//SPDX-License-Identifier: MIT
pragma solidity ^0.8.6;

import "./IERC20.sol";

contract CitizenToken is IERC20 {
    string public constant name = "Citizen";
    string public constant symbol = "Citizen";
    uint8 public constant decimals = 18;
    uint256 public override totalSupply = 1500000000 * 10**decimals;
    
    mapping (address => uint256) balances;
    mapping (address => mapping (address => uint256)) allowances;
    
    constructor() {
        balances[msg.sender] = totalSupply;
        emit Transfer(address(0), msg.sender, totalSupply);
    }
    
    function balanceOf(address account) external view override returns(uint256 balance) {
        balance = balances[account];
    }
    
    function allowance(address account, address spender) external view override returns(uint256){
        return allowances[account][spender];
    }
    
    function transfer(address recipient, uint256 amount) external override returns(bool success) {
        require(amount > 0, "HLK: amount must be greater than 0");
        require(balances[msg.sender] >= amount, "HLK: Insufficient balance");
        
        balances[msg.sender] -= amount;
        balances[recipient] += amount;
        emit Transfer(msg.sender, recipient, amount);
        success = true;
    }
    
    function approve(address spender, uint256 amount) external override returns(bool success) {
        allowances[msg.sender][spender] = amount;
        emit Approval(msg.sender, spender, amount);
        success = true;
    }
    
    function transferFrom(address sender, address recipient, uint256 amount) external override returns(bool success){
        require(amount > 0, "HLK: amount must be greater than 0");
        require(allowances[sender][msg.sender] >= amount, "HLK:Insufficient authorization");
        require(balances[sender] >= amount, "HLK:Insufficient balance");
        
        allowances[sender][msg.sender] -= amount;
        balances[sender] -= amount;
        balances[recipient] += amount;
        emit Transfer(sender, recipient, amount);
        success = true;
    }
}

//SPDX-License-Identifier: MIT
pragma solidity ^0.8.6;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see {ERC20Detailed}.
 */
interface IERC20 {
    /**
     * @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 `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, 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 `sender` to `recipient` 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 sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @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);
}

{
  "compilationTarget": {
    "Citizen.sol": "CitizenToken"
  },
  "evmVersion": "berlin",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}