using System.IO.Compression;
using Microsoft.Extensions.Logging;
using SteUp.Shared.Core.Dto;
using SteUp.Shared.Core.Interface.System;

namespace SteUp.Maui.Core.Services;

/// <summary>
/// Divide l'invio dei log in parti sotto <see cref="MaxPartBytes"/>: la prima porta log, database
/// e le prime immagini, le successive solo immagini. Gli zip vengono scritti su disco (mai in RAM)
/// una parte alla volta, così lo spazio occupato resta quello di una sola parte.
/// </summary>
internal sealed class LogExport : ILogExport
{
    // Ben sotto il max-file-size dei servizi (100 MB) e i limiti tipici dei server di posta.
    // Una parte piccola regge anche l'upload da rete mobile entro il timeout HTTP del client.
    internal const long MaxPartBytes = 40L * 1024 * 1024;

    private const int BufferSize = 81920;

    internal readonly record struct ZipItem(FileInfo File, string EntryName);

    private readonly string _workDir;
    private readonly List<ZipItem> _logFiles;
    private readonly List<ZipItem> _dbFiles;
    private readonly List<List<ZipItem>> _imageParts;
    private readonly ILogger _logger;
    private readonly List<string> _currentPartFiles = [];

    public int PartCount => _imageParts.Count;

    internal LogExport(string workDir, List<ZipItem> logFiles, List<ZipItem> dbFiles, List<ZipItem> images,
        ILogger logger)
    {
        _workDir = workDir;
        _logFiles = logFiles;
        _dbFiles = dbFiles;
        _logger = logger;
        _imageParts = SplitImages(images, logFiles.Concat(dbFiles).Sum(x => x.File.Length));
    }

    /// <summary>
    /// Riempie le parti in ordine (le foto di un'ispezione restano vicine). La prima parte parte
    /// già occupata da log e database: uso le dimensioni non compresse, una stima per eccesso.
    /// Un file più grande di una parte finisce da solo in una parte sua.
    /// </summary>
    private static List<List<ZipItem>> SplitImages(List<ZipItem> images, long firstPartReserved)
    {
        var parts = new List<List<ZipItem>> { new() };
        var currentSize = firstPartReserved;

        foreach (var image in images)
        {
            var length = image.File.Length;
            if (currentSize > 0 && currentSize + length > MaxPartBytes)
            {
                parts.Add([]);
                currentSize = 0;
            }

            parts[^1].Add(image);
            currentSize += length;
        }

        return parts;
    }

    public Task<List<SendEmailDto.AttachmentsDto>> BuildPartAsync(int index, CancellationToken ct = default)
    {
        ArgumentOutOfRangeException.ThrowIfNegative(index);
        ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual(index, PartCount);

        // Task.Run: la compressione non deve bloccare il thread della UI.
        return Task.Run(() =>
        {
            DeleteCurrentPartFiles();

            var attachments = new List<SendEmailDto.AttachmentsDto>();
            var date = DateTime.Today.ToString("yyyyMMdd");

            if (index == 0)
            {
                if (_logFiles.Count > 0)
                    attachments.Add(WriteZip($"logs_{date}.zip", _logFiles, CompressionLevel.Optimal, ct));

                if (_dbFiles.Count > 0)
                    attachments.Add(WriteZip($"database_{DateTime.Now:yyyyMMdd_HHmm}.zip", _dbFiles,
                        CompressionLevel.Optimal, ct));
            }

            var images = _imageParts[index];
            if (images.Count > 0)
            {
                var suffix = PartCount > 1 ? $"_parte{index + 1}di{PartCount}" : string.Empty;

                // JPEG già compressi: ricomprimerli costa CPU e non riduce quasi niente.
                attachments.Add(WriteZip($"immagini_allegate_{date}{suffix}.zip", images,
                    CompressionLevel.NoCompression, ct));
            }

            return attachments;
        }, ct);
    }

    private SendEmailDto.AttachmentsDto WriteZip(string fileName, List<ZipItem> items, CompressionLevel level,
        CancellationToken ct)
    {
        var path = Path.Combine(_workDir, fileName);
        _currentPartFiles.Add(path);

        using (var zipStream = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.None, BufferSize))
        using (var archive = new ZipArchive(zipStream, ZipArchiveMode.Create))
        {
            foreach (var item in items)
            {
                ct.ThrowIfCancellationRequested();

                try
                {
                    // FileShare.ReadWrite: log e database possono essere ancora aperti in scrittura.
                    using var source = item.File.Open(FileMode.Open, FileAccess.Read, FileShare.ReadWrite);

                    var entry = archive.CreateEntry(item.EntryName, level);
                    entry.LastWriteTime = item.File.LastWriteTime;

                    using var entryStream = entry.Open();
                    source.CopyTo(entryStream, BufferSize);
                }
                catch (Exception e) when (e is IOException or UnauthorizedAccessException)
                {
                    // Un file sparito o bloccato non deve far saltare tutto l'invio.
                    _logger.LogWarning(e, "Export log: file {File} saltato", item.File.FullName);
                }
            }
        }

        return new SendEmailDto.AttachmentsDto { FileName = fileName, FilePath = path };
    }

    private void DeleteCurrentPartFiles()
    {
        foreach (var path in _currentPartFiles)
        {
            try
            {
                File.Delete(path);
            }
            catch (Exception e)
            {
                _logger.LogWarning(e, "Export log: impossibile eliminare {File}", path);
            }
        }

        _currentPartFiles.Clear();
    }

    public ValueTask DisposeAsync()
    {
        try
        {
            if (Directory.Exists(_workDir))
                Directory.Delete(_workDir, true);
        }
        catch (Exception e)
        {
            _logger.LogWarning(e, "Export log: impossibile eliminare {Dir}", _workDir);
        }

        return ValueTask.CompletedTask;
    }
}