// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.12;
pragma experimental ABIEncoderV2;

import {ILendingPool} from '../../../interfaces/ILendingPool.sol';
import {Errors} from '../../libraries/helpers/Errors.sol';
import {PoolTokenBase} from './PoolTokenBase.sol';

import {IERC20} from '../../../dependencies/openzeppelin/contracts/IERC20.sol';
import {ERC20Events} from '../../../dependencies/openzeppelin/contracts/ERC20Events.sol';

import {SafeERC20} from '../../../dependencies/openzeppelin/contracts/SafeERC20.sol';
import {IDepositToken} from '../../../interfaces/IDepositToken.sol';
import {WadRayMath} from '../../../tools/math/WadRayMath.sol';
import {PermitForERC20} from '../../../misc/PermitForERC20.sol';

/**
 * @title Augmented Finance ERC20 deposit token (agToken)
 * @dev Implementation of the interest bearing token for the Augmented Finance protocol
 */
abstract contract DepositTokenBase is
  PoolTokenBase('DEPOSIT_STUB', 'DEPOSIT_STUB', 0),
  PermitForERC20,
  ERC20Events,
  IDepositToken
{
  using WadRayMath for uint256;
  using SafeERC20 for IERC20;

  mapping(address => mapping(address => uint256)) private _allowances;
  address internal _treasury;

  /**
   * @dev Returns the allowance of spender on the tokens owned by owner
   * @param owner The owner of the tokens
   * @param spender The user allowed to spend the owner's tokens
   * @return The amount of owner's tokens spender is allowed to spend
   **/
  function allowance(address owner, address spender)
    public
    view
    virtual
    override
    returns (uint256)
  {
    return _allowances[owner][spender];
  }

  /**
   * @dev Allows `spender` to spend the tokens owned by _msgSender()
   * @param spender The user allowed to spend _msgSender() tokens
   * @return `true`
   **/
  function approve(address spender, uint256 amount) public virtual override returns (bool) {
    _approve(_msgSender(), spender, amount);
    return true;
  }

  /**
   * @dev Atomically increases the allowance granted to `spender` by the caller.
   *
   * This is an alternative to {approve} that can be used as a mitigation for
   * problems described in {IERC20-approve}.
   *
   * Emits an {Approval} event indicating the updated allowance.
   *
   * Requirements:
   *
   * - `spender` cannot be the zero address.
   */
  function increaseAllowance(address spender, uint256 addedValue) public override returns (bool) {
    _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
    return true;
  }

  /**
   * @dev Atomically decreases the allowance granted to `spender` by the caller.
   *
   * This is an alternative to {approve} that can be used as a mitigation for
   * problems described in {IERC20-approve}.
   *
   * Emits an {Approval} event indicating the updated allowance.
   *
   * Requirements:
   *
   * - `spender` cannot be the zero address.
   * - `spender` must have allowance for the caller of at least
   * `subtractedValue`.
   */
  function decreaseAllowance(address spender, uint256 subtractedValue)
    public
    override
    returns (bool)
  {
    _approve(
      _msgSender(),
      spender,
      _allowances[_msgSender()][spender].sub(
        subtractedValue,
        'ERC20: decreased allowance below zero'
      )
    );
    return true;
  }

  /**
   * @dev Burns aTokens from `user` and sends the equivalent amount of underlying to `receiverOfUnderlying`
   * - Only callable by the LendingPool, as extra state updates there need to be managed
   * @param user The owner of the aTokens, getting them burned
   * @param receiverOfUnderlying The address that will receive the underlying
   * @param amount The amount being burned
   * @param index The new liquidity index of the reserve
   **/
  function burn(
    address user,
    address receiverOfUnderlying,
    uint256 amount,
    uint256 index
  ) external override onlyLendingPool {
    uint256 amountScaled = amount.rayDiv(index);
    require(amountScaled != 0, Errors.CT_INVALID_BURN_AMOUNT);
    _burnBalance(user, amountScaled, index);

    IERC20(_underlyingAsset).safeTransfer(receiverOfUnderlying, amount);

    emit Transfer(user, address(0), amount);
    emit Burn(user, receiverOfUnderlying, amount, index);
  }

  /**
   * @dev Mints `amount` aTokens to `user`
   * - Only callable by the LendingPool, as extra state updates there need to be managed
   * @param user The address receiving the minted tokens
   * @param amount The amount of tokens getting minted
   * @param index The new liquidity index of the reserve
   * @return `true` if the the previous balance of the user was 0
   */
  function mint(
    address user,
    uint256 amount,
    uint256 index
  ) external override onlyLendingPool returns (bool) {
    uint256 previousBalance = super.balanceOf(user);

    uint256 amountScaled = amount.rayDiv(index);
    require(amountScaled != 0, Errors.CT_INVALID_MINT_AMOUNT);
    _mintBalance(user, amountScaled, index);

    emit Transfer(address(0), user, amount);
    emit Mint(user, amount, index);

    return previousBalance == 0;
  }

  function setTreasury(address treasury) external override onlyLendingPool {
    _treasury = treasury;
  }

  /**
   * @dev Mints aTokens to the reserve treasury
   * - Only callable by the LendingPool
   * @param amount The amount of tokens getting minted
   * @param index The new liquidity index of the reserve
   */
  function mintToTreasury(uint256 amount, uint256 index) external override onlyLendingPool {
    if (amount == 0) {
      return;
    }

    address treasury = _treasury;

    // Compared to the normal mint, we don't check for rounding errors.
    // The amount to mint can easily be very small since it is a fraction of the interest ccrued.
    // In that case, the treasury will experience a (very small) loss, but it
    // wont cause potentially valid transactions to fail.
    _mintBalance(treasury, amount.rayDiv(index), index);

    emit Transfer(address(0), treasury, amount);
    emit Mint(treasury, amount, index);
  }

  /**
   * @dev Transfers aTokens in the event of a borrow being liquidated, in case the liquidators reclaims the aToken
   * - Only callable by the LendingPool
   * @param from The address getting liquidated, current owner of the aTokens
   * @param to The recipient
   * @param value The amount of tokens getting transferred
   **/
  function transferOnLiquidation(
    address from,
    address to,
    uint256 value
  ) external override onlyLendingPool {
    // Being a normal transfer, the Transfer() and BalanceTransfer() are emitted
    // so no need to emit a specific event here
    _transfer(from, to, value, false);

    emit Transfer(from, to, value);
  }

  /**
   * @dev Calculates the balance of the user: principal balance + interest generated by the principal
   * @param user The user whose balance is calculated
   * @return The balance of the user
   **/
  function balanceOf(address user) public view override(IERC20, PoolTokenBase) returns (uint256) {
    return super.balanceOf(user).rayMul(_pool.getReserveNormalizedIncome(_underlyingAsset));
  }

  /**
   * @dev Returns the scaled balance of the user. The scaled balance is the sum of all the
   * updated stored balance divided by the reserve's liquidity index at the moment of the update
   * @param user The user whose balance is calculated
   * @return The scaled balance of the user
   **/
  function scaledBalanceOf(address user) external view override returns (uint256) {
    return super.balanceOf(user);
  }

  /**
   * @dev Returns the scaled balance of the user and the scaled total supply.
   * @param user The address of the user
   * @return The scaled balance of the user
   * @return The scaled balance and the scaled total supply
   **/
  function getScaledUserBalanceAndSupply(address user)
    external
    view
    override
    returns (uint256, uint256)
  {
    return (super.balanceOf(user), super.totalSupply());
  }

  /**
   * @dev calculates the total supply of the specific aToken
   * since the balance of every single user increases over time, the total supply
   * does that too.
   * @return the current total supply
   **/
  function totalSupply() public view override(IERC20, PoolTokenBase) returns (uint256) {
    uint256 currentSupplyScaled = super.totalSupply();

    if (currentSupplyScaled == 0) {
      return 0;
    }

    return currentSupplyScaled.rayMul(_pool.getReserveNormalizedIncome(_underlyingAsset));
  }

  /**
   * @dev Returns the scaled total supply of the variable debt token. Represents sum(debt/index)
   * @return the scaled total supply
   **/
  function scaledTotalSupply() public view virtual override returns (uint256) {
    return super.totalSupply();
  }

  /**
   * @dev Returns the address of the Aave treasury, receiving the fees on this aToken
   **/
  function RESERVE_TREASURY_ADDRESS() public view returns (address) {
    return _treasury;
  }

  /**
   * @dev Executes a transfer of tokens from _msgSender() to recipient
   * @param recipient The recipient of the tokens
   * @param amount The amount of tokens being transferred
   * @return `true` if the transfer succeeds, `false` otherwise
   **/
  function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
    _transfer(_msgSender(), recipient, amount, true);
    emit Transfer(_msgSender(), recipient, amount);
    return true;
  }

  /**
   * @dev Executes a transfer of token from sender to recipient, if _msgSender() is allowed to do so
   * @param sender The owner of the tokens
   * @param recipient The recipient of the tokens
   * @param amount The amount of tokens being transferred
   * @return `true` if the transfer succeeds, `false` otherwise
   **/
  function transferFrom(
    address sender,
    address recipient,
    uint256 amount
  ) public virtual override returns (bool) {
    _transfer(sender, recipient, amount, true);
    _approve(
      sender,
      _msgSender(),
      _allowances[sender][_msgSender()].sub(amount, 'ERC20: transfer amount exceeds allowance')
    );
    emit Transfer(sender, recipient, amount);
    return true;
  }

  /**
   * @dev Transfers the underlying asset to `target`. Used by the LendingPool to transfer
   * assets in borrow(), withdraw() and flashLoan()
   * @param target The recipient of the aTokens
   * @param amount The amount getting transferred
   * @return The amount transferred
   **/
  function transferUnderlyingTo(address target, uint256 amount)
    external
    override
    onlyLendingPool
    returns (uint256)
  {
    IERC20(_underlyingAsset).safeTransfer(target, amount);
    return amount;
  }

  /**
   * @dev Invoked to execute actions on the aToken side after a repayment.
   * @param user The user executing the repayment
   * @param amount The amount getting repaid
   **/
  function handleRepayment(address user, uint256 amount) external override onlyLendingPool {}

  /**
   * @dev Transfers the aTokens between two users. Validates the transfer
   * (ie checks for valid HF after the transfer) if required
   * @param from The source address
   * @param to The destination address
   * @param amount The amount getting transferred
   * @param validate `true` if the transfer needs to be validated
   **/
  function _transfer(
    address from,
    address to,
    uint256 amount,
    bool validate
  ) internal {
    address underlyingAsset = _underlyingAsset;
    ILendingPool pool = _pool;

    uint256 index = pool.getReserveNormalizedIncome(underlyingAsset);

    uint256 fromBalanceBefore = super.balanceOf(from).rayMul(index);
    uint256 toBalanceBefore = super.balanceOf(to).rayMul(index);

    super._transferBalance(from, to, amount.rayDiv(index), index);

    if (validate) {
      pool.finalizeTransfer(underlyingAsset, from, to, amount, fromBalanceBefore, toBalanceBefore);
    }

    emit BalanceTransfer(from, to, amount, index);
  }

  function _approveByPermit(
    address owner,
    address spender,
    uint256 amount
  ) internal override {
    _approve(owner, spender, amount);
  }

  function _getPermitDomainName() internal view override returns (bytes memory) {
    return bytes(super.name());
  }

  function _approve(
    address owner,
    address spender,
    uint256 amount
  ) internal virtual {
    require(owner != address(0), 'ERC20: approve from the zero address');
    require(spender != address(0), 'ERC20: approve to the zero address');

    _allowances[owner][spender] = amount;
    emit Approval(owner, spender, amount);
  }
}