// SPDX-License-Identifier: MIT

pragma solidity 0.8.9;

/**
 * @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);
}

/**
 * @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);
}

/**
 * @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;
    }
}

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(
        address indexed previousOwner,
        address indexed newOwner
    );

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _transferOwnership(_msgSender());
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        _checkOwner();
        _;
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if the sender is not the owner.
     */
    function _checkOwner() internal view virtual {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby disabling any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _transferOwnership(address(0));
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(
            newOwner != address(0),
            "Ownable: new owner is the zero address"
        );
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

contract BTC20Token is Context, IERC20Metadata, Ownable {
    mapping(address => uint256) private _balances;

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

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private constant _decimals = 18;
    uint256 public constant hardCap = 21_000_000 * (10 ** _decimals); //21 milion

    /**
     * @dev Contract constructor.
     * @param name_ The name of the token.
     * @param symbol_ The symbol of the token.
     * @param _to The initial address to mint the total supply to.
     */
    constructor(string memory name_, string memory symbol_, address _to) {
        _name = name_;
        _symbol = symbol_;
        _mint(_to, hardCap);
    }

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

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

    /**
     * @dev Returns the number of decimals used for token display.
     * @return The number of decimals.
     */
    function decimals() public view virtual override returns (uint8) {
        return _decimals;
    }

    /**
     * @dev Returns the total supply of the token.
     * @return The total supply.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev Returns the balance of the specified account.
     * @param account The address to check the balance for.
     * @return The balance of the account.
     */
    function balanceOf(
        address account
    ) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev Transfers tokens from the caller to a specified recipient.
     * @param recipient The address to transfer tokens to.
     * @param amount The amount of tokens to transfer.
     * @return A boolean value indicating whether the transfer was successful.
     */
    function transfer(
        address recipient,
        uint256 amount
    ) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev Returns the amount of tokens that the spender is allowed to spend on behalf of the owner.
     * @param from The address that approves the spending.
     * @param to The address that is allowed to spend.
     * @return The remaining allowance for the spender.
     */
    function allowance(
        address from,
        address to
    ) public view virtual override returns (uint256) {
        return _allowances[from][to];
    }

    /**
     * @dev Approves the specified address to spend the specified amount of tokens on behalf of the caller.
     * @param to The address to approve the spending for.
     * @param amount The amount of tokens to approve.
     * @return A boolean value indicating whether the approval was successful.
     */
    function approve(
        address to,
        uint256 amount
    ) public virtual override returns (bool) {
        _approve(_msgSender(), to, amount);
        return true;
    }

    /**
     * @dev Transfers tokens from one address to another.
     * @param sender The address to transfer tokens from.
     * @param recipient The address to transfer tokens to.
     * @param amount The amount of tokens to transfer.
     * @return A boolean value indicating whether the transfer was successful.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);

        uint256 currentAllowance = _allowances[sender][_msgSender()];
        require(
            currentAllowance >= amount,
            "ERC20: transfer amount exceeds allowance"
        );
        unchecked {
            _approve(sender, _msgSender(), currentAllowance - amount);
        }

        return true;
    }

    /**
     * @dev Increases the allowance of the specified address to spend tokens on behalf of the caller.
     * @param to The address to increase the allowance for.
     * @param addedValue The amount of tokens to increase the allowance by.
     * @return A boolean value indicating whether the increase was successful.
     */
    function increaseAllowance(
        address to,
        uint256 addedValue
    ) public virtual returns (bool) {
        _approve(_msgSender(), to, _allowances[_msgSender()][to] + addedValue);
        return true;
    }

    /**
     * @dev Decreases the allowance granted by the owner of the tokens to `to` account.
     * @param to The account allowed to spend the tokens.
     * @param subtractedValue The amount of tokens to decrease the allowance by.
     * @return A boolean value indicating whether the operation succeeded.
     */
    function decreaseAllowance(
        address to,
        uint256 subtractedValue
    ) public virtual returns (bool) {
        uint256 currentAllowance = _allowances[_msgSender()][to];
        require(
            currentAllowance >= subtractedValue,
            "ERC20: decreased allowance below zero"
        );
        unchecked {
            _approve(_msgSender(), to, currentAllowance - subtractedValue);
        }

        return true;
    }

    /**
     * @dev Transfers `amount` tokens from `sender` to `recipient`.
     * @param sender The account to transfer tokens from.
     * @param recipient The account to transfer tokens to.
     * @param amount The amount of tokens to transfer.
     */
    function _transfer(
        address sender,
        address recipient,
        uint256 amount
    ) internal virtual {
        require(amount > 0, "ERC20: transfer amount zero");
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        uint256 senderBalance = _balances[sender];
        require(
            senderBalance >= amount,
            "ERC20: transfer amount exceeds balance"
        );
        unchecked {
            _balances[sender] = senderBalance - amount;
        }
        _balances[recipient] += amount;

        emit Transfer(sender, recipient, amount);
    }

    /**
     * @dev Creates `amount` tokens and assigns them to `account`.
     * @param account The account to assign the newly created tokens to.
     * @param amount The amount of tokens to create.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

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

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the total supply.
     * @param account The account to burn tokens from.
     * @param amount The amount of tokens to burn.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

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

        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Destroys `amount` tokens from the caller's account, reducing the total supply.
     * @param amount The amount of tokens to burn.
     */
    function burn(uint256 amount) external {
        _burn(_msgSender(), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `to` over the caller's tokens.
     * @param from The account granting the allowance.
     * @param to The account allowed to spend the tokens.
     * @param amount The amount of tokens to allow.
     */
    function _approve(
        address from,
        address to,
        uint256 amount
    ) internal virtual {
        require(from != address(0), "ERC20: approve from the zero address");
        require(to != address(0), "ERC20: approve to the zero address");

        _allowances[from][to] = amount;
        emit Approval(from, to, amount);
    }
}

{
  "compilationTarget": {
    "BTC20Token.sol": "BTC20Token"
  },
  "evmVersion": "london",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": false,
    "runs": 200
  },
  "remappings": []
}