impact/lib/services/opencv_target_service.dart

import 'dart:math' as math;
import 'package:opencv_dart/opencv_dart.dart' as cv;

class TargetDetectionResult {
  final double centerX;
  final double centerY;
  final double radius;
  final bool success;

  TargetDetectionResult({
    required this.centerX,
    required this.centerY,
    required this.radius,
    this.success = true,
  });

  factory TargetDetectionResult.failure() {
    return TargetDetectionResult(
      centerX: 0.5,
      centerY: 0.5,
      radius: 0.4,
      success: false,
    );
  }
}

class OpenCVTargetService {
  /// Detect the main target (center and radius) from an image file
  Future<TargetDetectionResult> detectTarget(String imagePath) async {
    try {
      // Read image
      final img = cv.imread(imagePath, flags: cv.IMREAD_COLOR);
      if (img.isEmpty) {
        return TargetDetectionResult.failure();
      }

      // Convert to grayscale
      final gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY);

      // Apply Gaussian blur to reduce noise
      final blurred = cv.gaussianBlur(gray, (9, 9), 2, sigmaY: 2);

      // Detect circles using Hough Transform
      // Parameters need to be tuned for the specific target type
      final circles = cv.HoughCircles(
        blurred,
        cv.HOUGH_GRADIENT,
        1, // dp: Inverse ratio of the accumulator resolution to the image resolution
        (img.rows / 8)
            .toDouble(), // minDist: Minimum distance between the centers of the detected circles
        param1: 100, // param1: Gradient value for Canny edge detection
        param2:
            30, // param2: Accumulator threshold for the circle centers at the detection stage
        minRadius: img.cols ~/ 20, // minRadius
        maxRadius: img.cols ~/ 2, // maxRadius
      );

      // HoughCircles returns a Mat in opencv_dart? Or a specific object?
      // Checking common bindings: usually returns a Mat (1, N, 3) of floats.
      // If circles is empty or null, return failure.

      if (circles.isEmpty) {
        // Try with different parameters if first attempt fails (more lenient)
        final looseCircles = cv.HoughCircles(
          blurred,
          cv.HOUGH_GRADIENT,
          1,
          (img.rows / 8).toDouble(),
          param1: 50,
          param2: 20,
          minRadius: img.cols ~/ 20,
          maxRadius: img.cols ~/ 2,
        );

        if (looseCircles.isEmpty) {
          return TargetDetectionResult.failure();
        }
        return _findBestCircle(looseCircles, img.cols, img.rows);
      }

      return _findBestCircle(circles, img.cols, img.rows);
    } catch (e) {
      // print('Error detecting target with OpenCV: $e');
      return TargetDetectionResult.failure();
    }
  }

  TargetDetectionResult _findBestCircle(cv.Mat circles, int width, int height) {
    // circles is a Mat of shape (1, N, 3) where N is number of circles
    // Each circle is (x, y, radius)

    // We want the circle that is closest to the center of the image and reasonably large
    double bestScore = -1.0;
    double bestX = 0.5;
    double bestY = 0.5;
    double bestRadius = 0.4;

    // The shape is typically (1, N, 3) for HoughCircles
    // We need to access the data.
    // Assuming we can iterate.
    // In opencv_dart 1.0+, Mat might not be directly iterable like a list.
    // We can use circles.at<Vec3f>(0, i) if available or similar.
    // Or we might need to interpret the memory.

    // For now, let's assume a simplified access pattern or that we can get a list.
    // If this fails to compile, we will fix it based on the error.

    // Attempting to access knowing standard layout:
    // circles.rows is 1, circles.cols is N.

    final int numCircles = circles.cols;

    for (int i = 0; i < numCircles; i++) {
      // Use the generic 'at' or specific getter if known.
      // Assuming Vec3f is returned as a specific type or List<double>
      // Note: in many dart bindings, we might get a list of points directly.
      // But HoughCircles typically returns Mat.

      // Let's try to use `at<cv.Vec3f>(0, i)` which is common in C++ and some bindings.
      // If not, we might need `ptr` access.

      final vec = circles.at<cv.Vec3f>(0, i);
      final double x = vec.val1;
      final double y = vec.val2;
      final double r = vec.val3;

      final relX = x / width;
      final relY = y / height;
      final relR = r / math.min(width, height);

      // Score based on centrality and size
      final distFromCenter = math.sqrt(
        math.pow(relX - 0.5, 2) + math.pow(relY - 0.5, 2),
      );
      final sizeScore =
          relR; // Larger is usually better for the main target outer ring

      // We penalize distance from center
      final score = sizeScore - (distFromCenter * 0.5);

      if (score > bestScore) {
        bestScore = score;
        bestX = relX;
        bestY = relY;
        bestRadius = relR;
      }
    }

    return TargetDetectionResult(
      centerX: bestX,
      centerY: bestY,
      radius: bestRadius,
    );
  }
}