teksilo-platform 0.24.1

// SPDX-License-Identifier: MPL-2.0
// SPDX-FileCopyrightText: 2026 FernTech

//! Window-manager capability probe for X11 client-side decorations.
//!
//! A borderless X11 window is only usable if the window manager implements
//! `_NET_WM_MOVERESIZE` — that is the *only* way a client can ask to be moved
//! or resized once it has told the WM not to draw a frame. Shipping
//! `with_decorations(false)` against a WM that lacks it produces a window the
//! user cannot move or resize at all, which is far worse than keeping native
//! decorations.
//!
//! So we probe before committing. The awkward part is ordering: winit needs the
//! decoration flag at `WindowAttributes` construction time, before any window —
//! and therefore any connection — exists, and winit exposes no way to borrow
//! its own connection early (`WindowExtX11` is an empty trait). We therefore
//! open a short-lived connection of our own, ask, and close it. The answer is
//! cached for the process.
//!
//! The probe is skipped entirely unless [`active_window_system`] predicts X11:
//! `DISPLAY` is set in virtually every Wayland session too, and some
//! compositors start XWayland lazily on the first X client connection — an
//! unconditional probe would spawn XWayland for apps that never need it.
//!
//! [`active_window_system`]: crate::window_system::active_window_system

use std::sync::OnceLock;

use x11rb::protocol::xproto::{Atom, AtomEnum, Window};

use super::connection::{Atoms, X11Connection, X11Error};

/// What the running window manager can do for a borderless window.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct WmCapabilities {
    /// An EWMH-compliant window manager is running (validated via the two-step
    /// `_NET_SUPPORTING_WM_CHECK` handshake).
    pub ewmh_wm_present: bool,
    /// `_NET_WM_MOVERESIZE` is advertised in `_NET_SUPPORTED`.
    pub move_resize: bool,
}

impl WmCapabilities {
    /// Nothing works — the answer for "no WM", "not X11", or "probe failed".
    pub const NONE: Self = Self {
        ewmh_wm_present: false,
        move_resize: false,
    };

    /// Whether a custom title bar is safe to install. Requires both a live
    /// EWMH window manager and interactive move/resize; without either, the
    /// window would be undecorated *and* immovable.
    pub fn supports_custom_chrome(self) -> bool {
        self.ewmh_wm_present && self.move_resize
    }
}

/// Validate `_NET_SUPPORTING_WM_CHECK` per the EWMH two-step rule.
///
/// The spec requires the root window's `_NET_SUPPORTING_WM_CHECK` to name a
/// window that carries the *same* property pointing at itself. A single check
/// is not enough: when a window manager dies without cleaning up, the root
/// property survives and names a window that is gone or has been recycled, so a
/// one-step check happily reports a WM that is not running.
///
/// Returns the validated check window.
pub fn validate_wm_check(root_value: Option<u32>, child_value: Option<u32>) -> Option<Window> {
    match root_value {
        Some(win) if win != 0 && child_value == Some(win) => Some(win),
        _ => None,
    }
}

/// Whether `_NET_SUPPORTED` advertises `atom`.
pub fn supports_atom(supported: &[Atom], atom: Atom) -> bool {
    supported.contains(&atom)
}

/// Ask the running window manager what it supports. Opens (and drops) its own
/// short-lived connection.
fn probe_uncached() -> Result<WmCapabilities, X11Error> {
    let conn = X11Connection::open()?;
    let atoms = conn.atoms();

    let root_check = conn
        .get_property_full(
            conn.root(),
            atoms.net_supporting_wm_check,
            AtomEnum::WINDOW.into(),
        )?
        .and_then(|value| value.as_u32());

    // Step two: the named window must point back at itself. A `BadWindow` here
    // means the window is gone — a stale property from a crashed WM — which is
    // exactly the case this handshake exists to catch, so treat the error as
    // "no WM" rather than propagating it.
    let child_check = match root_check {
        Some(win) => conn
            .get_property_full(win, atoms.net_supporting_wm_check, AtomEnum::WINDOW.into())
            .ok()
            .flatten()
            .and_then(|value| value.as_u32()),
        None => None,
    };

    let ewmh_wm_present = validate_wm_check(root_check, child_check).is_some();
    if !ewmh_wm_present {
        return Ok(WmCapabilities::NONE);
    }

    let supported = conn
        .get_property_full(conn.root(), atoms.net_supported, AtomEnum::ATOM.into())?
        .map(|value| value.as_u32s())
        .unwrap_or_default();

    Ok(WmCapabilities {
        ewmh_wm_present,
        move_resize: supports_atom(&supported, atoms.net_wm_moveresize),
    })
}

/// The running window manager's capabilities, probed once per process.
///
/// Returns [`WmCapabilities::NONE`] when the session is not X11, when no
/// EWMH-compliant WM is running, or when the probe itself fails. Every failure
/// mode lands on "assume custom chrome is unsafe", so the worst case is a
/// window with ordinary native decorations.
///
/// A WM that starts *after* this runs (the documented GDK login-race) is not
/// re-detected; the window keeps native decorations for its lifetime.
pub fn capabilities() -> WmCapabilities {
    static CACHE: OnceLock<WmCapabilities> = OnceLock::new();
    *CACHE.get_or_init(|| {
        use crate::window_system::{WindowSystem, active_window_system};

        if active_window_system() != WindowSystem::X11 {
            return WmCapabilities::NONE;
        }
        match probe_uncached() {
            Ok(caps) => caps,
            Err(err) => {
                eprintln!(
                    "teksilo-platform: X11 window-manager probe failed ({err}); \
                     keeping native window decorations"
                );
                WmCapabilities::NONE
            }
        }
    })
}

/// Keep an X11 window that is not mapped yet out of the taskbar, by adding
/// `_NET_WM_STATE_SKIP_TASKBAR` to its `_NET_WM_STATE`.
///
/// EWMH lets a client write `_NET_WM_STATE` itself only before the window is
/// first mapped; the window manager reads it at map time. Afterwards the
/// state changes only through a client message to the root window, and a
/// window manager removes the property when the window is withdrawn, so a
/// window unmapped and mapped again has to be marked again.
///
/// Atoms already in the property are kept, and the atom is added once. The
/// write goes over a connection of our own, not winit's, so this returns
/// only after the server confirmed it: that round trip is what orders it
/// before the map request winit sends over its own connection.
pub fn mark_skip_taskbar(window: Window) -> Result<(), X11Error> {
    add_net_wm_state(window, |atoms| atoms.net_wm_state_skip_taskbar)
}

/// Make an X11 window that is not mapped yet modal to its transient parent,
/// by adding `_NET_WM_STATE_MODAL` to its `_NET_WM_STATE`, as GTK marks a
/// modal dialog. A window manager keeps it above its parent and may refuse
/// the parent focus while it is up. Written before the first map, like
/// [`mark_skip_taskbar`].
#[doc(hidden)]
pub fn mark_modal(window: Window) -> Result<(), X11Error> {
    add_net_wm_state(window, |atoms| atoms.net_wm_state_modal)
}

/// Add the atom `which` picks to `window`'s `_NET_WM_STATE`, keeping the
/// atoms already there and adding it once; see [`mark_skip_taskbar`].
fn add_net_wm_state(window: Window, which: fn(&Atoms) -> Atom) -> Result<(), X11Error> {
    use x11rb::protocol::xproto::PropMode;
    use x11rb::wrapper::ConnectionExt as _;

    let conn = X11Connection::open()?;
    let atoms = conn.atoms();
    let atom = which(atoms);
    if read_net_wm_state(&conn, window)?.contains(&atom) {
        return Ok(());
    }
    conn.conn()
        .change_property32(
            PropMode::APPEND,
            window,
            atoms.net_wm_state,
            AtomEnum::ATOM,
            &[atom],
        )?
        .check()?;
    Ok(())
}

/// The atoms in `window`'s `_NET_WM_STATE`, empty when it has none. Opens
/// (and drops) its own short-lived connection.
pub fn net_wm_state(window: Window) -> Result<Vec<Atom>, X11Error> {
    read_net_wm_state(&X11Connection::open()?, window)
}

/// The window `window` is transient for (ICCCM `WM_TRANSIENT_FOR`, which
/// [`set_transient_for`] writes for a modal window; winit never writes it),
/// `None` when it has none. Opens (and drops) its own short-lived connection.
pub fn transient_for(window: Window) -> Result<Option<Window>, X11Error> {
    let conn = X11Connection::open()?;
    Ok(conn
        .get_property_full(
            window,
            AtomEnum::WM_TRANSIENT_FOR.into(),
            AtomEnum::WINDOW.into(),
        )?
        .and_then(|value| value.as_u32()))
}

/// Write ICCCM `WM_TRANSIENT_FOR` on `window`, naming `parent`. Like
/// [`mark_skip_taskbar`], over a connection of our own, returning once the
/// server confirmed it so the write is ordered before winit's map request.
pub fn set_transient_for(window: Window, parent: Window) -> Result<(), X11Error> {
    use x11rb::protocol::xproto::PropMode;
    use x11rb::wrapper::ConnectionExt as _;

    let conn = X11Connection::open()?;
    conn.conn()
        .change_property32(
            PropMode::REPLACE,
            window,
            AtomEnum::WM_TRANSIENT_FOR,
            AtomEnum::WINDOW,
            &[parent],
        )?
        .check()?;
    Ok(())
}

/// Whether `window`'s `_NET_WM_WINDOW_TYPE` names a dialog
/// (`_NET_WM_WINDOW_TYPE_DIALOG`), as a modal window's does. Opens (and
/// drops) its own short-lived connection.
pub fn is_dialog_type(window: Window) -> Result<bool, X11Error> {
    let conn = X11Connection::open()?;
    let types = conn
        .get_property_full(
            window,
            conn.atoms().net_wm_window_type,
            AtomEnum::ATOM.into(),
        )?
        .map(|value| value.as_u32s())
        .unwrap_or_default();
    Ok(types.contains(&conn.atoms().net_wm_window_type_dialog))
}

/// [`net_wm_state`] over a connection already open.
fn read_net_wm_state(conn: &X11Connection, window: Window) -> Result<Vec<Atom>, X11Error> {
    Ok(conn
        .get_property_full(window, conn.atoms().net_wm_state, AtomEnum::ATOM.into())?
        .map(|value| value.as_u32s())
        .unwrap_or_default())
}

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

    #[test]
    fn wm_check_needs_the_child_to_point_at_itself() {
        assert_eq!(validate_wm_check(Some(0x200), Some(0x200)), Some(0x200));
    }

    #[test]
    fn stale_wm_check_is_rejected() {
        // A window manager that died without cleaning up leaves the root
        // property naming a window that no longer answers. One-step checking
        // would report a live WM here.
        assert_eq!(validate_wm_check(Some(0x200), None), None);
        // Recycled XID now owned by someone else, pointing elsewhere.
        assert_eq!(validate_wm_check(Some(0x200), Some(0x999)), None);
    }

    #[test]
    fn absent_wm_check_means_no_window_manager() {
        assert_eq!(validate_wm_check(None, None), None);
        assert_eq!(validate_wm_check(Some(0), Some(0)), None);
    }

    #[test]
    fn custom_chrome_needs_both_a_wm_and_move_resize() {
        assert!(
            WmCapabilities {
                ewmh_wm_present: true,
                move_resize: true
            }
            .supports_custom_chrome()
        );
        // A WM that cannot move the window would leave it stranded.
        assert!(
            !WmCapabilities {
                ewmh_wm_present: true,
                move_resize: false
            }
            .supports_custom_chrome()
        );
        // No WM at all: nothing would honour the Motif hint either.
        assert!(
            !WmCapabilities {
                ewmh_wm_present: false,
                move_resize: true
            }
            .supports_custom_chrome()
        );
        assert!(!WmCapabilities::NONE.supports_custom_chrome());
    }

    #[test]
    fn supported_atom_lookup() {
        assert!(supports_atom(&[10, 20, 30], 20));
        assert!(!supports_atom(&[10, 30], 20));
        assert!(!supports_atom(&[], 20));
    }

    /// Talks to a **real** X server, so it is `#[ignore]`d by default. This is
    /// the only way to check the probe against an actual window manager, since
    /// no in-process X server or protocol double exists for `cargo test`.
    ///
    /// ```text
    /// WAYLAND_DISPLAY= cargo test -p teksilo-platform -- --ignored --nocapture x11_probe
    /// ```
    ///
    /// Clearing `WAYLAND_DISPLAY` is what makes the session read as X11 (under
    /// a Wayland desktop this then probes XWayland's window manager).
    /// Talks to a **real** X server; no window manager is needed, since the
    /// window is never mapped.
    ///
    /// ```text
    /// WAYLAND_DISPLAY= cargo test -p teksilo-platform -- --ignored x11_skip_taskbar
    /// ```
    #[test]
    #[ignore = "requires a live X server; run with --ignored"]
    fn x11_skip_taskbar_adds_the_state_once_and_keeps_the_others() {
        use x11rb::connection::Connection as _;
        use x11rb::protocol::xproto::{ConnectionExt as _, CreateWindowAux, WindowClass};

        let conn = X11Connection::open().expect("connect to $DISPLAY");
        let atoms = conn.atoms().clone();
        let raw = conn.conn();
        let window = raw.generate_id().expect("allocate an XID");
        raw.create_window(
            x11rb::COPY_DEPTH_FROM_PARENT,
            window,
            conn.root(),
            0,
            0,
            16,
            16,
            0,
            WindowClass::INPUT_OUTPUT,
            x11rb::COPY_FROM_PARENT,
            &CreateWindowAux::new(),
        )
        .expect("send CreateWindow")
        .check()
        .expect("create an unmapped window");
        let above = raw
            .intern_atom(false, b"_NET_WM_STATE_ABOVE")
            .expect("send InternAtom")
            .reply()
            .expect("intern _NET_WM_STATE_ABOVE")
            .atom;
        conn.set_property32(window, atoms.net_wm_state, AtomEnum::ATOM.into(), &[above])
            .expect("give the window a state of its own");

        mark_skip_taskbar(window).expect("mark the window");
        mark_skip_taskbar(window).expect("mark it again");

        assert_eq!(
            net_wm_state(window).expect("read _NET_WM_STATE"),
            vec![above, atoms.net_wm_state_skip_taskbar],
            "the window's own state is kept and the taskbar state is added once"
        );
        let _ = raw.destroy_window(window).map(|cookie| cookie.check());
    }

    #[test]
    #[ignore = "requires a live X server; run with --ignored"]
    fn x11_probe_against_a_live_server() {
        let caps = probe_uncached().expect("connect to $DISPLAY");
        eprintln!("probed window manager: {caps:?}");
        assert!(
            caps.ewmh_wm_present,
            "no EWMH window manager found on $DISPLAY — custom chrome would be refused"
        );
        assert!(
            caps.move_resize,
            "_NET_WM_MOVERESIZE missing from _NET_SUPPORTED — custom chrome would be refused"
        );
    }
}