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

namespace GermanApp.Application.Services;

/// <summary>
/// Application service for managing user progress through lessons.
/// This is part of the Application layer.
/// </summary>
public class ProgressService
{
    private readonly IUserProgressRepository _userProgressRepository;
    private readonly ILessonRepository _lessonRepository;
    private readonly ILevelRepository _levelRepository;

    public ProgressService(
        IUserProgressRepository userProgressRepository,
        ILessonRepository lessonRepository,
        ILevelRepository levelRepository)
    {
        _userProgressRepository = userProgressRepository;
        _lessonRepository = lessonRepository;
        _levelRepository = levelRepository;
    }

    /// <summary>
    /// Gets user progress for a specific lesson.
    /// </summary>
    public virtual async Task<UserProgressDto?> GetUserProgressAsync(int userId, int lessonId, CancellationToken cancellationToken = default)
    {
        var progress = await _userProgressRepository.GetByUserAndLessonAsync(userId, lessonId, cancellationToken);
        return progress?.ToDto();
    }

    /// <summary>
    /// Gets all progress records for a user.
    /// </summary>
    public virtual async Task<IReadOnlyList<UserProgressDto>> GetUserProgressAsync(int userId, CancellationToken cancellationToken = default)
    {
        var progressRecords = await _userProgressRepository.GetByUserAsync(userId, cancellationToken);
        return progressRecords.Select(p => p.ToDto()).ToList();
    }

    /// <summary>
    /// Gets progress for all lessons in a specific level for a user.
    /// </summary>
    public virtual async Task<IReadOnlyList<UserProgressDto>> GetUserProgressByLevelAsync(int userId, int levelId, CancellationToken cancellationToken = default)
    {
        var progressRecords = await _userProgressRepository.GetByUserAndLevelAsync(userId, levelId, cancellationToken);
        return progressRecords.Select(p => p.ToDto()).ToList();
    }

    /// <summary>
    /// Checks if a user has completed a lesson.
    /// </summary>
    public virtual async Task<bool> HasUserCompletedLessonAsync(int userId, int lessonId, CancellationToken cancellationToken = default)
    {
        return await _userProgressRepository.HasUserCompletedLessonAsync(userId, lessonId, cancellationToken);
    }

    /// <summary>
    /// Marks a lesson as completed for a user with a quiz score.
    /// </summary>
    public virtual async Task<UserProgressDto> MarkLessonAsCompletedAsync(int userId, int lessonId, int quizScore, CancellationToken cancellationToken = default)
    {
        var progress = await _userProgressRepository.GetByUserAndLessonAsync(userId, lessonId, cancellationToken);
        
        if (progress == null)
        {
            // Create new progress record
            progress = UserProgress.Create(userId, lessonId);
            progress.MarkAsCompleted(quizScore);
            await _userProgressRepository.AddAsync(progress, cancellationToken);
        }
        else
        {
            // Update existing progress record
            progress.MarkAsCompleted(quizScore);
            await _userProgressRepository.UpdateAsync(progress, cancellationToken);
        }
        
        return progress.ToDto();
    }

    /// <summary>
    /// Updates user progress for a lesson without marking as completed.
    /// </summary>
    public virtual async Task<UserProgressDto> UpdateUserProgressAsync(int userId, UpdateUserProgressDto dto, CancellationToken cancellationToken = default)
    {
        var progress = await _userProgressRepository.GetByUserAndLessonAsync(userId, dto.LessonId, cancellationToken);
        
        if (progress == null)
        {
            // Create new progress record
            progress = dto.ToEntity(userId);
            await _userProgressRepository.AddAsync(progress, cancellationToken);
        }
        else
        {
            // Update existing progress record
            progress.UpdateFromDto(dto);
            await _userProgressRepository.UpdateAsync(progress, cancellationToken);
        }
        
        return progress.ToDto();
    }

    /// <summary>
    /// Resets user progress for a lesson.
    /// </summary>
    public virtual async Task<bool> ResetLessonProgressAsync(int userId, int lessonId, CancellationToken cancellationToken = default)
    {
        var progress = await _userProgressRepository.GetByUserAndLessonAsync(userId, lessonId, cancellationToken);
        if (progress == null)
            return false;

        progress.Reset();
        await _userProgressRepository.UpdateAsync(progress, cancellationToken);
        return true;
    }

    /// <summary>
    /// Gets the user's average score for a level.
    /// </summary>
    public virtual async Task<double> GetAverageScoreForLevelAsync(int userId, int levelId, CancellationToken cancellationToken = default)
    {
        return await _userProgressRepository.GetAverageScoreForLevelAsync(userId, levelId, cancellationToken);
    }

    /// <summary>
    /// Gets the percentage of lessons completed in a level.
    /// </summary>
    public virtual async Task<double> GetLevelCompletionPercentageAsync(int userId, int levelId, CancellationToken cancellationToken = default)
    {
        return await _userProgressRepository.GetLevelCompletionPercentageAsync(userId, levelId, cancellationToken);
    }

    /// <summary>
    /// Gets level completion summaries for a user.
    /// </summary>
    public virtual async Task<IReadOnlyList<LevelCompletionDto>> GetLevelCompletionsAsync(int userId, CancellationToken cancellationToken = default)
    {
        var levels = await _levelRepository.GetAllOrderedAsync(cancellationToken);
        var completions = new List<LevelCompletionDto>();

        foreach (var level in levels)
        {
            var lessons = await _lessonRepository.GetByLevelAsync(level.Id, cancellationToken);
            var completedCount = 0;
            
            foreach (var lesson in lessons)
            {
                var hasCompleted = await _userProgressRepository.HasUserCompletedLessonAsync(userId, lesson.Id, cancellationToken);
                if (hasCompleted)
                    completedCount++;
            }
            
            var percentage = lessons.Count > 0 
                ? (double)completedCount / lessons.Count * 100 
                : 0;
            
            completions.Add(new LevelCompletionDto(
                level.Id,
                level.Name,
                level.Code,
                lessons.Count,
                completedCount,
                percentage
            ));
        }
        
        return completions;
    }

    /// <summary>
    /// Gets lessons that the user can access (completed previous lessons or first in level).
    /// </summary>
    public virtual async Task<IReadOnlyList<LessonDto>> GetAccessibleLessonsAsync(int userId, CancellationToken cancellationToken = default)
    {
        var lessons = await _lessonRepository.GetAccessibleLessonsAsync(userId, cancellationToken);
        return lessons.Select(l => l.ToDto()).ToList();
    }

    /// <summary>
    /// Checks if the next lesson in a level is unlocked for the user.
    /// </summary>
    public virtual async Task<bool> IsNextLessonUnlockedAsync(int userId, int currentLessonId, CancellationToken cancellationToken = default)
    {
        var currentLesson = await _lessonRepository.GetByIdAsync(currentLessonId, cancellationToken);
        if (currentLesson == null)
            return false;

        // If this is the first lesson in the level, the next one is always unlocked
        var firstLesson = await _lessonRepository.GetFirstLessonInLevelAsync(currentLesson.LevelId, cancellationToken);
        if (firstLesson?.Id == currentLessonId)
        {
            var nextLesson = await _lessonRepository.GetNextLessonAsync(currentLessonId, cancellationToken);
            return nextLesson != null;
        }

        // Check if the user has completed the current lesson
        var hasCompleted = await _userProgressRepository.HasUserCompletedLessonAsync(userId, currentLessonId, cancellationToken);
        return hasCompleted;
    }
}