Replace parameters in one step

This would avoid the unwanted effect of replacing parameter coming from
another parameter.

src/app/application.cpp

@@ -313,14 +313,6 @@ void Application::processMessage(const QString &message)
 
 void Application::runExternalProgram(const BitTorrent::Torrent *torrent) const
 {
-    QString program = Preferences::instance()->getAutoRunProgram().trimmed();
-    program.replace("%N", torrent->name());
-    program.replace("%L", torrent->category());
-
-    QStringList tags = torrent->tags().values();
-    std::sort(tags.begin(), tags.end(), Utils::String::naturalLessThan<Qt::CaseInsensitive>);
-    program.replace("%G", tags.join(','));
-
 #if defined(Q_OS_WIN)
     const auto chopPathSep = [](const QString &str) -> QString
     {
@@ -328,22 +320,74 @@ void Application::runExternalProgram(const BitTorrent::Torrent *torrent) const
             return str.mid(0, (str.length() -1));
         return str;
     };
-    program.replace("%F", chopPathSep(Utils::Fs::toNativePath(torrent->contentPath())));
-    program.replace("%R", chopPathSep(Utils::Fs::toNativePath(torrent->rootPath())));
-    program.replace("%D", chopPathSep(Utils::Fs::toNativePath(torrent->savePath())));
+#endif
+
+    QString program = Preferences::instance()->getAutoRunProgram().trimmed();
+
+    for (int i = (program.length() - 2); i >= 0; --i)
+    {
+        if (program[i] != QLatin1Char('%'))
+            continue;
+
+        const ushort specifier = program[i + 1].unicode();
+        switch (specifier)
+        {
+        case u'C':
+            program.replace(i, 2, QString::number(torrent->filesCount()));
+            break;
+        case u'D':
+#if defined(Q_OS_WIN)
+            program.replace(i, 2, chopPathSep(Utils::Fs::toNativePath(torrent->savePath())));
+#else
+            program.replace(i, 2, Utils::Fs::toNativePath(torrent->savePath()));
+#endif
+            break;
+        case u'F':
+#if defined(Q_OS_WIN)
+            program.replace(i, 2, chopPathSep(Utils::Fs::toNativePath(torrent->contentPath())));
 #else
-    program.replace("%F", Utils::Fs::toNativePath(torrent->contentPath()));
-    program.replace("%R", Utils::Fs::toNativePath(torrent->rootPath()));
-    program.replace("%D", Utils::Fs::toNativePath(torrent->savePath()));
+            program.replace(i, 2, Utils::Fs::toNativePath(torrent->contentPath()));
 #endif
-    program.replace("%C", QString::number(torrent->filesCount()));
-    program.replace("%Z", QString::number(torrent->totalSize()));
-    program.replace("%T", torrent->currentTracker());
-    // TODO: Update GUI/WebUI labels for this parameter to express its meaning more clearly
-    program.replace("%I", torrent->id().toString());
-
-    Logger *logger = Logger::instance();
-    logger->addMessage(tr("Torrent: %1, running external program, command: %2").arg(torrent->name(), program));
+            break;
+        case u'G':
+            {
+                QStringList tags = torrent->tags().values();
+                std::sort(tags.begin(), tags.end(), Utils::String::naturalLessThan<Qt::CaseInsensitive>);
+                program.replace(i, 2, tags.join(','));
+            }
+            break;
+        case u'I':
+            program.replace(i, 2, torrent->id().toString());
+            break;
+        case u'L':
+            program.replace(i, 2, torrent->category());
+            break;
+        case u'N':
+            program.replace(i, 2, torrent->name());
+            break;
+        case u'R':
+#if defined(Q_OS_WIN)
+            program.replace(i, 2, chopPathSep(Utils::Fs::toNativePath(torrent->rootPath())));
+#else
+            program.replace(i, 2, Utils::Fs::toNativePath(torrent->rootPath()));
+#endif
+            break;
+        case u'T':
+            program.replace(i, 2, torrent->currentTracker());
+            break;
+        case u'Z':
+            program.replace(i, 2, QString::number(torrent->totalSize()));
+            break;
+        default:
+            // do nothing
+            break;
+        }
+
+        // decrement `i` to avoid unwanted replacement, example pattern: "%%N"
+        --i;
+    }
+
+    LogMsg(tr("Torrent: %1, running external program, command: %2").arg(torrent->name(), program));
 
 #if defined(Q_OS_WIN)
     auto programWchar = std::make_unique<wchar_t[]>(program.length() + 1);