {
        require(_finalized, 'ERR_NOT_FINALIZED');

        uint poolTotal = totalSupply();
        uint exitFee = bmul(poolAmountIn, EXIT_FEE);
        uint pAiAfterExitFee = bsub(poolAmountIn, exitFee);
        uint ratio = bdiv(pAiAfterExitFee, poolTotal);
        require(ratio != 0, 'ERR_MATH_APPROX');

        _pullPoolShare(msg.sender, poolAmountIn);
        _pushPoolShare(_factory, exitFee);
        _burnPoolShare(pAiAfterExitFee);

        for (uint i = 0; i < _tokens.length; i++) {
            address t = _tokens[i];
            uint bal = _records[t].balance;
            uint tokenAmountOut = bmul(ratio, bal);
            require(tokenAmountOut != 0, 'ERR_MATH_APPROX');
            require(tokenAmountOut >= minAmountsOut[i], 'ERR_LIMIT_OUT');
            _records[t].balance = bsub(_records[t].balance, tokenAmountOut);
            emit LOG_EXIT(msg.sender, t, tokenAmountOut);
            _pushUnderlying(t, msg.sender, tokenAmountOut);
        }

    }


    function swapExactAmountIn(
        address tokenIn,
        uint tokenAmountIn,
        address tokenOut,
        uint minAmountOut,
        uint maxPrice
    )
        external
        _logs_
        _lock_
        returns (uint tokenAmountOut, uint spotPriceAfter)
    {

        require(_records[tokenIn].bound, 'ERR_NOT_BOUND');
        require(_records[tokenOut].bound, 'ERR_NOT_BOUND');
        require(_publicSwap, 'ERR_SWAP_NOT_PUBLIC');

        Record storage inRecord = _records[address(tokenIn)];
        Record storage outRecord = _records[address(tokenOut)];

        require(
            tokenAmountIn <= bmul(inRecord.balance, MAX_IN_RATIO), 
            'ERR_MAX_IN_RATIO'
        );

        uint spotPriceBefore = calcSpotPrice(
            inRecord.balance,
            inRecord.denorm,
            outRecord.balance,
            outRecord.denorm,
            _swapFee
        );
        require(spotPriceBefore <= maxPrice, 'ERR_BAD_LIMIT_PRICE');

        tokenAmountOut = calcOutGivenIn(
            inRecord.balance,
            inRecord.denorm,
            outRecord.balance,
            outRecord.denorm,
            tokenAmountIn,
            _swapFee
        );
        require(tokenAmountOut >= minAmountOut, 'ERR_LIMIT_OUT');

        inRecord.balance = badd(inRecord.balance, tokenAmountIn);
        outRecord.balance = bsub(outRecord.balance, tokenAmountOut);

        spotPriceAfter = calcSpotPrice(
            inRecord.balance,
            inRecord.denorm,
            outRecord.balance,
            outRecord.denorm,
            _swapFee
        );
        require(spotPriceAfter >= spotPriceBefore, 'ERR_MATH_APPROX');     
        require(spotPriceAfter <= maxPrice, 'ERR_LIMIT_PRICE');
        require(
            spotPriceBefore <= bdiv(tokenAmountIn, tokenAmountOut), 
            'ERR_MATH_APPROX'
        );

        emit LOG_SWAP(
            msg.sender, 
            tokenIn, 
            tokenOut, 
            tokenAmountIn, 
            tokenAmountOut
        );

        _pullUnderlying(tokenIn, msg.sender, tokenAmountIn);
        _pushUnderlying(tokenOut, msg.sender, tokenAmountOut);

        return (tokenAmountOut, spotPriceAfter);
    }

    function swapExactAmountOut(
        address tokenIn,
        uint maxAmountIn,
        address tokenOut,
        uint tokenAmountOut,
        uint maxPrice
    )
        external
        _logs_
        _lock_ 
        returns (uint tokenAmountIn, uint spotPriceAfter)
    {
        require(_records[tokenIn].bound, 'ERR_NOT_BOUND');
        require(_records[tokenOut].bound, 'ERR_NOT_BOUND');
        require(_publicSwap, 'ERR_SWAP_NOT_PUBLIC');

        Record storage inRecord = _records[address(tokenIn)];
        Record storage outRecord = _records[address(tokenOut)];

        require(
            tokenAmountOut <= bmul(outRecord.balance, MAX_OUT_RATIO), 
            'ERR_MAX_OUT_RATIO'
        );

        uint spotPriceBefore = calcSpotPrice(
            inRecord.balance,
            inRecord.denorm,
            outRecord.balance,
            outRecord.denorm,
            _swapFee
        );
        
        require(spotPriceBefore <= maxPrice, 'ERR_BAD_LIMIT_PRICE');

        tokenAmountIn = calcInGivenOut(
            inRecord.balance,
            inRecord.denorm,
            outRecord.balance,
            outRecord.denorm,
            tokenAmountOut,
            _swapFee
        );
        require(tokenAmountIn <= maxAmountIn, 'ERR_LIMIT_IN');

        inRecord.balance = badd(inRecord.balance, tokenAmountIn);
        outRecord.balance = bsub(outRecord.balance, tokenAmountOut);

        spotPriceAfter = calcSpotPrice(
            inRecord.balance,
            inRecord.denorm,
            outRecord.balance,
            outRecord.denorm,
            _swapFee
        );
        require(spotPriceAfter >= spotPriceBefore, 'ERR_MATH_APPROX');
        require(spotPriceAfter <= maxPrice, 'ERR_LIMIT_PRICE');
        require(
            spotPriceBefore <= bdiv(tokenAmountIn, tokenAmountOut), 
            'ERR_MATH_APPROX'
        );

        emit LOG_SWAP(
            msg.sender, 
            tokenIn, 
            tokenOut, 
            tokenAmountIn, 
            tokenAmountOut
        );

        _pullUnderlying(tokenIn, msg.sender, tokenAmountIn);
        _pushUnderlying(tokenOut, msg.sender, tokenAmountOut);

        return (tokenAmountIn, spotPriceAfter);
    }


    function joinswapExternAmountIn(
        address tokenIn, 
        uint tokenAmountIn, 
        uint minPoolAmountOut
    )
        external
        _logs_
        _lock_
        returns (uint poolAmountOut)

    {        
        require(_finalized, 'ERR_NOT_FINALIZED');
        require(_records[tokenIn].bound, 'ERR_NOT_BOUND');
        require(
            tokenAmountIn <= bmul(_records[tokenIn].balance, MAX_IN_RATIO), 
            'ERR_MAX_IN_RATIO'
        );

        Record storage inRecord = _records[tokenIn];

        poolAmountOut = calcPoolOutGivenSingleIn(
            inRecord.balance,
            inRecord.denorm,
            _totalSupply,
            _totalWeight,
            tokenAmountIn,
            _swapFee
        );

        require(poolAmountOut >= minPoolAmountOut, 'ERR_LIMIT_OUT');

        inRecord.balance = badd(inRecord.balance, tokenAmountIn);

        emit LOG_JOIN(msg.sender, tokenIn, tokenAmountIn);

        _mintPoolShare(poolAmountOut);
        _pushPoolShare(msg.sender, poolAmountOut);
        _pullUnderlying(tokenIn, msg.sender, tokenAmountIn);

        return poolAmountOut;
    }

    function joinswapPoolAmountOut(
        address tokenIn, 
        uint poolAmountOut, 
        uint maxAmountIn
    )
        external
        _logs_
        _lock_
        returns (uint tokenAmountIn)
    {
        require(_finalized, 'ERR_NOT_FINALIZED');
        require(_records[tokenIn].bound, 'ERR_NOT_BOUND');

        Record storage inRecord = _records[tokenIn];

        tokenAmountIn = calcSingleInGivenPoolOut(
            inRecord.balance,
            inRecord.denorm,
            _totalSupply,
            _totalWeight,
            poolAmountOut,
            _swapFee
        );

        require(tokenAmountIn != 0, 'ERR_MATH_APPROX');
        require(tokenAmountIn <= maxAmountIn, 'ERR_LIMIT_IN');
        
        require(
            tokenAmountIn <= bmul(_records[tokenIn].balance, MAX_IN_RATIO), 
            'ERR_MAX_IN_RATIO'
        );

        inRecord.balance = badd(inRecord.balance, tokenAmountIn);

        emit LOG_JOIN(msg.sender, tokenIn, tokenAmountIn);

        _mintPoolShare(poolAmountOut);
        _pushPoolShare(msg.sender, poolAmountOut);
        _pullUnderlying(tokenIn, msg.sender, tokenAmountIn);

        return tokenAmountIn;
    }

    function exitswapPoolAmountIn(
        address tokenOut, 
        uint poolAmountIn, 
        uint minAmountOut
    )
        external
        _logs_
        _lock_
        returns (uint tokenAmountOut)
    {
        require(_finalized, 'ERR_NOT_FINALIZED');
        require(_records[tokenOut].bound, 'ERR_NOT_BOUND');

        Record storage outRecord = _records[tokenOut];

        tokenAmountOut = calcSingleOutGivenPoolIn(
            outRecord.balance,
            outRecord.denorm,
            _totalSupply,
            _totalWeight,
            poolAmountIn,
            _swapFee
        );

        require(tokenAmountOut >= minAmountOut, 'ERR_LIMIT_OUT');
        
        require(
            tokenAmountOut <= bmul(_records[tokenOut].balance, MAX_OUT_RATIO), 
            'ERR_MAX_OUT_RATIO'
        );

        outRecord.balance = bsub(outRecord.balance, tokenAmountOut);

        uint exitFee = bmul(poolAmountIn, EXIT_FEE);

        emit LOG_EXIT(msg.sender, tokenOut, tokenAmountOut);

        _pullPoolShare(msg.sender, poolAmountIn);
        _burnPoolShare(bsub(poolAmountIn, exitFee));
        _pushPoolShare(_factory, exitFee);
        _pushUnderlying(tokenOut, msg.sender, tokenAmountOut);

        return tokenAmountOut;
    }

    function exitswapExternAmountOut(
        address tokenOut, 
        uint tokenAmountOut, 
        uint maxPoolAmountIn
    )
        external
        _logs_
        _lock_
        returns (uint poolAmountIn)
    {
        require(_finalized, 'ERR_NOT_FINALIZED');
        require(_records[tokenOut].bound, 'ERR_NOT_BOUND');
        require(
            tokenAmountOut <= bmul(_records[tokenOut].balance, MAX_OUT_RATIO), 
            'ERR_MAX_OUT_RATIO'
        );

        Record storage outRecord = _records[tokenOut];

        poolAmountIn = calcPoolInGivenSingleOut(
            outRecord.balance,
            outRecord.denorm,
            _totalSupply,
            _totalWeight,
            tokenAmountOut,
            _swapFee
        );

        require(poolAmountIn != 0, 'ERR_MATH_APPROX');
        require(poolAmountIn <= maxPoolAmountIn, 'ERR_LIMIT_IN');

        outRecord.balance = bsub(outRecord.balance, tokenAmountOut);

        uint exitFee = bmul(poolAmountIn, EXIT_FEE);

        emit LOG_EXIT(msg.sender, tokenOut, tokenAmountOut);

        _pullPoolShare(msg.sender, poolAmountIn);
        _burnPoolShare(bsub(poolAmountIn, exitFee));
        _pushPoolShare(_factory, exitFee);
        _pushUnderlying(tokenOut, msg.sender, tokenAmountOut);        

        return poolAmountIn;
    }


    // ==
    // 'Underlying' token-manipulation functions make external calls but are NOT locked
    // You must `_lock_` or otherwise ensure reentry-safety

    function _pullUnderlying(address erc20, address from, uint amount)
        internal
    {
        bool xfer = IERC20(erc20).transferFrom(from, address(this), amount);
        require(xfer, 'ERR_ERC20_FALSE');
    }

    function _pushUnderlying(address erc20, address to, uint amount)
        internal
    {
        bool xfer = IERC20(erc20).transfer(to, amount);
        require(xfer, 'ERR_ERC20_FALSE');
    }

    function _pullPoolShare(address from, uint amount)
        internal
    {
        _pull(from, amount);
    }

    function _pushPoolShare(address to, uint amount)
        internal
    {
        _push(to, amount);
    }

    function _mintPoolShare(uint amount)
        internal
    {
        _mint(amount);
    }

    function _burnPoolShare(uint amount)
        internal
    {
        _burn(amount);
    }

}

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

pragma solidity 0.5.7;

contract BConst {
    uint public constant BONE              = 10**18;

    uint public constant MIN_BOUND_TOKENS  = 2;
    uint public constant MAX_BOUND_TOKENS  = 8;

    uint public constant MIN_FEE           = BONE / 10**6;
    uint public constant MAX_FEE           = BONE / 10;
    uint public constant EXIT_FEE          = 0;

    uint public constant MIN_WEIGHT        = BONE;
    uint public constant MAX_WEIGHT        = BONE * 50;
    uint public constant MAX_TOTAL_WEIGHT  = BONE * 50;
    uint public constant MIN_BALANCE       = BONE / 10**12;

    uint public constant INIT_POOL_SUPPLY  = BONE * 100;

    uint public constant MIN_BPOW_BASE     = 1 wei;
    uint public constant MAX_BPOW_BASE     = (2 * BONE) - 1 wei;
    uint public constant BPOW_PRECISION    = BONE / 10**10;

    uint public constant MAX_IN_RATIO      = BONE / 2;
    uint public constant MAX_OUT_RATIO     = (BONE / 3) + 1 wei;
}

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

pragma solidity 0.5.7;

import './BNum.sol';

contract BMath is BConst, BNum {
    /**********************************************************************************************
    // calcSpotPrice                                                                             //
    // sP = spotPrice                                                                            //
    // bI = tokenBalanceIn                ( bI / wI )         1                                  //
    // bO = tokenBalanceOut         sP =  -----------  *  ----------                             //
    // wI = tokenWeightIn                 ( bO / wO )     ( 1 - sF )                             //
    // wO = tokenWeightOut                                                                       //
    // sF = swapFee                                                                              //
    **********************************************************************************************/
    function calcSpotPrice(
        uint tokenBalanceIn,
        uint tokenWeightIn,
        uint tokenBalanceOut,
        uint tokenWeightOut,
        uint swapFee
    )
        public pure
        returns (uint spotPrice)
    {
        uint numer = bdiv(tokenBalanceIn, tokenWeightIn);
        uint denom = bdiv(tokenBalanceOut, tokenWeightOut);
        uint ratio = bdiv(numer, denom);
        uint scale = bdiv(BONE, bsub(BONE, swapFee));
        return  (spotPrice = bmul(ratio, scale));
    }

    /**********************************************************************************************
    // calcOutGivenIn                                                                            //
    // aO = tokenAmountOut                                                                       //
    // bO = tokenBalanceOut                                                                      //
    // bI = tokenBalanceIn              /      /            bI             \    (wI / wO) \      //
    // aI = tokenAmountIn    aO = bO * |  1 - | --------------------------  | ^            |     //
    // wI = tokenWeightIn               \      \ ( bI + ( aI * ( 1 - sF )) /              /      //
    // wO = tokenWeightOut                                                                       //
    // sF = swapFee                                                                              //
    **********************************************************************************************/
    function calcOutGivenIn(
        uint tokenBalanceIn,
        uint tokenWeightIn,
        uint tokenBalanceOut,
        uint tokenWeightOut,
        uint tokenAmountIn,
        uint swapFee
    )
        public pure
        returns (uint tokenAmountOut)
    {
        uint weightRatio = bdiv(tokenWeightIn, tokenWeightOut);
        uint adjustedIn = bsub(BONE, swapFee);
        adjustedIn = bmul(tokenAmountIn, adjustedIn);
        uint y = bdiv(tokenBalanceIn, badd(tokenBalanceIn, adjustedIn));
        uint foo = bpow(y, weightRatio);
        uint bar = bsub(BONE, foo);
        tokenAmountOut = bmul(tokenBalanceOut, bar);
        return tokenAmountOut;
    }

    /**********************************************************************************************
    // calcInGivenOut                                                                            //
    // aI = tokenAmountIn                                                                        //
    // bO = tokenBalanceOut               /  /     bO      \    (wO / wI)      \                 //
    // bI = tokenBalanceIn          bI * |  | ------------  | ^            - 1  |                //
    // aO = tokenAmountOut    aI =        \  \ ( bO - aO ) /                   /                 //
    // wI = tokenWeightIn           --------------------------------------------                 //
    // wO = tokenWeightOut                          ( 1 - sF )                                   //
    // sF = swapFee                                                                              //
    **********************************************************************************************/
    function calcInGivenOut(
        uint tokenBalanceIn,
        uint tokenWeightIn,
        uint tokenBalanceOut,
        uint tokenWeightOut,
        uint tokenAmountOut,
        uint swapFee
    )
        public pure
        returns (uint tokenAmountIn)
    {
        uint weightRatio = bdiv(tokenWeightOut, tokenWeightIn);
        uint diff = bsub(tokenBalanceOut, tokenAmountOut);
        uint y = bdiv(tokenBalanceOut, diff);
        uint foo = bpow(y, weightRatio);
        foo = bsub(foo, BONE);
        tokenAmountIn = bsub(BONE, swapFee);
        tokenAmountIn = bdiv(bmul(tokenBalanceIn, foo), tokenAmountIn);
        return tokenAmountIn;
    }

    /**********************************************************************************************
    // calcPoolOutGivenSingleIn                                                                  //
    // pAo = poolAmountOut         /                                              \              //
    // tAi = tokenAmountIn        ///      /     //    wI \      \\       \     wI \             //
    // wI = tokenWeightIn        //| tAi *| 1 - || 1 - --  | * sF || + tBi \    --  \            //
    // tW = totalWeight     pAo=||  \      \     \\    tW /      //         | ^ tW   | * pS - pS //
    // tBi = tokenBalanceIn      \\  ------------------------------------- /        /            //
    // pS = poolSupply            \\                    tBi               /        /             //
    // sF = swapFee                \                                              /              //
    **********************************************************************************************/
    function calcPoolOutGivenSingleIn(
        uint tokenBalanceIn,
        uint tokenWeightIn,
        uint poolSupply,
        uint totalWeight,
        uint tokenAmountIn,
        uint swapFee
    )
        public pure
        returns (uint poolAmountOut)
    {
        // Charge the trading fee for the proportion of tokenAi
        ///  which is implicitly traded to the other pool tokens.
        // That proportion is (1- weightTokenIn)
        // tokenAiAfterFee = tAi * (1 - (1-weightTi) * poolFee);
        uint normalizedWeight = bdiv(tokenWeightIn, totalWeight);
        uint zaz = bmul(bsub(BONE, normalizedWeight), swapFee); 
        uint tokenAmountInAfterFee = bmul(tokenAmountIn, bsub(BONE, zaz));

        uint newTokenBalanceIn = badd(tokenBalanceIn, tokenAmountInAfterFee);
        uint tokenInRatio = bdiv(newTokenBalanceIn, tokenBalanceIn);

        // uint newPoolSupply = (ratioTi ^ weightTi) * poolSupply;
        uint poolRatio = bpow(tokenInRatio, normalizedWeight);
        uint newPoolSupply = bmul(poolRatio, poolSupply);
        poolAmountOut = bsub(newPoolSupply, poolSupply);
        return poolAmountOut;
    }

    /**********************************************************************************************
    // calcSingleInGivenPoolOut                                                                  //
    // tAi = tokenAmountIn              //(pS + pAo)\     /    1    \\                           //
    // pS = poolSupply                 || ---------  | ^ | --------- || * bI - bI                //
    // pAo = poolAmountOut              \\    pS    /     \(wI / tW)//                           //
    // bI = balanceIn          tAi =  --------------------------------------------               //
    // wI = weightIn                              /      wI  \                                   //
    // tW = totalWeight                          |  1 - ----  |  * sF                            //
    // sF = swapFee                               \      tW  /                                   //
    **********************************************************************************************/
    function calcSingleInGivenPoolOut(
        uint tokenBalanceIn,
        uint tokenWeightIn,
        uint poolSupply,
        uint totalWeight,
        uint poolAmountOut,
        uint swapFee
    )
        public pure
        returns (uint tokenAmountIn)
    {
        uint normalizedWeight = bdiv(tokenWeightIn, totalWeight);
        uint newPoolSupply = badd(poolSupply, poolAmountOut);
        uint poolRatio = bdiv(newPoolSupply, poolSupply);
      
        //uint newBalTi = poolRatio^(1/weightTi) * balTi;
        uint boo = bdiv(BONE, normalizedWeight); 
        uint tokenInRatio = bpow(poolRatio, boo);
        uint newTokenBalanceIn = bmul(tokenInRatio, tokenBalanceIn);
        uint tokenAmountInAfterFee = bsub(newTokenBalanceIn, tokenBalanceIn);
        // Do reverse order of fees charged in joinswap_ExternAmountIn, this way 
        //     ``` pAo == joinswap_ExternAmountIn(Ti, joinswap_PoolAmountOut(pAo, Ti)) ```
        //uint tAi = tAiAfterFee / (1 - (1-weightTi) * swapFee) ;
        uint zar = bmul(bsub(BONE, normalizedWeight), swapFee);
        tokenAmountIn = bdiv(tokenAmountInAfterFee, bsub(BONE, zar));
        return tokenAmountIn;
    }

    /**********************************************************************************************
    // calcSingleOutGivenPoolIn                                                                  //
    // tAo = tokenAmountOut            /      /                                             \\   //
    // bO = tokenBalanceOut           /      // pS - (pAi * (1 - eF)) \     /    1    \      \\  //
    // pAi = poolAmountIn            | bO - || ----------------------- | ^ | --------- | * b0 || //
    // ps = poolSupply                \      \\          pS           /     \(wO / tW)/      //  //
    // wI = tokenWeightIn      tAo =   \      \                                             //   //
    // tW = totalWeight                    /     /      wO \       \                             //
    // sF = swapFee                    *  | 1 - |  1 - ---- | * sF  |                            //
    // eF = exitFee                        \     \      tW /       /                             //
    **********************************************************************************************/
    function calcSingleOutGivenPoolIn(
        uint tokenBalanceOut,
        uint tokenWeightOut,
        uint poolSupply,
        uint totalWeight,
        uint poolAmountIn,
        uint swapFee
    )
        public pure
        returns (uint tokenAmountOut)
    {
        uint normalizedWeight = bdiv(tokenWeightOut, totalWeight);
        // charge exit fee on the pool token side
        // pAiAfterExitFee = pAi*(1-exitFee)
        uint poolAmountInAfterExitFee = bmul(
            poolAmountIn, 
            bsub(BONE, EXIT_FEE)
        );
        uint newPoolSupply = bsub(poolSupply, poolAmountInAfterExitFee);
        uint poolRatio = bdiv(newPoolSupply, poolSupply);
     
        // newBalTo = poolRatio^(1/weightTo) * balTo;
        uint tokenOutRatio = bpow(poolRatio, bdiv(BONE, normalizedWeight));
        uint newTokenBalanceOut = bmul(tokenOutRatio, tokenBalanceOut);

        uint tokenAmountOutBeforeSwapFee = bsub(
            tokenBalanceOut, 
            newTokenBalanceOut
        );

        // charge swap fee on the output token side 
        //uint tAo = tAoBeforeSwapFee * (1 - (1-weightTo) * swapFee)
        uint zaz = bmul(bsub(BONE, normalizedWeight), swapFee); 
        tokenAmountOut = bmul(tokenAmountOutBeforeSwapFee, bsub(BONE, zaz));
        return tokenAmountOut;
    }

    /**********************************************************************************************
    // calcPoolInGivenSingleOut                                                                  //
    // pAi = poolAmountIn               // /               tAo             \\     / wO \     \   //
    // bO = tokenBalanceOut            // | bO - -------------------------- |\   | ---- |     \  //
    // tAo = tokenAmountOut      pS - ||   \     1 - ((1 - (tO / tW)) * sF)/  | ^ \ tW /  * pS | //
    // ps = poolSupply                 \\ -----------------------------------/                /  //
    // wO = tokenWeightOut  pAi =       \\               bO                 /                /   //
    // tW = totalWeight           -------------------------------------------------------------  //
    // sF = swapFee                                        ( 1 - eF )                            //
    // eF = exitFee                                                                              //
    **********************************************************************************************/
    function calcPoolInGivenSingleOut(
        uint tokenBalanceOut,
        uint tokenWeightOut,
        uint poolSupply,
        uint totalWeight,
        uint tokenAmountOut,
        uint swapFee
    )
        public pure
        returns (uint poolAmountIn)
    {

        // charge swap fee on the output token side 
        uint normalizedWeight = bdiv(tokenWeightOut, totalWeight);
        //uint tAoBeforeSwapFee = tAo / (1 - (1-weightTo) * swapFee) ;
        uint zoo = bsub(BONE, normalizedWeight);
        uint zar = bmul(zoo, swapFee); 
        uint tokenAmountOutBeforeSwapFee = bdiv(
            tokenAmountOut, 
            bsub(BONE, zar)
        );

        uint newTokenBalanceOut = bsub(
            tokenBalanceOut, 
            tokenAmountOutBeforeSwapFee
        );
        uint tokenOutRatio = bdiv(newTokenBalanceOut, tokenBalanceOut);

        //uint newPoolSupply = (ratioTo ^ weightTo) * poolSupply;
        uint poolRatio = bpow(tokenOutRatio, normalizedWeight);
        uint newPoolSupply = bmul(poolRatio, poolSupply);
        uint poolAmountInAfterExitFee = bsub(poolSupply, newPoolSupply);

        // charge exit fee on the pool token side
        // pAi = pAiAfterExitFee/(1-exitFee)
        poolAmountIn = bdiv(poolAmountInAfterExitFee, bsub(BONE, EXIT_FEE));
        return poolAmountIn;
    }


}

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

pragma solidity 0.5.7;

import './BConst.sol';

contract BNum is BConst {

    function btoi(uint a)
        internal pure 
        returns (uint)
    {
        return a / BONE;
    }

    function bfloor(uint a)
        internal pure
        returns (uint)
    {
        return btoi(a) * BONE;
    }

    function badd(uint a, uint b)
        internal pure
        returns (uint)
    {
        uint c = a + b;
        require(c >= a, 'ERR_ADD_OVERFLOW');
        return c;
    }

    function bsub(uint a, uint b)
        internal pure
        returns (uint)
    {
        (uint c, bool flag) = bsubSign(a, b);
        require(!flag, 'ERR_SUB_UNDERFLOW');
        return c;
    }

    function bsubSign(uint a, uint b)
        internal pure
        returns (uint, bool)
    {
        if (a >= b) {
            return (a - b, false);
        } else {
            return (b - a, true);
        }
    }

    function bmul(uint a, uint b)
        internal pure
        returns (uint)
    {
        uint c0 = a * b;
        require(a == 0 || c0 / a == b, 'ERR_MUL_OVERFLOW');
        uint c1 = c0 + (BONE / 2);
        require(c1 >= c0, 'ERR_MUL_OVERFLOW');
        uint c2 = c1 / BONE;
        return c2;
    }

    function bdiv(uint a, uint b)
        internal pure
        returns (uint)
    {
        require(b != 0, 'ERR_DIV_ZERO');
        uint c0 = a * BONE;
        require(a == 0 || c0 / a == BONE, 'ERR_DIV_INTERNAL'); // bmul overflow
        uint c1 = c0 + (b / 2);
        require(c1 >= c0, 'ERR_DIV_INTERNAL'); //  badd require
        uint c2 = c1 / b;
        return c2;
    }

    // DSMath.wpow
    function bpowi(uint a, uint n)
        internal pure
        returns (uint)
    {
        uint b = a;
        uint z = n % 2 != 0 ? b : BONE;

        for (n /= 2; n != 0; n /= 2) {
            b = bmul(b, b);

            if (n % 2 != 0) {
                z = bmul(z, b);
            }
        }
        return z;
    }

    // Compute b^(e.w) by splitting it into (b^e)*(b^0.w).
    // Use `bpowi` for `b^e` and `bpowK` for k iterations
    // of approximation of b^0.w
    function bpow(uint base, uint exp)
        internal pure
        returns (uint)
    {
        require(base >= MIN_BPOW_BASE, 'ERR_BPOW_BASE_TOO_LOW');
        require(base <= MAX_BPOW_BASE, 'ERR_BPOW_BASE_TOO_HIGH');

        uint whole  = bfloor(exp);   
        uint remain = bsub(exp, whole);

        uint wholePow = bpowi(base, btoi(whole));

        if (remain == 0) {
            return wholePow;
        }

        uint partialResult = bpowApprox(base, remain, BPOW_PRECISION);
        return bmul(wholePow, partialResult);
    }

    function bpowApprox(uint base, uint exp, uint precision)
        internal pure
        returns (uint)
    {
        // term 0:
        uint a     = exp;
        (uint x, bool xneg)  = bsubSign(base, BONE);
        uint term = BONE;
        uint sum   = term;
        bool negative = false;


        // term(k) = numer / denom 
        //         = (product(a - i - 1, i=1-->k) * x^k) / (k!)
        // each iteration, multiply previous term by (a-(k-1)) * x / k
        // continue until term is less than precision
        for (uint i = 1; term >= precision; i++) {
            uint bigK = i * BONE;
            (uint c, bool cneg) = bsubSign(a, bsub(bigK, BONE));
            term = bmul(term, bmul(c, x));
            term = bdiv(term, bigK);
            if (term == 0) break;

            if (xneg) negative = !negative;
            if (cneg) negative = !negative;
            if (negative) {
                sum = bsub(sum, term);
            } else {
                sum = badd(sum, term);
            }
        }

        return sum;
    }

}

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

pragma solidity 0.5.7;

import './BNum.sol';
import 'openzeppelin-solidity/contracts/token/ERC20/IERC20.sol';

// Highly opinionated token implementation

// interface IERC20 {
//     event Approval(address indexed src, address indexed dst, uint amt);
//     event Transfer(address indexed src, address indexed dst, uint amt);

//     function totalSupply() external view returns (uint);
//     function balanceOf(address whom) external view returns (uint);
//     function allowance(address src, address dst) external view returns (uint);

//     function approve(address dst, uint amt) external returns (bool);
//     function transfer(address dst, uint amt) external returns (bool);
//     function transferFrom(
//         address src, address dst, uint amt
//     ) external returns (bool);
// }

contract BTokenBase is BNum {

    mapping(address => uint)                   internal _balance;
    mapping(address => mapping(address=>uint)) internal _allowance;
    uint internal _totalSupply;

    event Approval(address indexed src, address indexed dst, uint amt);
    event Transfer(address indexed src, address indexed dst, uint amt);

    function _mint(uint amt) internal {
        _balance[address(this)] = badd(_balance[address(this)], amt);
        _totalSupply = badd(_totalSupply, amt);
        emit Transfer(address(0), address(this), amt);
    }

    function _burn(uint amt) internal {
        require(
            _balance[address(this)] >= amt, 
            'ERR_INSUFFICIENT_BAL'
        );
        _balance[address(this)] = bsub(_balance[address(this)], amt);
        _totalSupply = bsub(_totalSupply, amt);
        emit Transfer(address(this), address(0), amt);
    }

    function _move(address src, address dst, uint amt) internal {
        require(_balance[src] >= amt, 'ERR_INSUFFICIENT_BAL');
        _balance[src] = bsub(_balance[src], amt);
        _balance[dst] = badd(_balance[dst], amt);
        emit Transfer(src, dst, amt);
    }

    function _push(address to, uint amt) internal {
        _move(address(this), to, amt);
    }

    function _pull(address from, uint amt) internal {
        _move(from, address(this), amt);
    }
}

contract BToken is BTokenBase, IERC20 {

    string  private _name     = 'Balancer Pool Token';
    string  private _symbol   = 'BPT';
    uint8   private _decimals = 18;

    function name() public view returns (string memory) {
        return _name;
    }

    function symbol() public view returns (string memory) {
        return _symbol;
    }

    function decimals() public view returns(uint8) {
        return _decimals;
    }

    function allowance(address src, address dst) external view returns (uint) {
        return _allowance[src][dst];
    }

    function balanceOf(address whom) external view returns (uint) {
        return _balance[whom];
    }

    function totalSupply() public view returns (uint) {
        return _totalSupply;
    }

    function approve(address dst, uint amt) external returns (bool) {
        _allowance[msg.sender][dst] = amt;
        emit Approval(msg.sender, dst, amt);
        return true;
    }

    function increaseApproval(address dst, uint amt) external returns (bool) {
        _allowance[msg.sender][dst] = badd(_allowance[msg.sender][dst], amt);
        emit Approval(msg.sender, dst, _allowance[msg.sender][dst]);
        return true;
    }

    function decreaseApproval(address dst, uint amt) external returns (bool) {
        uint oldValue = _allowance[msg.sender][dst];
        if (amt > oldValue) {
            _allowance[msg.sender][dst] = 0;
        } else {
            _allowance[msg.sender][dst] = bsub(oldValue, amt);
        }
        emit Approval(msg.sender, dst, _allowance[msg.sender][dst]);
        return true;
    }

    function transfer(address dst, uint amt) external returns (bool) {
        _move(msg.sender, dst, amt);
        return true;
    }

    function transferFrom(
        address src, 
        address dst, 
        uint amt
    ) 
    external 
    returns (bool) 
    {
        require(
            msg.sender == src || amt <= _allowance[src][msg.sender], 
            'ERR_BTOKEN_BAD_CALLER'
        );
        _move(src, dst, amt);
        if (msg.sender != src && _allowance[src][msg.sender] != uint256(-1)) {
            _allowance[src][msg.sender] = bsub(_allowance[src][msg.sender], amt);
            emit Approval(msg.sender, dst, _allowance[src][msg.sender]);
        }
        return true;
    }
}

pragma solidity ^0.5.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see {ERC20Detailed}.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

{
  "remappings": [],
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "evmVersion": "byzantium",
  "libraries": {
    "": {}
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