//! Runtime host surface (`host` feature).
//!
//! [`HostApi`] is the `acadrust`-typed adapter a plugin uses at *dispatch* time
//! — document access, entity creation, XDATA, undo, and the command line. It is
//! the stable counterpart to the dependency-free manifest/ribbon contract: a
//! plugin's `dispatch` receives `&mut dyn HostApi` rather than the host's
//! concrete session type, so an out-of-tree add-on compiles against this crate
//! alone.
//!
//! Per-tab plugin state is keyed by `manifest.id`. The trait exposes it in an
//! object-safe `Any` form; use the [`plugin_state`], [`plugin_state_mut`] and
//! [`ensure_plugin_state`] helpers for the ergonomic typed access.

use std::any::Any;

use serde::{Deserialize, Deserializer, Serialize, Serializer};

use crate::manifest::PluginManifest;
use crate::ribbon::CadModule;

// Re-export the acadrust crate and the types that appear in the HostApi trait
// so out-of-tree plugins can use them without adding their own acadrust
// dependency (which would risk an ABI-mismatching version).
pub use acadrust;
pub use acadrust::{CadDocument, EntityType, Handle};
pub use acadrust::xdata::ExtendedDataRecord;

use crate::ipc::protocol::{PluginRequest, PluginResponse};

/// Thread-safe handle that can issue host requests from plugin worker threads.
/// Out-of-process V4 plugins implement this; in-process hosts may return `None`.
pub trait PluginRequestSender: Send + Sync {
    fn request(&self, req: PluginRequest) -> Result<PluginResponse, PluginRequestError>;
}

/// Error returned when a plugin worker thread cannot issue a host request.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PluginRequestError(pub String);

impl std::fmt::Display for PluginRequestError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "PluginRequestError: {}", self.0)
    }
}

impl std::error::Error for PluginRequestError {}

/// Log level carried by [`PluginNotification::Log`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[non_exhaustive]
pub enum LogLevel {
    Debug,
    Info,
    Warn,
    Error,
}

/// A notification the host sends to a plugin. These are best-effort,
/// full-duplex messages correlated with an optional `command_id`.
#[derive(Debug, Clone, PartialEq)]
#[non_exhaustive]
pub enum HostNotification {
    InputLine { line: String },
    Cancel,
    DocumentChanged { version: u64 },
    SelectionChanged { handles: Vec<Handle> },
    Raw(Vec<u8>),
    /// V4 snapshot changed for a specific tab. Discriminant 5.
    DocumentChangedV4 { tab_id: u64, version: u64 },
    /// V4 tab closed notification. Discriminant 6.
    DocumentTabClosed { tab_id: u64 },
    /// V4 selection changed for a specific tab. Discriminant 7.
    SelectionChangedV4 { tab_id: u64, handles: Vec<Handle> },
    /// Fallback for notification variants added in future minor revisions.
    /// Carries the raw bincode payload so an older peer can ignore it without
    /// failing deserialization.
    Unknown(Vec<u8>),
}

impl Serialize for HostNotification {
    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        let mut bytes = Vec::new();
        match self {
            HostNotification::InputLine { line } => {
                bytes.push(0);
                bincode::serialize_into(&mut bytes, line)
                    .map_err(serde::ser::Error::custom)?;
            }
            HostNotification::Cancel => bytes.push(1),
            HostNotification::DocumentChanged { version } => {
                bytes.push(2);
                bincode::serialize_into(&mut bytes, version)
                    .map_err(serde::ser::Error::custom)?;
            }
            HostNotification::SelectionChanged { handles } => {
                bytes.push(3);
                bincode::serialize_into(&mut bytes, handles)
                    .map_err(serde::ser::Error::custom)?;
            }
            HostNotification::Raw(data) => {
                bytes.push(4);
                bincode::serialize_into(&mut bytes, data)
                    .map_err(serde::ser::Error::custom)?;
            }
            HostNotification::DocumentChangedV4 { tab_id, version } => {
                bytes.push(5);
                bincode::serialize_into(&mut bytes, tab_id)
                    .map_err(serde::ser::Error::custom)?;
                bincode::serialize_into(&mut bytes, version)
                    .map_err(serde::ser::Error::custom)?;
            }
            HostNotification::DocumentTabClosed { tab_id } => {
                bytes.push(6);
                bincode::serialize_into(&mut bytes, tab_id)
                    .map_err(serde::ser::Error::custom)?;
            }
            HostNotification::SelectionChangedV4 { tab_id, handles } => {
                bytes.push(7);
                bincode::serialize_into(&mut bytes, tab_id)
                    .map_err(serde::ser::Error::custom)?;
                bincode::serialize_into(&mut bytes, handles)
                    .map_err(serde::ser::Error::custom)?;
            }
            HostNotification::Unknown(raw) => bytes.extend_from_slice(raw),
        }
        bytes.serialize(serializer)
    }
}

impl<'de> Deserialize<'de> for HostNotification {
    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        let bytes = Vec::<u8>::deserialize(deserializer)?;
        if bytes.is_empty() {
            return Err(serde::de::Error::custom("empty HostNotification"));
        }
        let discriminant = bytes[0];
        let rest = &bytes[1..];
        match discriminant {
            0 => bincode::deserialize(rest)
                .map(|line| HostNotification::InputLine { line })
                .map_err(serde::de::Error::custom),
            1 => Ok(HostNotification::Cancel),
            2 => bincode::deserialize(rest)
                .map(|version| HostNotification::DocumentChanged { version })
                .map_err(serde::de::Error::custom),
            3 => bincode::deserialize(rest)
                .map(|handles| HostNotification::SelectionChanged { handles })
                .map_err(serde::de::Error::custom),
            4 => bincode::deserialize(rest)
                .map(HostNotification::Raw)
                .map_err(serde::de::Error::custom),
            5 => bincode::deserialize(rest)
                .map(|(tab_id, version)| HostNotification::DocumentChangedV4 { tab_id, version })
                .map_err(serde::de::Error::custom),
            6 => bincode::deserialize(rest)
                .map(|tab_id| HostNotification::DocumentTabClosed { tab_id })
                .map_err(serde::de::Error::custom),
            7 => bincode::deserialize(rest)
                .map(|(tab_id, handles)| HostNotification::SelectionChangedV4 { tab_id, handles })
                .map_err(serde::de::Error::custom),
            _ => Ok(HostNotification::Unknown(bytes)),
        }
    }
}

/// A notification a plugin sends to the host. These are best-effort,
/// full-duplex messages correlated with an optional `command_id`.
#[derive(Debug, Clone, PartialEq)]
#[non_exhaustive]
pub enum PluginNotification {
    Output { text: String },
    Error { text: String },
    Prompt { text: String },
    Progress { percent: u8 },
    Log { level: LogLevel, text: String },
    Raw(Vec<u8>),
    /// V4 REPL status update. Discriminant 6.
    ReplStatus { status: String, message: String },
    /// Fallback for notification variants added in future minor revisions.
    /// Carries the raw bincode payload so an older peer can ignore it without
    /// failing deserialization.
    Unknown(Vec<u8>),
}

impl Serialize for PluginNotification {
    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        let mut bytes = Vec::new();
        match self {
            PluginNotification::Output { text } => {
                bytes.push(0);
                bincode::serialize_into(&mut bytes, text)
                    .map_err(serde::ser::Error::custom)?;
            }
            PluginNotification::Error { text } => {
                bytes.push(1);
                bincode::serialize_into(&mut bytes, text)
                    .map_err(serde::ser::Error::custom)?;
            }
            PluginNotification::Prompt { text } => {
                bytes.push(2);
                bincode::serialize_into(&mut bytes, text)
                    .map_err(serde::ser::Error::custom)?;
            }
            PluginNotification::Progress { percent } => {
                bytes.push(3);
                bincode::serialize_into(&mut bytes, percent)
                    .map_err(serde::ser::Error::custom)?;
            }
            PluginNotification::Log { level, text } => {
                bytes.push(4);
                bincode::serialize_into(&mut bytes, level)
                    .map_err(serde::ser::Error::custom)?;
                bincode::serialize_into(&mut bytes, text)
                    .map_err(serde::ser::Error::custom)?;
            }
            PluginNotification::Raw(data) => {
                bytes.push(5);
                bincode::serialize_into(&mut bytes, data)
                    .map_err(serde::ser::Error::custom)?;
            }
            PluginNotification::ReplStatus { status, message } => {
                bytes.push(6);
                bincode::serialize_into(&mut bytes, status)
                    .map_err(serde::ser::Error::custom)?;
                bincode::serialize_into(&mut bytes, message)
                    .map_err(serde::ser::Error::custom)?;
            }
            PluginNotification::Unknown(raw) => bytes.extend_from_slice(raw),
        }
        bytes.serialize(serializer)
    }
}

impl<'de> Deserialize<'de> for PluginNotification {
    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        let bytes = Vec::<u8>::deserialize(deserializer)?;
        if bytes.is_empty() {
            return Err(serde::de::Error::custom("empty PluginNotification"));
        }
        let discriminant = bytes[0];
        let rest = &bytes[1..];
        match discriminant {
            0 => bincode::deserialize(rest)
                .map(|text| PluginNotification::Output { text })
                .map_err(serde::de::Error::custom),
            1 => bincode::deserialize(rest)
                .map(|text| PluginNotification::Error { text })
                .map_err(serde::de::Error::custom),
            2 => bincode::deserialize(rest)
                .map(|text| PluginNotification::Prompt { text })
                .map_err(serde::de::Error::custom),
            3 => bincode::deserialize(rest)
                .map(|percent| PluginNotification::Progress { percent })
                .map_err(serde::de::Error::custom),
            4 => {
                let (level, text): (LogLevel, String) = bincode::deserialize(rest)
                    .map_err(serde::de::Error::custom)?;
                Ok(PluginNotification::Log { level, text })
            }
            5 => bincode::deserialize(rest)
                .map(PluginNotification::Raw)
                .map_err(serde::de::Error::custom),
            6 => bincode::deserialize(rest)
                .map(|(status, message)| PluginNotification::ReplStatus { status, message })
                .map_err(serde::de::Error::custom),
            _ => Ok(PluginNotification::Unknown(bytes)),
        }
    }
}

/// An add-on package's entry point: its manifest, optional ribbon tab, and
/// command dispatch. Built-in (in-tree) and dynamically-loaded (cdylib) plugins
/// implement the same trait from this crate, so an out-of-tree add-on targets
/// the stable contract rather than the host binary.
pub trait BuiltinPlugin: Send + Sync {
    fn manifest(&self) -> &'static PluginManifest;
    fn ribbon(&self) -> Box<dyn CadModule>;
    fn dispatch(&self, host: &mut dyn HostApi, cmd: &str) -> bool;

    /// Long-running REPL code execution (API v4). The plugin may start the
    /// work on another thread and call `respond` when finished; the runner
    /// will forward the result to the host. The supplied `host` is the active
    /// document tab's API surface, so the REPL session is tied to a tab.
    ///
    /// Returning `false` means the plugin does not support code execution.
    fn start_execute_code(
        &mut self,
        _host: &mut dyn HostApi,
        _command_id: u64,
        _code: &str,
        _source: CommandSource,
        _respond: Box<dyn FnOnce(ExecutionResult) + Send>,
    ) -> bool {
        false
    }

    /// State-only callback for host-to-plugin notifications. Added in API v4;
    /// the V4 runner guarantees it is only called for plugins that report
    /// API major 4 or newer.
    fn on_notification(&mut self, _command_id: Option<u64>, _notification: HostNotification) {}
}

/// A point-driven interactive command a plugin starts via
/// [`HostApi::start_interactive`]. The host shows the prompt, collects points —
/// clicked in the viewport, or fed as coordinates over the `--serve` automation
/// API — and commits the entities the command yields, exactly like a built-in
/// tool. This is the plugin-facing slice of the host's command machinery; it
/// covers click-to-place placement without exposing the host's internal command
/// trait.
pub trait InteractiveCommand: Send {
    /// Prompt for the next point.
    fn prompt(&self) -> String;
    /// A point was supplied (clicked or typed `x,y[,z]`). Returns the next step.
    fn on_point(&mut self, pt: [f64; 3]) -> CommandStep;
    /// Enter pressed with no point — e.g. to finish a multi-point command.
    fn on_enter(&mut self) -> CommandStep {
        CommandStep::Cancel
    }

    /// When `true`, the next input picks an existing **entity** (the user clicks
    /// on it; over `--serve`, a handle is supplied) rather than a free point —
    /// the host then calls [`on_object_pick`](Self::on_object_pick). Use this to
    /// reference existing geometry (e.g. connect a pipe between two structures).
    fn needs_object_pick(&self) -> bool {
        false
    }
    /// An existing entity was picked: its `handle` and the pick point. Read the
    /// entity's data (XDATA / geometry) via `HostApi`, keyed by the handle.
    fn on_object_pick(&mut self, _handle: Handle, _pt: [f64; 3]) -> CommandStep {
        CommandStep::Cancel
    }
}

/// The outcome of an [`InteractiveCommand`] step.
#[derive(Debug)]
#[cfg_attr(feature = "host", derive(serde::Serialize, serde::Deserialize))]
pub enum CommandStep {
    /// Need another point; keep the command active.
    NeedPoint,
    /// Commit an entity to the document and keep collecting points.
    Commit(EntityType),
    /// Commit an entity and end the command.
    CommitAndEnd(EntityType),
    /// End the command without committing.
    Done,
    /// Cancel the command.
    Cancel,
}

/// Export a `BuiltinPlugin` from a `cdylib` so the host can load it at runtime.
///
/// Emits the two C symbols the loader looks for: `ocs_plugin_api_version`
/// (checked before anything else, so an ABI-incompatible build is rejected
/// without running its code) and `ocs_plugin_register` (constructs the plugin
/// and hands ownership to the host as a boxed trait object).
///
/// ```ignore
/// ocs_plugin_api::export_plugin!(MyPlugin::new());
/// ```
#[macro_export]
macro_rules! export_plugin {
    ($ctor:expr) => {
        #[no_mangle]
        pub extern "C" fn ocs_plugin_api_version() -> u32 {
            $crate::API_VERSION
        }

        #[no_mangle]
        pub extern "C" fn ocs_plugin_register(
        ) -> *mut ::std::boxed::Box<dyn $crate::host::BuiltinPlugin> {
            // The constructor runs across a C ABI boundary; a panic unwinding
            // past it is undefined behavior. Contain it and report failure as a
            // null pointer, which the host loader treats as "registration
            // failed" rather than crashing the runner process.
            match ::std::panic::catch_unwind(::std::panic::AssertUnwindSafe(|| {
                let plugin: ::std::boxed::Box<dyn $crate::host::BuiltinPlugin> =
                    ::std::boxed::Box::new($ctor);
                ::std::boxed::Box::into_raw(::std::boxed::Box::new(plugin))
            })) {
                ::std::result::Result::Ok(ptr) => ptr,
                ::std::result::Result::Err(_) => ::std::ptr::null_mut(),
            }
        }
    };
}

/// The plugin-facing runtime surface for one active document tab.
pub trait HostApi {
    /// Index of the tab this session targets.
    fn tab_index(&self) -> usize;

    // ── Document ────────────────────────────────────────────────────────────
    fn document(&self) -> &CadDocument;
    /// Mutable access to the active document.
    ///
    /// For an **out-of-process** plugin this borrows a *local snapshot*: edits
    /// to existing entities made through it are NOT sent back to the host and
    /// are silently discarded. To modify or delete entities from any plugin,
    /// use [`add_entity`](Self::add_entity), [`update_entity`](Self::update_entity)
    /// and [`remove_entity`](Self::remove_entity), which are committed to the
    /// host document over IPC.
    fn document_mut(&mut self) -> &mut CadDocument;

    /// Add an entity to the active document, returning its handle.
    fn add_entity(&mut self, entity: EntityType) -> Handle;
    /// Replace the existing entity that carries `entity`'s handle, preserving
    /// its identity (handle and owning block). Returns `false` when no entity
    /// has that handle. This is the sanctioned way to commit in-place edits
    /// from an out-of-process plugin — mutating `document_mut()` does not work
    /// across the process boundary.
    fn update_entity(&mut self, entity: EntityType) -> bool {
        let handle = entity.common().handle;
        match self.document_mut().get_entity_mut(handle) {
            Some(slot) => {
                *slot = entity;
                true
            }
            None => false,
        }
    }
    /// Delete the entity with `handle` (and any derived render caches). Returns
    /// `true` when an entity was removed.
    fn remove_entity(&mut self, handle: Handle) -> bool {
        self.document_mut().remove_entity(handle).is_some()
    }
    /// Mark the scene geometry dirty so it is re-tessellated next frame.
    fn bump_geometry(&mut self);

    // ── XDATA ───────────────────────────────────────────────────────────────
    /// Read the XDATA record for `app_name` on entity `handle`, if any.
    fn read_record(&self, handle: Handle, app_name: &str) -> Option<&ExtendedDataRecord>;
    /// Attach `record` to entity `handle`, replacing any existing record for the
    /// same application and registering the APPID. Returns `false` if the entity
    /// does not exist.
    fn write_record(&mut self, handle: Handle, record: ExtendedDataRecord) -> bool;
    /// Remove the XDATA record for `app_name` from entity `handle`. Returns
    /// `true` if a record was removed.
    fn remove_record(&mut self, handle: Handle, app_name: &str) -> bool;

    // ── Undo / dirty ────────────────────────────────────────────────────────
    fn push_undo(&mut self, label: &str);
    fn set_dirty(&mut self);

    // ── Command line ────────────────────────────────────────────────────────
    fn push_info(&mut self, msg: &str);
    fn push_output(&mut self, msg: &str);
    fn push_error(&mut self, msg: &str);

    /// Start a plugin-defined interactive (click-to-place) command on the active
    /// tab. The host drives it through its normal point-collection flow.
    fn start_interactive(&mut self, command: Box<dyn InteractiveCommand>);

    // ── Per-tab plugin state (object-safe; use the typed helpers below) ──────
    fn plugin_state_any(&self, plugin_id: &str) -> Option<&(dyn Any + Send + Sync)>;
    fn plugin_state_any_mut(&mut self, plugin_id: &str) -> Option<&mut (dyn Any + Send + Sync)>;
    /// Get the state for `plugin_id`, inserting `init()`'s result if absent.
    fn ensure_plugin_state_any(
        &mut self,
        plugin_id: &'static str,
        init: &mut dyn FnMut() -> Box<dyn Any + Send + Sync>,
    ) -> &mut (dyn Any + Send + Sync);

    // ── DocumentReader (added in API v3; appended at the end to keep vtable
    // indices stable for API v2 plugins) ─────────────────────────────────────

    /// Read-only, zero-copy view of the active document. For out-of-process
    /// plugins this is backed by host-owned shared memory; for in-process
    /// plugins it wraps `document()`.
    fn document_reader(&self) -> Box<dyn DocumentReader + '_>;

    /// Open (or refresh) the host-side shared document view and return the
    /// information the plugin needs to map it. In-process hosts implement this;
    /// out-of-process plugin proxies return `None`.
    fn document_view(&mut self) -> Option<crate::shm::DocumentViewInfo> {
        None
    }

    // ── Notifications (added in API v4; appended at the end to keep vtable
    // indices stable for V2/V3 plugins) ───────────────────────────────────────

    /// Send a best-effort notification from the plugin to the host.
    ///
    /// In-process plugins can override this to forward to the host event loop;
    /// out-of-process plugins send a V4 notification frame.
    fn notify_plugin(&mut self, _command_id: Option<u64>, _notification: PluginNotification) {}

    /// Poll for a host-to-plugin notification, if any.
    ///
    /// Returns the optional `command_id` used to correlate the notification
    /// with a running command, and the notification payload. Long-running
    /// plugins should call this periodically to drain the bounded queue.
    fn try_recv_notification(
        &mut self,
    ) -> Option<(Option<u64>, HostNotification)> {
        None
    }

    /// Returns a thread-safe handle that can issue host requests from worker
    /// threads. Out-of-process V4 plugins implement this; in-process hosts may
    /// return `None`.
    fn plugin_request_sender(&self) -> Option<Box<dyn PluginRequestSender>> {
        None
    }

    // ── V4 tab/document identity (added for REPL; appended at the end) ───────

    /// Stable tab identifier for the active document tab.
    fn tab_id(&self) -> u64 {
        self.tab_index() as u64
    }

    /// Open (or refresh) the host-side V4 shared document view for `tab_id`
    /// and return the mapping information. In-process hosts implement this;
    /// out-of-process plugin proxies return `None`.
    fn document_view_v4(&mut self, tab_id: u64) -> Option<crate::shm::DocumentViewInfo> {
        let _ = tab_id;
        None
    }

    /// Close the host-side V4 shared document view for `tab_id`.
    fn close_document_view_v4(&mut self, tab_id: u64) {
        let _ = tab_id;
    }

    // ── Batch entities (added after API v4; appended at the very end so older
    // plugins compiled without it keep stable vtable indices) ────────────────

    /// Add multiple entities to the active document, returning their handles.
    /// The default implementation calls [`add_entity`](Self::add_entity) for each
    /// entity; hosts should override it for batch efficiency.
    fn add_entities(&mut self, entities: Vec<EntityType>) -> Vec<Handle> {
        entities.into_iter().map(|e| self.add_entity(e)).collect()
    }
}

/// Simplified, read-only entity kind exposed by [`DocumentReader`].
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ReaderEntityKind {
    Point,
    Line,
    Circle,
    Arc,
    Polyline,
    Text,
    Other,
}

/// A 3D point returned by [`DocumentReader`].
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct ReaderPoint {
    pub x: f64,
    pub y: f64,
    pub z: f64,
}

/// A read-only view of one entity, borrowed from a [`DocumentReader`].
pub struct ReaderEntity<'a> {
    /// Entity handle in the host document.
    pub handle: Handle,
    /// Simplified entity type.
    pub kind: ReaderEntityKind,
    /// Name of the layer the entity lives on.
    pub layer_name: &'a str,
    /// If the entity is a point, its coordinates.
    pub point: Option<ReaderPoint>,
}

/// Read-only, zero-copy view of a CAD document.
///
/// For out-of-process plugins this is backed by host-owned shared memory. The
/// plugin receives only references into that mapping, so the document model is
/// not copied into the plugin's heap.
pub trait DocumentReader {
    /// Total number of entities in the document.
    fn entity_count(&self) -> usize;

    /// Iterate over all entities without allocating a full `CadDocument`.
    fn for_each_entity(&self, f: &mut dyn FnMut(ReaderEntity<'_>));

    /// Look up a layer name by handle.
    fn layer_name(&self, handle: Handle) -> Option<&str>;

    /// Look up an APPID name by handle.
    fn app_id_name(&self, handle: Handle) -> Option<&str>;
}

impl ReaderEntityKind {
    /// Map a concrete `EntityType` to the simplified reader kind.
    pub fn from_entity(entity: &EntityType) -> Self {
        match entity {
            EntityType::Point(_) => ReaderEntityKind::Point,
            EntityType::Line(_) => ReaderEntityKind::Line,
            EntityType::Circle(_) => ReaderEntityKind::Circle,
            EntityType::Arc(_) => ReaderEntityKind::Arc,
            EntityType::Polyline(_)
            | EntityType::Polyline2D(_)
            | EntityType::Polyline3D(_)
            | EntityType::LwPolyline(_) => ReaderEntityKind::Polyline,
            EntityType::Text(_) | EntityType::MText(_) => ReaderEntityKind::Text,
            _ => ReaderEntityKind::Other,
        }
    }
}

/// In-process `DocumentReader` implementation that wraps a borrowed `CadDocument`.
pub struct CadDocumentReader<'a>(pub &'a CadDocument);

impl<'a> DocumentReader for CadDocumentReader<'a> {
    fn entity_count(&self) -> usize {
        self.0.entities().count()
    }

    fn for_each_entity(&self, f: &mut dyn FnMut(ReaderEntity<'_>)) {
        for entity in self.0.entities() {
            let kind = ReaderEntityKind::from_entity(entity);
            let layer_name = entity.common().layer.as_str();
            let point = match entity {
                EntityType::Point(p) => Some(ReaderPoint {
                    x: p.location.x,
                    y: p.location.y,
                    z: p.location.z,
                }),
                _ => None,
            };
            f(ReaderEntity {
                handle: entity.common().handle,
                kind,
                layer_name,
                point,
            });
        }
    }

    fn layer_name(&self, handle: Handle) -> Option<&str> {
        self.0
            .layers
            .iter()
            .find(|layer| layer.handle == handle)
            .map(|layer| layer.name.as_str())
    }

    fn app_id_name(&self, handle: Handle) -> Option<&str> {
        self.0
            .app_ids
            .iter()
            .find(|app_id| app_id.handle == handle)
            .map(|app_id| app_id.name.as_str())
    }
}

/// Typed read of per-tab plugin state stored under `plugin_id`.
pub fn plugin_state<'a, T: Any + Send + Sync>(
    host: &'a dyn HostApi,
    plugin_id: &str,
) -> Option<&'a T> {
    host.plugin_state_any(plugin_id)?.downcast_ref::<T>()
}

/// Typed mutable access to per-tab plugin state stored under `plugin_id`.
pub fn plugin_state_mut<'a, T: Any + Send + Sync>(
    host: &'a mut dyn HostApi,
    plugin_id: &str,
) -> Option<&'a mut T> {
    host.plugin_state_any_mut(plugin_id)?.downcast_mut::<T>()
}

/// Typed get-or-insert of per-tab plugin state stored under `plugin_id`.
pub fn ensure_plugin_state<'a, T: Any + Send + Sync>(
    host: &'a mut dyn HostApi,
    plugin_id: &'static str,
    init: impl FnOnce() -> T,
) -> &'a mut T {
    let mut init = Some(init);
    let any = host.ensure_plugin_state_any(plugin_id, &mut || {
        Box::new((init.take().expect("init called once"))())
    });
    any.downcast_mut::<T>()
        .expect("plugin state type mismatch for plugin_id")
}

#[cfg(feature = "host")]
mod repl {
    use serde::{Deserialize, Serialize};

    /// Source surface that submitted a REPL code snippet.
    #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
    #[non_exhaustive]
    pub enum CommandSource {
        CommandLine,
        Script,
        Editor,
    }

    /// Outcome of a REPL `ExecuteCode` request.
    #[derive(Debug, Clone, Serialize, Deserialize)]
    #[non_exhaustive]
    pub struct ExecutionResult {
        pub success: bool,
        pub output: Option<String>,
        pub error: Option<String>,
        pub error_type: Option<String>,
        pub traceback: Option<String>,
        pub line_number: Option<u32>,
        pub column_number: Option<u32>,
        pub duration_ms: f64,
    }

    impl ExecutionResult {
        /// Create a new execution result.
        pub fn new(
            success: bool,
            output: Option<String>,
            error: Option<String>,
            error_type: Option<String>,
            traceback: Option<String>,
            line_number: Option<u32>,
            column_number: Option<u32>,
            duration_ms: f64,
        ) -> Self {
            Self {
                success,
                output,
                error,
                error_type,
                traceback,
                line_number,
                column_number,
                duration_ms,
            }
        }
    }

    /// Spawn a thread that runs `f` and calls `respond` with the returned
    /// `ExecutionResult`. If `f` panics, `respond` is called with a panic error
    /// result instead, so the host never waits indefinitely for a callback that
    /// will never arrive.
    pub fn execute_code_guard<F>(
        respond: Box<dyn FnOnce(ExecutionResult) + Send>,
        f: F,
    ) -> std::thread::JoinHandle<()>
    where
        F: FnOnce() -> ExecutionResult + Send + 'static,
    {
        std::thread::spawn(move || {
            let result = match std::panic::catch_unwind(std::panic::AssertUnwindSafe(f)) {
                Ok(result) => result,
                Err(payload) => {
                    let msg = payload
                        .downcast_ref::<&str>()
                        .copied()
                        .or_else(|| payload.downcast_ref::<String>().map(|s| s.as_str()))
                        .unwrap_or("execute_code panicked");
                    ExecutionResult {
                        success: false,
                        output: None,
                        error: Some(format!("panic: {}", msg)),
                        error_type: Some("panic".to_string()),
                        traceback: None,
                        line_number: None,
                        column_number: None,
                        duration_ms: 0.0,
                    }
                }
            };
            respond(result);
        })
    }
}

#[cfg(feature = "host")]
pub use repl::{execute_code_guard, CommandSource, ExecutionResult};