refactor: use extensible design for fetching playlist from single file

app/playlistmanager.cpp

@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: MIT
 
 #include "playlistmanager.h"
-#include "winplaylistpatch.h"
+#include "playlistscout.h"
 
 #include <QCollator>
 #include <QDir>
@@ -72,50 +72,14 @@ bool PlaylistManager::loadSingleFilePlaylist(const QUrl& url) {
     if (!checkUrl(url))
         return false;
 
-    QList<QUrl> playlist;
-    std::optional<qsizetype> idx = std::nullopt;
-
-#ifdef Q_OS_WIN
-    // In Windows, Qt approach can not aware Windows Explorer custom sort order.
-    // So we need to try using Win32 functions for fetching it at first
-    if (!WinPlaylistPatch::loadSingleFilePlaylist(url, m_allowedSuffixes, playlist, idx)) {
-#endif // Q_OS_WIN
-
-        // If Windows approach is failed or we are not in Windows,
-        // use Qt way to process it.
-
-        QFileInfo info(url.toLocalFile());
-        QDir dir(info.path());
-        QString currentFileName = info.fileName();
-
-        QStringList entryList = dir.entryList(
-            m_allowedSuffixes, QDir::Files | QDir::NoSymLinks, QDir::NoSort);
-
-        QCollator collator;
-        collator.setNumericMode(true);
-
-        std::sort(entryList.begin(), entryList.end(), collator);
-
-        playlist.clear();
-        idx = std::nullopt;
-        for (qsizetype i = 0; i < entryList.count(); i++) {
-            const QString &fileName = entryList.at(i);
-            const QString &oneEntry = dir.absoluteFilePath(fileName);
-            const QUrl &url = QUrl::fromLocalFile(oneEntry);
-            if (!checkUrl(url)) {
-                return false;
-            }
-            playlist.append(url);
-            if (fileName == currentFileName) {
-                idx = i;
-            }
-        }
-
-#ifdef Q_OS_WIN
+    // Scout playlist by given file
+    auto scoutResult = PlaylistScout::scout(url, m_allowedSuffixes);
+    if (!scoutResult.has_value()) {
+        return false;
     }
-#endif // Q_OS_WIN
 
-    setPlaylist(std::move(playlist), idx);
+    // Setup playlist with index
+    setPlaylist(std::move(scoutResult->playlist), scoutResult->indexHint);
     return true;
 }