[ProjectName].Shared/
├── Entities/           # Domain entities
├── DTOs/
│   ├── Auth/          # LoginDto, RegisterDto, TokenDto
│   ├── Entities/      # DTOs per entity
│   └── Common/        # PaginatedResult, etc.
├── Enums/             # Enumerations
├── Responses/         # ActionResponse
└── Extensions/        # Extension methods

public abstract class BaseEntity
{
    public int Id { get; set; }
    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
    public DateTime? UpdatedAt { get; set; }
    public bool IsActive { get; set; } = true;
}

public class Package : BaseEntity
{
    [Required(ErrorMessage = "Tracking number is required")]
    [MaxLength(50, ErrorMessage = "Maximum 50 characters")]
    public string TrackingNumber { get; set; } = null!;

    [MaxLength(500)]
    public string? Description { get; set; }

    [Required]
    public int StatusId { get; set; }

    [Required]
    public string UserId { get; set; } = null!;

    public decimal? Weight { get; set; }

    // Navigation properties
    public Status? Status { get; set; }
    public User? User { get; set; }
    public ICollection<Attachment>? Attachments { get; set; }
}

public class User : IdentityUser
{
    [Required]
    [MaxLength(100)]
    public string FirstName { get; set; } = null!;

    [Required]
    [MaxLength(100)]
    public string LastName { get; set; } = null!;

    [MaxLength(500)]
    public string? Address { get; set; }

    public string FullName => $"{FirstName} {LastName}";
}

public class ActionResponse<T>
{
    public bool WasSuccess { get; set; }
    public string? Message { get; set; }
    public T? Result { get; set; }

    public static ActionResponse<T> Success(T result) => new()
    {
        WasSuccess = true,
        Result = result
    };

    public static ActionResponse<T> Failure(string message) => new()
    {
        WasSuccess = false,
        Message = message
    };
}

// DTO for create
public class PackageCreateDto
{
    [Required(ErrorMessage = "Tracking number is required")]
    [StringLength(50, MinimumLength = 5, ErrorMessage = "Between 5 and 50 characters")]
    public string TrackingNumber { get; set; } = null!;

    [MaxLength(500)]
    public string? Description { get; set; }

    [Required(ErrorMessage = "Status is required")]
    [Range(1, int.MaxValue, ErrorMessage = "Select a valid status")]
    public int StatusId { get; set; }

    [Range(0.01, 999999.99, ErrorMessage = "Invalid weight")]
    public decimal? Weight { get; set; }
}

// DTO for read
public class PackageDto
{
    public int Id { get; set; }
    public string TrackingNumber { get; set; } = null!;
    public string? Description { get; set; }
    public int StatusId { get; set; }
    public string StatusName { get; set; } = null!;
    public string UserId { get; set; } = null!;
    public string UserName { get; set; } = null!;
    public decimal? Weight { get; set; }
    public DateTime CreatedAt { get; set; }
    public bool IsActive { get; set; }
}

// DTO for lists (lightweight)
public class PackageSummaryDto
{
    public int Id { get; set; }
    public string TrackingNumber { get; set; } = null!;
    public string StatusName { get; set; } = null!;
    public int AttachmentCount { get; set; }
    public DateTime CreatedAt { get; set; }
}

public class LoginDto
{
    [Required(ErrorMessage = "Email is required")]
    [EmailAddress(ErrorMessage = "Invalid email")]
    public string Email { get; set; } = null!;

    [Required(ErrorMessage = "Password is required")]
    public string Password { get; set; } = null!;
}

public class RegisterDto
{
    [Required]
    [EmailAddress]
    public string Email { get; set; } = null!;

    [Required]
    [StringLength(100, MinimumLength = 8)]
    public string Password { get; set; } = null!;

    [Compare("Password", ErrorMessage = "Passwords do not match")]
    public string ConfirmPassword { get; set; } = null!;

    [Required]
    [MaxLength(100)]
    public string FirstName { get; set; } = null!;

    [Required]
    [MaxLength(100)]
    public string LastName { get; set; } = null!;
}

public class TokenDto
{
    public string Token { get; set; } = null!;
    public string Email { get; set; } = null!;
    public string FullName { get; set; } = null!;
    public List<string> Roles { get; set; } = new();
    public DateTime Expiration { get; set; }
}

public class PaginatedResult<T>
{
    public IEnumerable<T> Items { get; set; } = new List<T>();
    public int TotalCount { get; set; }
    public int Page { get; set; }
    public int PageSize { get; set; }
    public int TotalPages { get; set; }
    public bool HasPreviousPage => Page > 1;
    public bool HasNextPage => Page < TotalPages;
}

public enum AttachmentType
{
    Image = 1,
    Document = 2,
    Receipt = 3,
    Other = 99
}

public enum PriorityLevel
{
    Low = 1,
    Normal = 2,
    High = 3,
    Urgent = 4
}

// In Backend - Extension methods
public static class PackageMappings
{
    public static PackageDto ToDto(this Package entity) => new()
    {
        Id = entity.Id,
        TrackingNumber = entity.TrackingNumber,
        Description = entity.Description,
        StatusId = entity.StatusId,
        StatusName = entity.Status?.Name ?? "N/A",
        UserId = entity.UserId,
        UserName = entity.User?.FullName ?? "N/A",
        Weight = entity.Weight,
        CreatedAt = entity.CreatedAt,
        IsActive = entity.IsActive
    };

    public static Package ToEntity(this PackageCreateDto dto) => new()
    {
        TrackingNumber = dto.TrackingNumber,
        Description = dto.Description,
        StatusId = dto.StatusId,
        Weight = dto.Weight
    };

    public static IEnumerable<PackageSummaryDto> ToSummaryList(this IEnumerable<Package> entities) =>
        entities.Select(e => new PackageSummaryDto
        {
            Id = e.Id,
            TrackingNumber = e.TrackingNumber,
            StatusName = e.Status?.Name ?? "N/A",
            CreatedAt = e.CreatedAt
        });
}