PngToWebp.cs

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Formats.Webp;

namespace ImageSharp.Converter;

/// <summary>
/// Converts PNG images to WebP format using ImageSharp library.
/// Scans a target directory (defaults to current working directory) recursively.
/// </summary>
abstract class ConvertToWebP
{
    private static int _quality = 85;
    private static bool _force = false;
    private static string? _targetPath = null;
    private static readonly List<string> _skipFolders = [];
    private static readonly List<string> _skipPrefixes = [];

    static async Task<int> Main(string[] args)
    {
        Console.ForegroundColor = ConsoleColor.Cyan;
        Console.WriteLine("PNG to WebP Converter using ImageSharp");
        Console.WriteLine("======================================\n");
        Console.ResetColor();

        ParseArguments(args);

        // Resolve target directory: explicit arg > cwd
        var searchPath = _targetPath ?? Directory.GetCurrentDirectory();

        if (!Directory.Exists(searchPath))
        {
            Console.ForegroundColor = ConsoleColor.Red;
            Console.WriteLine($"ERROR: Target directory not found: {searchPath}");
            Console.ResetColor();
            return 1;
        }

        Console.ForegroundColor = ConsoleColor.Cyan;
        Console.WriteLine($"Searching for PNG files in: {searchPath}");
        Console.WriteLine($"Quality: {_quality}");
        if (_skipFolders.Count > 0)
            Console.WriteLine($"Skipping folders: {string.Join(", ", _skipFolders)}");
        if (_skipPrefixes.Count > 0)
            Console.WriteLine($"Skipping file prefixes: {string.Join(", ", _skipPrefixes)}");
        Console.WriteLine();
        Console.ResetColor();

        var pngFiles = Directory.GetFiles(searchPath, "*.png", SearchOption.AllDirectories);
        var filesToConvert = FilterFiles(pngFiles, searchPath);

        Console.ForegroundColor = ConsoleColor.Green;
        Console.WriteLine($"Found {filesToConvert.Count} PNG file(s) to convert\n");
        Console.ResetColor();

        int converted = 0;
        int skipped = 0;
        int failed = 0;

        foreach (var pngFile in filesToConvert)
        {
            var webpFile = Path.ChangeExtension(pngFile, ".webp");
            var relativePath = pngFile[searchPath.Length..];

            if (File.Exists(webpFile) && !_force)
            {
                if (File.GetLastWriteTime(webpFile) > File.GetLastWriteTime(pngFile))
                {
                    Console.ForegroundColor = ConsoleColor.Yellow;
                    Console.WriteLine($"Skipping (up-to-date): {relativePath}");
                    Console.ResetColor();
                    skipped++;
                    continue;
                }
            }

            Console.WriteLine($"Converting: {relativePath}");

            try
            {
                var originalSize = new FileInfo(pngFile).Length;

                using (var image = await Image.LoadAsync(pngFile))
                {
                    var encoder = new WebpEncoder
                    {
                        Quality = _quality,
                        Method = WebpEncodingMethod.BestQuality,
                        FileFormat = WebpFileFormatType.Lossy
                    };

                    await image.SaveAsWebpAsync(webpFile, encoder);
                }

                var webpSize = new FileInfo(webpFile).Length;
                var savings = Math.Round((1 - (webpSize / (double)originalSize)) * 100, 1);

                Console.ForegroundColor = ConsoleColor.Green;
                Console.WriteLine($"  ✓ {savings}% saved ({FormatFileSize(originalSize)} → {FormatFileSize(webpSize)})");
                Console.ResetColor();
                converted++;
            }
            catch (Exception ex)
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.WriteLine($"  ✗ Error: {ex.Message}");
                Console.ResetColor();
                failed++;
            }
        }

        Console.ForegroundColor = ConsoleColor.Cyan;
        Console.WriteLine("\n========================================");
        Console.WriteLine("Conversion Summary:");
        Console.ForegroundColor = ConsoleColor.Green;
        Console.WriteLine($"  Converted:            {converted}");
        Console.ForegroundColor = ConsoleColor.Yellow;
        Console.WriteLine($"  Skipped (up-to-date): {skipped}");
        Console.ForegroundColor = failed > 0 ? ConsoleColor.Red : ConsoleColor.Gray;
        Console.WriteLine($"  Failed:               {failed}");
        Console.ForegroundColor = ConsoleColor.Cyan;
        Console.WriteLine("========================================\n");
        Console.ResetColor();

        return failed > 0 ? 1 : 0;
    }

    private static List<string> FilterFiles(string[] pngFiles, string basePath)
    {
        var result = new List<string>();

        foreach (var pngFile in pngFiles)
        {
            var relativePath = pngFile[basePath.Length..];
            var fileName = Path.GetFileName(pngFile);

            // Skip folders passed via --skip-folder
            var skipFolder = _skipFolders.Any(folder =>
                relativePath.Contains(Path.DirectorySeparatorChar + folder + Path.DirectorySeparatorChar,
                    StringComparison.OrdinalIgnoreCase));

            if (skipFolder)
            {
                Console.ForegroundColor = ConsoleColor.DarkGray;
                Console.WriteLine($"Skipping (excluded folder): {relativePath}");
                Console.ResetColor();
                continue;
            }

            // Skip filenames matching --skip-prefix
            var skipPrefix = _skipPrefixes.Any(prefix =>
                fileName.StartsWith(prefix, StringComparison.OrdinalIgnoreCase));

            if (skipPrefix)
            {
                Console.ForegroundColor = ConsoleColor.DarkGray;
                Console.WriteLine($"Skipping (excluded prefix): {relativePath}");
                Console.ResetColor();
                continue;
            }

            result.Add(pngFile);
        }

        return result;
    }

    private static void ParseArguments(string[] args)
    {
        foreach (var arg in args)
        {
            if (arg.StartsWith("--quality=") || arg.StartsWith("-q="))
            {
                var value = arg.Split('=')[1];
                if (int.TryParse(value, out var quality))
                    _quality = Math.Clamp(quality, 0, 100);
            }
            else if (arg.StartsWith("--path=") || arg.StartsWith("-p="))
            {
                _targetPath = arg.Split('=', 2)[1];
            }
            else if (arg.StartsWith("--skip-folder="))
            {
                _skipFolders.Add(arg.Split('=', 2)[1]);
            }
            else if (arg.StartsWith("--skip-prefix="))
            {
                _skipPrefixes.Add(arg.Split('=', 2)[1]);
            }
            else if (arg == "--force" || arg == "-f")
            {
                _force = true;
            }
            else if (arg == "--help" || arg == "-h")
            {
                ShowHelp();
                Environment.Exit(0);
            }
        }
    }

    private static void ShowHelp()
    {
        Console.WriteLine("Usage: dotnet run [options]");
        Console.WriteLine("\nOptions:");
        Console.WriteLine("  --path=<dir>, -p=<dir>          Directory to scan (default: current working directory)");
        Console.WriteLine("  --quality=<0-100>, -q=<0-100>   WebP quality (default: 85)");
        Console.WriteLine("  --force, -f                      Force reconversion of up-to-date files");
        Console.WriteLine("  --skip-folder=<name>             Skip a folder by name (repeatable)");
        Console.WriteLine("  --skip-prefix=<prefix>           Skip files whose name starts with prefix (repeatable)");
        Console.WriteLine("  --help, -h                       Show this help message");
        Console.WriteLine("\nExamples:");
        Console.WriteLine("  dotnet run");
        Console.WriteLine("  dotnet run --path=C:\\MyProject\\wwwroot");
        Console.WriteLine("  dotnet run --quality=90 --force");
        Console.WriteLine("  dotnet run --skip-folder=unity --skip-folder=vendor");
        Console.WriteLine("  dotnet run --skip-prefix=favicon --skip-prefix=apple-touch-icon");
    }

    private static string FormatFileSize(long size)
    {
        if (size > 1024 * 1024)
            return $"{size / (1024.0 * 1024.0):N2} MB";
        if (size > 1024)
            return $"{size / 1024.0:N2} KB";
        return $"{size} bytes";
    }
}