// File: BasicToken.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;


import "./ERC20Basic.sol";
import "./SafeMath.sol";


/**
 * @title Basic token
 * @dev Basic version of StandardToken, with no allowances.
 */
contract BasicToken is ERC20Basic {

  using SafeMath for uint256 ;

  mapping(address => uint256) internal balances;

  uint256 internal totalSupply_;

  /**
  * @dev Total number of tokens in existence
  */
  function totalSupply() public override view returns (uint256) {
    return totalSupply_;
  }

  /**
  * @dev Transfer token for a specified address
  * @param _to The address to transfer to.
  * @param _value The amount to be transferred.
  */
  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;
  }

  /**
  * @dev Gets the balance of the specified address.
  * @param _owner The address to query the the balance of.
  * @return An uint256 representing the amount owned by the passed address.
  */
  function balanceOf(address _owner) public override view returns (uint256) {
    return balances[_owner];
  }

}

// File: CustomizeToken.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "./StandardToken.sol";
import "./SafeMath.sol";

contract CustomizeToken is StandardToken {

    using SafeMath for uint256 ;
      
    string public name  ;
    string public symbol;
    uint8 public decimals = 18;
    address owner;

    // 事件，用来通知客户端代币被消耗
    event Burn(address indexed from, uint256 value);


    constructor (uint256 initialSupply_, string memory name_, string memory symbol_) public {
        totalSupply_ = initialSupply_ * 10 ** uint256(decimals);
        balances[msg.sender] = totalSupply_;
        name = name_;
        symbol = symbol_;
        owner = msg.sender;
    }


    function burn(uint256 _value) public returns (bool) {
        assert(owner == msg.sender);
        require(balances[msg.sender] >= _value);
        balances[msg.sender] = balances[msg.sender].sub(_value);
        totalSupply_ = totalSupply_.sub(_value);
        emit Burn(msg.sender, _value);
        return true;
    }
}

// File: ERC20.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "./ERC20Basic.sol";


/**
 * @title ERC20 interface
 */
abstract contract ERC20 is ERC20Basic {

    function allowance(address _owner, address _spender)  public virtual view returns (uint256);

    function transferFrom(address _from, address _to, uint256 _value) public virtual returns (bool);

    function approve(address _spender, uint256 _value) public virtual returns (bool);

    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
}

// File: ERC20Basic.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;


/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 */
abstract contract ERC20Basic {

  function totalSupply() public virtual view returns (uint256);

  function balanceOf(address _who) public virtual view returns (uint256);

  function transfer(address _to, uint256 _value) public  virtual returns (bool);

  event Transfer(address indexed from, address indexed to, uint256 value);
}

// File: SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;


/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {

  /**
  * @dev Multiplies two numbers, throws on overflow.
  */
  function mul(uint256 _a, uint256 _b) internal pure returns (uint256 c) {
    // Gas optimization: this is cheaper than asserting 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    if (_a == 0) {
      return 0;
    }

    c = _a * _b;
    assert(c / _a == _b);
    return c;
  }

  /**
  * @dev Integer division of two numbers, truncating the quotient.
  */
  function div(uint256 _a, uint256 _b) internal pure returns (uint256) {
    // assert(_b > 0); // Solidity automatically throws when dividing by 0
    // uint256 c = _a / _b;
    // assert(_a == _b * c + _a % _b); // There is no case in which this doesn't hold
    return _a / _b;
  }

  /**
  * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 _a, uint256 _b) internal pure returns (uint256) {
    assert(_b <= _a);
    return _a - _b;
  }

  /**
  * @dev Adds two numbers, throws on overflow.
  */
  function add(uint256 _a, uint256 _b) internal pure returns (uint256 c) {
    c = _a + _b;
    assert(c >= _a);
    return c;
  }
}

// File: StandardToken.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "./BasicToken.sol";
import "./ERC20.sol";


/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 */
contract StandardToken is ERC20, BasicToken {

    using SafeMath for uint256 ;

    mapping(address => mapping(address => uint256)) internal allowed;


    /**
     * @dev Transfer tokens from one address to another
     * @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 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;
    }

    /**
     * @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:
     * @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 override returns (bool) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    /**
     * @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 override  view returns (uint256) {
        return allowed[_owner][_spender];
    }

    /**
     * @dev Increase the amount of tokens that an owner allowed to a spender.
     * approve should be called when allowed[_spender] == 0. To increment
     * allowed value is better to use this function to avoid 2 calls (and wait until
     * the first transaction is mined)
     * From MonolithDAO Token.sol
     * @param _spender The address which will spend the funds.
     * @param _addedValue The amount of tokens to increase the allowance by.
     */
    function increaseApproval(address _spender, uint256 _addedValue) public returns (bool) {
        allowed[msg.sender][_spender] = (
        allowed[msg.sender][_spender].add(_addedValue));
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }

    /**
     * @dev Decrease the amount of tokens that an owner allowed to a spender.
     * approve should be called when allowed[_spender] == 0. To decrement
     * allowed value is better to use this function to avoid 2 calls (and wait until
     * the first transaction is mined)
     * From MonolithDAO Token.sol
     * @param _spender The address which will spend the funds.
     * @param _subtractedValue The amount of tokens to decrease the allowance by.
     */
    function decreaseApproval(address _spender, uint256 _subtractedValue) public returns (bool){
        uint256 oldValue = allowed[msg.sender][_spender];
        if (_subtractedValue >= oldValue) {
            allowed[msg.sender][_spender] = 0;
        } else {
            allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
        }
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }
}