// SPDX-License-Identifier: Apache-2.0
pragma solidity ^0.8.0;

interface IERC20 {
    function symbol() external view returns (string memory);

    function balanceOf(address account) external view returns (uint256);

    // Note this is non standard but nearly all ERC20 have exposed decimal functions
    function decimals() external view returns (uint8);

    function transfer(address recipient, uint256 amount)
        external
        returns (bool);

    function allowance(address owner, address spender)
        external
        view
        returns (uint256);

    function approve(address spender, uint256 amount) external returns (bool);

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
}

// Forked from openzepplin
// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "./IERC20.sol";

/**
 * @dev Interface of the ERC20 Permit extension allowing approvals to be made via signatures, as defined in
 * https://eips.ethereum.org/EIPS/eip-2612[EIP-2612].
 *
 * Adds the {permit} method, which can be used to change an account's ERC20 allowance (see {IERC20-allowance}) by
 * presenting a message signed by the account. By not relying on `{IERC20-approve}`, the token holder account doesn't
 * need to send a transaction, and thus is not required to hold Ether at all.
 */
interface IERC20Permit is IERC20 {
    /**
     * @dev Sets `value` as the allowance of `spender` over `owner`'s tokens,
     * given `owner`'s signed approval.
     *
     * IMPORTANT: The same issues {IERC20-approve} has related to transaction
     * ordering also apply here.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `deadline` must be a timestamp in the future.
     * - `v`, `r` and `s` must be a valid `secp256k1` signature from `owner`
     * over the EIP712-formatted function arguments.
     * - the signature must use ``owner``'s current nonce (see {nonces}).
     *
     * For more information on the signature format, see the
     * https://eips.ethereum.org/EIPS/eip-2612#specification[relevant EIP
     * section].
     */
    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external;

    /**
     * @dev Returns the current nonce for `owner`. This value must be
     * included whenever a signature is generated for {permit}.
     *
     * Every successful call to {permit} increases ``owner``'s nonce by one. This
     * prevents a signature from being used multiple times.
     */
    function nonces(address owner) external view returns (uint256);

    /**
     * @dev Returns the domain separator used in the encoding of the signature for `permit`, as defined by {EIP712}.
     */
    // solhint-disable-next-line func-name-mixedcase
    function DOMAIN_SEPARATOR() external view returns (bytes32);
}

// SPDX-License-Identifier: Apache-2.0
pragma solidity ^0.8.0;

import "./IERC20Permit.sol";

interface IInterestToken is IERC20Permit {
    function mint(address _account, uint256 _amount) external;

    function burn(address _account, uint256 _amount) external;
}

// SPDX-License-Identifier: Apache-2.0
pragma solidity ^0.8.0;

import "./IERC20Permit.sol";
import "./IInterestToken.sol";

interface ITranche is IERC20Permit {
    function deposit(uint256 _shares, address destination)
        external
        returns (uint256, uint256);

    function prefundedDeposit(address _destination)
        external
        returns (uint256, uint256);

    function withdrawPrincipal(uint256 _amount, address _destination)
        external
        returns (uint256);

    function withdrawInterest(uint256 _amount, address _destination)
        external
        returns (uint256);

    function interestToken() external view returns (IInterestToken);

    function interestSupply() external view returns (uint128);
}

// SPDX-License-Identifier: Apache-2.0
pragma solidity ^0.8.0;

import "./libraries/ERC20Permit.sol";
import "./libraries/DateString.sol";

import "./interfaces/IInterestToken.sol";
import "./interfaces/ITranche.sol";

contract InterestToken is ERC20Permit, IInterestToken {
    // The tranche address which controls the minting
    ITranche public immutable tranche;

    /// @dev Initializes the ERC20 and writes the correct names
    /// @param _tranche The tranche contract address
    /// @param _strategySymbol The symbol of the associated WrappedPosition contract
    /// @param _timestamp The unlock time on the tranche
    /// @param _decimals The decimal encoding for this token
    constructor(
        address _tranche,
        string memory _strategySymbol,
        uint256 _timestamp,
        uint8 _decimals
    )
        ERC20Permit(
            _processName("Element Yield Token ", _strategySymbol, _timestamp),
            _processSymbol("eY", _strategySymbol, _timestamp)
        )
    {
        tranche = ITranche(_tranche);
        _setupDecimals(_decimals);
    }

    /// @notice We use this function to add the date to the name string
    /// @param _name start of the name
    /// @param _strategySymbol the strategy symbol
    /// @param _timestamp the unix second timestamp to be encoded and added to the end of the string
    function _processName(
        string memory _name,
        string memory _strategySymbol,
        uint256 _timestamp
    ) internal returns (string memory) {
        // Set the name in the super
        name = _name;
        // Use the library to write the rest
        DateString._encodeAndWriteTimestamp(_strategySymbol, _timestamp, name);
        // load and return the name
        return name;
    }

    /// @notice We use this function to add the date to the name string
    /// @param _symbol start of the symbol
    /// @param _strategySymbol the strategy symbol
    /// @param _timestamp the unix second timestamp to be encoded and added to the end of the string
    function _processSymbol(
        string memory _symbol,
        string memory _strategySymbol,
        uint256 _timestamp
    ) internal returns (string memory) {
        // Set the symbol in the super
        symbol = _symbol;
        // Use the library to write the rest
        DateString._encodeAndWriteTimestamp(
            _strategySymbol,
            _timestamp,
            symbol
        );
        // load and return the name
        return symbol;
    }

    /// @dev Aliasing of the lookup method for the supply of yield tokens which
    ///      improves our ERC20 compatibility.
    /// @return The total supply of yield tokens
    function totalSupply() external view returns (uint256) {
        return uint256(tranche.interestSupply());
    }

    /// @dev Prevents execution if the caller isn't the tranche
    modifier onlyMintAuthority() {
        require(
            msg.sender == address(tranche),
            "caller is not an authorized minter"
        );
        _;
    }

    /// @dev Mints tokens to an address
    /// @param _account The account to mint to
    /// @param _amount The amount to mint
    function mint(address _account, uint256 _amount)
        external
        override
        onlyMintAuthority
    {
        _mint(_account, _amount);
    }

    /// @dev Burns tokens from an address
    /// @param _account The account to burn from
    /// @param _amount The amount of token to burn
    function burn(address _account, uint256 _amount)
        external
        override
        onlyMintAuthority
    {
        _burn(_account, _amount);
    }
}