Deliver remote file drags in one gesture using deferred MIME

tools/chatgui/src/member_files/browser.cpp

@@ -33,6 +33,7 @@
 #include <QDir>
 #include <QTemporaryDir>
 #include <QStandardPaths>
+#include <QEventLoop>
 #include <functional>
 #include <limits>
 #include <cstring>
@@ -53,6 +54,26 @@ public:
 protected:
     void startDrag(Qt::DropActions) override { exportRequested(); }
 };
+
+// Системный менеджер может запросить URI после drop. До завершения скачивания путь не выдаётся.
+class DeferredFileMimeData : public QMimeData {
+public:
+    std::function<QString()> localFile;
+    QStringList formats() const override { return {QStringLiteral("text/uri-list")}; }
+    bool hasFormat(const QString& format) const override { return format == QStringLiteral("text/uri-list"); }
+protected:
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
+    QVariant retrieveData(const QString& format, QMetaType type) const override {
+#else
+    QVariant retrieveData(const QString& format, QVariant::Type type) const override {
+#endif
+        if (!hasFormat(format)) return {};
+        QString local = localFile();
+        if (local.isEmpty()) return {};
+        const_cast<DeferredFileMimeData*>(this)->setUrls({QUrl::fromLocalFile(local)});
+        return QMimeData::retrieveData(format, type);
+    }
+};
 static QString quotaSize(quint64 bytes) {
     return bytes <= (quint64)std::numeric_limits<qint64>::max() ? QLocale().formattedDataSize((qint64)bytes, 2) :
         text("%1 bytes").arg(QLocale().toString(bytes));
@@ -585,9 +606,33 @@ void MemberFileBrowser::exportFile(bool clipboard) {
             if (local.isEmpty() || !startTransfer(remote, local, false, version)) {
                 DEBUG_ERROR(DEBUG_CATEGORY_MEDIA, "file browser: export could not start remote=%s local=%s", qPrintable(remote), qPrintable(local));
                 m_exportId = 0; updateActions(); m_status->setText(text("Cannot prepare a local copy"));
+                emit exportFinished();
             }
         }, Qt::QueuedConnection);
     }));
+    if (!clipboard) {
+        QPointer<MemberFileBrowser> guard(this);
+        auto* mime = new DeferredFileMimeData;
+        mime->localFile = [guard, id, key] {
+            if (!guard) return QString();
+            if (guard->m_exportId == id) {
+                DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "file browser: drag waiting for local copy id=%llu", (unsigned long long)id);
+                QEventLoop wait;
+                QObject::connect(guard, &MemberFileBrowser::exportFinished, &wait, &QEventLoop::quit);
+                QObject::connect(guard, &QObject::destroyed, &wait, &QEventLoop::quit);
+                wait.exec();
+            }
+            QString local = guard ? guard->m_exportCache.value(key) : QString();
+            DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "file browser: drag data ready id=%llu local=%s", (unsigned long long)id, qPrintable(local));
+            return local;
+        };
+        auto* drag = new QDrag(m_entries); drag->setParent(QCoreApplication::instance()); drag->setMimeData(mime);
+        // MIME живёт до возврата из native drag, даже если окно файлов закрыли во вложенном цикле событий.
+        connect(this, &QObject::destroyed, drag, [] { QDrag::cancel(); });
+        Qt::DropAction action = drag->exec(Qt::CopyAction, Qt::CopyAction);
+        if (guard && m_exportId == id) cancel();
+        DEBUG_INFO(DEBUG_CATEGORY_MEDIA, "file browser: native drag finished action=%d", int(action));
+    }
 }
 
 bool MemberFileBrowser::startTransfer(const QString& remote, const QString& local, bool uploading, const QByteArray& version) {
@@ -623,8 +668,9 @@ void MemberFileBrowser::onTransfer(const uint8_t* data, int length) {
             m_exportCache.insert(m_exportKey, m_local);
             DEBUG_INFO(DEBUG_CATEGORY_MEDIA, "file browser: local copy ready path=%s", qPrintable(m_local));
             if (m_exportClipboard) publishExport(m_local, true);
-            else m_status->setText(text("Local copy ready. Drag the file again, or use Copy file."));
+            else m_status->setText(text("Local copy ready"));
         }
+        emit exportFinished();
         return;
     }
     if (m_uploadBatchId) {
@@ -675,6 +721,7 @@ void MemberFileBrowser::cancel() {
     if (m_exportId) {
         DEBUG_INFO(DEBUG_CATEGORY_MEDIA, "file browser: export cancelled id=%llu", (unsigned long long)m_exportId);
         m_exportId = 0; m_status->setText(text("Copy cancelled")); updateActions();
+        emit exportFinished();
     }
     if (m_dropId) { m_dropId = 0; m_uploadStatus->setText(text("Upload queue cancelled")); updateActions(); }
     if (m_uploadBatchId) finishUploads(text("Upload queue cancelled"));