borrow.sol

pragma solidity ^0.6.8;

import 'https://github.com/aave/aave-protocol/blob/master/contracts/configuration/LendingPoolAddressesProvider.sol'
import 'https://github.com/aave/aave-protocol/blob/master/contracts/lendingpool/LendingPool.sol'
import 'https://github.com/aave/aave-protocol/blob/master/contracts/flashloan/base/FlashLoanReceiverBase.sol'

contract Borrower is FlashLoanReceiverBase {
  LendingPoolAddressesProvider provider;
  address dai;
  
  constructor(
      address _provider, 
      address _dai) 
      FlashLoanReceiverBase(_provider)
      public {
      provider = LendingPoolAddressesProvider(_provider);
      dai = _dai;
  }
  
  function startLoan(uint amount, bytes calldata _params) external {
      LendingPool lendingPool = provider.getLendingPool();
      lendingPool.flashLoan(address(this), dai, amount, _params);
  }
  
  function executeOperation(
      address _reserve,
      uint _amount,
      uint _fee,
      bytes memory _params
    ) external {
        // arbitrage, refinance loan 
        transferFundsBackToPoolInternal(_reserve, amount + fee);
    }
}