DeutschLernen/GermanApp/Domain/Entities/Lesson.cs

namespace GermanApp.Domain.Entities;

/// <summary>
/// Represents a lesson in the DeutschLernen system.
/// Lessons are organized within CEFR levels and must be completed in order.
/// </summary>
public class Lesson
{
    public int Id { get; private set; }
    public int LevelId { get; private set; }
    public string Title { get; private set; } = string.Empty;
    public int Order { get; private set; }
    public string Topic { get; private set; } = string.Empty;
    public string Description { get; private set; } = string.Empty;
    public bool IsActive { get; private set; } = true;
    public DateTime CreatedAt { get; private set; }
    public DateTime? UpdatedAt { get; private set; }

    // Navigation property (EF Core will handle this)
    public virtual Level? Level { get; private set; }

    /// <summary>
    /// Constructor for EF Core deserialization.
    /// </summary>
    private Lesson() { }

    /// <summary>
    /// Factory method to create a new lesson.
    /// </summary>
    /// <param name="levelId">ID of the parent level</param>
    /// <param name="title">Title of the lesson</param>
    /// <param name="order">Sort order within the level</param>
    /// <param name="topic">Main topic covered in the lesson</param>
    /// <param name="description">Description of what the lesson covers</param>
    public static Lesson Create(int levelId, string title, int order, string topic, string description = "")
    {
        return new Lesson
        {
            LevelId = levelId,
            Title = title,
            Order = order,
            Topic = topic,
            Description = description,
            CreatedAt = DateTime.UtcNow
        };
    }

    /// <summary>
    /// Updates the lesson's title.
    /// </summary>
    public void UpdateTitle(string newTitle)
    {
        Title = newTitle;
        UpdatedAt = DateTime.UtcNow;
    }

    /// <summary>
    /// Updates the lesson's topic.
    /// </summary>
    public void UpdateTopic(string newTopic)
    {
        Topic = newTopic;
        UpdatedAt = DateTime.UtcNow;
    }

    /// <summary>
    /// Updates the lesson's description.
    /// </summary>
    public void UpdateDescription(string newDescription)
    {
        Description = newDescription;
        UpdatedAt = DateTime.UtcNow;
    }

    /// <summary>
    /// Updates the lesson's sort order.
    /// </summary>
    public void UpdateOrder(int newOrder)
    {
        Order = newOrder;
        UpdatedAt = DateTime.UtcNow;
    }

    /// <summary>
    /// Updates the lesson's level.
    /// </summary>
    public void UpdateLevel(int newLevelId)
    {
        LevelId = newLevelId;
        UpdatedAt = DateTime.UtcNow;
    }

    /// <summary>
    /// Activates the lesson.
    /// </summary>
    public void Activate()
    {
        IsActive = true;
        UpdatedAt = DateTime.UtcNow;
    }

    /// <summary>
    /// Deactivates the lesson.
    /// </summary>
    public void Deactivate()
    {
        IsActive = false;
        UpdatedAt = DateTime.UtcNow;
    }

    // Navigation properties
    public virtual ICollection<StorySegment> StorySegments { get; private set; } = new List<StorySegment>();
}