Contract Address Details

// SPDX-License-Identifier: MIT

/*
This token serves to reward users with an ETH balance on DBK Chain
It is a simple Proof of Balance check that can be repeated every minute
The amount of tokens-per-ETH generated halves every 210k tokens minted
*/

// OpenZeppelin Contracts (last updated v4.9.0) (utils/Context.sol)

pragma solidity ^0.8.0;

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/IERC20.sol)

/**
 * @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 value of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

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

    /**
     * @dev Moves a `value` amount of 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 value) 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 a `value` amount of tokens 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 value) external returns (bool);

    /**
     * @dev Moves a `value` amount of tokens from `from` to `to` using the
     * allowance mechanism. `value` 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 value) external returns (bool);
}

// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/extensions/IERC20Metadata.sol)

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 */
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);
}

// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/ERC20.sol)

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way in which tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.openzeppelin.com/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * The default value of {decimals} is 18. To change this, you should override
 * this function so it returns a different value.
 *
 * We have followed general OpenZeppelin Contracts guidelines: functions revert
 * instead of returning `false` on failure. This behavior is nonetheless
 * conventional and does not conflict with the expectations of ERC20
 * applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {approve}.
 *
 * NOTE: {_} is an array of function parameters that are not used in the function
 * but are kept for compatibility with the original OpenZeppelin interface.
 */
contract ERC20 is Context, IERC20, IERC20Metadata {
    mapping(address => uint256) private _balances;

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

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    /**
     * @dev Sets the values for {name} and {symbol}.
     *
     * All two of these values are immutable: they can only be set once during
     * construction.
     */
    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual override returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5.05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the default value returned by this function, unless
     * it's overridden.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view virtual override returns (uint8) {
        return 18;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - the caller must have a balance of at least `value`.
     */
    function transfer(address to, uint256 value) public virtual override returns (bool) {
        address owner = _msgSender();
        _transfer(owner, to, value);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * NOTE: If `value` is the maximum `uint256`, the allowance is not updated on
     * `transferFrom`. This is semantically equivalent to an infinite approval.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 value) public virtual override returns (bool) {
        address owner = _msgSender();
        _approve(owner, spender, value);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
 *
     * NOTE: Does not update the allowance if the current allowance
     * is the maximum `uint256`.
     *
     * Requirements:
     *
     * - `from` and `to` cannot be the zero address.
     * - `from` must have a balance of at least `value`.
     * - the caller must have allowance for ``from``'s tokens of at least
     * `value`.
     */
    function transferFrom(address from, address to, uint256 value) public virtual override returns (bool) {
        address spender = _msgSender();
        _spendAllowance(from, spender, value);
        _transfer(from, to, value);
        return true;
    }

    /**
     * @dev Moves a `value` amount of tokens from `from` to `to`.
     *
     * This internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `from` must have a balance of at least `value`.
     */
    function _transfer(address from, address to, uint256 value) internal virtual {
        require(from != address(0), "ERC20: transfer from the zero address");
        require(to != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(from, to, value);

        uint256 fromBalance = _balances[from];
        require(fromBalance >= value, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[from] = fromBalance - value;
        }
        _balances[to] += value;

        emit Transfer(from, to, value);

        _afterTokenTransfer(from, to, value);
    }

    /** @dev Creates a `value` amount of tokens and assigns them to `account`, by transferring it from address(0).
     * Relines on the `_update` mechanism
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * NOTE: This function is not virtual, {_update} should be overridden instead.
     */
    function _mint(address account, uint256 value) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, value);

        _totalSupply += value;
        _balances[account] += value;
        emit Transfer(address(0), account, value);

        _afterTokenTransfer(address(0), account, value);
    }

    /**
     * @dev Destroys `value` amount of tokens from `account`, by transferring it to address(0).
     * Relies on the `_update` mechanism.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * NOTE: This function is not virtual, {_update} should be overridden instead
     */
    function _burn(address account, uint256 value) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), value);

        uint256 accountBalance = _balances[account];
        require(accountBalance >= value, "ERC20: burn amount exceeds balance");
        unchecked {
            _balances[account] = accountBalance - value;
        }
        _totalSupply -= value;

        emit Transfer(account, address(0), value);

        _afterTokenTransfer(account, address(0), value);
    }

    /**
     * @dev Sets `value` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 value) 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] = value;
        emit Approval(owner, spender, value);
    }

    /**
     * @dev Updates `owner` s allowance for `spender` based on spent `value`.
     *
     * Does not update the allowance amount in case of infinite allowance.
     * Revert if not enough allowance is available.
     *
     * Might emit an {Approval} event.
     */
    function _spendAllowance(address owner, address spender, uint256 value) internal virtual {
        uint256 currentAllowance = allowance(owner, spender);
        if (currentAllowance != type(uint256).max) {
            require(currentAllowance >= value, "ERC20: insufficient allowance");
            unchecked {
                _approve(owner, spender, currentAllowance - value);
            }
        }
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `value` of ``from``'s tokens
     * will be transferred to `to`.
     * - when `from` is zero, `value` tokens will be minted for `to`.
     * - when `to` is zero, `value` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 value) internal virtual {}

    /**
     * @dev Hook that is called after any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `value` of ``from``'s tokens
     * will be transferred to `to`.
     * - when `from` is zero, `value` tokens will be minted for `to`.
     * - when `to` is zero, `value` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _afterTokenTransfer(address from, address to, uint256 value) internal virtual {}
}

// OpenZeppelin Contracts (last updated v4.9.0) (security/ReentrancyGuard.sol)

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    /**
     * @dev Unauthorized reentrant call.
     */
    error ReentrancyGuardReentrantCall();

    constructor() {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and making it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        _nonReentrantBefore();
        _;
        _nonReentrantAfter();
    }

    function _nonReentrantBefore() private {
        // On the first call to nonReentrant, _status will be _NOT_ENTERED
        if (_status == _ENTERED) {
            revert ReentrancyGuardReentrantCall();
        }

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;
    }

    function _nonReentrantAfter() private {
        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Returns true if the reentrancy guard is currently set to "entered", which indicates there is a
     * `nonReentrant` function in the call stack.
     */
    function _reentrancyGuardEntered() internal view returns (bool) {
        return _status == _ENTERED;
    }
}


contract MintableToken is ERC20, ReentrancyGuard {
    uint256 public constant MAX_SUPPLY = 21000000 * 10**18; // 21 million tokens
    uint256 public constant MIN_ETH_BALANCE = 0.01 ether;
    uint256 public constant MINT_COOLDOWN = 60 seconds; // 1 minute
    uint256 public constant INITIAL_MULTIPLIER = 65536; 
    uint256 public constant HALVING_INTERVAL = 210000 * 10**18; // Halve every 210k tokens minted
    
    uint256 public currentMultiplier = INITIAL_MULTIPLIER;
    uint256 public nextHalvingThreshold = HALVING_INTERVAL;
    uint256 public totalMinted = 0;
    
    mapping(address => uint256) public lastMintTime;
    
    event Halving(uint256 newMultiplier, uint256 nextThreshold);
    
    constructor() ERC20("Mine on DBK Chain", "MINE") {}
    
    function mint() external nonReentrant {
        require(totalSupply() < MAX_SUPPLY, "Max supply reached");
        require(msg.sender.balance >= MIN_ETH_BALANCE, "Insufficient ETH balance");
        require(block.timestamp >= lastMintTime[msg.sender] + MINT_COOLDOWN, "Mint cooldown active");
        
        // Calculate mint amount based on ETH balance and current multiplier
        uint256 ethBalance = msg.sender.balance;
        uint256 mintAmount = ethBalance * currentMultiplier;
        
        // Check if we need to halve the multiplier
        if (totalMinted + mintAmount >= nextHalvingThreshold && currentMultiplier > 1) {
            _halveMultiplier();
        }
        
        // Ensure we don't exceed max supply
        uint256 remainingSupply = MAX_SUPPLY - totalSupply();
        if (mintAmount > remainingSupply) {
            mintAmount = remainingSupply;
        }
        
        lastMintTime[msg.sender] = block.timestamp;
        totalMinted += mintAmount;
        _mint(msg.sender, mintAmount);
    }
    
    function _halveMultiplier() internal {
        // Halve the multiplier (minimum 1)
        uint256 newMultiplier = currentMultiplier / 2;
        if (newMultiplier < 1) {
            newMultiplier = 1;
        }
        
        currentMultiplier = newMultiplier;
        nextHalvingThreshold += HALVING_INTERVAL;
        
        emit Halving(newMultiplier, nextHalvingThreshold);
    }
    
    // Helper function to check if an address can mint
    function canMint(address account) external view returns (bool) {
        return block.timestamp >= lastMintTime[account] + MINT_COOLDOWN && 
               account.balance >= MIN_ETH_BALANCE &&
               totalSupply() < MAX_SUPPLY;
    }
    
    // Helper function to get next mint time for an address
    function getNextMintTime(address account) external view returns (uint256) {
        return lastMintTime[account] + MINT_COOLDOWN;
    }
    
    // Helper function to calculate mint amount for an address
    function getMintAmount(address account) external view returns (uint256) {
        uint256 ethBalance = account.balance;
        uint256 mintAmount = ethBalance * currentMultiplier;
        uint256 remainingSupply = MAX_SUPPLY - totalSupply();
        return mintAmount > remainingSupply ? remainingSupply : mintAmount;
    }
    
    // Get current emission details
    function getEmissionInfo() external view returns (
        uint256 multiplier,
        uint256 nextHalvingAt,
        uint256 tokensUntilHalving,
        uint256 halvingCount
    ) {
        multiplier = currentMultiplier;
        nextHalvingAt = nextHalvingThreshold;
        tokensUntilHalving = nextHalvingThreshold > totalMinted ? nextHalvingThreshold - totalMinted : 0;
        halvingCount = (nextHalvingThreshold - HALVING_INTERVAL) / HALVING_INTERVAL;
    }
    
    // Override to prevent transfers to zero address
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual override {
        super._beforeTokenTransfer(from, to, amount);
        require(to != address(0), "MintableToken: transfer to the zero address");
    }
}