feat: debounce the calendar sync command after writes

3 files changed, 126 insertions, 0 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index e70039e..8f32fcc 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -47,6 +47,7 @@ add_library(qtmaildir_lib STATIC
     repeatrule.cpp
     calendarstore.cpp
     calendarwriter.cpp
+    calendarsync.cpp
 )
 
 target_include_directories(qtmaildir_lib
diff --git a/src/calendarsync.cpp b/src/calendarsync.cpp
new file mode 100644
index 0000000..2fc555f
--- /dev/null
+++ b/src/calendarsync.cpp
@@ -0,0 +1,71 @@
+/*
+ * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "calendarsync.h"
+
+CalendarSync::CalendarSync(const QString &command, int delayMs, QObject *parent)
+    : QObject(parent), m_command(command)
+{
+    m_timer.setSingleShot(true);
+    m_timer.setInterval(delayMs);
+    connect(&m_timer, &QTimer::timeout, this, &CalendarSync::run);
+    m_process.setProcessChannelMode(QProcess::MergedChannels);
+    connect(&m_process, &QProcess::readyRead, this,
+            [this]() { m_output += m_process.readAll(); });
+    connect(&m_process, &QProcess::finished, this,
+            [this](int code, QProcess::ExitStatus status) {
+        emit finished(status == QProcess::NormalExit && code == 0,
+                      QString::fromLocal8Bit(m_output));
+        if (m_again) {
+            m_again = false;
+            m_timer.start();
+        }
+    });
+    connect(&m_process, &QProcess::errorOccurred, this,
+            [this](QProcess::ProcessError error) {
+        if (error == QProcess::FailedToStart)
+            emit finished(false, m_process.errorString());
+    });
+}
+
+void CalendarSync::schedule()
+{
+    if (m_command.isEmpty())
+        return;
+    if (isRunning())
+        m_again = true;
+    else
+        m_timer.start();  // restarting is the debounce
+}
+
+bool CalendarSync::isRunning() const
+{
+    return m_process.state() != QProcess::NotRunning;
+}
+
+void CalendarSync::run()
+{
+    // splitCommand, not a shell: quoting works and nothing is interpreted.
+    QStringList parts = QProcess::splitCommand(m_command);
+    if (parts.isEmpty())
+        return;
+    const QString program = parts.takeFirst();
+    m_output.clear();
+    emit started();
+    m_process.start(program, parts);
+}
diff --git a/src/calendarsync.h b/src/calendarsync.h
new file mode 100644
index 0000000..c406f79
--- /dev/null
+++ b/src/calendarsync.h
@@ -0,0 +1,54 @@
+/*
+ * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#pragma once
+
+#include <QObject>
+#include <QProcess>
+#include <QTimer>
+
+/// Runs calendar_sync_command a short delay after the last write.
+///
+/// The calendar's counterpart to MailSync, and deliberately smaller: no lock
+/// monitoring and no status file, because the command itself takes the
+/// flock that cron shares. A write arriving while a run is in progress is not
+/// dropped: it queues exactly one more run for when this one finishes, since
+/// the running sync may have listed the vdir before the write landed.
+class CalendarSync : public QObject
+{
+    Q_OBJECT
+
+public:
+    CalendarSync(const QString &command, int delayMs, QObject *parent = nullptr);
+
+    void schedule();
+    bool isRunning() const;
+
+signals:
+    void started();
+    void finished(bool ok, const QString &output);
+
+private:
+    void run();
+
+    QString m_command;
+    QTimer m_timer;
+    QProcess m_process;
+    QByteArray m_output;
+    bool m_again = false;
+};