added categories, import export, settings

lib/utils/fuzzy.dart

@@ -0,0 +1,40 @@
+/// Lightweight fuzzy matching for product search.
+library;
+
+String _normalize(String value) =>
+    value.trim().toLowerCase().replaceAll(RegExp(r'\s+'), ' ');
+
+/// True when [query] fuzzily matches [text].
+bool fuzzyMatch(String query, String text) {
+  final q = _normalize(query);
+  if (q.isEmpty) return true;
+  final t = _normalize(text);
+  if (t.contains(q)) return true;
+
+  for (final word in q.split(' ')) {
+    if (word.isEmpty) continue;
+    if (!t.contains(word) && !_subsequence(word, t)) return false;
+  }
+  if (q.contains(' ')) return true;
+  return _subsequence(q, t);
+}
+
+/// Higher is better. Null when [query] does not match.
+int? fuzzyScore(String query, String text) {
+  final q = _normalize(query);
+  if (q.isEmpty) return 0;
+  final t = _normalize(text);
+  if (t == q) return 1000;
+  if (t.startsWith(q)) return 800;
+  if (t.contains(q)) return 600 - t.indexOf(q);
+  if (!fuzzyMatch(q, t)) return null;
+  return 200 - (t.length - q.length).abs().clamp(0, 150);
+}
+
+bool _subsequence(String query, String text) {
+  var i = 0;
+  for (var c = 0; c < text.length && i < query.length; c++) {
+    if (text.codeUnitAt(c) == query.codeUnitAt(i)) i++;
+  }
+  return i == query.length;
+}