Perform first OCR extraction

moneymgr_mobile/lib/utils/ocr_utils.dart

@@ -0,0 +1,44 @@
+import 'dart:math';
+import 'dart:typed_data';
+import 'dart:ui' as ui;
+
+import 'package:flutter/material.dart';
+import 'package:google_mlkit_text_recognition/google_mlkit_text_recognition.dart';
+import 'package:logging/logging.dart';
+
+/// Attempt to extract total amount from invoice image
+Future<double?> extractTotalFromBill(Uint8List imgBuff) async {
+  final decodedImage = await decodeImageFromList(imgBuff);
+
+  final byteData = await decodedImage.toByteData(
+    format: ui.ImageByteFormat.rawRgba,
+  );
+
+  final image = InputImage.fromBitmap(
+    bitmap: byteData!.buffer.asUint8List(),
+    width: decodedImage.width,
+    height: decodedImage.height,
+  );
+
+  final textRecognizer = TextRecognizer(script: TextRecognitionScript.latin);
+  final extractionResult = await textRecognizer.processImage(image);
+
+  Logger.root.fine("Expense text: ${extractionResult.text}");
+
+  // Check for highest amount on invoice
+  final regexp = RegExp(
+    r'([0-9]+([ ]*(\\.|,)[ ]*[0-9]{1,2}){0,1})[ \\t\\n]*(EUR|eur|€)',
+    multiLine: true,
+    caseSensitive: false,
+  );
+  var highest = 0.0;
+  for (final match in regexp.allMatches(extractionResult.text)) {
+    if (match.groupCount == 0) continue;
+
+    // Process only numeric value
+    final value = (match.group(1) ?? "").replaceAll(",", ".");
+    highest = max(highest, double.tryParse(value) ?? 0.0);
+  }
+
+  return highest == 0.0 ? null : highest;
+}