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/*
* 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 <QString>
#include "launchselectors.h"
class QLocalServer;
/// Makes a launch either the running instance or a messenger to it (item 200).
///
/// **This is not network protocol work.** A QLocalServer is a unix domain
/// socket between two copies of this program, owned by the user, in the user's
/// own state directory. The rule in AGENTS.md is about IMAP and SMTP.
///
/// Knows nothing about queries, accounts or mail: it carries a LaunchSelectors
/// from one process to another and emits what arrived.
class SingleInstance : public QObject
{
Q_OBJECT
public:
/// \p socketPath is a filesystem path, so a test can point it inside a
/// QTemporaryDir and never touch the user's real one.
explicit SingleInstance(const QString &socketPath,
QObject *parent = nullptr);
~SingleInstance() override;
/// Tries to become the instance others talk to.
///
/// Returns true when this process is now listening, false when another
/// instance already is OR when no socket could be created at all. The
/// caller treats both falses the same way for the second case: **a socket
/// that cannot be created must not stop the window opening**, or a
/// read-only state directory costs the user their mail client.
///
/// Handles the stale socket file, which is the ordinary aftermath of a
/// crash: it attempts a CONNECTION first, and a refused connection on an
/// existing file proves nothing is serving it, so the file may be
/// replaced. Connecting first is what stops a live instance being removed
/// out from under itself, and it is the ONLY guard: listen() replaces a
/// taken path rather than refusing it (see the .cpp).
bool tryBecomeServer();
/// True when tryBecomeServer() succeeded and this process is listening.
bool isServer() const;
/// Sends \p selectors to the running instance. Returns false when there is
/// none, or when the write could not be completed.
///
/// An EMPTY selector set is still sent: a bare `qtmaildir` against a
/// running window means "raise yourself", which is a request and not a
/// no-op.
bool sendToRunningInstance(const LaunchSelectors &selectors);
signals:
/// A later launch handed these over. Emitted on the server side only.
void selectorsReceived(const LaunchSelectors &selectors);
private:
QString m_socketPath;
QLocalServer *m_server = nullptr;
};
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