DeutschLernen/GermanApp/Application/UseCases/Commands/CreateLessonCommand.cs

using GermanApp.Application.DTOs;
using GermanApp.Domain.Entities;
using GermanApp.Domain.Exceptions;
using GermanApp.Domain.Interfaces;

namespace GermanApp.Application.UseCases.Commands;

/// <summary>
/// Command for creating a new lesson.
/// This follows the CQRS pattern - commands represent write operations.
/// </summary>
public record CreateLessonCommand(CreateLessonDto LessonData) : ICommand<LessonDto>;

/// <summary>
/// Handler for the CreateLessonCommand.
/// </summary>
public class CreateLessonCommandHandler : ICommandHandler<CreateLessonCommand, LessonDto>
{
    private readonly ILessonRepository _lessonRepository;

    public CreateLessonCommandHandler(ILessonRepository lessonRepository)
    {
        _lessonRepository = lessonRepository;
    }

    public async Task<LessonDto> Handle(CreateLessonCommand command, CancellationToken cancellationToken)
    {
        // Convert DTO to domain entity
        var lesson = command.LessonData.ToEntity();

        // Validate business rules (could be extracted to a validator)
        if (lesson.Level < 1 || lesson.Level > 5)
        {
            throw new ValidationException("Level must be between 1 and 5");
        }

        // Add to repository
        var createdLesson = await _lessonRepository.AddAsync(lesson, cancellationToken);

        // Return DTO representation
        return createdLesson.ToDto();
    }
}

/// <summary>
/// Generic command interface.
/// </summary>
/// <typeparam name="TResult">The result type</typeparam>
public interface ICommand<out TResult>
{
}

/// <summary>
/// Generic command handler interface.
/// </summary>
/// <typeparam name="TCommand">The command type</typeparam>
/// <typeparam name="TResult">The result type</typeparam>
public interface ICommandHandler<in TCommand, TResult> 
    where TCommand : ICommand<TResult>
{
    Task<TResult> Handle(TCommand command, CancellationToken cancellationToken);
}

// Note: For MediatR integration, you would implement IRequestHandler<TCommand, TResult>
// instead of the custom interfaces above.