Add TorrentHandle::availableFileFractions() function

The function returns list of availability values for all torrent files.
The availability here is different to that one in the progress bar. Here
it shows what part of the file's pieces is available (i.e. we do not count
availability > 1 for a piece).

src/base/bittorrent/torrenthandle.cpp

@@ -1953,3 +1953,24 @@ void TorrentHandle::prioritizeFiles(const QVector<int> &priorities)
 
     updateStatus();
 }
+
+QVector<qreal> TorrentHandle::availableFileFractions() const
+{
+    QVector<int> piecesAvailability = pieceAvailability();
+    const auto filesCount = this->filesCount();
+    // libtorrent returns empty array for seeding only torrents
+    if (piecesAvailability.empty()) return QVector<qreal>(filesCount, -1.);
+
+    QVector<qreal> res;
+    res.reserve(filesCount);
+    TorrentInfo info = this->info();
+    for (int file = 0; file < filesCount; ++file) {
+        TorrentInfo::PieceRange filePieces = info.filePieces(file);
+        int availablePieces = 0;
+        for (int piece = filePieces.first(); piece <= filePieces.last(); ++piece) {
+            availablePieces += piecesAvailability[piece] > 0 ? 1 : 0;
+        }
+        res.push_back(static_cast<qreal>(availablePieces) / filePieces.size());
+    }
+    return res;
+}

src/base/bittorrent/torrenthandle.h

@@ -361,6 +361,14 @@ namespace BitTorrent
         void handleAppendExtensionToggled();
         void saveResumeData(bool updateStatus = false);
 
+        /**
+         * @brief fraction of file pieces that are available at least from one peer
+         *
+         * This is not the same as torrrent availability, it is just a fraction of pieces
+         * that can be downloaded right now. It varies between 0 to 1.
+         */
+        QVector<qreal> availableFileFractions() const;
+
     private:
         typedef boost::function<void ()> EventTrigger;