using System.Text.RegularExpressions;
using FluentResults;
using MediatR;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using NexusReader.Application.Abstractions.Messaging;
using NexusReader.Application.Abstractions.Persistence;
using NexusReader.Application.Abstractions.Services;

namespace NexusReader.Application.Commands.Library;

public record ProcessEbookCommand(
    Guid EbookId,
    string UserId,
    string TenantId
) : ICommand<bool>;

public class ProcessEbookCommandHandler : IRequestHandler<ProcessEbookCommand, Result<bool>>
{
    private readonly IEbookRepository _ebookRepository;
    private readonly IKnowledgeService _knowledgeService;
    private readonly IEpubExtractor _epubExtractor;
    private readonly ISyncBroadcaster _broadcaster;
    private readonly ILogger<ProcessEbookCommandHandler> _logger;

    public ProcessEbookCommandHandler(
        IEbookRepository ebookRepository,
        IKnowledgeService knowledgeService,
        IEpubExtractor epubExtractor,
        ISyncBroadcaster broadcaster,
        ILogger<ProcessEbookCommandHandler> logger)
    {
        _ebookRepository = ebookRepository;
        _knowledgeService = knowledgeService;
        _epubExtractor = epubExtractor;
        _broadcaster = broadcaster;
        _logger = logger;
    }

    public async Task<Result<bool>> Handle(ProcessEbookCommand request, CancellationToken cancellationToken)
    {
        _logger.LogInformation("[ProcessEbook] Starting background processing for Ebook: {EbookId}", request.EbookId);
        
        try
        {
            await _broadcaster.BroadcastIngestionProgressAsync(request.UserId, "Wyszukiwanie e-booka w bazie danych...", 0.05, cancellationToken);

            var ebook = await _ebookRepository.FindByIdAsync(request.EbookId, cancellationToken);
            if (ebook == null)
            {
                _logger.LogError("[ProcessEbook] Ebook not found in database: {EbookId}", request.EbookId);
                return Result.Fail<bool>($"Ebook nie znaleziony w bazie danych: {request.EbookId}");
            }

            _logger.LogInformation("[ProcessEbook] Extracting chapters text for Ebook: {Title} ({FilePath})", ebook.Title, ebook.FilePath);
            await _broadcaster.BroadcastIngestionProgressAsync(request.UserId, "Otwieranie i parsowanie pliku EPUB...", 0.1, cancellationToken);
            
            var extractionResult = await _epubExtractor.ExtractChaptersTextAsync(ebook.FilePath, cancellationToken);
            if (extractionResult.IsFailed)
            {
                var errorMsg = extractionResult.Errors.FirstOrDefault()?.Message ?? "Failed to extract text chapters.";
                _logger.LogError("[ProcessEbook] Extraction failed: {Error}", errorMsg);
                return Result.Fail<bool>(extractionResult.Errors);
            }

            var chapters = extractionResult.Value;
            if (chapters == null || !chapters.Any())
            {
                _logger.LogWarning("[ProcessEbook] EPUB has no readable content files: {EbookId}", request.EbookId);
                return Result.Fail<bool>("EPUB nie zawiera czytelnych rozdziałów.");
            }

            int totalChapters = chapters.Count;
            _logger.LogInformation("[ProcessEbook] Processing {Count} chapters for Ebook: {Title}", totalChapters, ebook.Title);
            
            await _broadcaster.BroadcastIngestionProgressAsync(request.UserId, $"Analizowanie struktury ({totalChapters} rozdziałów)...", 0.15, cancellationToken);

            int processedChapters = 0;

            for (int i = 0; i < totalChapters; i++)
            {
                var cleanText = chapters[i];

                if (cleanText.Length < 100)
                {
                    _logger.LogInformation("[ProcessEbook] Skipping chapter {Index} (text too short: {Length} chars)", i, cleanText.Length);
                    processedChapters++;
                    continue;
                }

                // Chunk the text to maintain granular Knowledge Units
                var chunks = ChunkText(cleanText, 3000);
                _logger.LogInformation("[ProcessEbook] Chapter {Index} split into {ChunkCount} chunk(s)", i, chunks.Count);

                foreach (var chunk in chunks)
                {
                    try
                    {
                        // Invoke GetKnowledgeMapAsync to extract, embed, and upsert knowledge units
                        var result = await _knowledgeService.GetKnowledgeMapAsync(chunk, request.TenantId, request.EbookId, cancellationToken);
                        if (result.IsFailed)
                        {
                            _logger.LogWarning("[ProcessEbook] Failed to generate knowledge map for a chunk of chapter {Index}: {Error}", i, result.Errors.FirstOrDefault()?.Message);
                        }
                    }
                    catch (Exception ex)
                    {
                        _logger.LogError(ex, "[ProcessEbook] Exception during AI vectorization of chapter {Index} chunk", i);
                    }
                }

                processedChapters++;
                double progress = 0.15 + (0.75 * processedChapters / totalChapters);
                await _broadcaster.BroadcastIngestionProgressAsync(
                    request.UserId, 
                    $"Przetwarzanie rozdziału {processedChapters} z {totalChapters} przez AI...", 
                    progress, 
                    cancellationToken);
            }

            // Mark the ebook as ready
            ebook.IsReadyForReading = true;
            await _ebookRepository.SaveChangesAsync(cancellationToken);

            _logger.LogInformation("[ProcessEbook] Ingestion and vector indexing completed for: {Title}", ebook.Title);
            
            await _broadcaster.BroadcastIngestionProgressAsync(
                request.UserId, 
                "Indeksowanie wektorowe e-booka przez Nexus AI zakończone pomyślnie!", 
                1.0, 
                cancellationToken);

            return Result.Ok(true);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "[ProcessEbook] Critical error during background EPUB vectorization of ebook {EbookId}", request.EbookId);
            await _broadcaster.BroadcastIngestionProgressAsync(
                request.UserId, 
                $"Błąd indeksowania: {ex.Message}", 
                1.0, 
                cancellationToken);
            return Result.Fail<bool>(new Error("Wystąpił błąd podczas indeksowania e-booka przez AI").CausedBy(ex));
        }
    }

    private static List<string> ChunkText(string text, int maxWords = 3000)
    {
        var words = text.Split(' ', StringSplitOptions.RemoveEmptyEntries);
        var chunks = new List<string>();
        if (words.Length <= maxWords)
        {
            chunks.Add(text);
            return chunks;
        }
        var currentChunk = new List<string>();
        int count = 0;
        foreach (var word in words)
        {
            currentChunk.Add(word);
            count++;
            if (count >= maxWords)
            {
                chunks.Add(string.Join(" ", currentChunk));
                currentChunk.Clear();
                count = 0;
            }
        }
        if (currentChunk.Any())
        {
            chunks.Add(string.Join(" ", currentChunk));
        }
        return chunks;
    }
}