xa11y-linux 0.6.1

//! Real AT-SPI2 backend implementation using zbus D-Bus bindings.

use std::collections::{HashMap, HashSet};
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::Mutex;
use std::time::Duration;

use rayon::prelude::*;
use xa11y_core::selector::{Combinator, MatchOp, SelectorSegment};
use xa11y_core::{
    CancelHandle, ElementData, Error, Event, EventReceiver, EventType, Provider, Rect, Result,
    Role, Selector, StateSet, Subscription, Toggled,
};
use zbus::blocking::{Connection, Proxy};

/// Global handle counter for mapping ElementData back to AccessibleRefs.
static NEXT_HANDLE: AtomicU64 = AtomicU64::new(1);

/// Linux accessibility provider using AT-SPI2 over D-Bus.
pub struct LinuxProvider {
    a11y_bus: Connection,
    /// Cached AT-SPI accessible refs keyed by handle ID.
    handle_cache: Mutex<HashMap<u64, AccessibleRef>>,
    /// Cached AT-SPI2 action indices keyed by element handle.
    /// Maps each action name (snake_case) to the integer index used by `DoAction(i)`.
    action_indices: Mutex<HashMap<u64, HashMap<String, i32>>>,
}

/// AT-SPI2 accessible reference: (bus_name, object_path).
#[derive(Debug, Clone)]
struct AccessibleRef {
    bus_name: String,
    path: String,
}

impl LinuxProvider {
    /// Create a new Linux accessibility provider.
    ///
    /// Connects to the AT-SPI2 bus. Falls back to the session bus
    /// if the dedicated AT-SPI bus is unavailable.
    pub fn new() -> Result<Self> {
        let a11y_bus = Self::connect_a11y_bus()?;
        Ok(Self {
            a11y_bus,
            handle_cache: Mutex::new(HashMap::new()),
            action_indices: Mutex::new(HashMap::new()),
        })
    }

    fn connect_a11y_bus() -> Result<Connection> {
        // Try getting the AT-SPI bus address from the a11y bus launcher,
        // then connect to it. If that fails, fall back to the session bus
        // (AT-SPI2 may use the session bus directly).
        if let Ok(session) = Connection::session() {
            let proxy = Proxy::new(&session, "org.a11y.Bus", "/org/a11y/bus", "org.a11y.Bus")
                .map_err(|e| Error::Platform {
                    code: -1,
                    message: format!("Failed to create a11y bus proxy: {}", e),
                })?;

            if let Ok(addr_reply) = proxy.call_method("GetAddress", &()) {
                if let Ok(address) = addr_reply.body().deserialize::<String>() {
                    if let Ok(addr) = zbus::Address::try_from(address.as_str()) {
                        if let Ok(Ok(conn)) =
                            zbus::blocking::connection::Builder::address(addr).map(|b| b.build())
                        {
                            return Ok(conn);
                        }
                    }
                }
            }

            // Fall back to session bus
            return Ok(session);
        }

        Connection::session().map_err(|e| Error::Platform {
            code: -1,
            message: format!("Failed to connect to D-Bus session bus: {}", e),
        })
    }

    fn make_proxy(&self, bus_name: &str, path: &str, interface: &str) -> Result<Proxy<'_>> {
        // Use uncached proxy to avoid GetAll calls — Qt's AT-SPI adaptor
        // doesn't support GetAll on all objects, causing spurious errors.
        zbus::blocking::proxy::Builder::<Proxy>::new(&self.a11y_bus)
            .destination(bus_name.to_owned())
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("Failed to set proxy destination: {}", e),
            })?
            .path(path.to_owned())
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("Failed to set proxy path: {}", e),
            })?
            .interface(interface.to_owned())
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("Failed to set proxy interface: {}", e),
            })?
            .cache_properties(zbus::proxy::CacheProperties::No)
            .build()
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("Failed to create proxy: {}", e),
            })
    }

    /// Check whether an accessible object implements a given interface.
    /// Queries the AT-SPI GetInterfaces method on the Accessible interface.
    fn has_interface(&self, aref: &AccessibleRef, iface: &str) -> bool {
        let proxy = match self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Accessible") {
            Ok(p) => p,
            Err(_) => return false,
        };
        let reply = match proxy.call_method("GetInterfaces", &()) {
            Ok(r) => r,
            Err(_) => return false,
        };
        let interfaces: Vec<String> = match reply.body().deserialize() {
            Ok(v) => v,
            Err(_) => return false,
        };
        interfaces.iter().any(|i| i.contains(iface))
    }

    /// Get the numeric AT-SPI role via GetRole method.
    fn get_role_number(&self, aref: &AccessibleRef) -> Result<u32> {
        let proxy = self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Accessible")?;
        let reply = proxy
            .call_method("GetRole", &())
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("GetRole failed: {}", e),
            })?;
        reply
            .body()
            .deserialize::<u32>()
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("GetRole deserialize failed: {}", e),
            })
    }

    /// Get the AT-SPI role name string.
    fn get_role_name(&self, aref: &AccessibleRef) -> Result<String> {
        let proxy = self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Accessible")?;
        let reply = proxy
            .call_method("GetRoleName", &())
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("GetRoleName failed: {}", e),
            })?;
        reply
            .body()
            .deserialize::<String>()
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("GetRoleName deserialize failed: {}", e),
            })
    }

    /// Get the name of an accessible element.
    fn get_name(&self, aref: &AccessibleRef) -> Result<String> {
        let proxy = self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Accessible")?;
        proxy
            .get_property::<String>("Name")
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("Get Name property failed: {}", e),
            })
    }

    /// Get the description of an accessible element.
    fn get_description(&self, aref: &AccessibleRef) -> Result<String> {
        let proxy = self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Accessible")?;
        proxy
            .get_property::<String>("Description")
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("Get Description property failed: {}", e),
            })
    }

    /// Get children via the GetChildren method.
    /// AT-SPI registryd doesn't always implement standard D-Bus Properties,
    /// so we use GetChildren which is more reliable.
    fn get_atspi_children(&self, aref: &AccessibleRef) -> Result<Vec<AccessibleRef>> {
        let proxy = self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Accessible")?;
        let reply = proxy
            .call_method("GetChildren", &())
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("GetChildren failed: {}", e),
            })?;
        let children: Vec<(String, zbus::zvariant::OwnedObjectPath)> =
            reply.body().deserialize().map_err(|e| Error::Platform {
                code: -1,
                message: format!("GetChildren deserialize failed: {}", e),
            })?;
        Ok(children
            .into_iter()
            .map(|(bus_name, path)| AccessibleRef {
                bus_name,
                path: path.to_string(),
            })
            .collect())
    }

    /// Get the state set as raw u32 values.
    fn get_state(&self, aref: &AccessibleRef) -> Result<Vec<u32>> {
        let proxy = self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Accessible")?;
        let reply = proxy
            .call_method("GetState", &())
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("GetState failed: {}", e),
            })?;
        reply
            .body()
            .deserialize::<Vec<u32>>()
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("GetState deserialize failed: {}", e),
            })
    }

    /// Return true if the element reports the AT-SPI MULTI_LINE state.
    /// Used to distinguish multi-line text areas (TextArea) from single-line
    /// text inputs (TextField), since both use the AT-SPI "text" role name.
    /// Note: Qt's AT-SPI bridge does not reliably set SINGLE_LINE, so we
    /// check MULTI_LINE and default to TextField when neither is set.
    fn is_multi_line(&self, aref: &AccessibleRef) -> bool {
        let state_bits = self.get_state(aref).unwrap_or_default();
        let bits: u64 = if state_bits.len() >= 2 {
            (state_bits[0] as u64) | ((state_bits[1] as u64) << 32)
        } else if state_bits.len() == 1 {
            state_bits[0] as u64
        } else {
            0
        };
        // ATSPI_STATE_MULTI_LINE = 17 in AtspiStateType enum
        const MULTI_LINE: u64 = 1 << 17;
        (bits & MULTI_LINE) != 0
    }

    /// Get bounds via Component interface.
    /// Checks for Component support first to avoid GTK CRITICAL warnings
    /// on objects (e.g. TreeView cell renderers) that don't implement it.
    fn get_extents(&self, aref: &AccessibleRef) -> Option<Rect> {
        if !self.has_interface(aref, "Component") {
            return None;
        }
        let proxy = self
            .make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Component")
            .ok()?;
        // GetExtents(coord_type: u32) -> (x, y, width, height)
        // coord_type 0 = screen coordinates
        let reply = proxy.call_method("GetExtents", &(0u32,)).ok()?;
        let (x, y, w, h): (i32, i32, i32, i32) = reply.body().deserialize().ok()?;
        if w <= 0 && h <= 0 {
            return None;
        }
        Some(Rect {
            x,
            y,
            width: w.max(0) as u32,
            height: h.max(0) as u32,
        })
    }

    /// Get available actions via Action interface, returning both the action list
    /// and a map of each action name to its AT-SPI2 integer index for direct `DoAction(i)`.
    ///
    /// Probes the interface directly rather than relying on the Interfaces property,
    /// which some AT-SPI adapters (e.g. AccessKit) don't expose.
    fn get_actions(&self, aref: &AccessibleRef) -> (Vec<String>, HashMap<String, i32>) {
        let mut actions = Vec::new();
        let mut indices = HashMap::new();

        // Try Action interface directly
        if let Ok(proxy) = self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Action") {
            // NActions may be returned as i32 or u32 depending on AT-SPI implementation.
            let n_actions = proxy
                .get_property::<i32>("NActions")
                .or_else(|_| proxy.get_property::<u32>("NActions").map(|n| n as i32))
                .unwrap_or(0);
            for i in 0..n_actions {
                if let Ok(reply) = proxy.call_method("GetName", &(i,)) {
                    if let Ok(name) = reply.body().deserialize::<String>() {
                        if let Some(action_name) = map_atspi_action_name(&name) {
                            if !actions.contains(&action_name) {
                                indices.insert(action_name.clone(), i);
                                actions.push(action_name);
                            }
                        }
                    }
                }
            }
        }

        // Try Component interface for Focus
        if !actions.contains(&"focus".to_string()) {
            if let Ok(proxy) =
                self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Component")
            {
                // Verify the interface exists by trying a method
                if proxy.call_method("GetExtents", &(0u32,)).is_ok() {
                    actions.push("focus".to_string());
                }
            }
        }

        (actions, indices)
    }

    /// Get value via Value or Text interface.
    /// Probes interfaces directly rather than relying on the Interfaces property.
    fn get_value(&self, aref: &AccessibleRef) -> Option<String> {
        // Try Text interface first for text content (text fields, labels, combo boxes).
        // This must come before Value because some AT-SPI adapters (e.g. AccessKit)
        // may expose both interfaces, and Value.CurrentValue returns 0.0 for text elements.
        let text_value = self.get_text_content(aref);
        if text_value.is_some() {
            return text_value;
        }
        // Try Value interface (sliders, progress bars, scroll bars, spinners)
        if let Ok(proxy) = self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Value") {
            if let Ok(val) = proxy.get_property::<f64>("CurrentValue") {
                return Some(val.to_string());
            }
        }
        None
    }

    /// Read text content via the AT-SPI Text interface.
    fn get_text_content(&self, aref: &AccessibleRef) -> Option<String> {
        let proxy = self
            .make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Text")
            .ok()?;
        let char_count: i32 = proxy.get_property("CharacterCount").ok()?;
        if char_count > 0 {
            let reply = proxy.call_method("GetText", &(0i32, char_count)).ok()?;
            let text: String = reply.body().deserialize().ok()?;
            if !text.is_empty() {
                return Some(text);
            }
        }
        None
    }

    /// Cache an AccessibleRef and return a new handle ID.
    fn cache_element(&self, aref: AccessibleRef) -> u64 {
        let handle = NEXT_HANDLE.fetch_add(1, Ordering::Relaxed);
        self.handle_cache.lock().unwrap().insert(handle, aref);
        handle
    }

    /// Look up a cached AccessibleRef by handle.
    fn get_cached(&self, handle: u64) -> Result<AccessibleRef> {
        self.handle_cache
            .lock()
            .unwrap()
            .get(&handle)
            .cloned()
            .ok_or(Error::ElementStale {
                selector: format!("handle:{}", handle),
            })
    }

    /// Build an ElementData from an AccessibleRef, caching the ref for later lookup.
    ///
    /// After resolving the role (1-3 sequential D-Bus calls), all remaining
    /// property fetches are independent and run in parallel via rayon::join.
    fn build_element_data(&self, aref: &AccessibleRef, pid: Option<u32>) -> ElementData {
        let role_name = self.get_role_name(aref).unwrap_or_default();
        let role_num = self.get_role_number(aref).unwrap_or(0);
        let role = {
            let by_name = if !role_name.is_empty() {
                map_atspi_role(&role_name)
            } else {
                Role::Unknown
            };
            let coarse = if by_name != Role::Unknown {
                by_name
            } else {
                map_atspi_role_number(role_num)
            };
            if coarse == Role::TextArea && !self.is_multi_line(aref) {
                Role::TextField
            } else {
                coarse
            }
        };

        // Fetch all independent properties in parallel.
        // Left tree: (name+value, description)
        // Right tree: ((states, bounds), (actions, numeric_values))
        let (
            ((mut name, value), description),
            (
                (states, bounds),
                ((actions, action_index_map), (numeric_value, min_value, max_value)),
            ),
        ) = rayon::join(
            || {
                rayon::join(
                    || {
                        let name = self.get_name(aref).ok().filter(|s| !s.is_empty());
                        let value = if role_has_value(role) {
                            self.get_value(aref)
                        } else {
                            None
                        };
                        (name, value)
                    },
                    || self.get_description(aref).ok().filter(|s| !s.is_empty()),
                )
            },
            || {
                rayon::join(
                    || {
                        rayon::join(
                            || self.parse_states(aref, role),
                            || {
                                if role != Role::Application {
                                    self.get_extents(aref)
                                } else {
                                    None
                                }
                            },
                        )
                    },
                    || {
                        rayon::join(
                            || {
                                if role_has_actions(role) {
                                    self.get_actions(aref)
                                } else {
                                    (vec![], HashMap::new())
                                }
                            },
                            || {
                                if matches!(
                                    role,
                                    Role::Slider
                                        | Role::ProgressBar
                                        | Role::ScrollBar
                                        | Role::SpinButton
                                ) {
                                    if let Ok(proxy) = self.make_proxy(
                                        &aref.bus_name,
                                        &aref.path,
                                        "org.a11y.atspi.Value",
                                    ) {
                                        (
                                            proxy.get_property::<f64>("CurrentValue").ok(),
                                            proxy.get_property::<f64>("MinimumValue").ok(),
                                            proxy.get_property::<f64>("MaximumValue").ok(),
                                        )
                                    } else {
                                        (None, None, None)
                                    }
                                } else {
                                    (None, None, None)
                                }
                            },
                        )
                    },
                )
            },
        );

        // For label/static text elements, AT-SPI may put content in the Text
        // interface (returned as value) rather than the Name property.
        if name.is_none() && role == Role::StaticText {
            if let Some(ref v) = value {
                name = Some(v.clone());
            }
        }

        let raw = {
            let raw_role = if role_name.is_empty() {
                format!("role_num:{}", role_num)
            } else {
                role_name
            };
            {
                let mut raw = HashMap::new();
                raw.insert("atspi_role".into(), serde_json::Value::String(raw_role));
                raw.insert(
                    "bus_name".into(),
                    serde_json::Value::String(aref.bus_name.clone()),
                );
                raw.insert(
                    "object_path".into(),
                    serde_json::Value::String(aref.path.clone()),
                );
                raw
            }
        };

        let handle = self.cache_element(aref.clone());
        if !action_index_map.is_empty() {
            self.action_indices
                .lock()
                .unwrap()
                .insert(handle, action_index_map);
        }

        let mut data = ElementData {
            role,
            name,
            value,
            description,
            bounds,
            actions,
            states,
            numeric_value,
            min_value,
            max_value,
            pid,
            stable_id: Some(aref.path.clone()),
            attributes: HashMap::new(),
            raw,
            handle,
        };
        data.populate_attributes();
        data
    }

    /// Get the AT-SPI parent of an accessible ref.
    fn get_atspi_parent(&self, aref: &AccessibleRef) -> Result<Option<AccessibleRef>> {
        // Read the Parent property via the D-Bus Properties interface.
        let proxy = self.make_proxy(
            &aref.bus_name,
            &aref.path,
            "org.freedesktop.DBus.Properties",
        )?;
        let reply = proxy
            .call_method("Get", &("org.a11y.atspi.Accessible", "Parent"))
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("Get Parent property failed: {}", e),
            })?;
        // The reply is a Variant containing (so) — a struct of (bus_name, object_path)
        let variant: zbus::zvariant::OwnedValue =
            reply.body().deserialize().map_err(|e| Error::Platform {
                code: -1,
                message: format!("Parent deserialize variant failed: {}", e),
            })?;
        let (bus, path): (String, zbus::zvariant::OwnedObjectPath) =
            zbus::zvariant::Value::from(variant).try_into().map_err(
                |e: zbus::zvariant::Error| Error::Platform {
                    code: -1,
                    message: format!("Parent deserialize struct failed: {}", e),
                },
            )?;
        let path_str = path.as_str();
        if path_str == "/org/a11y/atspi/null" || bus.is_empty() || path_str.is_empty() {
            return Ok(None);
        }
        // If the parent is the registry root, this is a top-level app — no parent
        if path_str == "/org/a11y/atspi/accessible/root" {
            return Ok(None);
        }
        Ok(Some(AccessibleRef {
            bus_name: bus,
            path: path_str.to_string(),
        }))
    }

    /// Parse AT-SPI2 state bitfield into xa11y StateSet.
    fn parse_states(&self, aref: &AccessibleRef, role: Role) -> StateSet {
        let state_bits = self.get_state(aref).unwrap_or_default();

        // AT-SPI2 states are a bitfield across two u32s
        let bits: u64 = if state_bits.len() >= 2 {
            (state_bits[0] as u64) | ((state_bits[1] as u64) << 32)
        } else if state_bits.len() == 1 {
            state_bits[0] as u64
        } else {
            0
        };

        // AT-SPI2 state bit positions (AtspiStateType enum values)
        const BUSY: u64 = 1 << 3;
        const CHECKED: u64 = 1 << 4;
        const EDITABLE: u64 = 1 << 7;
        const ENABLED: u64 = 1 << 8;
        const EXPANDABLE: u64 = 1 << 9;
        const EXPANDED: u64 = 1 << 10;
        const FOCUSABLE: u64 = 1 << 11;
        const FOCUSED: u64 = 1 << 12;
        const MODAL: u64 = 1 << 16;
        const SELECTED: u64 = 1 << 23;
        const SENSITIVE: u64 = 1 << 24;
        const SHOWING: u64 = 1 << 25;
        const VISIBLE: u64 = 1 << 30;
        const INDETERMINATE: u64 = 1 << 32;
        const REQUIRED: u64 = 1 << 33;

        let enabled = (bits & ENABLED) != 0 || (bits & SENSITIVE) != 0;
        let visible = (bits & VISIBLE) != 0 || (bits & SHOWING) != 0;

        let checked = match role {
            Role::CheckBox | Role::RadioButton | Role::MenuItem => {
                if (bits & INDETERMINATE) != 0 {
                    Some(Toggled::Mixed)
                } else if (bits & CHECKED) != 0 {
                    Some(Toggled::On)
                } else {
                    Some(Toggled::Off)
                }
            }
            _ => None,
        };

        let expanded = if (bits & EXPANDABLE) != 0 {
            Some((bits & EXPANDED) != 0)
        } else {
            None
        };

        StateSet {
            enabled,
            visible,
            focused: (bits & FOCUSED) != 0,
            checked,
            selected: (bits & SELECTED) != 0,
            expanded,
            editable: (bits & EDITABLE) != 0,
            focusable: (bits & FOCUSABLE) != 0,
            modal: (bits & MODAL) != 0,
            required: (bits & REQUIRED) != 0,
            busy: (bits & BUSY) != 0,
        }
    }

    /// Find an application by PID.
    fn find_app_by_pid(&self, pid: u32) -> Result<AccessibleRef> {
        let registry = AccessibleRef {
            bus_name: "org.a11y.atspi.Registry".to_string(),
            path: "/org/a11y/atspi/accessible/root".to_string(),
        };
        let children = self.get_atspi_children(&registry)?;

        for child in &children {
            if child.path == "/org/a11y/atspi/null" {
                continue;
            }
            // Try Application.Id first
            if let Ok(proxy) =
                self.make_proxy(&child.bus_name, &child.path, "org.a11y.atspi.Application")
            {
                if let Ok(app_pid) = proxy.get_property::<i32>("Id") {
                    if app_pid as u32 == pid {
                        return Ok(child.clone());
                    }
                }
            }
            // Fall back to D-Bus connection PID
            if let Some(app_pid) = self.get_dbus_pid(&child.bus_name) {
                if app_pid == pid {
                    return Ok(child.clone());
                }
            }
        }

        Err(Error::Platform {
            code: -1,
            message: format!("No application found with PID {}", pid),
        })
    }

    /// Get PID via D-Bus GetConnectionUnixProcessID.
    fn get_dbus_pid(&self, bus_name: &str) -> Option<u32> {
        let proxy = self
            .make_proxy(
                "org.freedesktop.DBus",
                "/org/freedesktop/DBus",
                "org.freedesktop.DBus",
            )
            .ok()?;
        let reply = proxy
            .call_method("GetConnectionUnixProcessID", &(bus_name,))
            .ok()?;
        let pid: u32 = reply.body().deserialize().ok()?;
        if pid > 0 {
            Some(pid)
        } else {
            None
        }
    }

    /// Perform an AT-SPI2 action by name (scans action names to find the index).
    /// Only used for actions not stored during discovery (e.g. scroll directions).
    fn do_atspi_action_by_name(&self, aref: &AccessibleRef, action_name: &str) -> Result<()> {
        let proxy = self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Action")?;
        let n_actions = proxy
            .get_property::<i32>("NActions")
            .or_else(|_| proxy.get_property::<u32>("NActions").map(|n| n as i32))
            .unwrap_or(0);
        for i in 0..n_actions {
            if let Ok(reply) = proxy.call_method("GetName", &(i,)) {
                if let Ok(name) = reply.body().deserialize::<String>() {
                    if name.eq_ignore_ascii_case(action_name) {
                        proxy
                            .call_method("DoAction", &(i,))
                            .map_err(|e| Error::Platform {
                                code: -1,
                                message: format!("DoAction failed: {}", e),
                            })?;
                        return Ok(());
                    }
                }
            }
        }
        Err(Error::Platform {
            code: -1,
            message: format!("Action '{}' not found", action_name),
        })
    }

    /// Perform an AT-SPI2 action by its integer index (from discovery).
    fn do_atspi_action_by_index(&self, aref: &AccessibleRef, index: i32) -> Result<()> {
        let proxy = self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Action")?;
        proxy
            .call_method("DoAction", &(index,))
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("DoAction({}) failed: {}", index, e),
            })?;
        Ok(())
    }

    /// Look up the stored AT-SPI2 action index for the given element and action.
    fn get_action_index(&self, handle: u64, action: &str) -> Result<i32> {
        self.action_indices
            .lock()
            .unwrap()
            .get(&handle)
            .and_then(|map| map.get(action).copied())
            .ok_or_else(|| Error::ActionNotSupported {
                action: action.to_string(),
                role: Role::Unknown, // caller will provide better context
            })
    }

    /// Get PID from Application interface, falling back to D-Bus connection PID.
    fn get_app_pid(&self, aref: &AccessibleRef) -> Option<u32> {
        // Try Application.Id first
        if let Ok(proxy) = self.make_proxy(&aref.bus_name, &aref.path, "org.a11y.atspi.Application")
        {
            if let Ok(pid) = proxy.get_property::<i32>("Id") {
                if pid > 0 {
                    return Some(pid as u32);
                }
            }
        }

        // Fall back to D-Bus GetConnectionUnixProcessID
        if let Ok(proxy) = self.make_proxy(
            "org.freedesktop.DBus",
            "/org/freedesktop/DBus",
            "org.freedesktop.DBus",
        ) {
            if let Ok(reply) =
                proxy.call_method("GetConnectionUnixProcessID", &(aref.bus_name.as_str(),))
            {
                if let Ok(pid) = reply.body().deserialize::<u32>() {
                    if pid > 0 {
                        return Some(pid);
                    }
                }
            }
        }

        None
    }

    /// Resolve the mapped Role for an accessible ref (1-3 D-Bus calls).
    fn resolve_role(&self, aref: &AccessibleRef) -> Role {
        let role_name = self.get_role_name(aref).unwrap_or_default();
        let by_name = if !role_name.is_empty() {
            map_atspi_role(&role_name)
        } else {
            Role::Unknown
        };
        let coarse = if by_name != Role::Unknown {
            by_name
        } else {
            // Unmapped or missing role name — fall back to numeric role.
            let role_num = self.get_role_number(aref).unwrap_or(0);
            map_atspi_role_number(role_num)
        };
        // Refine TextArea → TextField for single-line text widgets.
        if coarse == Role::TextArea && !self.is_multi_line(aref) {
            Role::TextField
        } else {
            coarse
        }
    }

    /// Check if an accessible ref matches a simple selector, fetching only the
    /// attributes the selector actually requires.
    fn matches_ref(
        &self,
        aref: &AccessibleRef,
        simple: &xa11y_core::selector::SimpleSelector,
    ) -> bool {
        // Resolve role only if the selector needs it
        let needs_role = simple.role.is_some() || simple.filters.iter().any(|f| f.attr == "role");
        let role = if needs_role {
            Some(self.resolve_role(aref))
        } else {
            None
        };

        if let Some(ref role_match) = simple.role {
            match role_match {
                xa11y_core::selector::RoleMatch::Normalized(expected) => {
                    if role != Some(*expected) {
                        return false;
                    }
                }
                xa11y_core::selector::RoleMatch::Platform(platform_role) => {
                    // Match against the raw AT-SPI2 role name
                    let raw_role = self.get_role_name(aref).unwrap_or_default();
                    if raw_role != *platform_role {
                        return false;
                    }
                }
            }
        }

        for filter in &simple.filters {
            let attr_value: Option<String> = match filter.attr.as_str() {
                "role" => role.map(|r| r.to_snake_case().to_string()),
                "name" => {
                    let name = self.get_name(aref).ok().filter(|s| !s.is_empty());
                    // Mirror build_element_data: StaticText may have name in Text interface
                    if name.is_none() && role == Some(Role::StaticText) {
                        self.get_value(aref)
                    } else {
                        name
                    }
                }
                "value" => self.get_value(aref),
                "description" => self.get_description(aref).ok().filter(|s| !s.is_empty()),
                // Unknown attributes: not resolvable in lightweight matching
                _ => None,
            };

            let matches = match &filter.op {
                MatchOp::Exact => attr_value.as_deref() == Some(filter.value.as_str()),
                MatchOp::Contains => {
                    let fl = filter.value.to_lowercase();
                    attr_value
                        .as_deref()
                        .is_some_and(|v| v.to_lowercase().contains(&fl))
                }
                MatchOp::StartsWith => {
                    let fl = filter.value.to_lowercase();
                    attr_value
                        .as_deref()
                        .is_some_and(|v| v.to_lowercase().starts_with(&fl))
                }
                MatchOp::EndsWith => {
                    let fl = filter.value.to_lowercase();
                    attr_value
                        .as_deref()
                        .is_some_and(|v| v.to_lowercase().ends_with(&fl))
                }
            };

            if !matches {
                return false;
            }
        }

        true
    }

    /// DFS collect AccessibleRefs matching a SimpleSelector without building
    /// full ElementData. Only the attributes required by the selector are
    /// fetched for each candidate.
    ///
    /// Children at each level are processed in parallel via rayon.
    fn collect_matching_refs(
        &self,
        parent: &AccessibleRef,
        simple: &xa11y_core::selector::SimpleSelector,
        depth: u32,
        max_depth: u32,
        limit: Option<usize>,
    ) -> Result<Vec<AccessibleRef>> {
        if depth > max_depth {
            return Ok(vec![]);
        }

        let children = self.get_atspi_children(parent)?;

        // Filter valid children, flattening nested application nodes
        let mut to_search: Vec<AccessibleRef> = Vec::new();
        for child in children {
            if child.path == "/org/a11y/atspi/null"
                || child.bus_name.is_empty()
                || child.path.is_empty()
            {
                continue;
            }

            let child_role = self.get_role_name(&child).unwrap_or_default();
            if child_role == "application" {
                let grandchildren = self.get_atspi_children(&child).unwrap_or_default();
                for gc in grandchildren {
                    if gc.path == "/org/a11y/atspi/null"
                        || gc.bus_name.is_empty()
                        || gc.path.is_empty()
                    {
                        continue;
                    }
                    let gc_role = self.get_role_name(&gc).unwrap_or_default();
                    if gc_role == "application" {
                        continue;
                    }
                    to_search.push(gc);
                }
                continue;
            }
            to_search.push(child);
        }

        // Process each child subtree in parallel: check match + recurse
        let per_child: Vec<Vec<AccessibleRef>> = to_search
            .par_iter()
            .map(|child| {
                let mut child_results = Vec::new();
                if self.matches_ref(child, simple) {
                    child_results.push(child.clone());
                }
                if let Ok(sub) =
                    self.collect_matching_refs(child, simple, depth + 1, max_depth, limit)
                {
                    child_results.extend(sub);
                }
                child_results
            })
            .collect();

        // Merge results, respecting limit
        let mut results = Vec::new();
        for batch in per_child {
            for r in batch {
                results.push(r);
                if let Some(limit) = limit {
                    if results.len() >= limit {
                        return Ok(results);
                    }
                }
            }
        }
        Ok(results)
    }
}

impl Provider for LinuxProvider {
    fn get_children(&self, element: Option<&ElementData>) -> Result<Vec<ElementData>> {
        match element {
            None => {
                // Top-level: list all AT-SPI application elements
                let registry = AccessibleRef {
                    bus_name: "org.a11y.atspi.Registry".to_string(),
                    path: "/org/a11y/atspi/accessible/root".to_string(),
                };
                let children = self.get_atspi_children(&registry)?;

                // Filter valid children first, then build in parallel
                let valid: Vec<(&AccessibleRef, String)> = children
                    .iter()
                    .filter(|c| c.path != "/org/a11y/atspi/null")
                    .filter_map(|c| {
                        let name = self.get_name(c).unwrap_or_default();
                        if name.is_empty() {
                            None
                        } else {
                            Some((c, name))
                        }
                    })
                    .collect();

                let results: Vec<ElementData> = valid
                    .par_iter()
                    .map(|(child, app_name)| {
                        let pid = self.get_app_pid(child);
                        let mut data = self.build_element_data(child, pid);
                        data.name = Some(app_name.clone());
                        data
                    })
                    .collect();

                Ok(results)
            }
            Some(element_data) => {
                let aref = self.get_cached(element_data.handle)?;
                let children = self.get_atspi_children(&aref).unwrap_or_default();
                let pid = element_data.pid;

                // Pre-filter invalid refs and flatten nested application nodes,
                // collecting the concrete refs to build in parallel.
                let mut to_build: Vec<AccessibleRef> = Vec::new();
                for child_ref in &children {
                    if child_ref.path == "/org/a11y/atspi/null"
                        || child_ref.bus_name.is_empty()
                        || child_ref.path.is_empty()
                    {
                        continue;
                    }
                    let child_role = self.get_role_name(child_ref).unwrap_or_default();
                    if child_role == "application" {
                        let grandchildren = self.get_atspi_children(child_ref).unwrap_or_default();
                        for gc_ref in grandchildren {
                            if gc_ref.path == "/org/a11y/atspi/null"
                                || gc_ref.bus_name.is_empty()
                                || gc_ref.path.is_empty()
                            {
                                continue;
                            }
                            let gc_role = self.get_role_name(&gc_ref).unwrap_or_default();
                            if gc_role == "application" {
                                continue;
                            }
                            to_build.push(gc_ref);
                        }
                        continue;
                    }
                    to_build.push(child_ref.clone());
                }

                let results: Vec<ElementData> = to_build
                    .par_iter()
                    .map(|r| self.build_element_data(r, pid))
                    .collect();

                Ok(results)
            }
        }
    }

    fn find_elements(
        &self,
        root: Option<&ElementData>,
        selector: &Selector,
        limit: Option<usize>,
        max_depth: Option<u32>,
    ) -> Result<Vec<ElementData>> {
        if selector.segments.is_empty() {
            return Ok(vec![]);
        }

        let max_depth_val = max_depth.unwrap_or(xa11y_core::MAX_TREE_DEPTH);

        // Phase 1: lightweight ref-based search for first segment.
        // Only the attributes the selector needs are fetched per candidate.
        let first = &selector.segments[0].simple;

        let phase1_limit = if selector.segments.len() == 1 {
            limit
        } else {
            None
        };
        let phase1_limit = match (phase1_limit, first.nth) {
            (Some(l), Some(n)) => Some(l.max(n)),
            (_, Some(n)) => Some(n),
            (l, None) => l,
        };

        // Applications are always direct children of the registry root
        let phase1_depth = if root.is_none()
            && matches!(
                first.role,
                Some(xa11y_core::selector::RoleMatch::Normalized(
                    Role::Application
                ))
            ) {
            0
        } else {
            max_depth_val
        };

        let start_ref = match root {
            None => AccessibleRef {
                bus_name: "org.a11y.atspi.Registry".to_string(),
                path: "/org/a11y/atspi/accessible/root".to_string(),
            },
            Some(el) => self.get_cached(el.handle)?,
        };

        let mut matching_refs =
            self.collect_matching_refs(&start_ref, first, 0, phase1_depth, phase1_limit)?;

        let pid_from_root = root.and_then(|r| r.pid);

        // Single-segment: build ElementData only for matches, apply nth/limit
        if selector.segments.len() == 1 {
            if let Some(nth) = first.nth {
                if nth <= matching_refs.len() {
                    let aref = &matching_refs[nth - 1];
                    let pid = if root.is_none() {
                        self.get_app_pid(aref)
                            .or_else(|| self.get_dbus_pid(&aref.bus_name))
                    } else {
                        pid_from_root
                    };
                    return Ok(vec![self.build_element_data(aref, pid)]);
                } else {
                    return Ok(vec![]);
                }
            }

            if let Some(limit) = limit {
                matching_refs.truncate(limit);
            }

            let is_root_search = root.is_none();
            return Ok(matching_refs
                .par_iter()
                .map(|aref| {
                    let pid = if is_root_search {
                        self.get_app_pid(aref)
                            .or_else(|| self.get_dbus_pid(&aref.bus_name))
                    } else {
                        pid_from_root
                    };
                    self.build_element_data(aref, pid)
                })
                .collect());
        }

        // Multi-segment: build ElementData for phase 1 matches, then narrow
        // using standard matching on the (small) candidate set.
        let is_root_search = root.is_none();
        let mut candidates: Vec<ElementData> = matching_refs
            .par_iter()
            .map(|aref| {
                let pid = if is_root_search {
                    self.get_app_pid(aref)
                        .or_else(|| self.get_dbus_pid(&aref.bus_name))
                } else {
                    pid_from_root
                };
                self.build_element_data(aref, pid)
            })
            .collect();

        for segment in &selector.segments[1..] {
            let mut next_candidates = Vec::new();
            for candidate in &candidates {
                match segment.combinator {
                    Combinator::Child => {
                        let children = self.get_children(Some(candidate))?;
                        for child in children {
                            if xa11y_core::selector::matches_simple(&child, &segment.simple) {
                                next_candidates.push(child);
                            }
                        }
                    }
                    Combinator::Descendant => {
                        let sub_selector = Selector {
                            segments: vec![SelectorSegment {
                                combinator: Combinator::Root,
                                simple: segment.simple.clone(),
                            }],
                        };
                        let mut sub_results = xa11y_core::selector::find_elements_in_tree(
                            |el| self.get_children(el),
                            Some(candidate),
                            &sub_selector,
                            None,
                            Some(max_depth_val),
                        )?;
                        next_candidates.append(&mut sub_results);
                    }
                    Combinator::Root => unreachable!(),
                }
            }
            let mut seen = HashSet::new();
            next_candidates.retain(|e| seen.insert(e.handle));
            candidates = next_candidates;
        }

        // Apply :nth on last segment
        if let Some(nth) = selector.segments.last().and_then(|s| s.simple.nth) {
            if nth <= candidates.len() {
                candidates = vec![candidates.remove(nth - 1)];
            } else {
                candidates.clear();
            }
        }

        if let Some(limit) = limit {
            candidates.truncate(limit);
        }

        Ok(candidates)
    }

    fn get_parent(&self, element: &ElementData) -> Result<Option<ElementData>> {
        let aref = self.get_cached(element.handle)?;
        match self.get_atspi_parent(&aref)? {
            Some(parent_ref) => {
                let data = self.build_element_data(&parent_ref, element.pid);
                Ok(Some(data))
            }
            None => Ok(None),
        }
    }

    fn press(&self, element: &ElementData) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let index = self
            .get_action_index(element.handle, "press")
            .map_err(|_| Error::ActionNotSupported {
                action: "press".to_string(),
                role: element.role,
            })?;
        self.do_atspi_action_by_index(&target, index)
    }

    fn focus(&self, element: &ElementData) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        // Try Component.GrabFocus first, then fall back to stored action index
        if let Ok(proxy) =
            self.make_proxy(&target.bus_name, &target.path, "org.a11y.atspi.Component")
        {
            if proxy.call_method("GrabFocus", &()).is_ok() {
                return Ok(());
            }
        }
        if let Ok(index) = self.get_action_index(element.handle, "focus") {
            return self.do_atspi_action_by_index(&target, index);
        }
        Err(Error::ActionNotSupported {
            action: "focus".to_string(),
            role: element.role,
        })
    }

    fn blur(&self, element: &ElementData) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        // Grab focus on parent element to blur the current one
        if let Ok(Some(parent_ref)) = self.get_atspi_parent(&target) {
            if parent_ref.path != "/org/a11y/atspi/null" {
                if let Ok(p) = self.make_proxy(
                    &parent_ref.bus_name,
                    &parent_ref.path,
                    "org.a11y.atspi.Component",
                ) {
                    let _ = p.call_method("GrabFocus", &());
                    return Ok(());
                }
            }
        }
        Ok(())
    }

    fn toggle(&self, element: &ElementData) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let index = self
            .get_action_index(element.handle, "toggle")
            .map_err(|_| Error::ActionNotSupported {
                action: "toggle".to_string(),
                role: element.role,
            })?;
        self.do_atspi_action_by_index(&target, index)
    }

    fn select(&self, element: &ElementData) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let index = self
            .get_action_index(element.handle, "select")
            .map_err(|_| Error::ActionNotSupported {
                action: "select".to_string(),
                role: element.role,
            })?;
        self.do_atspi_action_by_index(&target, index)
    }

    fn expand(&self, element: &ElementData) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let index = self
            .get_action_index(element.handle, "expand")
            .map_err(|_| Error::ActionNotSupported {
                action: "expand".to_string(),
                role: element.role,
            })?;
        self.do_atspi_action_by_index(&target, index)
    }

    fn collapse(&self, element: &ElementData) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let index = self
            .get_action_index(element.handle, "collapse")
            .map_err(|_| Error::ActionNotSupported {
                action: "collapse".to_string(),
                role: element.role,
            })?;
        self.do_atspi_action_by_index(&target, index)
    }

    fn show_menu(&self, element: &ElementData) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let index = self
            .get_action_index(element.handle, "show_menu")
            .map_err(|_| Error::ActionNotSupported {
                action: "show_menu".to_string(),
                role: element.role,
            })?;
        self.do_atspi_action_by_index(&target, index)
    }

    fn increment(&self, element: &ElementData) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        // Try stored AT-SPI2 action index first, fall back to Value interface
        if let Ok(index) = self.get_action_index(element.handle, "increment") {
            return self.do_atspi_action_by_index(&target, index);
        }
        let proxy = self.make_proxy(&target.bus_name, &target.path, "org.a11y.atspi.Value")?;
        let current: f64 = proxy
            .get_property("CurrentValue")
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("Value.CurrentValue failed: {}", e),
            })?;
        let step: f64 = proxy.get_property("MinimumIncrement").unwrap_or(1.0);
        let step = if step <= 0.0 { 1.0 } else { step };
        proxy
            .set_property("CurrentValue", current + step)
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("Value.SetCurrentValue failed: {}", e),
            })
    }

    fn decrement(&self, element: &ElementData) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        if let Ok(index) = self.get_action_index(element.handle, "decrement") {
            return self.do_atspi_action_by_index(&target, index);
        }
        let proxy = self.make_proxy(&target.bus_name, &target.path, "org.a11y.atspi.Value")?;
        let current: f64 = proxy
            .get_property("CurrentValue")
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("Value.CurrentValue failed: {}", e),
            })?;
        let step: f64 = proxy.get_property("MinimumIncrement").unwrap_or(1.0);
        let step = if step <= 0.0 { 1.0 } else { step };
        proxy
            .set_property("CurrentValue", current - step)
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("Value.SetCurrentValue failed: {}", e),
            })
    }

    fn scroll_into_view(&self, element: &ElementData) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let proxy = self.make_proxy(&target.bus_name, &target.path, "org.a11y.atspi.Component")?;
        proxy
            .call_method("ScrollTo", &(0u32,))
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("ScrollTo failed: {}", e),
            })?;
        Ok(())
    }

    fn set_value(&self, element: &ElementData, value: &str) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let proxy = self
            .make_proxy(
                &target.bus_name,
                &target.path,
                "org.a11y.atspi.EditableText",
            )
            .map_err(|_| Error::TextValueNotSupported)?;
        // Try SetTextContents first (WebKit2GTK exposes this but not InsertText).
        if proxy.call_method("SetTextContents", &(value,)).is_ok() {
            return Ok(());
        }
        // Fall back to delete-then-insert for other AT-SPI2 implementations.
        let _ = proxy.call_method("DeleteText", &(0i32, i32::MAX));
        proxy
            .call_method("InsertText", &(0i32, value, value.len() as i32))
            .map_err(|_| Error::TextValueNotSupported)?;
        Ok(())
    }

    fn set_numeric_value(&self, element: &ElementData, value: f64) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let proxy = self.make_proxy(&target.bus_name, &target.path, "org.a11y.atspi.Value")?;
        proxy
            .set_property("CurrentValue", value)
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("SetValue failed: {}", e),
            })
    }

    fn type_text(&self, element: &ElementData, text: &str) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        // Insert text via EditableText interface (accessibility API, not input simulation).
        // Get cursor position from Text interface, then insert at that position.
        let text_proxy = self.make_proxy(&target.bus_name, &target.path, "org.a11y.atspi.Text");
        let insert_pos = text_proxy
            .as_ref()
            .ok()
            .and_then(|p| p.get_property::<i32>("CaretOffset").ok())
            .unwrap_or(-1); // -1 = append at end

        let proxy = self
            .make_proxy(
                &target.bus_name,
                &target.path,
                "org.a11y.atspi.EditableText",
            )
            .map_err(|_| Error::TextValueNotSupported)?;
        let pos = if insert_pos >= 0 {
            insert_pos
        } else {
            i32::MAX
        };
        proxy
            .call_method("InsertText", &(pos, text, text.len() as i32))
            .map_err(|e| Error::Platform {
                code: -1,
                message: format!("EditableText.InsertText failed: {}", e),
            })?;
        Ok(())
    }

    fn set_text_selection(&self, element: &ElementData, start: u32, end: u32) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let proxy = self.make_proxy(&target.bus_name, &target.path, "org.a11y.atspi.Text")?;
        // Try SetSelection first, fall back to AddSelection
        if proxy
            .call_method("SetSelection", &(0i32, start as i32, end as i32))
            .is_err()
        {
            proxy
                .call_method("AddSelection", &(start as i32, end as i32))
                .map_err(|e| Error::Platform {
                    code: -1,
                    message: format!("Text.AddSelection failed: {}", e),
                })?;
        }
        Ok(())
    }

    fn scroll_down(&self, element: &ElementData, amount: f64) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let count = (amount.abs() as u32).max(1);
        for _ in 0..count {
            if self
                .do_atspi_action_by_name(&target, "scroll down")
                .is_err()
            {
                // Fall back to Component.ScrollTo (single call, not repeatable).
                // If both fail, return ActionNotSupported for clearer error handling.
                // Fixes GitHub issue #99.
                if let Ok(proxy) =
                    self.make_proxy(&target.bus_name, &target.path, "org.a11y.atspi.Component")
                {
                    // BOTTOM_EDGE = 3
                    if proxy.call_method("ScrollTo", &(3u32,)).is_ok() {
                        return Ok(());
                    }
                }
                return Err(Error::ActionNotSupported {
                    action: "scroll_down".to_string(),
                    role: element.role,
                });
            }
        }
        Ok(())
    }

    fn scroll_up(&self, element: &ElementData, amount: f64) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let count = (amount.abs() as u32).max(1);
        for _ in 0..count {
            if self.do_atspi_action_by_name(&target, "scroll up").is_err() {
                // Fall back to Component.ScrollTo (single call, not repeatable).
                // If both fail, return ActionNotSupported for clearer error handling.
                // Fixes GitHub issue #99.
                if let Ok(proxy) =
                    self.make_proxy(&target.bus_name, &target.path, "org.a11y.atspi.Component")
                {
                    // TOP_EDGE = 2
                    if proxy.call_method("ScrollTo", &(2u32,)).is_ok() {
                        return Ok(());
                    }
                }
                return Err(Error::ActionNotSupported {
                    action: "scroll_up".to_string(),
                    role: element.role,
                });
            }
        }
        Ok(())
    }

    fn scroll_right(&self, element: &ElementData, amount: f64) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let count = (amount.abs() as u32).max(1);
        for _ in 0..count {
            if self
                .do_atspi_action_by_name(&target, "scroll right")
                .is_err()
            {
                // Fall back to Component.ScrollTo (single call, not repeatable).
                // If both fail, return ActionNotSupported for clearer error handling.
                // Fixes GitHub issue #99.
                if let Ok(proxy) =
                    self.make_proxy(&target.bus_name, &target.path, "org.a11y.atspi.Component")
                {
                    // RIGHT_EDGE = 5
                    if proxy.call_method("ScrollTo", &(5u32,)).is_ok() {
                        return Ok(());
                    }
                }
                return Err(Error::ActionNotSupported {
                    action: "scroll_right".to_string(),
                    role: element.role,
                });
            }
        }
        Ok(())
    }

    fn scroll_left(&self, element: &ElementData, amount: f64) -> Result<()> {
        let target = self.get_cached(element.handle)?;
        let count = (amount.abs() as u32).max(1);
        for _ in 0..count {
            if self
                .do_atspi_action_by_name(&target, "scroll left")
                .is_err()
            {
                // Fall back to Component.ScrollTo (single call, not repeatable).
                // If both fail, return ActionNotSupported for clearer error handling.
                // Fixes GitHub issue #99.
                if let Ok(proxy) =
                    self.make_proxy(&target.bus_name, &target.path, "org.a11y.atspi.Component")
                {
                    // LEFT_EDGE = 4
                    if proxy.call_method("ScrollTo", &(4u32,)).is_ok() {
                        return Ok(());
                    }
                }
                return Err(Error::ActionNotSupported {
                    action: "scroll_left".to_string(),
                    role: element.role,
                });
            }
        }
        Ok(())
    }

    fn perform_action(&self, element: &ElementData, action: &str) -> Result<()> {
        match action {
            "press" => self.press(element),
            "focus" => self.focus(element),
            "blur" => self.blur(element),
            "toggle" => self.toggle(element),
            "select" => self.select(element),
            "expand" => self.expand(element),
            "collapse" => self.collapse(element),
            "show_menu" => self.show_menu(element),
            "increment" => self.increment(element),
            "decrement" => self.decrement(element),
            "scroll_into_view" => self.scroll_into_view(element),
            _ => Err(Error::ActionNotSupported {
                action: action.to_string(),
                role: element.role,
            }),
        }
    }

    fn subscribe(&self, element: &ElementData) -> Result<Subscription> {
        let pid = element.pid.ok_or(Error::Platform {
            code: -1,
            message: "Element has no PID for subscribe".to_string(),
        })?;
        let app_name = element.name.clone().unwrap_or_default();
        self.subscribe_impl(app_name, pid, pid)
    }
}

// ── Event subscription ──────────────────────────────────────────────────────

impl LinuxProvider {
    /// Spawn a polling thread that detects focus and structure changes.
    fn subscribe_impl(&self, app_name: String, app_pid: u32, pid: u32) -> Result<Subscription> {
        let (tx, rx) = std::sync::mpsc::channel();
        let poll_provider = LinuxProvider::new()?;
        let stop = std::sync::Arc::new(std::sync::atomic::AtomicBool::new(false));
        let stop_clone = stop.clone();

        let handle = std::thread::spawn(move || {
            let mut prev_focused: Option<String> = None;
            let mut prev_element_count: usize = 0;

            while !stop_clone.load(std::sync::atomic::Ordering::Relaxed) {
                std::thread::sleep(Duration::from_millis(100));

                // Find the app element by PID
                let app_ref = match poll_provider.find_app_by_pid(pid) {
                    Ok(r) => r,
                    Err(_) => continue,
                };
                let app_data = poll_provider.build_element_data(&app_ref, Some(pid));

                // Walk the tree lazily to find focused element and count
                let mut stack = vec![app_data];
                let mut element_count: usize = 0;
                let mut focused_element: Option<ElementData> = None;
                let mut visited = HashSet::new();

                while let Some(el) = stack.pop() {
                    let path_key = format!("{:?}:{}", el.raw, el.handle);
                    if !visited.insert(path_key) {
                        continue;
                    }
                    element_count += 1;
                    if el.states.focused && focused_element.is_none() {
                        focused_element = Some(el.clone());
                    }
                    if let Ok(children) = poll_provider.get_children(Some(&el)) {
                        stack.extend(children);
                    }
                }

                let focused_name = focused_element.as_ref().and_then(|e| e.name.clone());
                if focused_name != prev_focused {
                    if prev_focused.is_some() {
                        let _ = tx.send(Event {
                            event_type: EventType::FocusChanged,
                            app_name: app_name.clone(),
                            app_pid,
                            target: focused_element,
                            state_flag: None,
                            state_value: None,
                            text_change: None,
                            timestamp: std::time::Instant::now(),
                        });
                    }
                    prev_focused = focused_name;
                }

                if element_count != prev_element_count && prev_element_count > 0 {
                    let _ = tx.send(Event {
                        event_type: EventType::StructureChanged,
                        app_name: app_name.clone(),
                        app_pid,
                        target: None,
                        state_flag: None,
                        state_value: None,
                        text_change: None,
                        timestamp: std::time::Instant::now(),
                    });
                }
                prev_element_count = element_count;
            }
        });

        let cancel = CancelHandle::new(move || {
            stop.store(true, std::sync::atomic::Ordering::Relaxed);
            let _ = handle.join();
        });

        Ok(Subscription::new(EventReceiver::new(rx), cancel))
    }
}

/// Whether a role typically has text or Value interface content.
/// Container/structural roles are skipped to save D-Bus round-trips.
fn role_has_value(role: Role) -> bool {
    !matches!(
        role,
        Role::Application
            | Role::Window
            | Role::Dialog
            | Role::Group
            | Role::MenuBar
            | Role::Toolbar
            | Role::TabGroup
            | Role::SplitGroup
            | Role::Table
            | Role::TableRow
            | Role::Separator
    )
}

/// Whether a role typically supports actions via the Action interface.
/// Container and display-only roles are skipped to save D-Bus round-trips.
fn role_has_actions(role: Role) -> bool {
    matches!(
        role,
        Role::Button
            | Role::CheckBox
            | Role::RadioButton
            | Role::MenuItem
            | Role::Link
            | Role::ComboBox
            | Role::TextField
            | Role::TextArea
            | Role::SpinButton
            | Role::Tab
            | Role::TreeItem
            | Role::ListItem
            | Role::ScrollBar
            | Role::Slider
            | Role::Menu
            | Role::Image
            | Role::Unknown
    )
}

/// Map AT-SPI2 role name to xa11y Role.
fn map_atspi_role(role_name: &str) -> Role {
    match role_name.to_lowercase().as_str() {
        "application" => Role::Application,
        "window" | "frame" => Role::Window,
        "dialog" | "file chooser" => Role::Dialog,
        "alert" | "notification" => Role::Alert,
        "push button" | "push button menu" => Role::Button,
        "toggle button" => Role::Switch,
        "check box" | "check menu item" => Role::CheckBox,
        "radio button" | "radio menu item" => Role::RadioButton,
        "entry" | "password text" => Role::TextField,
        "spin button" | "spinbutton" => Role::SpinButton,
        // "textbox" is the ARIA role name returned by WebKit2GTK for both
        // <input type="text"> and <textarea>.  Map to TextArea here so the
        // multi-line refinement below can downgrade single-line ones to TextField.
        "text" | "textbox" => Role::TextArea,
        "label" | "static" | "caption" => Role::StaticText,
        "combo box" | "combobox" => Role::ComboBox,
        // "listbox" is the ARIA role name returned by WebKit2GTK for role="listbox".
        "list" | "list box" | "listbox" => Role::List,
        "list item" => Role::ListItem,
        "menu" => Role::Menu,
        "menu item" | "tearoff menu item" => Role::MenuItem,
        "menu bar" => Role::MenuBar,
        "page tab" => Role::Tab,
        "page tab list" => Role::TabGroup,
        "table" | "tree table" => Role::Table,
        "table row" => Role::TableRow,
        "table cell" | "table column header" | "table row header" => Role::TableCell,
        "tool bar" => Role::Toolbar,
        "scroll bar" => Role::ScrollBar,
        "slider" => Role::Slider,
        "image" | "icon" | "desktop icon" => Role::Image,
        "link" => Role::Link,
        "panel" | "section" | "form" | "filler" | "viewport" | "scroll pane" => Role::Group,
        "progress bar" => Role::ProgressBar,
        "tree item" => Role::TreeItem,
        "document web" | "document frame" => Role::WebArea,
        "heading" => Role::Heading,
        "separator" => Role::Separator,
        "split pane" => Role::SplitGroup,
        "tooltip" | "tool tip" => Role::Tooltip,
        "status bar" | "statusbar" => Role::Status,
        "landmark" | "navigation" => Role::Navigation,
        _ => xa11y_core::unknown_role(role_name),
    }
}

/// Map AT-SPI2 numeric role (AtspiRole enum) to xa11y Role.
/// Values from atspi-common Role enum (repr(u32)).
fn map_atspi_role_number(role: u32) -> Role {
    match role {
        2 => Role::Alert,        // Alert
        7 => Role::CheckBox,     // CheckBox
        8 => Role::CheckBox,     // CheckMenuItem
        11 => Role::ComboBox,    // ComboBox
        16 => Role::Dialog,      // Dialog
        19 => Role::Dialog,      // FileChooser
        20 => Role::Group,       // Filler
        23 => Role::Window,      // Frame
        26 => Role::Image,       // Icon
        27 => Role::Image,       // Image
        29 => Role::StaticText,  // Label
        31 => Role::List,        // List
        32 => Role::ListItem,    // ListItem
        33 => Role::Menu,        // Menu
        34 => Role::MenuBar,     // MenuBar
        35 => Role::MenuItem,    // MenuItem
        37 => Role::Tab,         // PageTab
        38 => Role::TabGroup,    // PageTabList
        39 => Role::Group,       // Panel
        40 => Role::TextField,   // PasswordText
        42 => Role::ProgressBar, // ProgressBar
        43 => Role::Button,      // Button (push button)
        44 => Role::RadioButton, // RadioButton
        45 => Role::RadioButton, // RadioMenuItem
        48 => Role::ScrollBar,   // ScrollBar
        49 => Role::Group,       // ScrollPane
        50 => Role::Separator,   // Separator
        51 => Role::Slider,      // Slider
        52 => Role::SpinButton,  // SpinButton
        53 => Role::SplitGroup,  // SplitPane
        55 => Role::Table,       // Table
        56 => Role::TableCell,   // TableCell
        57 => Role::TableCell,   // TableColumnHeader
        58 => Role::TableCell,   // TableRowHeader
        61 => Role::TextArea,    // Text
        62 => Role::Switch,      // ToggleButton
        63 => Role::Toolbar,     // ToolBar
        65 => Role::Group,       // Tree
        66 => Role::Table,       // TreeTable
        67 => Role::Unknown,     // Unknown
        68 => Role::Group,       // Viewport
        69 => Role::Window,      // Window
        75 => Role::Application, // Application
        78 => Role::TextArea, // Embedded — WebKit2GTK uses this for <input type="text"> and <textarea>;
        // multi-line refinement below downgrades single-line ones to TextField
        79 => Role::TextField,   // Entry
        82 => Role::WebArea,     // DocumentFrame
        83 => Role::Heading,     // Heading
        85 => Role::Group,       // Section
        86 => Role::Group,       // RedundantObject
        87 => Role::Group,       // Form
        88 => Role::Link,        // Link
        90 => Role::TableRow,    // TableRow
        91 => Role::TreeItem,    // TreeItem
        95 => Role::WebArea,     // DocumentWeb
        97 => Role::List,        // WebKit2GTK uses this for <ul role="listbox">
        98 => Role::List,        // ListBox
        93 => Role::Tooltip,     // Tooltip
        101 => Role::Alert,      // Notification
        116 => Role::StaticText, // Static
        129 => Role::Button,     // PushButtonMenu
        _ => xa11y_core::unknown_role(&format!("AT-SPI role number {role}")),
    }
}

/// Map an AT-SPI2 action name to its canonical `snake_case` xa11y action name.
///
/// Toolkit-specific aliases are normalised to the single canonical name:
///   "click" / "activate" / "press" / "invoke" → "press"
///   "toggle" / "check" / "uncheck"            → "toggle"
///   "expand" / "open"                          → "expand"
///   "collapse" / "close"                       → "collapse"
///   "menu" / "showmenu" / "popup" / "show menu" → "show_menu"
///   "select"                                    → "select"
///   "increment"                                 → "increment"
///   "decrement"                                 → "decrement"
///
/// Returns `None` for unrecognised names.
fn map_atspi_action_name(action_name: &str) -> Option<String> {
    let lower = action_name.to_lowercase();
    let canonical = match lower.as_str() {
        "click" | "activate" | "press" | "invoke" => "press",
        "toggle" | "check" | "uncheck" => "toggle",
        "expand" | "open" => "expand",
        "collapse" | "close" => "collapse",
        "select" => "select",
        "menu" | "showmenu" | "show_menu" | "popup" | "show menu" => "show_menu",
        "increment" => "increment",
        "decrement" => "decrement",
        _ => return None,
    };
    Some(canonical.to_string())
}

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

    #[test]
    fn test_role_mapping() {
        assert_eq!(map_atspi_role("push button"), Role::Button);
        assert_eq!(map_atspi_role("toggle button"), Role::Switch);
        assert_eq!(map_atspi_role("check box"), Role::CheckBox);
        assert_eq!(map_atspi_role("entry"), Role::TextField);
        assert_eq!(map_atspi_role("label"), Role::StaticText);
        assert_eq!(map_atspi_role("window"), Role::Window);
        assert_eq!(map_atspi_role("frame"), Role::Window);
        assert_eq!(map_atspi_role("dialog"), Role::Dialog);
        assert_eq!(map_atspi_role("combo box"), Role::ComboBox);
        assert_eq!(map_atspi_role("slider"), Role::Slider);
        assert_eq!(map_atspi_role("panel"), Role::Group);
        assert_eq!(map_atspi_role("unknown_thing"), Role::Unknown);
    }

    #[test]
    fn test_numeric_role_mapping() {
        // ToggleButton (62) must map to Switch, not Button.
        // GTK4's Gtk.Switch and Gtk.ToggleButton both report numeric role 62.
        assert_eq!(map_atspi_role_number(62), Role::Switch);
        // Sanity-check a few well-established numeric mappings.
        assert_eq!(map_atspi_role_number(43), Role::Button); // PushButton
        assert_eq!(map_atspi_role_number(7), Role::CheckBox);
        assert_eq!(map_atspi_role_number(67), Role::Unknown); // AT-SPI Unknown
    }

    #[test]
    fn test_action_name_mapping() {
        assert_eq!(map_atspi_action_name("click"), Some("press".to_string()));
        assert_eq!(map_atspi_action_name("activate"), Some("press".to_string()));
        assert_eq!(map_atspi_action_name("press"), Some("press".to_string()));
        assert_eq!(map_atspi_action_name("invoke"), Some("press".to_string()));
        assert_eq!(map_atspi_action_name("toggle"), Some("toggle".to_string()));
        assert_eq!(map_atspi_action_name("check"), Some("toggle".to_string()));
        assert_eq!(map_atspi_action_name("uncheck"), Some("toggle".to_string()));
        assert_eq!(map_atspi_action_name("expand"), Some("expand".to_string()));
        assert_eq!(map_atspi_action_name("open"), Some("expand".to_string()));
        assert_eq!(
            map_atspi_action_name("collapse"),
            Some("collapse".to_string())
        );
        assert_eq!(map_atspi_action_name("close"), Some("collapse".to_string()));
        assert_eq!(map_atspi_action_name("select"), Some("select".to_string()));
        assert_eq!(map_atspi_action_name("menu"), Some("show_menu".to_string()));
        assert_eq!(
            map_atspi_action_name("showmenu"),
            Some("show_menu".to_string())
        );
        assert_eq!(
            map_atspi_action_name("popup"),
            Some("show_menu".to_string())
        );
        assert_eq!(
            map_atspi_action_name("show menu"),
            Some("show_menu".to_string())
        );
        assert_eq!(
            map_atspi_action_name("increment"),
            Some("increment".to_string())
        );
        assert_eq!(
            map_atspi_action_name("decrement"),
            Some("decrement".to_string())
        );
        assert_eq!(map_atspi_action_name("foobar"), None);
    }

    /// All known AT-SPI2 aliases map to one of the well-known action names,
    /// and re-mapping the canonical name produces the same canonical name.
    #[test]
    fn test_action_name_aliases_roundtrip() {
        let atspi_names = [
            "click",
            "activate",
            "press",
            "invoke",
            "toggle",
            "check",
            "uncheck",
            "expand",
            "open",
            "collapse",
            "close",
            "select",
            "menu",
            "showmenu",
            "popup",
            "show menu",
            "increment",
            "decrement",
        ];
        for name in atspi_names {
            let canonical = map_atspi_action_name(name).unwrap_or_else(|| {
                panic!("AT-SPI2 name {:?} should map to a canonical name", name)
            });
            // Re-mapping the canonical name must produce itself.
            let back = map_atspi_action_name(&canonical)
                .unwrap_or_else(|| panic!("canonical {:?} should map back to itself", canonical));
            assert_eq!(
                canonical, back,
                "AT-SPI2 {:?} -> {:?} -> {:?} (expected {:?})",
                name, canonical, back, canonical
            );
        }
    }

    /// Case-insensitive mapping works.
    #[test]
    fn test_action_name_case_insensitive() {
        assert_eq!(map_atspi_action_name("Click"), Some("press".to_string()));
        assert_eq!(map_atspi_action_name("TOGGLE"), Some("toggle".to_string()));
        assert_eq!(
            map_atspi_action_name("Increment"),
            Some("increment".to_string())
        );
    }
}