//! Managed subscriptions and occurrence-specific propagation. A validated VM
//! function sequences calls, so all handlers share one execution budget.
use crate::{block, mount::Mount, ui_bridge::attach_desktop_type};
use endor_core::{
    ContextNativeFunction, NativeCallable, NativeContext, NativeResult, ObjectPayload, ObjectRef,
    Value, Vm, VmError, WeakObjectRef,
};

const MAX_DELIVERIES: usize = 10_000;
fn invalid(message: &'static str) -> VmError {
    VmError::InvalidArgument(message)
}

pub fn validate_handler(
    store: &endor_core::ObjectStore,
    function: ObjectRef,
) -> Result<(), VmError> {
    if !store.object(function)?.payload().is_function() {
        return Err(invalid("event handler must be a Function"));
    }
    let arity = store
        .call_arity(function)?
        .ok_or(invalid("event handler requires positional metadata"))?;
    if !arity.accepts(0) && !arity.accepts(1) {
        return Err(invalid(
            "event handler must accept zero arguments or one Event",
        ));
    }
    Ok(())
}

#[derive(Debug, Clone, Default)]
pub struct Event {
    dispatch: Option<WeakObjectRef>,
    group: usize,
    stopped_at: Option<usize>,
    immediate: bool,
    prevented: bool,
}
impl ObjectPayload for Event {
    fn reference_assignment_only(&self) -> bool {
        true
    }
    fn as_any(&self) -> &dyn std::any::Any {
        self
    }
    fn kind_name(&self) -> &'static str {
        "tessera-event"
    }
    fn allows_attributes(&self) -> bool {
        true
    }
}

#[derive(Debug, Clone)]
pub struct Connection {
    pub handler: Option<ObjectRef>,
    pub kind: String,
    pub capture: bool,
}
impl ObjectPayload for Connection {
    fn reference_assignment_only(&self) -> bool {
        true
    }
    fn as_any(&self) -> &dyn std::any::Any {
        self
    }
    fn kind_name(&self) -> &'static str {
        "tessera-event-connection"
    }
    fn trace(&self, visit: &mut dyn FnMut(ObjectRef)) {
        if let Some(handler) = self.handler {
            visit(handler);
        }
    }
}

/// A token never retains its target or callback. The Block owns the connection.
#[derive(Debug)]
pub struct Subscription {
    pub connection: WeakObjectRef,
}
impl ObjectPayload for Subscription {
    fn reference_assignment_only(&self) -> bool {
        true
    }
    fn as_any(&self) -> &dyn std::any::Any {
        self
    }
    fn kind_name(&self) -> &'static str {
        "tessera-subscription"
    }
}

#[derive(Debug, Clone, Copy)]
enum Method {
    Stop,
    StopImmediate,
    Prevent,
    Prevented,
    Disconnect,
    Connected,
}
impl NativeCallable for Method {
    fn arity(&self) -> Option<endor_core::CallArity> {
        Some(endor_core::CallArity::exact(1))
    }

    fn invoke(&self, cx: &mut NativeContext<'_>, args: &[Value]) -> Result<NativeResult, VmError> {
        let [Value::Object(owner)] = args else {
            return Err(invalid("event method receiver"));
        };
        let result = match self {
            Self::Disconnect | Self::Connected => {
                let weak = cx
                    .store()
                    .payload::<Subscription>(*owner, "Subscription")?
                    .connection;
                let connection = cx.upgrade(weak)?;
                let connected = if let Some(connection) = connection {
                    if cx
                        .store()
                        .object(connection)?
                        .payload()
                        .as_any()
                        .is::<crate::binding::Binding>()
                    {
                        let mut data = cx
                            .store()
                            .payload::<crate::binding::Binding>(connection, "Binding")?
                            .clone();
                        let connected = data.compute.is_some();
                        if matches!(self, Self::Disconnect) {
                            data.compute = None;
                            cx.replace_payload(connection, data)?;
                        }
                        connected
                    } else {
                        let mut data = cx
                            .store()
                            .payload::<Connection>(connection, "Connection")?
                            .clone();
                        let connected = data.handler.is_some();
                        if matches!(self, Self::Disconnect) {
                            data.handler = None;
                            cx.replace_payload(connection, data)?;
                        }
                        connected
                    }
                } else {
                    false
                };
                if matches!(self, Self::Disconnect) {
                    Value::Nil
                } else {
                    Value::Bool(connected)
                }
            }
            _ => {
                let mut event = cx.store().payload::<Event>(*owner, "Event")?.clone();
                if matches!(self, Self::Prevented) {
                    Value::Bool(event.prevented)
                } else {
                    match self {
                        Self::Stop | Self::StopImmediate => {
                            event.stopped_at = Some(event.group);
                            event.immediate |= matches!(self, Self::StopImmediate);
                        }
                        Self::Prevent => event.prevented = true,
                        _ => unreachable!(),
                    }
                    cx.replace_payload(*owner, event)?;
                    Value::Nil
                }
            }
        };
        Ok(NativeResult::Return(result))
    }
}

#[derive(Debug)]
pub struct Constructor {
    pub signature: Option<endor_core::CallSignature>,
}
impl NativeCallable for Constructor {
    fn signature(&self) -> Option<endor_core::CallSignature> {
        self.signature.clone()
    }
    fn arity(&self) -> Option<endor_core::CallArity> {
        Some(endor_core::CallArity::range(2, usize::MAX))
    }

    fn invoke(&self, cx: &mut NativeContext<'_>, args: &[Value]) -> Result<NativeResult, VmError> {
        let [Value::Object(definition), Value::Text(kind), values @ ..] = args else {
            return Err(invalid("Event requires an event kind"));
        };
        let fields = cx
            .store()
            .payload::<endor_core::EndorTypeObject>(*definition, "Type")?
            .fields()
            .to_vec();
        if fields.len() != values.len() {
            return Err(invalid("incorrect Event field arguments"));
        }
        cx.store()
            .check_class_field_arguments(*definition, values)?;
        let event = new_event(cx, *definition, kind)?;
        for (field, value) in fields.iter().zip(values) {
            cx.set_attr(event, &field.name, value.clone())?;
        }
        Ok(NativeResult::Return(Value::Object(event)))
    }
}

pub fn new_event(
    cx: &mut NativeContext<'_>,
    definition: ObjectRef,
    kind: &str,
) -> Result<ObjectRef, VmError> {
    if kind.is_empty() || kind.len() > 128 {
        return Err(invalid("event kind must contain 1..128 UTF-8 bytes"));
    }
    let event = cx.allocate(Event::default())?;
    cx.attach_type(event, definition)?;
    cx.set_attr(event, "kind", Value::Text(kind.into()))?;
    for name in ["target", "mount", "currentTarget", "currentMount"] {
        cx.set_attr(event, name, Value::Nil)?;
    }
    cx.set_attr(event, "phase", Value::Text("none".into()))?;
    Ok(event)
}

#[derive(Debug)]
struct TypedMethod {
    method: Method,
    signature: endor_core::CallSignature,
}
impl NativeCallable for TypedMethod {
    fn signature(&self) -> Option<endor_core::CallSignature> {
        Some(self.signature.clone())
    }
    fn invoke(&self, cx: &mut NativeContext<'_>, args: &[Value]) -> Result<NativeResult, VmError> {
        self.method.invoke(cx, args)
    }
}

pub fn install(
    vm: &mut Vm,
    roots: &mut Vec<ObjectRef>,
    event_type: ObjectRef,
    token_type: ObjectRef,
    function_type: ObjectRef,
) -> Result<(), VmError> {
    for (definition, name, method) in [
        (event_type, "stopPropagation", Method::Stop),
        (
            event_type,
            "stopImmediatePropagation",
            Method::StopImmediate,
        ),
        (event_type, "preventDefault", Method::Prevent),
        (event_type, "isDefaultPrevented", Method::Prevented),
        (token_type, "disconnect", Method::Disconnect),
        (token_type, "isConnected", Method::Connected),
    ] {
        let query = matches!(method, Method::Prevented | Method::Connected);
        let function = vm.allocate(ContextNativeFunction::new(
            name,
            TypedMethod {
                method,
                signature: endor_core::CallSignature::exact(
                    vec![endor_core::AnnotationType::Nominal(definition)],
                    if query {
                        endor_core::AnnotationType::Bool
                    } else {
                        endor_core::AnnotationType::Unit
                    },
                    if query {
                        endor_core::CallEffect::ReadOnly
                    } else {
                        endor_core::CallEffect::Mutating
                    },
                ),
            },
            vec![],
        ))?;
        roots.push(function);
        vm.attach_type(function, function_type)?;
        vm.define_method(definition, name, function)?;
    }
    Ok(())
}

#[derive(Debug)]
enum Handler {
    Token(ObjectRef),
    Legacy(ObjectRef),
    ObjectMethod,
}
#[derive(Debug)]
struct Delivery {
    event: ObjectRef,
    owner: ObjectRef,
    mount: Option<ObjectRef>,
    group: usize,
    phase: &'static str,
    handler: Handler,
}
impl NativeCallable for Delivery {
    fn arity(&self) -> Option<endor_core::CallArity> {
        Some(endor_core::CallArity::exact(0))
    }

    fn invoke(&self, cx: &mut NativeContext<'_>, _: &[Value]) -> Result<NativeResult, VmError> {
        let mut event = cx.store().payload::<Event>(self.event, "Event")?.clone();
        if event.immediate || event.stopped_at.is_some_and(|group| group != self.group) {
            return Ok(NativeResult::Return(Value::Nil));
        }
        let (function, mut arguments) = match self.handler {
            Handler::Token(token) => {
                let Some(handler) = cx
                    .store()
                    .payload::<Connection>(token, "Connection")?
                    .handler
                else {
                    return Ok(NativeResult::Return(Value::Nil));
                };
                (handler, vec![])
            }
            Handler::Legacy(function) => (function, vec![]),
            Handler::ObjectMethod => {
                let Some(definition) = cx.store().type_of(self.owner)? else {
                    return Err(invalid("untyped event target"));
                };
                let function = cx
                    .store()
                    .lookup_method(definition, "onEvent")?
                    .ok_or(invalid("Block has no onEvent method"))?;
                (function, vec![Value::Object(self.owner)])
            }
        };
        event.group = self.group;
        cx.replace_payload(self.event, event)?;
        cx.set_attr(self.event, "phase", Value::Text(self.phase.into()))?;
        cx.set_attr(self.event, "currentTarget", Value::Object(self.owner))?;
        cx.set_attr(
            self.event,
            "currentMount",
            self.mount.map(Value::Object).unwrap_or(Value::Nil),
        )?;
        if matches!(self.handler, Handler::ObjectMethod)
            || cx
                .store()
                .call_arity(function)?
                .is_some_and(|arity| arity.accepts(1))
        {
            arguments.push(Value::Object(self.event));
        }
        Ok(NativeResult::Invoke {
            function,
            arguments,
        })
    }
}
#[derive(Debug)]
struct Finish(ObjectRef);
impl NativeCallable for Finish {
    fn arity(&self) -> Option<endor_core::CallArity> {
        Some(endor_core::CallArity::exact(0))
    }

    fn invoke(&self, cx: &mut NativeContext<'_>, _: &[Value]) -> Result<NativeResult, VmError> {
        let mut event = cx.store().payload::<Event>(self.0, "Event")?.clone();
        event.dispatch = None;
        cx.replace_payload(self.0, event)?;
        cx.set_attr(self.0, "phase", Value::Text("none".into()))?;
        cx.set_attr(self.0, "currentTarget", Value::Nil)?;
        cx.set_attr(self.0, "currentMount", Value::Nil)?;
        Ok(NativeResult::Return(Value::Object(self.0)))
    }
}

/// Snapshot the selected occurrence's route and listener order. Disconnection
/// before a listener's turn skips it; newly registered listeners wait for the
/// next dispatch. A code event without a Mount visits only its target object.
pub fn dispatch(
    cx: &mut NativeContext<'_>,
    owner: ObjectRef,
    event_ref: ObjectRef,
    mount: Option<ObjectRef>,
    desktop: ObjectRef,
) -> Result<NativeResult, VmError> {
    let mut event = cx.store().payload::<Event>(event_ref, "Event")?.clone();
    if let Some(weak) = event.dispatch
        && cx.upgrade(weak)?.is_some()
    {
        return Err(invalid("Event is already being dispatched"));
    }
    let Value::Text(kind) = cx.store().get_attr(event_ref, "kind")? else {
        return Err(invalid("Event kind must be text"));
    };
    if kind.is_empty() || kind.len() > 128 {
        return Err(invalid("invalid event kind"));
    }
    let mut route = vec![(owner, mount)];
    if let Some(mount) = mount {
        let target = cx.store().payload::<Mount>(mount, "Mount")?.clone();
        if !target.mounted || target.block != owner {
            return Err(invalid("event context does not belong to this Block"));
        }
        let mut parent = target.parent;
        let mut seen = std::collections::HashSet::from([mount]);
        while let Some(weak) = parent {
            let ancestor = cx
                .upgrade(weak)?
                .ok_or(invalid("event route has expired"))?;
            if !seen.insert(ancestor) {
                return Err(invalid("cyclic event route"));
            }
            let data = cx.store().payload::<Mount>(ancestor, "Mount")?;
            if !data.mounted {
                return Err(invalid("event route is detached"));
            }
            route.push((data.block, Some(ancestor)));
            parent = data.parent;
        }
        if let Some(weak) = target.page {
            let page = cx.upgrade(weak)?.ok_or(invalid("event Page has expired"))?;
            route.push((page, None));
        }
    }
    let guard = cx.new_object()?;
    let mut calls = Vec::new();
    let mut group = 0;
    // Each occurrence is its own propagation group, even for shared Blocks.
    let traversal = route
        .iter()
        .enumerate()
        .rev()
        .map(|(index, entry)| (index, entry, true))
        .chain(
            route
                .iter()
                .enumerate()
                .map(|(index, entry)| (index, entry, false)),
        );
    for (index, &(block, current_mount), capture) in traversal {
        let (_, data) = block::resolve(cx.store(), block)?;
        let mut handlers = Vec::new();
        for token in &data.subscriptions {
            let token_data = cx.store().payload::<Connection>(*token, "Connection")?;
            if token_data.handler.is_some()
                && token_data.kind == kind
                && token_data.capture == capture
            {
                handlers.push(Handler::Token(*token));
            }
        }
        if !capture {
            handlers.insert(0, Handler::ObjectMethod);
            if kind == "click"
                && let Some(handler) = data.click
            {
                handlers.push(Handler::Legacy(handler));
            }
        }
        for handler in handlers {
            if calls.len() >= MAX_DELIVERIES {
                return Err(invalid("event delivery budget exceeded"));
            }
            let mut captures = vec![event_ref, guard, block];
            if let Some(mount) = current_mount {
                captures.push(mount);
            }
            match handler {
                Handler::Token(token) | Handler::Legacy(token) => captures.push(token),
                Handler::ObjectMethod => {}
            }
            let function = cx.allocate(ContextNativeFunction::new(
                "event delivery",
                Delivery {
                    event: event_ref,
                    owner: block,
                    mount: current_mount,
                    group,
                    phase: if index == 0 {
                        "target"
                    } else if capture {
                        "capture"
                    } else {
                        "bubble"
                    },
                    handler,
                },
                captures,
            ))?;
            attach_desktop_type(cx, function, "Function", desktop)?;
            calls.push(function);
        }
        // Capture and bubble at the target are one group: stopPropagation at
        // target capture still permits other target listeners.
        if index != 0 || !capture {
            group += 1;
        }
    }
    let finish = cx.allocate(ContextNativeFunction::new(
        "event finish",
        Finish(event_ref),
        vec![event_ref, guard],
    ))?;
    calls.push(finish);
    let driver = crate::vm_sequence::build(cx, calls, "<event dispatch>", desktop)?;
    event.dispatch = Some(cx.store().downgrade(guard)?);
    event.group = 0;
    event.stopped_at = None;
    event.immediate = false;
    event.prevented = false;
    cx.replace_payload(event_ref, event)?;
    cx.set_attr(event_ref, "target", Value::Object(owner))?;
    cx.set_attr(
        event_ref,
        "mount",
        mount.map(Value::Object).unwrap_or(Value::Nil),
    )?;
    Ok(NativeResult::Invoke {
        function: driver,
        arguments: vec![],
    })
}