// https://etherchat.app/ 

// SPDX-License-Identifier: MIT

pragma solidity ^0.7.6;

interface ERC20 {
    function totalSupply() external view returns (uint);
    function balanceOf(address who) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);
    function transfer(address to, uint value) external returns (bool);
    function approve(address spender, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);
    event Transfer(address indexed from, address indexed to, uint value);
    event Approval(address indexed owner, address indexed spender, uint value);
}

interface ApproveAndCallFallBack {
    function receiveApproval(address from, uint tokens, address token, bytes calldata data) external;
}

contract EtherChat is ERC20 {
  using SafeMath for uint256;
  mapping (address => uint256) private balances;
  mapping (address => mapping (address => uint256)) private allowed;
  string public constant name  = "EtherChat";
  string public constant symbol = "CHAT";
  uint8 public constant decimals = 18;
  address deployer;
  uint256 _totalSupply = 1000000000 * 10**18;

  constructor()  {
    deployer = msg.sender;
    balances[deployer] = _totalSupply;
    emit Transfer(address(0), deployer, _totalSupply);
  }

  function totalSupply() public view override returns (uint256) {
    return _totalSupply;
  }

  function balanceOf(address addr) public view override returns (uint256) {
    return balances[addr];
  }

  function allowance(address addr, address spender) public view override returns (uint256) {
    return allowed[addr][spender];
  }

  function transfer(address to, uint256 value) public override returns (bool) {
    require(value <= balances[msg.sender]);
    require(to != address(0));

    balances[msg.sender] = balances[msg.sender].sub(value);
    balances[to] = balances[to].add(value);

    emit Transfer(msg.sender, to, value);
    return true;
  }

  function multiTransfer(address[] memory receivers, uint256[] memory amounts) public {
    for (uint256 i = 0; i < receivers.length; i++) {
      transfer(receivers[i], amounts[i]);
    }
  }

  function approve(address spender, uint256 value) public override returns (bool) {
    require(spender != address(0));
    allowed[msg.sender][spender] = value;
    emit Approval(msg.sender, spender, value);
    return true;
  }

  function transferFrom(address from, address to, uint256 value) public override returns (bool) {
    require(value <= balances[from]);
    require(value <= allowed[from][msg.sender]);
    require(to != address(0));

    balances[from] = balances[from].sub(value);
    balances[to] = balances[to].add(value);

    allowed[from][msg.sender] = allowed[from][msg.sender].sub(value);

    emit Transfer(from, to, value);
    return true;
  }

  function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
    require(spender != address(0));
    allowed[msg.sender][spender] = allowed[msg.sender][spender].add(addedValue);
    emit Approval(msg.sender, spender, allowed[msg.sender][spender]);
    return true;
  }

  function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
    require(spender != address(0));
    allowed[msg.sender][spender] = allowed[msg.sender][spender].sub(subtractedValue);
    emit Approval(msg.sender, spender, allowed[msg.sender][spender]);
    return true;
  }

}

library SafeMath {
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }
    uint256 c = a * b;
    require(c / a == b);
    return c;
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a / b;
    return c;
  }

  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b <= a);
    return a - b;
  }

  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a);
    return c;
  }

  function ceil(uint256 a, uint256 m) internal pure returns (uint256) {
    uint256 c = add(a,m);
    uint256 d = sub(c,1);
    return mul(div(d,m),m);
  }
}