Add project files

.gitignore

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+## A streamlined .gitignore for modern .NET projects
+## including temporary files, build results, and
+## files generated by popular .NET tools. If you are
+## developing with Visual Studio, the VS .gitignore
+## https://github.com/github/gitignore/blob/main/VisualStudio.gitignore
+## has more thorough IDE-specific entries.
+##
+## Get latest from https://github.com/github/gitignore/blob/main/Dotnet.gitignore
+
+# Build results
+[Dd]ebug/
+[Dd]ebugPublic/
+[Rr]elease/
+[Rr]eleases/
+x64/
+x86/
+[Ww][Ii][Nn]32/
+[Aa][Rr][Mm]/
+[Aa][Rr][Mm]64/
+bld/
+[Bb]in/
+[Oo]bj/
+[Ll]og/
+[Ll]ogs/
+
+# .NET Core
+project.lock.json
+project.fragment.lock.json
+artifacts/
+
+# ASP.NET Scaffolding
+ScaffoldingReadMe.txt
+
+# NuGet Packages
+*.nupkg
+# NuGet Symbol Packages
+*.snupkg
+
+# dotenv environment variables file
+.env
+
+# Others
+~$*
+*~
+CodeCoverage/
+
+# MSBuild Binary and Structured Log
+*.binlog
+
+# MSTest test Results
+[Tt]est[Rr]esult*/
+[Bb]uild[Ll]og.*
+
+# NUnit
+*.VisualState.xml
+TestResult.xml
+nunit-*.xml
+
+# Custom
+Properties/launchsettings.json
+*.user

Program.cs

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+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);
+    }
+}

Properties/PublishProfiles/FolderProfile.pubxml

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+<?xml version="1.0" encoding="utf-8"?>
+<!-- https://go.microsoft.com/fwlink/?LinkID=208121. -->
+<Project>
+  <PropertyGroup>
+    <Configuration>Release</Configuration>
+    <Platform>Any CPU</Platform>
+    <PublishDir>bin\Release\net10.0\win-x64\publish\win-x64\</PublishDir>
+    <PublishProtocol>FileSystem</PublishProtocol>
+    <_TargetId>Folder</_TargetId>
+    <TargetFramework>net10.0</TargetFramework>
+    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
+    <SelfContained>true</SelfContained>
+    <PublishReadyToRun>false</PublishReadyToRun>
+    <PublishTrimmed>false</PublishTrimmed>
+  </PropertyGroup>
+</Project>

WSiPBookDownloader.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+  <OutputType>Exe</OutputType>
+  <TargetFramework>net10.0</TargetFramework>
+	<PublishSingleFile>true</PublishSingleFile>
+	<SelfContained>true</SelfContained>
+	<RuntimeIdentifier>win-x64</RuntimeIdentifier>
+  <ImplicitUsings>enable</ImplicitUsings>
+  <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="PDFsharp" Version="6.2.4" />
+  </ItemGroup>
+
+</Project>

WSiPBookDownloader.slnx

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+<Solution>
+  <Project Path="WSiPBookDownloader.csproj" />
+</Solution>