CleanCodeFunctions.cs

//--------------------------------------------------------------------------------------
// 3. Function - Hàm   
//--------------------------------------------------------------------------------------


//--------------------------------------------------------------------------------------
// Tránh side effects 
// Bad
// Global variable referenced by following function.
// If we had another function that used this name, now it'd be an array and it could break it.
var name = 'Ryan McDermott';

public string SplitIntoFirstAndLastName()
{
   return name.Split(" ");
}

SplitIntoFirstAndLastName();

Console.PrintLine(name); // ['Ryan', 'McDermott'];
// Good
public string SplitIntoFirstAndLastName(string name)
{
    return name.Split(" ");
}

var name = 'Ryan McDermott';
var newName = SplitIntoFirstAndLastName(name);

Console.PrintLine(name); // 'Ryan McDermott';
Console.PrintLine(newName); // ['Ryan', 'McDermott'];


//--------------------------------------------------------------------------------------
// Tránh điều kiện negative false 
// Bad
public bool IsDOMNodeNotPresent(string node)
{
    // ...
}

if (!IsDOMNodeNotPresent(node))
{
    // ...
}
// Good
public bool IsDOMNodePresent(string node)
{
    // ...
}

if (IsDOMNodePresent(node))
{
    // ...
}

//--------------------------------------------------------------------------------------
// Hạn chế dùng điều kiện mà thay vào đó hãy dùng kế thừa  
// Bad
class Airplane
{
    // ...

    public double GetCruisingAltitude()
    {
        switch (_type)
        {
            case '777':
                return GetMaxAltitude() - GetPassengerCount();
            case 'Air Force One':
                return GetMaxAltitude();
            case 'Cessna':
                return GetMaxAltitude() - GetFuelExpenditure();
        }
    }
}
// Good
interface IAirplane
{
    // ...

    double GetCruisingAltitude();
}

class Boeing777 : IAirplane
{
    // ...

    public double GetCruisingAltitude()
    {
        return GetMaxAltitude() - GetPassengerCount();
    }
}

class AirForceOne : IAirplane
{
    // ...

    public double GetCruisingAltitude()
    {
        return GetMaxAltitude();
    }
}

class Cessna : IAirplane
{
    // ...

    public double GetCruisingAltitude()
    {
        return GetMaxAltitude() - GetFuelExpenditure();
    }
}


//--------------------------------------------------------------------------------------
// Tránh kiểm tra kiểu dữ liệu 
// Bad
public Path TravelToTexas(object vehicle)
{
    if (vehicle.GetType() == typeof(Bicycle))
    {
        (vehicle as Bicycle).PeddleTo(new Location("texas"));
    }
    else if (vehicle.GetType() == typeof(Car))
    {
        (vehicle as Car).DriveTo(new Location("texas"));
    }
}

public int Combine(dynamic val1, dynamic val2)
{
    int value;
    if (!int.TryParse(val1, out value) || !int.TryParse(val2, out value))
    {
        throw new Exception('Must be of type Number');
    }

    return val1 + val2;
}

// Good
public Path TravelToTexas(Traveler vehicle)
{
    vehicle.TravelTo(new Location("texas"));
}

// pattern matching
public Path TravelToTexas(object vehicle)
{
    if (vehicle is Bicycle bicycle)
    {
        bicycle.PeddleTo(new Location("texas"));
    }
    else if (vehicle is Car car)
    {
        car.DriveTo(new Location("texas"));
    }
}

public int Combine(int val1, int val2)
{
    return val1 + val2;
}

//--------------------------------------------------------------------------------------
// Tránh đặt các cờ kiểu bool trong parameters
// Bad
public void CreateFile(string name, bool temp = false)
{
    if (temp)
    {
        Touch("./temp/" + name);
    }
    else
    {
        Touch(name);
    }
}
// Good
public void CreateFile(string name)
{
    Touch(name);
}

public void CreateTempFile(string name)
{
    Touch("./temp/"  + name);
}


//--------------------------------------------------------------------------------------
// Không được write vào các hàm toàn cục 
// Bad
public string[] Config()
{
    return  [
        "foo" => "bar",
    ]
}
// Good
class Configuration
{
    private string[] _configuration = [];

    public Configuration(string[] configuration)
    {
        _configuration = configuration;
    }

    public string[] Get(string key)
    {
        return (_configuration[key]!= null) ? _configuration[key] : null;
    }
}
// Load configuration and create instance of Configuration class
var configuration = new Configuration(new string[] {
    "foo" => "bar",
});


//--------------------------------------------------------------------------------------
// Hạn chế sử dụng Singleton thay vào đó hãy dùng options 
// Bad
class DBConnection
{
    private static DBConnection _instance;

    private DBConnection()
    {
        // ...
    }

    public static GetInstance()
    {
        if (_instance == null)
        {
            _instance = new DBConnection();
        }

        return _instance;
    }

    // ...
}

var singleton = DBConnection.GetInstance();
// Good
class DBConnection
{
    public DBConnection(IOptions<DbConnectionOption> options)
    {
        // ...
    }

    // ...
}
// Create instance of DBConnection class and configure it with Option pattern.
var options = <resolve from IOC>;
var connection = new DBConnection(options);


//--------------------------------------------------------------------------------------
// Nên sử dụng tối đa 2 parameters cho một hàm  
// Bad
public void CreateMenu(string title, string body, string buttonText, bool cancellable)
{
    // ...
}
// Good
pubic class MenuConfig
{
    public string Title { get; set; }
    public string Body { get; set; }
    public string ButtonText { get; set; }
    public bool Cancellable { get; set; }
}

var config = new MenuConfig
{
    Title = "Foo",
    Body = "Bar",
    ButtonText = "Baz",
    Cancellable = true
};

public void CreateMenu(MenuConfig config)
{
    // ...
}


//--------------------------------------------------------------------------------------
// Một hàm nên và chỉ nên làm một nhiệm vụ duy nhất 
// Bad
public void SendEmailToListOfClients(string[] clients)
{
    foreach (var client in clients)
    {
        var clientRecord = db.Find(client);
        if (clientRecord.IsActive())
        {
            Email(client);
        }
    }
}
// Good
public void SendEmailToListOfClients(string[] clients)
{
    var activeClients = GetActiveClients(clients);
    // Do some logic
}

public List<Client> GetActiveClients(string[] clients)
{
    return db.Find(clients).Where(s => s.Status == "Active");
}


//--------------------------------------------------------------------------------------
// Đặt tên hàm theo mục đích rõ ràng  
// Bad
public class Email
{
    //...

    public void Handle()
    {
        SendMail(this._to, this._subject, this._body);
    }
}

var message = new Email(...);
// What is this? A handle for the message? Are we writing to a file now?
message.Handle();
// Good
public class Email
{
    //...

    public void Send()
    {
        SendMail(this._to, this._subject, this._body);
    }
}

var message = new Email(...);
// Clear and obvious
message.Send();

//--------------------------------------------------------------------------------------
// Functions should only be one level of abstraction
// Bad
public string ParseBetterJSAlternative(string code)
{
    var regexes = [
        // ...
    ];

    var statements = explode(" ", code);
    var tokens = new string[] {};
    foreach (var regex in regexes)
    {
        foreach (var statement in statements)
        {
            // ...
        }
    }

    var ast = new string[] {};
    foreach (var token in tokens)
    {
        // lex...
    }

    foreach (var node in ast)
    {
        // parse...
    }
}
// Good
class Tokenizer
{
    public string Tokenize(string code)
    {
        var regexes = new string[] {
            // ...
        };

        var statements = explode(" ", code);
        var tokens = new string[] {};
        foreach (var regex in regexes)
        {
            foreach (var statement in statements)
            {
                tokens[] = /* ... */;
            }
        }

        return tokens;
    }
}

class Lexer
{
    public string Lexify(string[] tokens)
    {
        var ast = new[] {};
        foreach (var token in tokens)
        {
            ast[] = /* ... */;
        }

        return ast;
    }
}

class BetterJSAlternative
{
    private string _tokenizer;
    private string _lexer;

    public BetterJSAlternative(Tokenizer tokenizer, Lexer lexer)
    {
        _tokenizer = tokenizer;
        _lexer = lexer;
    }

    public string Parse(string code)
    {
        var tokens = _tokenizer.Tokenize(code);
        var ast = _lexer.Lexify(tokens);
        foreach (var node in ast)
        {
            // parse...
        }
    }
}


//--------------------------------------------------------------------------------------
// Các hàm callers và callees nên đặt gần nhau 
// Bad
class PerformanceReview
{
    private readonly Employee _employee;

    public PerformanceReview(Employee employee)
    {
        _employee = employee;
    }

    private IEnumerable<PeersData> LookupPeers()
    {
        return db.lookup(_employee, 'peers');
    }

    private ManagerData LookupManager()
    {
        return db.lookup(_employee, 'manager');
    }

    private IEnumerable<PeerReviews> GetPeerReviews()
    {
        var peers = LookupPeers();
        // ...
    }

    public PerfReviewData PerfReview()
    {
        GetPeerReviews();
        GetManagerReview();
        GetSelfReview();
    }

    public ManagerData GetManagerReview()
    {
        var manager = LookupManager();
    }

    public EmployeeData GetSelfReview()
    {
        // ...
    }
}

var  review = new PerformanceReview(employee);
review.PerfReview();
// Good
class PerformanceReview
{
    private readonly Employee _employee;

    public PerformanceReview(Employee employee)
    {
        _employee = employee;
    }

    public PerfReviewData PerfReview()
    {
        GetPeerReviews();
        GetManagerReview();
        GetSelfReview();
    }

    private IEnumerable<PeerReviews> GetPeerReviews()
    {
        var peers = LookupPeers();
        // ...
    }

    private IEnumerable<PeersData> LookupPeers()
    {
        return db.lookup(_employee, 'peers');
    }

    private ManagerData GetManagerReview()
    {
        var manager = LookupManager();
        return manager;
    }

    private ManagerData LookupManager()
    {
        return db.lookup(_employee, 'manager');
    }

    private EmployeeData GetSelfReview()
    {
        // ...
    }
}

var review = new PerformanceReview(employee);
review.PerfReview();


//--------------------------------------------------------------------------------------
// Nên gom các biểu thức điều kiện và tách thành hàm riêng
// Bad
if (article.state == "published")
{
    // ...
}
// Good
if (article.IsPublished())
{
    // ...
}



//--------------------------------------------------------------------------------------
// Xóa hết các code không dùng 
// Bad
public void OldRequestModule(string url)
{
    // ...
}

public void NewRequestModule(string url)
{
    // ...
}

var request = NewRequestModule(requestUrl);
InventoryTracker("apples", request, "www.inventory-awesome.io");
// Good
public void RequestModule(string url)
{
    // ...
}

var request = RequestModule(requestUrl);
InventoryTracker("apples", request, "www.inventory-awesome.io");