pragma solidity >=0.4.22 <0.6.0;

/**
 * @title ERC20 interface
 * @dev see https://eips.ethereum.org/EIPS/eip-20
 */
interface IERC20 {
    function transfer(address to, uint256 value) external returns (bool);

    function approve(address spender, uint256 value) external returns (bool);

    function transferFrom(address from, address to, uint256 value) external returns (bool);

    function totalSupply() external view returns (uint256);

    function balanceOf(address who) external view returns (uint256);

    function allowance(address owner, address spender) external view returns (uint256);

    event Transfer(address indexed from, address indexed to, uint256 value);

    event Approval(address indexed owner, address indexed spender, uint256 value);
}

/**
 * @title SafeMath
 * @dev Unsigned math operations with safety checks that revert on error.
 */
library SafeMath {
    /**
     * @dev Multiplies two unsigned integers, reverts on overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b);

        return c;
    }

    /**
     * @dev Integer division of two unsigned integers truncating the quotient, reverts on division by zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Subtracts two unsigned integers, reverts on overflow (i.e. if subtrahend is greater than minuend).
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Adds two unsigned integers, reverts on overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a);

        return c;
    }

    /**
     * @dev Divides two unsigned integers and returns the remainder (unsigned integer modulo),
     * reverts when dividing by zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0);
        return a % b;
    }
}

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {
    address payable private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev The Ownable constructor sets the original `owner` of the contract to the sender
     * account.
     */
    constructor () internal {
        _owner = msg.sender;
        emit OwnershipTransferred(address(0), _owner);
    }

    /**
     * @return the address of the owner.
     */
    function owner() public view returns (address payable) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner(),"Invalid owner");
        _;
    }

    /**
     * @return true if `msg.sender` is the owner of the contract.
     */
    function isOwner() public view returns (bool) {
        return msg.sender == _owner;
    }

    /**
     * @dev Allows the current owner to transfer control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function transferOwnership(address payable newOwner) public onlyOwner {
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function _transferOwnership(address payable newOwner) internal {
        require(newOwner != address(0));
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

/**
 * @title ERC20Detailed token
 * @dev The decimals are only for visualization purposes.
 * All the operations are done using the smallest and indivisible token unit,
 * just as on Ethereum all the operations are done in wei.
 */
contract ERC20Detailed is IERC20 {
    string private _name;
    string private _symbol;
    uint8 public _decimals;

    constructor (string memory name, string memory symbol, uint8 decimals) public {
        _name = name;
        _symbol = symbol;
        _decimals = decimals;
    }

    /**
     * @return the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }

    /**
     * @return the symbol of the token.
     */
    function symbol() public view returns (string memory) {
        return _symbol;
    }

    /**
     * @return the number of decimals of the token.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }
}


/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * https://eips.ethereum.org/EIPS/eip-20
 * Originally based on code by FirstBlood:
 * https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 *
 * This implementation emits additional Approval events, allowing applications to reconstruct the allowance status for
 * all accounts just by listening to said events. Note that this isn't required by the specification, and other
 * compliant implementations may not do it.
 */
contract ERC20 is IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) public _balances;

    mapping (address => mapping (address => uint256)) private _allowed;
    
    mapping (address => bool) public frozenAccount;

    uint256 private _totalSupply;
    
    /**
     * @dev Total number of tokens in existence.
     */
    function totalSupply() public view returns (uint256) {
        return _totalSupply;
    }


    /**
     * @dev Gets the balance of the specified address.
     * @param owner The address to query the balance of.
     * @return A uint256 representing the amount owned by the passed address.
     */
    function balanceOf(address owner) public view returns (uint256) {
        return _balances[owner];
    }

    /**
     * @dev Function to check the amount of tokens that an owner allowed to a spender.
     * @param owner address The address which owns the funds.
     * @param spender address The address which will spend the funds.
     * @return A uint256 specifying the amount of tokens still available for the spender.
     */
    function allowance(address owner, address spender) public view returns (uint256) {
        return _allowed[owner][spender];
    }

    /**
     * @dev Transfer token to a specified address.
     * @param to The address to transfer to.
     * @param value The amount to be transferred.
     */
    function transfer(address to, uint256 value) public returns (bool) {
        _transfer(msg.sender, to, value);
        return true;
    }

    /**
     * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
     * 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
     * @param spender The address which will spend the funds.
     * @param value The amount of tokens to be spent.
     */
    function approve(address spender, uint256 value) public returns (bool) {
        _approve(msg.sender, spender, value);
        return true;
    }

    /**
     * @dev Transfer tokens from one address to another.
     * Note that while this function emits an Approval event, this is not required as per the specification,
     * and other compliant implementations may not emit the event.
     * @param from address The address which you want to send tokens from
     * @param to address The address which you want to transfer to
     * @param value uint256 the amount of tokens to be transferred
     */
    function transferFrom(address from, address to, uint256 value) public returns (bool) {
        _transfer(from, to, value);
        _approve(from, msg.sender, _allowed[from][msg.sender].sub(value));
        return true;
    }

    /**
     * @dev Transfer token for a specified addresses.
     * @param from The address to transfer from.
     * @param to The address to transfer to.
     * @param value The amount to be transferred.
     */
    function _transfer(address from, address to, uint256 value) internal {
        require(to != address(0),"Check recipient is owner");
        // Check if sender is frozen
        require(!frozenAccount[from],"Check if sender is frozen");
        // Check if recipient is frozen
        require(!frozenAccount[to],"Check if recipient is frozen");
        
        _balances[from] = _balances[from].sub(value);
        _balances[to] = _balances[to].add(value);
        emit Transfer(from, to, value);
    }

    /**
     * @dev Internal function that mints an amount of the token and assigns it to
     * an account. This encapsulates the modification of balances such that the
     * proper events are emitted.
     * @param account The account that will receive the created tokens.
     * @param value The amount that will be created.
     */
    function _mint(address account, uint256 value) internal {
        require(account != address(0),"Check recipient is '0x0'");

        _totalSupply = _totalSupply.add(value);
        _balances[account] = _balances[account].add(value);
        emit Transfer(address(0), account, value);
    }

    /**
     * @dev Internal function that burns an amount of the token of a given
     * account.
     * @param account The account whose tokens will be burnt.
     * @param value The amount that will be burnt.
     */
    function _burn(address account, uint256 value) internal {
        require(account != address(0),"Check recipient is owner");

        _totalSupply = _totalSupply.sub(value);
        _balances[account] = _balances[account].sub(value);
        emit Transfer(account, address(0), value);
    }

    /**
     * @dev Approve an address to spend another addresses' tokens.
     * @param owner The address that owns the tokens.
     * @param spender The address that will spend the tokens.
     * @param value The number of tokens that can be spent.
     */
    function _approve(address owner, address spender, uint256 value) internal {
        require(spender != address(0));
        require(owner != address(0));

        _allowed[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    
}

/**
 * @title Roles
 * @dev Library for managing addresses assigned to a Role.
 */
library Roles {
    struct Role {
        mapping (address => bool) bearer;
    }

    /**
     * @dev Give an account access to this role.
     */
    function add(Role storage role, address account) internal {
        require(account != address(0));
        require(!has(role, account));

        role.bearer[account] = true;
    }

    /**
     * @dev Remove an account's access to this role.
     */
    function remove(Role storage role, address account) internal {
        require(account != address(0));
        require(has(role, account));

        role.bearer[account] = false;
    }

    /**
     * @dev Check if an account has this role.
     * @return bool
     */
    function has(Role storage role, address account) internal view returns (bool) {
        require(account != address(0));
        return role.bearer[account];
    }
}

contract MinterRole is Ownable {
    using Roles for Roles.Role;

    event MinterAdded(address indexed account);
    event MinterRemoved(address indexed account);

    Roles.Role private _minters;

    constructor () internal {
        _addMinter(msg.sender);
    }

    function isMinter(address account) public view returns (bool) {
        return _minters.has(account);
    }

    function _addMinter(address account) internal {
        _minters.add(account);
        emit MinterAdded(account);
    }

    function _removeMinter(address account) internal {
        _minters.remove(account);
        emit MinterRemoved(account);
    }
}

/**
 * @title ERC20Mintable
 * @dev ERC20 minting logic.
 */
contract ERC20Mintable is ERC20, Ownable {
    /**
     * @dev Function to mint tokens
     * @param to The address that will receive the minted tokens.
     * @param value The amount of tokens to mint.
     * @return A boolean that indicates if the operation was successful.
     */
    function mint(address to, uint256 value) public onlyOwner returns (bool) {
        _mint(to, value);
        return true;
    }
}


/**
 * @title Burnable Token
 * @dev Token that can be irreversibly burned (destroyed).
 */
contract ERC20Burnable is ERC20,Ownable{
    /**
     * @dev Burns a specific amount of tokens.
     * @param value The amount of token to be burned.
     */
    function burn(uint256 value) onlyOwner public {
        _burn(msg.sender, value);
    }

}

contract PauserRole is Ownable {
    using Roles for Roles.Role;

    event PauserAdded(address indexed account);
    event PauserRemoved(address indexed account);

    Roles.Role private _pausers;

    constructor () internal {
        _addPauser(msg.sender);
    }

    modifier onlyPauser() {
        require(isPauser(msg.sender));
        _;
    }

    function isPauser(address account) public view returns (bool) {
        return _pausers.has(account);
    }

    function _addPauser(address account) internal {
        _pausers.add(account);
        emit PauserAdded(account);
    }

    function _removePauser(address account) internal {
        _pausers.remove(account);
        emit PauserRemoved(account);
    }
}


/**
 * @title Pausable
 * @dev Base contract which allows children to implement an emergency stop mechanism.
 */
contract Pausable is PauserRole {
    event Paused(address account);
    event Unpaused(address account);

    bool private _paused;

    constructor () internal {
        _paused = false;
    }
    
    // modifier onlyPauser() {
    //     require(isPauser(msg.sender));
    //     _;
    // }
    /**
     * @return True if the contract is paused, false otherwise.
     */
    function paused() public view returns (bool) {
        return _paused;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     */
    modifier whenNotPaused() {
        require(!_paused);
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     */
    modifier whenPaused() {
        require(_paused);
        _;
    }

    /**
     * @dev Called by a pauser to pause, triggers stopped state.
     */
    function pause() public onlyOwner whenNotPaused {
        _paused = true;
        emit Paused(msg.sender);
    }

    /**
     * @dev Called by a pauser to unpause, returns to normal state.
     */
    function unpause() public onlyOwner whenPaused {
        _paused = false;
        emit Unpaused(msg.sender);
    }
}


/**
 * @title Pausable token
 * @dev ERC20 modified with pausable transfers.
 */
contract ERC20Pausable is ERC20, Pausable {
    function transfer(address to, uint256 value) public whenNotPaused returns (bool) {
        return super.transfer(to, value);
    }

    function transferFrom(address from, address to, uint256 value) public whenNotPaused returns (bool) {
        return super.transferFrom(from, to, value);
    }

    function approve(address spender, uint256 value) public whenNotPaused returns (bool) {
        return super.approve(spender, value);
    }

}


/**
 * @title Heart Number Token
 * @dev Very simple ERC20 Token example, where all tokens are pre-assigned to the creator.
 * Note they can later distribute these tokens as they wish using `transfer` and other
 * `ERC20` functions.
 */
contract HTN_TOKEN is ERC20, ERC20Detailed, ERC20Burnable, ERC20Mintable, ERC20Pausable {

    string private constant NAME = "Heart Number"; 
    string private constant SYMBOL = "HTN"; 
    uint8 private constant DECIMALS = 18; 
    
    /**
     * @dev The price of tokenBuy.
     */
    uint256 public TokenPerETHBuy = 100000;
    
    /**
     * @dev The price of tokenSell.
     */
    uint256 public TokenPerETHSell = 100000;
    
    /**
    * @dev Sell token is enabled
    */
    bool public SellTokenAllowed;
    
    /**
    * @dev Buy token is enabled
    */
    bool public BuyTokenAllowed;
    
    /**
     * @dev This notifies clients about the new Buy price.
     */
    event BuyRateChanged(uint256 oldValue, uint256 newValue);
    
    /**
     * @dev This notifies clients about the new Sell price.
     */
    event SellRateChanged(uint256 oldValue, uint256 newValue);
    
    /**
     * @dev This notifies clients about the Buy Token.
     */
    event BuyToken(address user, uint256 eth, uint256 token);
    
     /**
     * @dev This notifies clients about the Sell Token.
     */
    event SellToken(address user, uint256 eth, uint256 token);
    
    /**
     * @dev This notifies clients about frozen accounts.
     */
    event FrozenFunds(address target, bool frozen);    
    
    /**
    * @dev This notifies sell token status.
    */
    event SellTokenAllowedEvent(bool isAllowed);
    
    /**
    * @dev This notifies buy token status.
    */
    event BuyTokenAllowedEvent(bool isAllowed);
    
    uint256 public constant INITIAL_SUPPLY = 10000000000 *(10 ** uint256(DECIMALS));

    
    /**
     * @dev Constructor that gives msg.sender all of existing tokens.
     */
    constructor () public ERC20Detailed(NAME, SYMBOL, DECIMALS) {
        _mint(msg.sender, INITIAL_SUPPLY);
        SellTokenAllowed = false;
        BuyTokenAllowed = true;
    }
    
    /// @notice `freeze? Prevent | Allow` `target` from sending & receiving tokens
    /// @param target Address to be frozen
    /// @param freeze either to freeze it or not
    function freezeAccount(address target, bool freeze) onlyOwner  public {
        frozenAccount[target] = freeze;
        emit FrozenFunds(target, freeze);
    }
    
    /**
    * Set price function for Buy
    *
    * @param value the amount new Buy Price
    */
    function setBuyRate(uint256 value) onlyOwner public {
        require(value > 0);
        emit BuyRateChanged(TokenPerETHBuy, value);
        TokenPerETHBuy = value;
    }
    
    /**
    * Set price function for Sell
    *
    * @param value the amount new Sell Price
    */
    function setSellRate(uint256 value) onlyOwner public {
        require(value > 0);
        emit SellRateChanged(TokenPerETHSell, value);
        TokenPerETHSell = value;
    }
    
    /**
    *  function for Buy Token
    */
    function buy() payable public  returns (uint amount){
        require(msg.value > 0 , "Ivalid Ether amount");
        require(!frozenAccount[msg.sender], "Accout is frozen");                      // check sender is not frozen account
        require(BuyTokenAllowed, "Buy Token is not allowed");                         // check buy token allowed
        amount = ((msg.value.mul(TokenPerETHBuy)).mul( 10 ** uint256(decimals()))).div(1 ether);
        _balances[address(this)] -= amount;                        // adds the amount to owner's 
        _balances[msg.sender] += amount; 
        emit Transfer(address(this),msg.sender ,amount);
        return amount;
    }
    
    /**
    *  function for Sell Token
    */
    function sell(uint amount) public  returns (uint revenue){
        
        require(_balances[msg.sender] >= amount,"Checks if the sender has enough to sell");         // checks if the sender has enough to sell
        require(!frozenAccount[msg.sender],"Check if sender is frozen");              // check sender is not frozen account
        require(SellTokenAllowed);                        // check sell token allowed  
        _balances[address(this)] += amount;               // adds the amount to owner's balance
        _balances[msg.sender] -= amount;                  // subtracts the amount from seller's balance
        revenue = (amount.mul(1 ether)).div(TokenPerETHSell.mul(10 ** uint256(decimals()))) ;
        msg.sender.transfer(revenue);                     // sends ether to the seller: it's important to do this last to prevent recursion attacks
        emit Transfer(msg.sender, address(this), amount);               // executes an event reflecting on the change
        return revenue;                                   // ends function and returns
        
    }
    
    /**
    * Enable Sell Token
    */
    function enableSellToken() onlyOwner public {
        SellTokenAllowed = true;
        emit SellTokenAllowedEvent (true);
    }

    /**
    * Disable Sell Token
    */
    function disableSellToken() onlyOwner public {
        SellTokenAllowed = false;
        emit SellTokenAllowedEvent (false);
    }
    
    /**
    * Enable Buy Token
    */
    function enableBuyToken() onlyOwner public {
        BuyTokenAllowed = true;
        emit BuyTokenAllowedEvent (true);
    }

    /**
    * Disable Buy Token
    */
    function disableBuyToken() onlyOwner public {
        BuyTokenAllowed = false;
        emit BuyTokenAllowedEvent (false);
    }
    
    /**
    * @dev Withdraw for Ether
    */
     function withdraw(uint withdrawAmount) onlyOwner public  {
          if (withdrawAmount <= address(this).balance) {
            owner().transfer(withdrawAmount);
        }
    }
}