// Confusing — what does each parameter mean?
var email = new Email("alice@example.com", "bob@example.com", "Welcome!", "<h1>Hi</h1>", true, 3, null, "urgent");

// Better with named parameters... but still not great at scale
var email = new Email(
    from:     "alice@example.com",
    to:       "bob@example.com",
    subject:  "Welcome!",
    body:     "<h1>Hi</h1>",
    isHtml:   true,
    retryCount: 3,
    cc:       null,
    priority: "urgent"
);

public class Email
{
    public string From     { get; init; } = string.Empty;
    public string To       { get; init; } = string.Empty;
    public string Subject  { get; init; } = string.Empty;
    public string Body     { get; init; } = string.Empty;
    public bool   IsHtml   { get; init; }
    public string Priority { get; init; } = "normal";
    public List<string> Cc { get; init; } = [];
}

public class EmailBuilder
{
    private string _from    = string.Empty;
    private string _to      = string.Empty;
    private string _subject = string.Empty;
    private string _body    = string.Empty;
    private bool   _isHtml  = false;
    private string _priority = "normal";
    private readonly List<string> _cc = [];

    public EmailBuilder From(string from)       { _from = from;       return this; }
    public EmailBuilder To(string to)           { _to = to;           return this; }
    public EmailBuilder WithSubject(string sub) { _subject = sub;     return this; }
    public EmailBuilder WithBody(string body)   { _body = body;       return this; }
    public EmailBuilder AsHtml()                { _isHtml = true;     return this; }
    public EmailBuilder Urgent()                { _priority = "high"; return this; }
    public EmailBuilder Cc(string address)      { _cc.Add(address);   return this; }

    public Email Build()
    {
        if (string.IsNullOrWhiteSpace(_from)) throw new InvalidOperationException("From is required");
        if (string.IsNullOrWhiteSpace(_to))   throw new InvalidOperationException("To is required");

        return new Email
        {
            From     = _from,
            To       = _to,
            Subject  = _subject,
            Body     = _body,
            IsHtml   = _isHtml,
            Priority = _priority,
            Cc       = [.._cc]
        };
    }
}

// Usage — reads like English
var email = new EmailBuilder()
    .From("alice@example.com")
    .To("bob@example.com")
    .WithSubject("Welcome!")
    .WithBody("<h1>Hello Bob!</h1>")
    .AsHtml()
    .Cc("manager@example.com")
    .Urgent()
    .Build();

public class OrderBuilder
{
    private int     _customerId = 1;
    private decimal _total      = 100m;
    private string  _status     = "pending";
    private DateTime _createdAt = DateTime.UtcNow;

    public OrderBuilder WithCustomer(int id)    { _customerId = id;  return this; }
    public OrderBuilder WithTotal(decimal t)    { _total = t;        return this; }
    public OrderBuilder WithStatus(string s)    { _status = s;       return this; }
    public OrderBuilder CreatedAt(DateTime dt)  { _createdAt = dt;   return this; }

    public Order Build() => new Order
    {
        CustomerId = _customerId,
        Total      = _total,
        Status     = _status,
        CreatedAt  = _createdAt,
    };
}

// Tests read clearly — only the relevant property is set
[Fact]
public void LargeOrders_GetFreeShipping()
{
    var order = new OrderBuilder().WithTotal(500m).Build();
    Assert.True(shippingService.IsFreeShipping(order));
}

[Fact]
public void CancelledOrders_CannotBeShipped()
{
    var order = new OrderBuilder().WithStatus("cancelled").Build();
    Assert.False(shippingService.CanShip(order));
}

public class ProductQueryBuilder
{
    private string?  _search;
    private string?  _category;
    private decimal? _minPrice;
    private decimal? _maxPrice;
    private string   _sort = "name";
    private bool     _ascending = true;
    private int      _page = 1;
    private int      _pageSize = 20;

    public ProductQueryBuilder Search(string term)       { _search = term;   return this; }
    public ProductQueryBuilder Category(string cat)      { _category = cat;  return this; }
    public ProductQueryBuilder PriceRange(decimal min, decimal max)
    {
        _minPrice = min; _maxPrice = max; return this;
    }
    public ProductQueryBuilder SortBy(string field, bool asc = true)
    {
        _sort = field; _ascending = asc; return this;
    }
    public ProductQueryBuilder Page(int page, int size = 20)
    {
        _page = page; _pageSize = size; return this;
    }

    public IQueryable<Product> Apply(IQueryable<Product> query)
    {
        if (_search is not null)
            query = query.Where(p => p.Name.Contains(_search));
        if (_category is not null)
            query = query.Where(p => p.Category == _category);
        if (_minPrice.HasValue)
            query = query.Where(p => p.Price >= _minPrice.Value);
        if (_maxPrice.HasValue)
            query = query.Where(p => p.Price <= _maxPrice.Value);

        query = _ascending
            ? query.OrderBy(p => EF.Property<object>(p, _sort))
            : query.OrderByDescending(p => EF.Property<object>(p, _sort));

        return query.Skip((_page - 1) * _pageSize).Take(_pageSize);
    }
}

// Usage
var results = new ProductQueryBuilder()
    .Category("Electronics")
    .PriceRange(50, 500)
    .SortBy("price", ascending: false)
    .Page(1, 10)
    .Apply(db.Products)
    .ToListAsync();