benscode-StitcherApi/Services/ImageService.cs

using SkiaSharp;
using StitcherApi.Models;
using StitcherApi.Services.Utilities;

namespace StitcherApi.Services;

public class ImageService : IImageService
{
    private const int TileDimension = 720;
    private const long HighQualityMemoryThreshold = 512 * 1024 * 1024 * 3;
    private readonly string _assetPath;
    private readonly ILogger<ImageService> _logger;

    public ImageService(IConfiguration configuration, ILogger<ImageService> logger)
    {
        _assetPath =
            configuration["AssetPath"]
            ?? throw new InvalidOperationException("AssetPath is not configured.");
        _logger = logger;
    }

    public Task<byte[]> GenerateImageAsync(GenerateImageRequest request)
    {
        return Task.Run(() =>
        {
            try
            {
                _logger.LogInformation(
                    "Starting image generation for canvas_rect: {CanvasRect}",
                    request.CanvasRect
                );

                var (startRow, endRow, startCol, endCol) = CoordinateHelper.ParseCanvasRect(
                    request.CanvasRect
                );
                int canvasWidth = (endCol - startCol + 1) * TileDimension;
                int canvasHeight = (endRow - startRow + 1) * TileDimension;
                int cropX = (int)(request.CropOffset[0] * canvasWidth);
                int cropY = (int)(request.CropOffset[1] * canvasHeight);
                int cropW = (int)(request.CropSize[0] * canvasWidth);
                int cropH = (int)(request.CropSize[1] * canvasHeight);

                int outputW = (int)(cropW * request.OutputScale);
                int outputH = (int)(cropH * request.OutputScale);
                if (outputW <= 0 || outputH <= 0)
                {
                    _logger.LogWarning(
                        "Output dimensions are zero or negative ({Width}x{Height}). Returning empty byte array.",
                        outputW,
                        outputH
                    );
                    return Array.Empty<byte>();
                }

                _logger.LogDebug("Calculated final dimensions: {Width}x{Height}", outputW, outputH);

                long requiredMemory = (long)cropW * cropH * 4;
                if (requiredMemory <= HighQualityMemoryThreshold)
                {
                    _logger.LogInformation(
                        "Using high-quality rendering path (required memory: {Memory}MB)",
                        requiredMemory / (1024 * 1024)
                    );
                    return GenerateWithHighQuality(
                        cropX,
                        cropY,
                        cropW,
                        cropH,
                        outputW,
                        outputH,
                        startRow,
                        startCol
                    );
                }
                else
                {
                    _logger.LogWarning(
                        "Required memory ({Memory}MB) exceeds threshold. Using low-memory fallback path. Image quality may be reduced.",
                        requiredMemory / (1024 * 1024)
                    );
                    return GenerateWithLowMemory(
                        cropX,
                        cropY,
                        cropW,
                        cropH,
                        outputW,
                        outputH,
                        startRow,
                        startCol,
                        request.OutputScale
                    );
                }
            }
            catch (Exception ex)
            {
                _logger.LogError(
                    ex,
                    "An unhandled exception occurred during image generation for request: {@Request}",
                    request
                );
                throw;
            }
        });
    }

    private byte[] GenerateWithHighQuality(
        int cropX,
        int cropY,
        int cropW,
        int cropH,
        int outputW,
        int outputH,
        int startRow,
        int startCol
    )
    {
        using var cropBufferBitmap = new SKBitmap(cropW, cropH);
        using var cropBufferCanvas = new SKCanvas(cropBufferBitmap);

        DrawTilesToCanvas(cropBufferCanvas, cropX, cropY, cropW, cropH, startRow, startCol);

        using var finalBitmap = new SKBitmap(outputW, outputH);

        var sampling = new SKSamplingOptions(SKCubicResampler.Mitchell);
        cropBufferBitmap.ScalePixels(finalBitmap, sampling);

        return EncodeBitmap(finalBitmap);
    }

    private byte[] GenerateWithLowMemory(
        int cropX,
        int cropY,
        int cropW,
        int cropH,
        int outputW,
        int outputH,
        int startRow,
        int startCol,
        float scale
    )
    {
        using var finalBitmap = new SKBitmap(outputW, outputH);
        using var finalCanvas = new SKCanvas(finalBitmap);
        var sampling = new SKSamplingOptions(SKCubicResampler.Mitchell);

        int firstTileCol = cropX / TileDimension;
        int lastTileCol = (cropX + cropW - 1) / TileDimension;
        int firstTileRow = cropY / TileDimension;
        int lastTileRow = (cropY + cropH - 1) / TileDimension;

        for (int r = firstTileRow; r <= lastTileRow; r++)
        {
            for (int c = firstTileCol; c <= lastTileCol; c++)
            {
                var tilePath = Path.Combine(
                    _assetPath,
                    $"{CoordinateHelper.IndexToRow(startRow + r)}{startCol + c + 1}.png"
                );
                using var tileBitmap = SKBitmap.Decode(tilePath);
                if (tileBitmap == null)
                    continue;
                using var tileImage = SKImage.FromBitmap(tileBitmap);

                int tileCanvasX = c * TileDimension;
                int tileCanvasY = r * TileDimension;
                int intersectX = Math.Max(cropX, tileCanvasX);
                int intersectY = Math.Max(cropY, tileCanvasY);
                int intersectEndX = Math.Min(cropX + cropW, tileCanvasX + TileDimension);
                int intersectEndY = Math.Min(cropY + cropH, tileCanvasY + TileDimension);

                var sourceRect = SKRect.Create(
                    intersectX - tileCanvasX,
                    intersectY - tileCanvasY,
                    intersectEndX - intersectX,
                    intersectEndY - intersectY
                );
                var destRect = SKRect.Create(
                    (intersectX - cropX) * scale,
                    (intersectY - cropY) * scale,
                    (intersectEndX - intersectX) * scale,
                    (intersectEndY - intersectY) * scale
                );

                finalCanvas.DrawImage(tileImage, sourceRect, destRect, sampling);
            }
        }
        return EncodeBitmap(finalBitmap);
    }

    private void DrawTilesToCanvas(
        SKCanvas canvas,
        int cropX,
        int cropY,
        int cropW,
        int cropH,
        int startRow,
        int startCol
    )
    {
        int firstTileCol = cropX / TileDimension;
        int lastTileCol = (cropX + cropW - 1) / TileDimension;
        int firstTileRow = cropY / TileDimension;
        int lastTileRow = (cropY + cropH - 1) / TileDimension;

        for (int r = firstTileRow; r <= lastTileRow; r++)
        {
            for (int c = firstTileCol; c <= lastTileCol; c++)
            {
                var tilePath = Path.Combine(
                    _assetPath,
                    $"{CoordinateHelper.IndexToRow(startRow + r)}{startCol + c + 1}.png"
                );
                using var tileBitmap = SKBitmap.Decode(tilePath);
                if (tileBitmap == null)
                    continue;

                int tileCanvasX = c * TileDimension;
                int tileCanvasY = r * TileDimension;
                int intersectX = Math.Max(cropX, tileCanvasX);
                int intersectY = Math.Max(cropY, tileCanvasY);
                int intersectEndX = Math.Min(cropX + cropW, tileCanvasX + TileDimension);
                int intersectEndY = Math.Min(cropY + cropH, tileCanvasY + TileDimension);

                var sourceRect = SKRect.Create(
                    intersectX - tileCanvasX,
                    intersectY - tileCanvasY,
                    intersectEndX - intersectX,
                    intersectEndY - intersectY
                );
                var destRect = SKRect.Create(
                    intersectX - cropX,
                    intersectY - cropY,
                    intersectEndX - intersectX,
                    intersectEndY - intersectY
                );

                canvas.DrawBitmap(tileBitmap, sourceRect, destRect);
            }
        }
    }

    private byte[] EncodeBitmap(SKBitmap bitmap)
    {
        using var image = SKImage.FromBitmap(bitmap);
        using var data = image.Encode(SKEncodedImageFormat.Png, 100);
        _logger.LogInformation(
            "Image generation successful. Returning {ByteCount} bytes.",
            data.Size
        );
        return data.ToArray();
    }
}