DeutschLernen/GermanApp/Infrastructure/Data/Repositories/LessonRepository.cs

using GermanApp.Domain.Entities;
using GermanApp.Domain.Interfaces;
using GermanApp.Infrastructure.Data.DbContext;
using Microsoft.EntityFrameworkCore;

namespace GermanApp.Infrastructure.Data.Repositories;

/// <summary>
/// Entity Framework Core implementation of ILessonRepository.
/// This is part of the Infrastructure layer.
/// </summary>
public class LessonRepository : ILessonRepository
{
    private readonly AppDbContext _context;

    public LessonRepository(AppDbContext context)
    {
        _context = context;
    }

    public async Task<Lesson?> GetByIdAsync(int id, CancellationToken cancellationToken = default)
    {
        return await _context.Lessons
            .Include(l => l.Level)
            .FirstOrDefaultAsync(l => l.Id == id, cancellationToken);
    }

    public async Task<IReadOnlyList<Lesson>> GetAllAsync(CancellationToken cancellationToken = default)
    {
        return await _context.Lessons
            .Include(l => l.Level)
            .AsNoTracking()
            .ToListAsync(cancellationToken);
    }

    public async Task<Lesson> AddAsync(Lesson entity, CancellationToken cancellationToken = default)
    {
        await _context.Lessons.AddAsync(entity, cancellationToken);
        await _context.SaveChangesAsync(cancellationToken);
        return entity;
    }

    public async Task UpdateAsync(Lesson entity, CancellationToken cancellationToken = default)
    {
        _context.Lessons.Update(entity);
        await _context.SaveChangesAsync(cancellationToken);
    }

    public async Task DeleteAsync(Lesson entity, CancellationToken cancellationToken = default)
    {
        _context.Lessons.Remove(entity);
        await _context.SaveChangesAsync(cancellationToken);
    }

    public async Task<bool> ExistsAsync(int id, CancellationToken cancellationToken = default)
    {
        return await _context.Lessons
            .AnyAsync(l => l.Id == id, cancellationToken);
    }

    public async Task<IReadOnlyList<Lesson>> GetByLevelAsync(int levelId, CancellationToken cancellationToken = default)
    {
        return await _context.Lessons
            .Include(l => l.Level)
            .Where(l => l.LevelId == levelId)
            .OrderBy(l => l.Order)
            .AsNoTracking()
            .ToListAsync(cancellationToken);
    }

    public async Task<IReadOnlyList<Lesson>> GetAllOrderedAsync(CancellationToken cancellationToken = default)
    {
        return await _context.Lessons
            .Include(l => l.Level)
            .OrderBy(l => l.Level.Order)
            .ThenBy(l => l.Order)
            .AsNoTracking()
            .ToListAsync(cancellationToken);
    }

    public async Task<Lesson?> GetFirstLessonInLevelAsync(int levelId, CancellationToken cancellationToken = default)
    {
        return await _context.Lessons
            .Include(l => l.Level)
            .Where(l => l.LevelId == levelId)
            .OrderBy(l => l.Order)
            .FirstOrDefaultAsync(cancellationToken);
    }

    public async Task<Lesson?> GetNextLessonAsync(int currentLessonId, CancellationToken cancellationToken = default)
    {
        var currentLesson = await _context.Lessons
            .Where(l => l.Id == currentLessonId)
            .Select(l => new { l.LevelId, l.Order })
            .FirstOrDefaultAsync(cancellationToken);

        if (currentLesson == null)
            return null;

        return await _context.Lessons
            .Include(l => l.Level)
            .Where(l => l.LevelId == currentLesson.LevelId && l.Order > currentLesson.Order)
            .OrderBy(l => l.Order)
            .FirstOrDefaultAsync(cancellationToken);
    }

    public async Task<IReadOnlyList<Lesson>> GetAccessibleLessonsAsync(int userId, CancellationToken cancellationToken = default)
    {
        // Get all lessons ordered by level and lesson order
        var allLessons = await _context.Lessons
            .Include(l => l.Level)
            .OrderBy(l => l.Level.Order)
            .ThenBy(l => l.Order)
            .AsNoTracking()
            .ToListAsync(cancellationToken);

        if (allLessons.Count == 0)
            return new List<Lesson>();

        // Get completed lessons for this user
        var completedLessonIds = await _context.UserProgress
            .Where(up => up.UserId == userId && up.IsCompleted)
            .Select(up => up.LessonId)
            .ToListAsync(cancellationToken);

        // Find the first lesson in the first level
        var firstLesson = allLessons.First();
        
        // If user hasn't completed any lessons, they can only access the first one
        if (completedLessonIds.Count == 0)
            return new List<Lesson> { firstLesson };

        // Get the highest ordered lesson that the user has completed
        var completedLessons = allLessons
            .Where(l => completedLessonIds.Contains(l.Id))
            .OrderBy(l => l.Level.Order)
            .ThenBy(l => l.Order)
            .ToList();

        if (completedLessons.Count == 0)
            return new List<Lesson> { firstLesson };

        var lastCompleted = completedLessons.Last();
        
        // User can access all lessons up to and including the next one after the last completed
        var accessibleLessons = allLessons
            .TakeWhile(l => l.Id != lastCompleted.Id)
            .ToList();
        
        // Add the last completed and the next one
        accessibleLessons.Add(lastCompleted);
        
        var nextLessonIndex = allLessons.FindIndex(l => l.Id == lastCompleted.Id) + 1;
        if (nextLessonIndex < allLessons.Count)
        {
            accessibleLessons.Add(allLessons[nextLessonIndex]);
        }

        return accessibleLessons;
    }
}