using GermanApp.Application.DTOs;
using GermanApp.Application.Interfaces;
using GermanApp.Domain.Entities;
using GermanApp.Domain.Interfaces;
using Microsoft.EntityFrameworkCore;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace GermanApp.Application.Services;

/// <summary>
/// Service for generating user progress reports.
/// Part of the Application layer.
/// </summary>
public class UserReportService : IUserReportService
{
    private readonly IRepository<User, int> _userRepository;
    private readonly IUserProgressRepository _userProgressRepository;
    private readonly ILessonRepository _lessonRepository;
    private readonly ILevelRepository _levelRepository;
    private readonly IQuizRepository _quizRepository;
    private readonly IStoryProgressRepository _storyProgressRepository;

    public UserReportService(
        IRepository<User, int> userRepository,
        IUserProgressRepository userProgressRepository,
        ILessonRepository lessonRepository,
        ILevelRepository levelRepository,
        IQuizRepository quizRepository,
        IStoryProgressRepository storyProgressRepository)
    {
        _userRepository = userRepository;
        _userProgressRepository = userProgressRepository;
        _lessonRepository = lessonRepository;
        _levelRepository = levelRepository;
        _quizRepository = quizRepository;
        _storyProgressRepository = storyProgressRepository;
    }

    /// <summary>
    /// Generates a progress report for a specific user.
    /// </summary>
    /// <param name="userId">The user ID</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>User progress report</returns>
    public async Task<UserProgressReportDto> GenerateUserReportAsync(int userId, CancellationToken cancellationToken = default)
    {
        var user = await _userRepository.GetByIdAsync(userId, cancellationToken);
        if (user == null)
            throw new ArgumentException("User not found", nameof(userId));

        var userProgress = await _userProgressRepository.GetByUserAsync(userId, cancellationToken);
        var allLessons = await _lessonRepository.GetAllAsync(cancellationToken);

        var totalLessonsCompleted = userProgress.Count(up => up.IsCompleted);
        var totalQuizzesCompleted = userProgress.Count(up => up.IsCompleted && up.QuizScore > 0);
        var averageQuizScore = userProgress.Where(up => up.QuizScore > 0).Select(up => up.QuizScore).DefaultIfEmpty().Average();

        // Find last activity date
        var lastActivityDate = userProgress
            .OrderByDescending(up => up.LastAttemptDate)
            .FirstOrDefault()?.LastAttemptDate ?? user.CreatedAt;

        return new UserProgressReportDto(
            user.Id,
            user.Username,
            user.Email,
            user.CurrentLevel,
            totalLessonsCompleted,
            totalQuizzesCompleted,
            averageQuizScore,
            user.TotalPoints,
            user.Streak,
            lastActivityDate);
    }

    /// <summary>
    /// Generates progress reports for all users.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>List of all user progress reports</returns>
    public async Task<IReadOnlyList<UserProgressReportDto>> GenerateAllUserReportsAsync(CancellationToken cancellationToken = default)
    {
        var users = await _userRepository.GetAllAsync(cancellationToken);
        var reports = new List<UserProgressReportDto>();

        foreach (var user in users)
        {
            var report = await GenerateUserReportAsync(user.Id, cancellationToken);
            reports.Add(report);
        }

        return reports;
    }

    /// <summary>
    /// Gets lesson completion data for a user.
    /// </summary>
    /// <param name="userId">The user ID</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>List of lesson completion data</returns>
    public async Task<IReadOnlyList<LessonCompletionDto>> GetUserLessonProgressAsync(int userId, CancellationToken cancellationToken = default)
    {
        var userProgress = await _userProgressRepository.GetByUserAsync(userId, cancellationToken);
        var allLessons = await _lessonRepository.GetAllAsync(cancellationToken);
        var allLevels = await _levelRepository.GetAllAsync(cancellationToken);

        var levelDict = allLevels.ToDictionary(l => l.Id, l => l.Code);

        return userProgress
            .Select(up => new LessonCompletionDto(
                up.LessonId,
                up.Lesson?.Title ?? "Unknown",
                up.Lesson?.LevelId != null && levelDict.TryGetValue(up.Lesson.LevelId, out var levelCode) ? levelCode : "Unknown",
                up.IsCompleted,
                up.IsCompleted ? up.LastAttemptDate : null))
            .OrderBy(l => l.LevelCode)
            .ThenBy(l => l.LessonTitle)
            .ToList();
    }

    /// <summary>
    /// Gets quiz results for a user.
    /// </summary>
    /// <param name="userId">The user ID</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>List of quiz results</returns>
    public async Task<IReadOnlyList<UserQuizResultDto>> GetUserQuizResultsAsync(int userId, CancellationToken cancellationToken = default)
    {
        var userProgress = await _userProgressRepository.GetByUserAsync(userId, cancellationToken);

        return userProgress
            .Where(up => up.QuizScore > 0)
            .Select(up => new UserQuizResultDto(
                up.Lesson?.Id ?? 0,  // Using LessonId as QuizId proxy (simplified)
                up.Lesson?.Title ?? "Unknown Quiz",
                up.QuizScore,
                80,  // Default passing score
                up.QuizScore >= 80,
                up.LastAttemptDate))
            .OrderByDescending(r => r.AttemptDate)
            .ToList();
    }

    /// <summary>
    /// Exports user reports as CSV.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>CSV content as string</returns>
    public async Task<string> ExportReportsAsCsvAsync(CancellationToken cancellationToken = default)
    {
        var reports = await GenerateAllUserReportsAsync(cancellationToken);
        var sb = new StringBuilder();

        // Header row
        sb.AppendLine("User ID,Username,Email,Current Level,Lessons Completed,Quizzes Completed,Average Score,Total Points,Streak,Last Activity");

        // Data rows
        foreach (var report in reports)
        {
            sb.AppendLine($"{EscapeCsv(report.UserId.ToString())},{EscapeCsv(report.Username)},{EscapeCsv(report.Email)},{EscapeCsv(report.CurrentLevel)},{report.TotalLessonsCompleted},{report.TotalQuizzesCompleted},{report.AverageQuizScore:F2},{report.TotalPoints},{report.CurrentStreak},{EscapeCsv(report.LastActivityDate.ToString("yyyy-MM-dd HH:mm:ss"))}");
        }

        return sb.ToString();
    }

    /// <summary>
    /// Escapes a value for CSV output.
    /// </summary>
    /// <param name="value">The value to escape</param>
    /// <returns>Escaped value</returns>
    private static string EscapeCsv(string value)
    {
        if (value == null)
            return string.Empty;

        // If the value contains commas, quotes, or newlines, wrap it in quotes and escape quotes
        if (value.Contains(",") || value.Contains("\"") || value.Contains("\n") || value.Contains("\r"))
        {
            return $"\"{value.Replace("\"", "\"\"")}\"";
        }

        return value;
    }
}