// SPDX-License-Identifier: Unlicensed

pragma solidity 0.7.2;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function allowance(address owner, address spender) external view returns (uint256);
    function transfer(address trecipient, uint256 amount) external returns (bool);
    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);
}

library SafeMath {
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }
  
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }
  
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;
        return c;
    }
  
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {return 0;}
        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }
  
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }
  
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        return c;
    }
  
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }
  
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

abstract contract ERC20Detailed is IERC20 {
    uint8 private _Tokendecimals;
    string private _Tokenname;
    string private _Tokensymbol;
    
    constructor(string memory name, string memory symbol, uint8 decimals) {
    _Tokendecimals = decimals;
    _Tokenname = name;
    _Tokensymbol = symbol;
    }
    
    function name() public view returns(string memory) {
        return _Tokenname;
    }
    
    function symbol() public view returns(string memory) {
        return _Tokensymbol;
    }
    
    function decimals() public view returns(uint8) {
        return _Tokendecimals;
    }
}

contract OwnableDistributor {
    address private _owner;
    address private _distributor;
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    event distributorTransferred(address indexed previousDistributor, address indexed newDistributor);

    constructor () {
        address msgSender = msg.sender;
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
        _distributor = address(0);
    }

    function owner() public view returns (address) {
        return _owner;
    }
    
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    modifier onlyOwner() {
        require(_owner == msg.sender, "Ownable: caller is not the owner");
        _;
    }

    function setDistributor(address _address) external onlyOwner {
        require (_distributor == address(0));
        _distributor = _address;
        emit distributorTransferred(address(0), _address);
    }
    
    function rewardDistributor() public view returns (address) {
        return _distributor;
    }
    
    modifier onlyDistributor() {
        require(_distributor == msg.sender, "caller is not rewards distributor");
        _;
    }
}

contract BagOfHoldingRewards is OwnableDistributor {
    using SafeMath for uint256;
    mapping (address => uint256) public balances;
    mapping (address => mapping (address => uint256)) internal allowed;
    
    mapping (address => bool) private gamersDatabase;
    uint256 gamerRewardLimit;
    event gamerAddedToDatabase (address gamerAddress, bool isAdded);
    event gamerRemovedFromDatabase (address gamerAddress, bool isAdded);
    event rewardTransfer(address indexed from, address indexed to, uint256 value);
    
    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 public totalSupply;
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
    
    constructor() {
        name = "Bag of Holding Rewards";
        symbol = "Rewards";
        decimals = 9;
        gamerRewardLimit = 500000000000; //maximum amount of tokens per gamer (500) + decimals (9)
    }
    
    function balanceOf(address _owner) public view returns (uint256 balance) {
        return balances[_owner];
    }

    function transfer(address _to, uint256 _value) public returns (bool) {
        _transfer(msg.sender, _to, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
        _transfer(_from, _to, _value);
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
        return true;
    }

    function approve(address _spender, uint256 _value) public returns (bool) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    function allowance(address _owner, address _spender) internal view returns (uint256) {
        return allowed[_owner][_spender];
    }
  
    function _transfer(address _from, address _to, uint256 _value) private {
        require(_from != address(0), "ERC20: transfer from the zero address");
        require(_to != address(0), "ERC20: transfer to the zero address");
        require(_value > 0, "Transfer amount must be greater than zero");
        balances[_from] = balances[_from].sub(_value, "ERC20: transfer amount exceeds balance");
        balances[_to] = balances[_to].add(_value);
        emit Transfer(_from, _to, _value);
    }

    function addNewGamerToDatabase(address _address) public onlyDistributor {
        gamersDatabase[_address] = true;
        emit gamerAddedToDatabase (_address, gamersDatabase[_address]);
    }

    function removeGamerFromDatabase(address _address) public onlyDistributor {
        gamersDatabase[_address] = false;
        emit gamerRemovedFromDatabase (_address, gamersDatabase[_address]);
    }
        
    function isGamerInDatabase(address _address) public view returns(bool) {
        return gamersDatabase[_address];
    }
    
    function rewardLimitPerGamer() public view returns (uint256) {
        return gamerRewardLimit.div(1*10**9);
        //return the maximum amount of tokens per gamer, devied only here by decimals (9) for better clarity
    }
    
    function sendRewardToWinner(address _address, uint256 amount) external onlyDistributor {
        require (owner() == address(0), "renouce owership required. The Owner must be zero address");
        require (gamersDatabase[_address] == true, "address is not registred in gamers database");
        require (amount <= gamerRewardLimit, "amount cannot be higher than limit");
        require (_address != address(0), "zero address not allowed");
        require (amount != 0, "amount cannot be zero");
        balances[address(this)] = balances[address(this)].sub(amount, "reward pool is empty already");
        balances[_address] = balances[_address].add(amount);
        emit rewardTransfer(address(this), _address, amount);
    }
}