// SPDX-License-Identifier: LGPL-2.1-only
// Copyright (C) 2026 Liberux Labs, S. L. <info@liberux.net>

//! `xdg-session-management-v1` client glue plus the runtime hooks that
//! persist `App::save_state` and turn signals into a clean exit.

use std::os::fd::{ AsRawFd, FromRawFd, OwnedFd };
use std::sync::atomic::{ AtomicI32, Ordering };
use std::time::Duration;

use calloop::timer::{ TimeoutAction, Timer };
use calloop::LoopHandle;
use smithay_client_toolkit::reexports::client::globals::GlobalList;
use smithay_client_toolkit::reexports::client::{ Connection, Dispatch, QueueHandle };
use smithay_client_toolkit::shell::xdg::window::Window;

use crate::app::App;
use crate::protocol::xdg_session_management_v1::
{
	xdg_session_manager_v1::{ self, XdgSessionManagerV1 },
	xdg_session_v1::{ self, XdgSessionV1 },
	xdg_toplevel_session_v1::{ self, XdgToplevelSessionV1 },
};
use crate::session_state::{ RestoreReason, Startup, StateStore };

use super::error::RunError;
use super::AppData;

pub( crate ) const TOPLEVEL_NAME: &str = "main";
pub( crate ) const SAVE_INTERVAL: Duration = Duration::from_secs( 30 );
pub( crate ) const RESTORE_ENV: &str = "LTK_SESSION_RESTORE";

pub( crate ) struct SessionRuntime
{
	pub session:          Option<XdgSessionV1>,
	pub toplevel_session: Option<XdgToplevelSessionV1>,
	/// `None` when persistence is off: layer / lock surfaces, an unusable
	/// app_id, a concurrent instance, or after `replaced`.
	pub store:            Option<StateStore>,
	pub reason:           RestoreReason,
	pub replaced:         bool,
}

impl SessionRuntime
{
	pub fn disabled() -> Self
	{
		Self {
			session:          None,
			toplevel_session: None,
			store:            None,
			reason:           RestoreReason::Launch,
			replaced:         false,
		}
	}

	/// Phase 1, before any window exists: read the restore hint from the
	/// environment, decide the reason, hand saved bytes to the app and mark
	/// the run as live.
	pub fn bootstrap<A: App>( app: &mut A ) -> Self
	{
		let env_restore = std::env::var_os( RESTORE_ENV ).is_some_and( |v| v == "1" );
		if std::env::var_os( RESTORE_ENV ).is_some()
		{
			// SAFETY: removing an env var is sound only when no other thread
			// is reading the environment concurrently. We are still in the
			// init phase before `set_channel_sender`, so the app has had
			// no opportunity to spawn worker threads yet.
			unsafe { std::env::remove_var( RESTORE_ENV ); }
		}

		let mut rt = Self::disabled();
		let Some( mut store ) = StateStore::open( app.app_id() ) else { return rt };
		match store.decide( env_restore )
		{
			Startup::Concurrent =>
			{
				eprintln!( "ltk: another instance of {} is running; session persistence disabled", app.app_id() );
				return rt;
			}
			Startup::Reason( reason ) => rt.reason = reason,
		}
		if rt.reason != RestoreReason::Launch
		{
			if let Some( bytes ) = store.load_state()
			{
				app.restore_state( bytes );
			}
		}
		store.mark_running();
		rt.store = Some( store );
		rt
	}

	/// Phase 2: bind the manager and open the session. Silent when the
	/// compositor lacks the global. The manager proxy is not kept: it has
	/// no state of its own and the session outlives it server-side.
	pub fn bind<A: App>( &mut self, globals: &GlobalList, qh: &QueueHandle<AppData<A>> )
	{
		let Some( store ) = &self.store else { return };
		let manager: Option<XdgSessionManagerV1> = globals.bind( qh, 1..=1, () ).ok();
		let Some( manager ) = manager else { return };
		let reason = match self.reason
		{
			RestoreReason::Launch         => xdg_session_manager_v1::Reason::Launch,
			RestoreReason::Recover        => xdg_session_manager_v1::Reason::Recover,
			RestoreReason::SessionRestore => xdg_session_manager_v1::Reason::SessionRestore,
		};
		self.session = Some( manager.get_session( reason, store.session_id(), qh, () ) );
	}

	/// Phase 3: register the main toplevel. Must run before the window's
	/// first commit or the compositor raises `already_mapped`.
	pub fn attach_toplevel<A: App>( &mut self, window: &Window, qh: &QueueHandle<AppData<A>> )
	{
		let Some( session ) = &self.session else { return };
		self.toplevel_session =
			Some( session.restore_toplevel( window.xdg_toplevel(), TOPLEVEL_NAME.to_string(), qh, () ) );
	}

	pub fn periodic_save<A: App>( &mut self, app: &A )
	{
		if self.replaced { return; }
		if let Some( store ) = &mut self.store
		{
			store.save_state_if_changed( app.save_state() );
		}
	}

	pub fn on_exit<A: App>( &mut self, app: &A )
	{
		if self.replaced { return; }
		if let Some( store ) = &mut self.store
		{
			store.mark_clean_exit( app.save_state() );
		}
	}

	pub fn on_replaced( &mut self )
	{
		eprintln!( "ltk: session taken over by another instance; this one stops persisting state" );
		if let Some( t ) = self.toplevel_session.take() { t.destroy(); }
		if let Some( s ) = self.session.take() { s.destroy(); }
		self.replaced = true;
		self.store = None;
	}
}

static SIGNAL_PIPE_WR: AtomicI32 = AtomicI32::new( -1 );

/// Async-signal-safe: an atomic load and a `write`, errno preserved.
extern "C" fn on_termination_signal( sig: libc::c_int )
{
	unsafe
	{
		let errno = *libc::__errno_location();
		let fd = SIGNAL_PIPE_WR.load( Ordering::Acquire );
		if fd >= 0
		{
			let byte = sig as u8;
			let _ = libc::write( fd, ( &byte as *const u8 ).cast(), 1 );
		}
		*libc::__errno_location() = errno;
	}
}

/// Self-pipe rather than a signalfd: a `sigaction` handler is process-
/// wide, so the clean exit works no matter which thread the kernel
/// picks, without blocking the signal in every thread — a mask that
/// children would inherit across exec.
pub( crate ) fn install_signal_source<A: App>( handle: &LoopHandle<'static, AppData<A>> ) -> Result<(), RunError>
{
	use calloop::generic::Generic;
	use calloop::{ Interest, Mode, PostAction };

	let mut fds = [ -1i32; 2 ];
	if unsafe { libc::pipe2( fds.as_mut_ptr(), libc::O_CLOEXEC | libc::O_NONBLOCK ) } != 0
	{
		return Err( RunError::EventLoop( format!( "signal pipe2: {}", std::io::Error::last_os_error() ) ) );
	}
	SIGNAL_PIPE_WR.store( fds[ 1 ], Ordering::Release );

	unsafe
	{
		let mut action: libc::sigaction = std::mem::zeroed();
		action.sa_sigaction = on_termination_signal as usize;
		action.sa_flags = libc::SA_RESTART;
		libc::sigemptyset( &mut action.sa_mask );
		for sig in [ libc::SIGTERM, libc::SIGINT ]
		{
			if libc::sigaction( sig, &action, std::ptr::null_mut() ) != 0
			{
				return Err( RunError::EventLoop( format!( "sigaction: {}", std::io::Error::last_os_error() ) ) );
			}
		}
	}

	let read_end = unsafe { OwnedFd::from_raw_fd( fds[ 0 ] ) };
	handle
		.insert_source( Generic::new( read_end, Interest::READ, Mode::Level ), |_, fd, data: &mut AppData<A>|
		{
			let mut sig = None;
			let mut buf = [ 0u8; 16 ];
			loop
			{
				let n = unsafe { libc::read( fd.as_raw_fd(), buf.as_mut_ptr().cast(), buf.len() ) };
				if n <= 0 { break; }
				sig = Some( buf[ 0 ] as i32 );
			}
			if let Some( sig ) = sig
			{
				let name = match sig
				{
					libc::SIGTERM => "SIGTERM",
					libc::SIGINT  => "SIGINT",
					_             => "signal",
				};
				eprintln!( "ltk: {name} received, exiting cleanly" );
				data.exit_requested = true;
			}
			Ok( PostAction::Continue )
		} )
		.map_err( |e| RunError::EventLoop( format!( "signal pipe insert_source: {e:?}" ) ) )?;
	Ok( () )
}

pub( crate ) fn install_save_timer<A: App>( handle: &LoopHandle<'static, AppData<A>> ) -> Result<(), RunError>
{
	handle
		.insert_source( Timer::from_duration( SAVE_INTERVAL ), |_, _, data: &mut AppData<A>|
		{
			data.session.periodic_save( &data.app );
			TimeoutAction::ToDuration( SAVE_INTERVAL )
		} )
		.map_err( |e| RunError::EventLoop( format!( "save timer insert_source: {e:?}" ) ) )?;
	Ok( () )
}

impl<A: App> Dispatch<XdgSessionManagerV1, ()> for AppData<A>
{
	fn event(
		_state: &mut Self,
		_proxy: &XdgSessionManagerV1,
		_event: xdg_session_manager_v1::Event,
		_data:  &(),
		_conn:  &Connection,
		_qh:    &QueueHandle<Self>,
	)
	{
	}
}

impl<A: App> Dispatch<XdgSessionV1, ()> for AppData<A>
{
	fn event(
		state:  &mut Self,
		_proxy: &XdgSessionV1,
		event:  xdg_session_v1::Event,
		_data:  &(),
		_conn:  &Connection,
		_qh:    &QueueHandle<Self>,
	)
	{
		match event
		{
			xdg_session_v1::Event::Created { session_id } =>
			{
				if let Some( store ) = &mut state.session.store
				{
					store.set_session_id( session_id );
				}
			}
			xdg_session_v1::Event::Restored => {}
			xdg_session_v1::Event::Replaced => state.session.on_replaced(),
		}
	}
}

impl<A: App> Dispatch<XdgToplevelSessionV1, ()> for AppData<A>
{
	fn event(
		_state: &mut Self,
		_proxy: &XdgToplevelSessionV1,
		_event: xdg_toplevel_session_v1::Event,
		_data:  &(),
		_conn:  &Connection,
		_qh:    &QueueHandle<Self>,
	)
	{
	}
}

#[ cfg( test ) ]
mod tests
{
	use super::*;

	fn read_one( fd: i32 ) -> Option<u8>
	{
		let mut buf = [ 0u8; 4 ];
		let n = unsafe { libc::read( fd, buf.as_mut_ptr().cast(), buf.len() ) };
		( n == 1 ).then( || buf[ 0 ] )
	}

	#[ test ]
	fn handler_writes_signal_to_pipe()
	{
		let mut fds = [ -1i32; 2 ];
		assert_eq!( unsafe { libc::pipe2( fds.as_mut_ptr(), libc::O_CLOEXEC | libc::O_NONBLOCK ) }, 0 );
		SIGNAL_PIPE_WR.store( fds[ 1 ], Ordering::Release );

		on_termination_signal( libc::SIGTERM );
		assert_eq!( read_one( fds[ 0 ] ), Some( libc::SIGTERM as u8 ) );

		// The real wiring: raise() delivers synchronously to this
		// thread, so the handler has run before it returns.
		unsafe
		{
			let mut action: libc::sigaction = std::mem::zeroed();
			action.sa_sigaction = on_termination_signal as usize;
			action.sa_flags = libc::SA_RESTART;
			libc::sigemptyset( &mut action.sa_mask );
			assert_eq!( libc::sigaction( libc::SIGTERM, &action, std::ptr::null_mut() ), 0 );
			libc::raise( libc::SIGTERM );
		}
		assert_eq!( read_one( fds[ 0 ] ), Some( libc::SIGTERM as u8 ) );

		unsafe
		{
			let mut dfl: libc::sigaction = std::mem::zeroed();
			dfl.sa_sigaction = libc::SIG_DFL;
			libc::sigemptyset( &mut dfl.sa_mask );
			libc::sigaction( libc::SIGTERM, &dfl, std::ptr::null_mut() );
		}
		SIGNAL_PIPE_WR.store( -1, Ordering::Release );
		unsafe
		{
			libc::close( fds[ 0 ] );
			libc::close( fds[ 1 ] );
		}
	}
}