DeutschLernen/GermanApp/Application/UseCases/Commands/CreateQuizCommand.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 quiz.
/// This follows the CQRS pattern - commands represent write operations.
/// </summary>
public record CreateQuizCommand(CreateQuizDto QuizData) : ICommand<QuizDto>;

/// <summary>
/// Handler for the CreateQuizCommand.
/// </summary>
public class CreateQuizCommandHandler : ICommandHandler<CreateQuizCommand, QuizDto>
{
    private readonly IQuizRepository _quizRepository;
    private readonly ILessonRepository _lessonRepository;

    public CreateQuizCommandHandler(
        IQuizRepository quizRepository,
        ILessonRepository lessonRepository)
    {
        _quizRepository = quizRepository;
        _lessonRepository = lessonRepository;
    }

    public async Task<QuizDto> Handle(CreateQuizCommand command, CancellationToken cancellationToken)
    {
        // Validate that the lesson exists
        var lesson = await _lessonRepository.GetByIdAsync(command.QuizData.LessonId, cancellationToken);
        if (lesson == null)
            throw new NotFoundException("Lesson does not exist");

        // Validate business rules
        if (command.QuizData.PassingScore < 0 || command.QuizData.PassingScore > 100)
        {
            throw new ValidationException("Passing score must be between 0 and 100");
        }

        if (command.QuizData.TimeLimitMinutes < 0)
        {
            throw new ValidationException("Time limit cannot be negative");
        }

        // Convert DTO to domain entity
        var quiz = command.QuizData.ToEntity();

        // Add to repository
        var createdQuiz = await _quizRepository.AddAsync(quiz, cancellationToken);

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

/// <summary>
/// Command for updating an existing quiz.
/// </summary>
public record UpdateQuizCommand(int Id, UpdateQuizDto QuizData) : ICommand<QuizDto?>;

/// <summary>
/// Handler for the UpdateQuizCommand.
/// </summary>
public class UpdateQuizCommandHandler : ICommandHandler<UpdateQuizCommand, QuizDto?>
{
    private readonly IQuizRepository _quizRepository;
    private readonly ILessonRepository _lessonRepository;

    public UpdateQuizCommandHandler(
        IQuizRepository quizRepository,
        ILessonRepository lessonRepository)
    {
        _quizRepository = quizRepository;
        _lessonRepository = lessonRepository;
    }

    public async Task<QuizDto?> Handle(UpdateQuizCommand command, CancellationToken cancellationToken)
    {
        var quiz = await _quizRepository.GetByIdAsync(command.Id, cancellationToken);
        if (quiz == null)
            return null;

        // Validate that the lesson exists
        var lesson = await _lessonRepository.GetByIdAsync(command.QuizData.LessonId, cancellationToken);
        if (lesson == null)
            throw new NotFoundException("Lesson does not exist");

        // Validate business rules
        if (command.QuizData.PassingScore < 0 || command.QuizData.PassingScore > 100)
        {
            throw new ValidationException("Passing score must be between 0 and 100");
        }

        if (command.QuizData.TimeLimitMinutes < 0)
        {
            throw new ValidationException("Time limit cannot be negative");
        }

        // Update the quiz
        quiz.UpdateFromDto(command.QuizData);
        await _quizRepository.UpdateAsync(quiz, cancellationToken);

        // Reload and return
        var updatedQuiz = await _quizRepository.GetByIdAsync(command.Id, cancellationToken);
        return updatedQuiz?.ToDto();
    }
}

/// <summary>
/// Command for deleting a quiz.
/// </summary>
public record DeleteQuizCommand(int Id) : ICommand<bool>;

/// <summary>
/// Handler for the DeleteQuizCommand.
/// </summary>
public class DeleteQuizCommandHandler : ICommandHandler<DeleteQuizCommand, bool>
{
    private readonly IQuizRepository _quizRepository;

    public DeleteQuizCommandHandler(IQuizRepository quizRepository)
    {
        _quizRepository = quizRepository;
    }

    public async Task<bool> Handle(DeleteQuizCommand command, CancellationToken cancellationToken)
    {
        var quiz = await _quizRepository.GetByIdAsync(command.Id, cancellationToken);
        if (quiz == null)
            return false;

        await _quizRepository.DeleteAsync(quiz, cancellationToken);
        return true;
    }
}

/// <summary>
/// Command for getting a quiz with its questions.
/// </summary>
public record GetQuizWithQuestionsCommand(int Id) : ICommand<QuizWithQuestionsDto?>;

/// <summary>
/// Handler for the GetQuizWithQuestionsCommand.
/// </summary>
public class GetQuizWithQuestionsCommandHandler : ICommandHandler<GetQuizWithQuestionsCommand, QuizWithQuestionsDto?>
{
    private readonly IQuizRepository _quizRepository;

    public GetQuizWithQuestionsCommandHandler(IQuizRepository quizRepository)
    {
        _quizRepository = quizRepository;
    }

    public async Task<QuizWithQuestionsDto?> Handle(GetQuizWithQuestionsCommand command, CancellationToken cancellationToken)
    {
        var quiz = await _quizRepository.GetWithQuestionsAsync(command.Id, cancellationToken);
        return quiz?.ToQuizWithQuestionsDto();
    }
}