import 'dart:convert';
import 'dart:math';
import 'package:image/image.dart' as img;

class FingerprintValidation {
  final bool isComplete;
  final double coverageRatio;   // % of "ridge" pixels
  final double contrast;        // std dev of pixel intensity
  final String reason;

  FingerprintValidation({
    required this.isComplete,
    required this.coverageRatio,
    required this.contrast,
    required this.reason,
  });
}

FingerprintValidation validateFingerprintBase64(
    String base64Image, {
      double minCoverage = 0.20,   // tune per scanner DPI/size
      double maxCoverage = 0.65,
      double minContrast = 25.0,
      double edgeCutoffThreshold = 0.45, // % of border pixels that are "ridge"
    }) {
  final bytes = base64Decode(base64Image);
  final image = img.decodeImage(bytes);

  if (image == null) {
    return FingerprintValidation(
      isComplete: false,
      coverageRatio: 0,
      contrast: 0,
      reason: 'decode_failed',
    );
  }

  final gray = img.grayscale(image);
  final w = gray.width, h = gray.height;

  int ridgePixels = 0;
  int total = 0;
  double sum = 0, sumSq = 0;

  // simple Otsu-ish threshold: use mean as baseline, refine below
  final List<int> intensities = [];
  for (final px in gray) {
    final v = img.getLuminance(px).toDouble();
    intensities.add(v.toInt());
    sum += v;
    total++;
  }
  final mean = sum / total;
  for (final v in intensities) {
    sumSq += (v - mean) * (v - mean);
  }
  final contrast = sqrt(sumSq / total);

  // threshold: pixels darker than mean - 0.5*std are "ridges"
  final threshold = mean - (contrast * 0.5);
  for (final v in intensities) {
    if (v < threshold) ridgePixels++;
  }
  final coverage = ridgePixels / total;

  // edge/border check — if ridge pattern is heavily cut off at edges,
  // finger was likely partial or misplaced
  int borderRidge = 0, borderTotal = 0;
  for (int x = 0; x < w; x++) {
    for (final y in [0, h - 1]) {
      final v = img.getLuminance(gray.getPixel(x, y)).toDouble();
      borderTotal++;
      if (v < threshold) borderRidge++;
    }
  }
  for (int y = 0; y < h; y++) {
    for (final x in [0, w - 1]) {
      final v = img.getLuminance(gray.getPixel(x, y)).toDouble();
      borderTotal++;
      if (v < threshold) borderRidge++;
    }
  }
  final borderRatio = borderTotal == 0 ? 0 : borderRidge / borderTotal;

  String reason = 'ok';
  bool isComplete = true;

  if (contrast < minContrast) {
    isComplete = false;
    reason = 'Press finger on the scanner with more pressure';
  } else if (coverage < minCoverage) {
    isComplete = false;
    reason = 'Place finger fully on the scanner';
  } else if (coverage > maxCoverage) {
    isComplete = false;
    reason = 'Place finger lightly on the scanner';
  } else if (borderRatio > edgeCutoffThreshold) {
    isComplete = false;
    reason = 'Finger is not centered on the scanner';
  }

  return FingerprintValidation(
    isComplete: isComplete,
    coverageRatio: coverage,
    contrast: contrast,
    reason: reason,
  );
}