2 files changed, 119 insertions, 18 deletions

diff --git a/src/views/draganddrophelper.cpp b/src/views/draganddrophelper.cpp
index 7b9949df4..7163507a6 100644
--- a/src/views/draganddrophelper.cpp
+++ b/src/views/draganddrophelper.cpp
@@ -73,20 +73,85 @@ bool DragAndDropHelper::supportsDropping(const KFileItem &destItem)
     return (destItem.isDir() && destItem.isWritable()) || destItem.isDesktopFile();
 }
 
+DragAndDropHelper::DragAndDropHelper(QObject *parent)
+    : QObject(parent)
+{
+    m_destItemCacheInvalidationTimer.setSingleShot(true);
+    m_destItemCacheInvalidationTimer.setInterval(30000);
+    connect(&m_destItemCacheInvalidationTimer, &QTimer::timeout, this, [this]() {
+        m_destItemCache = KFileItem();
+    });
+}
+
 void DragAndDropHelper::updateDropAction(QDropEvent *event, const QUrl &destUrl)
 {
+    auto processEvent = [this](QDropEvent *event) {
+        if (supportsDropping(m_destItemCache)) {
+            event->setDropAction(event->proposedAction());
+            event->accept();
+        } else {
+            event->setDropAction(Qt::IgnoreAction);
+            event->ignore();
+        }
+    };
+
+    m_lastUndecidedEvent = nullptr;
+
     if (urlListMatchesUrl(event->mimeData()->urls(), destUrl)) {
         event->setDropAction(Qt::IgnoreAction);
         event->ignore();
+        return;
     }
-    KFileItem item(destUrl);
-    if (!item.isLocalFile() || supportsDropping(item)) {
-        event->setDropAction(event->proposedAction());
-        event->accept();
-    } else {
-        event->setDropAction(Qt::IgnoreAction);
-        event->ignore();
+
+    if (destUrl == m_destItemCache.url()) {
+        // We already received events for this URL, and already have the
+        // stat result cached because:
+        // 1. it's a local file, and we already called KFileItem(destUrl)
+        // 2. it's a remote file, and StatJob finished
+        processEvent(event);
+        return;
     }
+
+    if (m_statJob) {
+        if (destUrl == m_statJobUrl) {
+            // We already received events for this URL. Still waiting for
+            // the stat result. StatJob will process the event when it finishes.
+            m_lastUndecidedEvent = event;
+            return;
+        }
+
+        // We are waiting for the stat result of a different URL. Cancel.
+        m_statJob->kill();
+        m_statJob = nullptr;
+        m_statJobUrl.clear();
+    }
+
+    if (destUrl.isLocalFile()) {
+        // New local URL. KFileItem will stat on demand.
+        m_destItemCache = KFileItem(destUrl);
+        m_destItemCacheInvalidationTimer.start();
+        processEvent(event);
+        return;
+    }
+
+    // New remote URL. Start a StatJob and process the event when it finishes.
+    m_lastUndecidedEvent = event;
+    m_statJob = KIO::stat(destUrl, KIO::StatJob::SourceSide, KIO::StatDetail::StatBasic, KIO::JobFlag::HideProgressInfo);
+    m_statJobUrl = destUrl;
+    connect(m_statJob, &KIO::StatJob::result, this, [this, processEvent](KJob *job) {
+        KIO::StatJob *statJob = static_cast<KIO::StatJob *>(job);
+
+        m_destItemCache = KFileItem(statJob->statResult(), m_statJobUrl);
+        m_destItemCacheInvalidationTimer.start();
+
+        if (m_lastUndecidedEvent) {
+            processEvent(m_lastUndecidedEvent);
+            m_lastUndecidedEvent = nullptr;
+        }
+
+        m_statJob = nullptr;
+        m_statJobUrl.clear();
+    });
 }
 
 void DragAndDropHelper::clearUrlListMatchesUrlCache()
diff --git a/src/views/draganddrophelper.h b/src/views/draganddrophelper.h
index 73043febc..df3b49966 100644
--- a/src/views/draganddrophelper.h
+++ b/src/views/draganddrophelper.h
@@ -11,9 +11,11 @@
 #include "dolphin_export.h"
 
 #include <KFileItem>
+#include <KIO/StatJob>
 
 #include <QList>
 #include <QString>
+#include <QTimer>
 #include <QUrl>
 
 class QDropEvent;
@@ -24,7 +26,7 @@ namespace KIO
 class DropJob;
 }
 
-class DOLPHIN_EXPORT DragAndDropHelper
+class DOLPHIN_EXPORT DragAndDropHelper : public QObject
 {
 public:
     /**
@@ -52,16 +54,6 @@ public:
     static bool supportsDropping(const KFileItem &destItem);
 
     /**
-     * Updates the drop action according to whether the destination supports dropping.
-     * If supportsDropping(destUrl), set dropAction = proposedAction. Otherwise, set
-     * dropAction = Qt::IgnoreAction.
-     *
-     * @param event     Drop event.
-     * @param destUrl   Destination URL.
-     */
-    static void updateDropAction(QDropEvent *event, const QUrl &destUrl);
-
-    /**
      * @return True if destUrl is contained in the urls parameter.
      */
     static bool urlListMatchesUrl(const QList<QUrl> &urls, const QUrl &destUrl);
@@ -84,11 +76,55 @@ public:
      */
     static void clearUrlListMatchesUrlCache();
 
+    DragAndDropHelper(QObject *parent);
+
+    /**
+     * Updates the drop action according to whether the destination supports dropping.
+     * If supportsDropping(destUrl), set dropAction = proposedAction. Otherwise, set
+     * dropAction = Qt::IgnoreAction.
+     *
+     * @param event     Drop event.
+     * @param destUrl   Destination URL.
+     */
+    void updateDropAction(QDropEvent *event, const QUrl &destUrl);
+
 private:
     /**
      * Stores the results of the expensive checks made in urlListMatchesUrl.
      */
     static QHash<QUrl, bool> m_urlListMatchesUrlCache;
+
+    /**
+     * When updateDropAction() is called with a remote URL, we create a StatJob to
+     * check if the destination is a directory or a desktop file. We cache the result
+     * here to avoid doing the stat again on subsequent calls to updateDropAction().
+     */
+    KFileItem m_destItemCache;
+
+    /**
+     * Only keep the cache for 30 seconds, because the stat of the destUrl might change.
+     */
+    QTimer m_destItemCacheInvalidationTimer;
+
+    /**
+     * A StatJob on-fly to fill the cache for a remote URL. We shouldn't create more
+     * than one StatJob at a time, so we keep a pointer to the current one.
+     */
+    KIO::StatJob *m_statJob = nullptr;
+
+    /**
+     * The URL for which the StatJob is running.
+     * Note: We can't use m_statJob->url() because StatJob might resolve the URL to be
+     *       different from what we passed into stat(). E.g. "mtp:<bus-name>" is resolved
+     *       to "mtp:<phone name>"
+     */
+    QUrl m_statJobUrl;
+
+    /**
+     * The last event we received in updateDropAction(), but can't react to yet,
+     * because a StatJob is on-fly.
+     */
+    QDropEvent *m_lastUndecidedEvent = nullptr;
 };
 
 #endif