Simplify fast path in ArchiveModel::parentFor

Instead of splitting the path and comparing its pieces compare the whole
strings. This simplifies the code and makes it easier to get rid of the
costly string splitting in the future

part/archivemodel.cpp

@@ -42,7 +42,7 @@ using namespace Kerfuffle;
 
 // Used to speed up the loading of large archives.
 static Archive::Entry *s_previousMatch = nullptr;
-Q_GLOBAL_STATIC(QStringList, s_previousPieces)
+Q_GLOBAL_STATIC(QString, s_previousPath)
 
 ArchiveModel::ArchiveModel(const QString &dbusPathName, QObject *parent)
     : QAbstractItemModel(parent)
@@ -362,40 +362,28 @@ void ArchiveModel::initRootEntry()
 
 Archive::Entry *ArchiveModel::parentFor(const Archive::Entry *entry, InsertBehaviour behaviour)
 {
-#if QT_VERSION < QT_VERSION_CHECK(5, 15, 0)
-    QStringList pieces = entry->fullPath().split(QLatin1Char('/'), QString::SkipEmptyParts);
-#else
-    QStringList pieces = entry->fullPath().split(QLatin1Char('/'), Qt::SkipEmptyParts);
-#endif
-    if (pieces.isEmpty()) {
-        return nullptr;
-    }
-    pieces.removeLast();
+    QString fullPath = entry->fullPath();
 
-    // Used to speed up loading of large archives.
-    if (s_previousMatch) {
-        // The number of path elements must be the same for the shortcut
-        // to work.
-        if (s_previousPieces->count() == pieces.count()) {
-            bool equal = true;
+    // Remove the last segment from the path
+    if (fullPath.endsWith(QLatin1Char('/'))) {
+        fullPath = fullPath.chopped(1);
+    }
 
-            // Check if all pieces match.
-            for (int i = 0; i < s_previousPieces->count(); ++i) {
-                if (s_previousPieces->at(i) != pieces.at(i)) {
-                    equal = false;
-                    break;
-                }
-            }
+    const int index = fullPath.lastIndexOf(QLatin1Char('/'));
+    const QString folderPath = index != -1 ? fullPath.left(index) : QString();
 
-            // If match return it.
-            if (equal) {
-                return s_previousMatch;
-            }
-        }
+    if (s_previousMatch && *s_previousPath == folderPath) {
+        return s_previousMatch;
     }
 
     Archive::Entry *parent = m_rootEntry.data();
 
+#if QT_VERSION < QT_VERSION_CHECK(5, 15, 0)
+    QStringList pieces = folderPath.split(QLatin1Char('/'), QString::SkipEmptyParts);
+#else
+    QStringList pieces = folderPath.split(QLatin1Char('/'), Qt::SkipEmptyParts);
+#endif
+
     for (const QString &piece : qAsConst(pieces)) {
         Archive::Entry *entry = parent->find(piece);
         if (!entry) {
@@ -421,7 +409,7 @@ Archive::Entry *ArchiveModel::parentFor(const Archive::Entry *entry, InsertBehav
     }
 
     s_previousMatch = parent;
-    *s_previousPieces = pieces;
+    *s_previousPath = folderPath;
 
     return parent;
 }
@@ -595,7 +583,7 @@ void ArchiveModel::reset()
 {
     m_archive.reset(nullptr);
     s_previousMatch = nullptr;
-    s_previousPieces->clear();
+    s_previousPath->clear();
     initRootEntry();
 
     // TODO: make sure if it's ok to not have calls to beginRemoveColumns here