using System.Diagnostics;
using System.Net;
using PdfSharp.Drawing;
using PdfSharp.Pdf;

namespace WSiPBookDownloader;

internal class BookMissingException : Exception
{
    public int BookId { get; }

    public BookMissingException(int bookId)
        : base($"Book with ID {bookId} does not exist.")
    {
        BookId = bookId;
    }
}

internal class Program
{
    private static readonly HttpClient httpClient = new
    (
        new HttpClientHandler
        {
            AllowAutoRedirect = false,
        }
    )
    {
        BaseAddress = new Uri("https://appwsipnet.eduranga.pl/"),
    };

    private static readonly Lock _consoleLock = new();

    private static void Log(string message, ConsoleColor? color = null)
    {
        lock (_consoleLock)
        {
            if (color.HasValue)
                Console.ForegroundColor = color.Value;

            Console.WriteLine(message);
            Console.ResetColor();
        }
    }

    static async Task Main(string[] args)
    {
        if (args.Length < 2 || args.Length > 4)
        {
            Log("Usage: [outputDirectory] [startBookId] [endBookId] [--only-covers]", ConsoleColor.DarkRed);
            return;
        }

        var outputDirectory = args[0];
        if (!Path.Exists(outputDirectory))
        {
            Log($"Output directory \"{outputDirectory}\" does not exist.", ConsoleColor.DarkRed);
            return;
        }

        var startBookId = int.Parse(args[1]);
        var endBookId = (args.Length >= 3 && int.TryParse(args[2], out var parsedEndBookId))
            ? parsedEndBookId
            : startBookId;
        var onlyCovers = args.FirstOrDefault(arg => arg.Equals("--only-covers", StringComparison.OrdinalIgnoreCase)) != null;

        var bookIds = Enumerable.Range(startBookId, endBookId - startBookId + 1);
        var parallelOptions = new ParallelOptions { MaxDegreeOfParallelism = onlyCovers ? 100 : 10 };

        await Parallel.ForEachAsync(bookIds, parallelOptions, async (bookId, cancellationToken) =>
        {
            var outputPath = Path.Combine(outputDirectory, $"{bookId}.pdf");
            if (File.Exists(outputPath))
            {
                Log($"[!] Book with ID {bookId} already downloaded, skipping...", ConsoleColor.Yellow);
                return;
            }

            Log($"[?] Starting download of book with ID {bookId}", ConsoleColor.Cyan);
            var jpgDir = Path.Combine(Path.GetTempPath(), "WSiPBookDownloader", bookId.ToString());

            try
            {
                if (onlyCovers)
                {
                    await DownloadBookCoverJpg(bookId, outputDirectory, cancellationToken);
                    Log($"[✓] Downloaded book cover {bookId}", ConsoleColor.DarkGreen);
                    return;
                }

                await DownloadBookJpg(bookId, jpgDir, cancellationToken);
                BuildPdf(bookId, jpgDir, outputPath);

                Log($"[✓] Downloaded book {bookId}", ConsoleColor.DarkGreen);
            }
            catch (Exception ex)
            {
                Log($"[×] Failed to download book {bookId}:\n    {ex.Message}", ConsoleColor.DarkRed);
            } finally
            {
                if (Directory.Exists(jpgDir))
                    Directory.Delete(jpgDir, recursive: true);
            }
        });
    }

    private static async Task DownloadBookCoverJpg(int bookId, string outputDir, CancellationToken cancellationToken = default)
    {
        var outputPath = Path.Combine(outputDir, $"{bookId}.jpg");
        if (File.Exists(outputPath))
        {
            Debug.WriteLine($"Cover for book {bookId} already exists, skipping...");
            return;
        }

        var response = await httpClient.GetAsync($"e-podreczniki/podglad/{bookId}/files/mobile/1.jpg", cancellationToken);
        if (response.StatusCode == HttpStatusCode.NotFound || response.StatusCode == HttpStatusCode.Found)
            throw new BookMissingException(bookId);

        response.EnsureSuccessStatusCode();

        var content = await response.Content.ReadAsByteArrayAsync(cancellationToken);
        Directory.CreateDirectory(outputDir);
        await File.WriteAllBytesAsync(outputPath, content, cancellationToken);

        Debug.WriteLine($"Downloaded cover for book {bookId}");
    }

    private static async Task DownloadBookJpg(int bookId, string outputDir, CancellationToken cancellationToken = default)
    {
        var currentPage = 1;
        while (true)
        {
            var outputPath = Path.Combine(outputDir, $"{currentPage}.jpg");
            if (File.Exists(outputPath))
            {
                Debug.WriteLine($"Page {currentPage} of book {bookId} already exists, skipping...");

                currentPage++;
                continue;
            }

            var response = await httpClient.GetAsync($"e-podreczniki/podglad/{bookId}/files/mobile/{currentPage}.jpg", cancellationToken);
            if (
                (response.StatusCode == HttpStatusCode.Found || response.StatusCode == HttpStatusCode.NotFound) &&
                currentPage > 1
            )
            {
                Debug.WriteLine($"No more pages for book {bookId}, stopping...");
                break;
            } else if (response.StatusCode == HttpStatusCode.NotFound || response.StatusCode == HttpStatusCode.Found)
                throw new BookMissingException(bookId);

            response.EnsureSuccessStatusCode();

            var content = await response.Content.ReadAsByteArrayAsync(cancellationToken);
            Directory.CreateDirectory(outputDir);
            await File.WriteAllBytesAsync(outputPath, content, cancellationToken);

            Debug.WriteLine($"Downloaded page {currentPage} of book {bookId}");

            currentPage++;
        }
    }

    private static void BuildPdf(int bookId, string jpgDir, string outputPath)
    {
        var pages = Directory.GetFiles(jpgDir, "*.jpg")
            .OrderBy(file => int.Parse(Path.GetFileNameWithoutExtension(file)))
            .ToList();

        using var document = new PdfDocument();
        document.Options.FlateEncodeMode = PdfFlateEncodeMode.BestCompression;
        document.Options.UseFlateDecoderForJpegImages = PdfUseFlateDecoderForJpegImages.Never;

        foreach (var pagePath in pages)
        {
            using var stream = new MemoryStream(File.ReadAllBytes(pagePath));
            using var image = XImage.FromStream(stream);

            var pdfPage = document.AddPage();
            pdfPage.Width = XUnit.FromPoint(image.PointWidth);
            pdfPage.Height = XUnit.FromPoint(image.PointHeight);

            using var gfx = XGraphics.FromPdfPage(pdfPage);
            gfx.DrawImage(image, 0, 0, image.PointWidth, image.PointHeight);

            Debug.WriteLine($"Added page {Path.GetFileNameWithoutExtension(pagePath)} to PDF for book {bookId}");
        }

        Directory.CreateDirectory(Path.GetDirectoryName(outputPath)!);
        document.Save(outputPath);
    }
}