// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.6.8;

import {IERC20} from '@openzeppelin/contracts/token/ERC20/IERC20.sol';

interface IAToken is IERC20 {
  /**
   * @dev redirects the interest generated to a target address.
   * when the interest is redirected, the user balance is added to
   * the recepient redirected balance.
   * @param _to the address to which the interest will be redirected
   **/
  function redirectInterestStream(address _to) external;

  /**
   * @dev redirects the interest generated by _from to a target address.
   * when the interest is redirected, the user balance is added to
   * the recepient redirected balance. The caller needs to have allowance on
   * the interest redirection to be able to execute the function.
   * @param _from the address of the user whom interest is being redirected
   * @param _to the address to which the interest will be redirected
   **/
  function redirectInterestStreamOf(address _from, address _to) external;

  /**
   * @dev gives allowance to an address to execute the interest redirection
   * on behalf of the caller.
   * @param _to the address to which the interest will be redirected. Pass address(0) to reset
   * the allowance.
   **/
  function allowInterestRedirectionTo(address _to) external;

  /**
   * @dev burns the aTokens and sends the equivalent amount of underlying to the target.
   * only lending pools can call this function
   * @param _amount the amount being burned
   **/
  function burn(
    address _user,
    address _underlyingTarget,
    uint256 _amount
  ) external;

  /**
   * @dev mints aTokens to _user
   * only lending pools can call this function
   * @param _user the address receiving the minted tokens
   * @param _amount the amount of tokens to mint
   */
  function mint(address _user, uint256 _amount) external;

  /**
   * @dev transfers tokens in the event of a borrow being liquidated, in case the liquidators reclaims the aToken
   *      only lending pools can call this function
   * @param _from the address from which transfer the aTokens
   * @param _to the destination address
   * @param _value the amount to transfer
   **/
  function transferOnLiquidation(
    address _from,
    address _to,
    uint256 _value
  ) external;

  /**
   * @dev returns the principal balance of the user. The principal balance is the last
   * updated stored balance, which does not consider the perpetually accruing interest.
   * @param _user the address of the user
   * @return the principal balance of the user
   **/
  function principalBalanceOf(address _user) external view returns (uint256);

  /**
   * @dev Used to validate transfers before actually executing them.
   * @param _user address of the user to check
   * @param _amount the amount to check
   * @return true if the _user can transfer _amount, false otherwise
   **/
  function isTransferAllowed(address _user, uint256 _amount) external view returns (bool);

  /**
   * @dev returns the last index of the user, used to calculate the balance of the user
   * @param _user address of the user
   * @return the last user index
   **/
  function getUserIndex(address _user) external view returns (uint256);

  /**
   * @dev returns the address to which the interest is redirected
   * @param _user address of the user
   * @return 0 if there is no redirection, an address otherwise
   **/
  function getInterestRedirectionAddress(address _user) external view returns (address);

  /**
   * @dev returns the redirected balance of the user. The redirected balance is the balance
   * redirected by other accounts to the user, that is accrueing interest for him.
   * @param _user address of the user
   * @return the total redirected balance
   **/
  function getRedirectedBalance(address _user) external view returns (uint256);

  /**
   * @dev transfers the underlying asset to the target. Used by the lendingpool to transfer
   * assets in borrow(), redeem() and flashLoan()
   * @param _target the target of the transfer
   * @param _amount the amount to transfer
   * @return the amount transferred
   **/

  function transferUnderlyingTo(address _target, uint256 _amount) external returns (uint256);
}