perf(history): early-exit scanner for the history one-line preview (#1545)

lib/features/workspace/sql_query_history_dialog.dart

@@ -85,13 +85,7 @@ class _SqlQueryHistoryDialogContentState
     });
   }
 
-  static final _whitespacePattern = RegExp(r'\s+');
-
-  static String _previewOneLine(String sql) {
-    final collapsed = sql.replaceAll(_whitespacePattern, ' ').trim();
-    if (collapsed.length <= 96) return collapsed;
-    return '${collapsed.substring(0, 93)}…';
-  }
+  static String _previewOneLine(String sql) => previewSqlOneLine(sql);
 
   static String? _formatWhen(String iso) {
     final t = DateTime.tryParse(iso)?.toLocal();
@@ -405,3 +399,52 @@ class _SqlQueryHistoryDialogContentState
     );
   }
 }
+
+/// Longest one-line preview kept whole; longer text is cut to
+/// [_previewKeep] characters plus an ellipsis.
+const int _previewMax = 96;
+const int _previewKeep = 93;
+
+/// Same set as the regex `\s` (what the old `replaceAll(RegExp(r'\s+'), ' ')`
+/// collapsed).
+bool _isPreviewWhitespace(int c) =>
+    (c >= 0x09 && c <= 0x0D) ||
+    c == 0x20 ||
+    c == 0xA0 ||
+    c == 0x1680 ||
+    (c >= 0x2000 && c <= 0x200A) ||
+    c == 0x2028 ||
+    c == 0x2029 ||
+    c == 0x202F ||
+    c == 0x205F ||
+    c == 0x3000 ||
+    c == 0xFEFF;
+
+/// One-line, whitespace-collapsed, trimmed preview of [sql] for a list row.
+///
+/// Reads only as far as it needs: a 100 KB migration is cut after about a
+/// hundred characters instead of being copied whole by a regex replace (#1545).
+@visibleForTesting
+String previewSqlOneLine(String sql) {
+  final out = StringBuffer();
+  var length = 0;
+  var pendingSpace = false;
+  for (var i = 0; i < sql.length; i++) {
+    if (_isPreviewWhitespace(sql.codeUnitAt(i))) {
+      pendingSpace = length > 0;
+      continue;
+    }
+    if (pendingSpace) {
+      out.writeCharCode(0x20);
+      length++;
+      pendingSpace = false;
+      if (length > _previewMax) break;
+    }
+    out.writeCharCode(sql.codeUnitAt(i));
+    length++;
+    if (length > _previewMax) break;
+  }
+  final text = out.toString();
+  if (length <= _previewMax) return text;
+  return '${text.substring(0, _previewKeep)}…';
+}

test/features/workspace/sql_query_history_preview_test.dart

@@ -0,0 +1,44 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:querya_desktop/features/workspace/sql_query_history_dialog.dart';
+
+/// The implementation before #1545: collapse the whole text, then cut.
+String _reference(String sql) {
+  final collapsed = sql.replaceAll(RegExp(r'\s+'), ' ').trim();
+  if (collapsed.length <= 96) return collapsed;
+  return '${collapsed.substring(0, 93)}…';
+}
+
+void main() {
+  group('previewSqlOneLine (#1545)', () {
+    test('matches the old collapse-then-cut result', () {
+      final inputs = <String>[
+        '',
+        ' ',
+        '   \n\t  ',
+        'SELECT 1',
+        '  SELECT   1 \n FROM\tt  ',
+        'SELECT a, b　FROM t',
+        'a' * 96,
+        'a' * 97,
+        '${'a' * 96}   ',
+        '${'a' * 96} b',
+        '${'a' * 95} b',
+        '${'a' * 94} b c',
+        ('select x from t\n' * 20),
+        '\n\n\n${'x ' * 200}',
+        'a' * 5000,
+        'word ' * 30000,
+      ];
+      for (final sql in inputs) {
+        expect(previewSqlOneLine(sql), _reference(sql),
+            reason: 'input of length ${sql.length}');
+      }
+    });
+
+    test('long text is cut to 93 characters and an ellipsis', () {
+      final out = previewSqlOneLine('SELECT ${'column_name, ' * 100}FROM t');
+      expect(out.length, 94);
+      expect(out.endsWith('…'), isTrue);
+    });
+  });
+}