// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.12;

/**
 * @title IStableDebtToken
 * @notice Defines the interface for the stable debt token
 * @dev It does not inherit from IERC20 to save in code size
 * @author Aave
 **/

interface IStableDebtToken {
  /**
   * @dev Emitted when new stable debt is minted
   * @param user The address of the user who triggered the minting
   * @param onBehalfOf The recipient of stable debt tokens
   * @param amount The amount minted
   * @param currentBalance The current balance of the user
   * @param balanceIncrease The increase in balance since the last action of the user
   * @param newRate The rate of the debt after the minting
   * @param avgStableRate The new average stable rate after the minting
   * @param newTotalSupply The new total supply of the stable debt token after the action
   **/
  event Mint(
    address indexed user,
    address indexed onBehalfOf,
    uint256 amount,
    uint256 currentBalance,
    uint256 balanceIncrease,
    uint256 newRate,
    uint256 avgStableRate,
    uint256 newTotalSupply
  );

  /**
   * @dev Emitted when new stable debt is burned
   * @param user The address of the user
   * @param amount The amount being burned
   * @param currentBalance The current balance of the user
   * @param balanceIncrease The the increase in balance since the last action of the user
   * @param avgStableRate The new average stable rate after the burning
   * @param newTotalSupply The new total supply of the stable debt token after the action
   **/
  event Burn(
    address indexed user,
    uint256 amount,
    uint256 currentBalance,
    uint256 balanceIncrease,
    uint256 avgStableRate,
    uint256 newTotalSupply
  );

  /**
   * @dev Mints debt token to the `onBehalfOf` address.
   * - The resulting rate is the weighted average between the rate of the new debt
   * and the rate of the previous debt
   * @param user The address receiving the borrowed underlying, being the delegatee in case
   * of credit delegate, or same as `onBehalfOf` otherwise
   * @param onBehalfOf The address receiving the debt tokens
   * @param amount The amount of debt tokens to mint
   * @param rate The rate of the debt being minted
   **/
  function mint(
    address user,
    address onBehalfOf,
    uint256 amount,
    uint256 rate
  ) external returns (bool);

  /**
   * @dev Burns debt of `user`
   * - The resulting rate is the weighted average between the rate of the new debt
   * and the rate of the previous debt
   * @param user The address of the user getting his debt burned
   * @param amount The amount of debt tokens getting burned
   **/
  function burn(address user, uint256 amount) external;

  /**
   * @dev Returns the average rate of all the stable rate loans.
   * @return The average stable rate
   **/
  function getAverageStableRate() external view returns (uint256);

  /**
   * @dev Returns the stable rate of the user debt
   * @return The stable rate of the user
   **/
  function getUserStableRate(address user) external view returns (uint256);

  /**
   * @dev Returns the timestamp of the last update of the user
   * @return The timestamp
   **/
  function getUserLastUpdated(address user) external view returns (uint40);

  /**
   * @dev Returns the principal, the total supply and the average stable rate
   **/
  function getSupplyData()
    external
    view
    returns (
      uint256,
      uint256,
      uint256,
      uint40
    );

  /**
   * @dev Returns the timestamp of the last update of the total supply
   * @return The timestamp
   **/
  function getTotalSupplyLastUpdated() external view returns (uint40);

  /**
   * @dev Returns the total supply and the average stable rate
   **/
  function getTotalSupplyAndAvgRate() external view returns (uint256, uint256);

  /**
   * @dev Returns the principal debt balance of the user
   * @return The debt balance of the user since the last burn/mint action
   **/
  function principalBalanceOf(address user) external view returns (uint256);
}