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

contract tokenAddress {
    string public name; // 代币的名称
    string public symbol;// 代币符号
    uint8 public decimals;// 精确小数点位数
    uint public totalPublic;// 代币发行量

    mapping (address => uint256) public balances;// 余额map
    mapping (address => mapping(address =>uint256)) public allowed;// 授权map

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);

    constructor() {
        totalPublic = 10000000000000000000000000;
        balances[msg.sender] = totalPublic;
    }

    // balanceOf 根据地址获取获取代币金额
    function balanceOf(address _owner) public view returns (uint256 balance) {
        return balances[_owner];
    }

    // approve 授权额度申请
    function approve(address _spender, uint256 _value) public returns (bool success) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    // allowance 根据 _owner 和 _spender查询,_owner 给 _spender授权了多少额度
    function allowance(address _owner, address _spender) public view returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }

    // transfer 从合约调用地址向指定地址转移代币
    function transfer(address _to, uint256 _value) public returns (bool success) {
        require(balances[msg.sender] >= _value);
        require(balances[_to] + _value >= balances[_to]);
        balances[msg.sender] -= _value;
        balances[_to] += _value;
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    // transferFrom 从一个地址向另一个地址转移已授权的代币
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        uint256 allowanceValue = allowed[_from][msg.sender];
        require(balances[_from] >= _value && allowanceValue >= _value);
        require(balances[_to] + _value > balances[_to]);
        allowed[_from][msg.sender] -= _value;
        balances[_to] += _value;
        balances[_from] -= _value;
        emit Transfer(_from, _to, _value);
        return true;
    }
}