internal class TicketRenderer()

in src/Relecloud.TicketRenderer/Services/TicketRenderer.cs [12:118]
78 lines of code
9 McCabe index (conditional complexity)

    internal class TicketRenderer(ILogger<TicketRenderer> logger, IImageStorage imageStorage, IBarcodeGenerator barcodeGenerator) : ITicketRenderer
    {
        // Default ticket image name format string (in case no path is specified).
        private const string TicketNameFormatString = "ticket-{0}.png";

        private static readonly Dictionary<string, SKTypeface> Typefaces = GetFonts();

        public async Task<string?> RenderTicketAsync(TicketRenderRequestMessage request, CancellationToken cancellationToken)
        {
            logger.LogInformation("Rendering ticket {ticket} for message {message}", request.Ticket?.Id.ToString() ?? "<null>", request.MessageId);

            // Error checking to ensure that we have all the necessary information to render the ticket.
            if (request.Ticket == null)
            {
                logger.LogWarning("Nothing to render for null ticket");
                return null;
            }
            if (request.Ticket.Concert == null)
            {
                logger.LogWarning("Cannot find the concert related to this ticket");
                return null;
            }
            if (request.Ticket.User == null)
            {
                logger.LogWarning("Cannot find the user related to this ticket");
                return null;
            }
            if (request.Ticket.Customer == null)
            {
                logger.LogWarning("Cannot find the customer related to this ticket");
                return null;
            }

            // Generate Skia assets for creating the image.
            // SkiaSharp is a recommended cross-platform third-party open source alternative to System.Drawing which works.
            // See https://learn.microsoft.com/dotnet/core/compatibility/core-libraries/6.0/system-drawing-common-windows-only#recommended-action
            using var headerFont = new SKFont(Typefaces["OpenSans-Bold"], 18);
            using var textFont = new SKFont(Typefaces["OpenSans-Regular"], 12);
            using var bluePaint = new SKPaint { Color = SKColors.DarkSlateBlue, Style = SKPaintStyle.StrokeAndFill, IsAntialias = true };
            using var grayPaint = new SKPaint { Color = SKColors.Gray, Style = SKPaintStyle.StrokeAndFill, IsAntialias = true };
            using var blackPaint = new SKPaint { Color = SKColors.Black, Style = SKPaintStyle.StrokeAndFill, IsAntialias = true };
            using var surface = SKSurface.Create(new SKImageInfo(640, 200, SKColorType.Rgb888x)); 
            
            // Initialize and clear the canvas.
            var canvas = surface.Canvas;
            canvas.Clear(SKColors.White);

            // Print concert details.
            canvas.DrawText(SKTextBlob.Create(request.Ticket.Concert.Artist, headerFont), 10, 30, bluePaint);
            canvas.DrawText(SKTextBlob.Create($"{request.Ticket.Concert.Location}   |   {request.Ticket.Concert.StartTime.UtcDateTime:yyyy-MM-dd hh:mm tt}", textFont), 10, 50, grayPaint);
            canvas.DrawText(SKTextBlob.Create($"{request.Ticket.Customer.Email}   |   ${request.Ticket.Concert.Price:F2}", textFont), 10, 70, grayPaint);

            // Print a fake barcode.
            var barcode = barcodeGenerator.GenerateBarcode(request.Ticket).GetEnumerator();
            var offset = 15;

            while (barcode.MoveNext())
            {
                var width = barcode.Current;
                canvas.DrawRect(offset, 95, width, 90, blackPaint);

                if (barcode.MoveNext())
                {
                    offset += width + barcode.Current;
                }
            }

            using var image = surface.Snapshot();
            using var data = image.Encode(SKEncodedImageFormat.Png, 100);
            
            // Generate an output path for the image if none is specified.
            var outputPath = string.IsNullOrEmpty(request.OutputPath)
                ? string.Format(TicketNameFormatString, request.Ticket.Id)
                : request.OutputPath;

            if (await imageStorage.StoreImageAsync(data.AsStream(), outputPath, cancellationToken))
            {
                return outputPath;
            }
            else
            {
                logger.LogError("Failed to store image for ticket {TicketId}", request.Ticket.Id);
                return null;
            }
        }

        // Helper method to load fonts from embedded resources.
        // Small Linux images (like the chiseled ones used with this project)
        // don't have fonts installed by default, so we need to load them from resources.
        private static Dictionary<string, SKTypeface> GetFonts()
        {
            static string GetFontName(string resourceName)
            {
                // The resource names are in the format "Relecloud.TicketRenderer.Fonts.<font name>.ttf".
                // This finds the last period in the name prior to the .ttf extension and takes the substring
                // between that index and the extension.
                var index = resourceName.LastIndexOf('.', resourceName.Length - 5);
                return resourceName.Substring(index + 1, resourceName.Length - (index + 1) - 4);
            }

            var assembly = typeof(TicketRenderer).Assembly;
            var fontResourceNames = assembly.GetManifestResourceNames().Where(s => s.Contains("Fonts"));
            return fontResourceNames.ToDictionary(
                GetFontName,
                name => SKTypeface.FromStream(assembly.GetManifestResourceStream(name)));
        }
    }