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

import {ILendingPool} from '../../interfaces/ILendingPool.sol';
import {
  VersionedInitializable
} from '../../libraries/aave-upgradeability/VersionedInitializable.sol';
import {IncentivizedERC20} from '../IncentivizedERC20.sol';
import {Errors} from '../../libraries/helpers/Errors.sol';

/**
 * @title DebtTokenBase
 * @notice Base contract for different types of debt tokens, like StableDebtToken or VariableDebtToken
 * @author Aave
 */

abstract contract DebtTokenBase is IncentivizedERC20, VersionedInitializable {
  event BorrowAllowanceDelegated(
    address indexed fromUser,
    address indexed toUser,
    address asset,
    uint256 amount
  );

  address public immutable UNDERLYING_ASSET_ADDRESS;
  ILendingPool public immutable POOL;

  mapping(address => mapping(address => uint256)) internal _borrowAllowances;

  /**
   * @dev Only lending pool can call functions marked by this modifier
   **/
  modifier onlyLendingPool {
    require(_msgSender() == address(POOL), Errors.AT_CALLER_MUST_BE_LENDING_POOL);
    _;
  }

  /**
   * @dev The metadata of the token will be set on the proxy, that the reason of
   * passing "NULL" and 0 as metadata
   */
  constructor(
    address pool,
    address underlyingAssetAddress,
    string memory name,
    string memory symbol,
    address incentivesController
  ) public IncentivizedERC20(name, symbol, 18, incentivesController) {
    POOL = ILendingPool(pool);
    UNDERLYING_ASSET_ADDRESS = underlyingAssetAddress;
  }

  /**
   * @dev Initializes the debt token.
   * @param name The name of the token
   * @param symbol The symbol of the token
   * @param decimals The decimals of the token
   */
  function initialize(
    uint8 decimals,
    string memory name,
    string memory symbol
  ) public initializer {
    _setName(name);
    _setSymbol(symbol);
    _setDecimals(decimals);
  }

  /**
   * @dev delegates borrowing power to a user on the specific debt token
   * @param delegatee the address receiving the delegated borrowing power
   * @param amount the maximum amount being delegated. Delegation will still
   * respect the liquidation constraints (even if delegated, a delegatee cannot
   * force a delegator HF to go below 1)
   **/
  function approveDelegation(address delegatee, uint256 amount) external {
    _borrowAllowances[_msgSender()][delegatee] = amount;
    emit BorrowAllowanceDelegated(_msgSender(), delegatee, UNDERLYING_ASSET_ADDRESS, amount);
  }

  /**
   * @dev returns the borrow allowance of the user
   * @param fromUser The user to giving allowance
   * @param toUser The user to give allowance to
   * @return the current allowance of toUser
   **/
  function borrowAllowance(address fromUser, address toUser) external view returns (uint256) {
    return _borrowAllowances[fromUser][toUser];
  }

  /**
   * @dev Being non transferrable, the debt token does not implement any of the
   * standard ERC20 functions for transfer and allowance.
   **/
  function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
    recipient;
    amount;
    revert('TRANSFER_NOT_SUPPORTED');
  }

  function allowance(address owner, address spender)
    public
    virtual
    override
    view
    returns (uint256)
  {
    owner;
    spender;
    revert('ALLOWANCE_NOT_SUPPORTED');
  }

  function approve(address spender, uint256 amount) public virtual override returns (bool) {
    spender;
    amount;
    revert('APPROVAL_NOT_SUPPORTED');
  }

  function transferFrom(
    address sender,
    address recipient,
    uint256 amount
  ) public virtual override returns (bool) {
    sender;
    recipient;
    amount;
    revert('TRANSFER_NOT_SUPPORTED');
  }

  function increaseAllowance(address spender, uint256 addedValue)
    public
    virtual
    override
    returns (bool)
  {
    spender;
    addedValue;
    revert('ALLOWANCE_NOT_SUPPORTED');
  }

  function decreaseAllowance(address spender, uint256 subtractedValue)
    public
    virtual
    override
    returns (bool)
  {
    spender;
    subtractedValue;
    revert('ALLOWANCE_NOT_SUPPORTED');
  }

  function _decreaseBorrowAllowance(
    address delegator,
    address delegatee,
    uint256 amount
  ) internal {
    uint256 newAllowance = _borrowAllowances[delegator][delegatee].sub(
      amount,
      Errors.BORROW_ALLOWANCE_NOT_ENOUGH
    );

    _borrowAllowances[delegator][delegatee] = newAllowance;

    emit BorrowAllowanceDelegated(delegator, delegatee, UNDERLYING_ASSET_ADDRESS, newAllowance);
  }
}