// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);

    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `from` to `to` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address from, address to, uint256 amount) external returns (bool);
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)

pragma solidity ^0.8.0;

import "../IERC20.sol";

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}

// SPDX-License-Identifier: AGPL-3.0
pragma solidity 0.8.19;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

interface IsPER is IERC20 {
    function rebase(uint256 amount_, uint epoch_) external returns (uint256);
    function circulatingSupply() external view returns (uint256);
    function gonsForBalance(uint amount) external view returns (uint);
    function balanceForGons(uint gons) external view returns (uint);
    function index() external view returns (uint);
}

// SPDX-License-Identifier: AGPL-3.0
pragma solidity 0.8.19;

import "@openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol";
import "./interface/IsPER.sol";

interface IPER {
    function uniswapV2Pair() external view returns (address);
    function burnFrom(address account, uint256 amount) external;
}

interface ITreasury {
    function mint() external;
}

/// @title   PERStaking
/// @notice  PER Staking
contract PERStaking {
    /// DATA STRUCTURES ///

    struct Epoch {
        uint256 length; // in seconds
        uint256 number; // since inception
        uint256 end; // timestamp
        uint256 distribute; // amount
    }

    /// STATE VARIABLES ///

    /// @notice PER address
    IERC20 public immutable PER;
    /// @notice sPER address
    IsPER public immutable sPER;

    /// @notice Current epoch details
    Epoch public epoch;

    /// @notice treasury address
    ITreasury public immutable treasury;

    /// CONSTRUCTOR ///

    /// @param _PER   Address of PER
    /// @param _sPER  Address of sPER
    constructor(address _PER, address _sPER, address _treasury) {
        PER = IERC20(_PER);
        sPER = IsPER(_sPER);
        treasury = ITreasury(_treasury);

        epoch = Epoch({length: 8 hours, number: 0, end: block.timestamp + 8 hours, distribute: 0});
    }

    /// MUTATIVE FUNCTIONS ///

    /// @notice stake PER
    /// @param _to address
    /// @param _amount uint
    function stake(address _to, uint256 _amount) external {
        rebase();
        PER.transferFrom(msg.sender, address(this), _amount);
        sPER.transfer(_to, _amount);
    }

    /// @notice redeem sPER for PER
    /// @param _to address
    /// @param _amount uint
    function unstake(address _to, uint256 _amount, bool _rebase) external {
        if (_rebase) rebase();
        sPER.transferFrom(msg.sender, address(this), _amount);
        require(_amount <= PER.balanceOf(address(this)), "Insufficient PER balance in contract");
        PER.transfer(_to, _amount);
    }

    ///@notice Trigger rebase if epoch over
    function rebase() public {
        if (epoch.end <= block.timestamp) {
            sPER.rebase(epoch.distribute, epoch.number);

            epoch.end = epoch.end + epoch.length;
            epoch.number++;

            if (address(treasury) != address(0)) {
                treasury.mint();
            }

            uint256 balance = PER.balanceOf(address(this));
            uint256 staked = sPER.circulatingSupply();

            if (balance <= staked) {
                epoch.distribute = 0;
            } else {
                epoch.distribute = balance - staked;
            }
        }
    }

    /// INTERNAL FUNCTIONS ///

    /// @notice         Send sPER upon staking
    /// @param _to      Address of where sending sPER
    /// @param _amount  Amount of sPER to send
    /// @return _sent   Amount of sPER sent
    function _send(address _to, uint256 _amount) internal returns (uint256 _sent) {
        sPER.transfer(_to, _amount); // send as sPER (equal unit as PER)
        return _amount;
    }

    /// VIEW FUNCTIONS ///

    /// @notice           Returns econds until the next epoch begins
    /// @return seconds_  Till next epoch
    function secondsToNextEpoch() external view returns (uint256 seconds_) {
        if (epoch.end < block.timestamp) return 0;
        return epoch.end - block.timestamp;
    }
}

{
  "compilationTarget": {
    "contracts/launchpad/rebasing/Staking.sol": "PERStaking"
  },
  "evmVersion": "paris",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": true,
    "runs": 1000
  },
  "remappings": []
}