Implement ERC20

src/ERC20.sol

@@ -4,33 +4,82 @@ pragma solidity ^0.8.17;
 import "./interfaces/IERC20.sol";
 
 contract ERC20 is IERC20Metadata {
-    constructor (string memory name, string memory symbol) {}
+    mapping(address => uint256) private _balances;
+    address _owner;
+    string _name;
+    string _symbol;
+    uint256 _totalSupply;
+    uint8 _decimals = 18;
+    mapping(address => mapping(address => uint256)) _approvals;
 
-    function name() external view returns (string memory) {}
+    constructor(string memory newName, string memory newSymbol) {
+        _owner = msg.sender;
+        _name = newName;
+        _symbol = newSymbol;
+    }
 
-    function symbol() external view returns (string memory) {}
+    function name() external view returns (string memory) {
+        return _name;
+    }
 
-    function decimals() external view returns (uint8) {}
+    function symbol() external view returns (string memory) {
+        return _symbol;
+    }
 
-    function totalSupply() external view returns (uint256) {}
+    function decimals() external view returns (uint8) {
+        return _decimals;
+    }
 
-    function balanceOf(address account) external view returns (uint256) {}
+    function totalSupply() external view returns (uint256) {
+        return _totalSupply;
+    }
 
-    function transfer(address to, uint256 amount) external returns (bool) {}
+    function balanceOf(address account) external view returns (uint256) {
+        return _balances[account];
+    }
+
+    function transfer(address to, uint256 amount) external returns (bool) {
+        require(_balances[msg.sender] >= amount, "insufficient balance");
+        _balances[msg.sender] -= amount;
+        _balances[to] += amount;
+        emit Transfer(msg.sender, to, amount);
+        return true;
+    }
 
     function allowance(address owner, address spender)
         external
         view
         returns (uint256)
-    {}
+    {
+        return _approvals[owner][spender];
+    }
 
-    function approve(address spender, uint256 amount) external returns (bool) {}
+    function approve(address spender, uint256 amount) external returns (bool) {
+        _approvals[msg.sender][spender] += amount;
+        emit Approval(msg.sender, spender, amount);
+        return true;
+    }
 
     function transferFrom(
         address from,
         address to,
         uint256 amount
-    ) external returns (bool) {}
-
-    function mint(address to, uint256 amount) external {}
+    ) external returns (bool) {
+        require(_balances[from] >= amount, "insufficient balance");
+        require(
+            _approvals[from][msg.sender] >= amount,
+            "insufficient allowance"
+        );
+        _balances[from] -= amount;
+        _balances[to] += amount;
+        _approvals[from][msg.sender] -= amount;
+        emit Transfer(from, to, amount);
+        return true;
+    }
+
+    function mint(address to, uint256 amount) external {
+        require(msg.sender == _owner, "only minter can mint");
+        _balances[to] += amount;
+        _totalSupply += amount;
+    }
 }