1  pragma solidity >=0.5.0 <0.7.0;
 2  
 3  import "./ERC20Token.sol";
 4  
 5  contract ERC20Receiver {
 6  
 7      event TokenDeposited(address indexed token, address indexed sender, uint256 amount);
 8      event TokenWithdrawn(address indexed token, address indexed sender, uint256 amount);
 9  
10      mapping (address => mapping(address => uint256)) tokenBalances;
11  
12      constructor() public {
13  
14      }
15  
16      function depositToken(
17          ERC20Token _token
18      )
19          external
20      {
21          _depositToken(
22              msg.sender,
23              _token,
24              _token.allowance(
25                  msg.sender,
26                  address(this)
27              )
28          );
29      }
30  
31      function withdrawToken(
32          ERC20Token _token,
33          uint256 _amount
34      )
35          external
36      {
37          _withdrawToken(msg.sender, _token, _amount);
38      }
39  
40      function depositToken(
41          ERC20Token _token,
42          uint256 _amount
43      )
44          external
45      {
46          require(_token.allowance(msg.sender, address(this)) >= _amount, "Bad argument");
47          _depositToken(msg.sender, _token, _amount);
48      }
49  
50      function tokenBalanceOf(
51          ERC20Token _token,
52          address _from
53      )
54          external
55          view
56          returns(uint256 fromTokenBalance)
57      {
58          return tokenBalances[address(_token)][_from];
59      }
60  
61      function _depositToken(
62          address _from,
63          ERC20Token _token,
64          uint256 _amount
65      )
66          private
67      {
68          require(_amount > 0, "Bad argument");
69          if (_token.transferFrom(_from, address(this), _amount)) {
70              tokenBalances[address(_token)][_from] += _amount;
71              emit TokenDeposited(address(_token), _from, _amount);
72          }
73      }
74  
75      function _withdrawToken(
76          address _from,
77          ERC20Token _token,
78          uint256 _amount
79      )
80          private
81      {
82          require(_amount > 0, "Bad argument");
83          require(tokenBalances[address(_token)][_from] >= _amount, "Insufficient funds");
84          tokenBalances[address(_token)][_from] -= _amount;
85          require(_token.transfer(_from, _amount), "Transfer fail");
86          emit TokenWithdrawn(address(_token), _from, _amount);
87      }
88  
89  
90  }