starweaver-model 0.9.0

use std::{collections::VecDeque, sync::Arc};

use async_trait::async_trait;
use serde_json::Value;
use starweaver_core::CancellationToken;

use crate::ModelError;

use super::{HttpRequest, HttpResponse};

/// Async HTTP client abstraction used by production model adapters.
#[async_trait]
pub trait ModelHttpClient: Send + Sync {
    /// Send a JSON model request.
    ///
    /// # Errors
    ///
    /// Returns an error when transport, status, or response decoding fails.
    async fn send(&self, request: HttpRequest) -> Result<HttpResponse, ModelError>;

    /// Send a server-sent events model request and return JSON `data:` payloads.
    ///
    /// # Errors
    ///
    /// Returns an error when transport, status, or event decoding fails.
    async fn send_event_stream(&self, request: HttpRequest) -> Result<Vec<Value>, ModelError> {
        let mut stream = self.send_event_stream_incremental(request).await?;
        let mut events = Vec::new();
        while let Some(event) = stream.recv().await {
            events.push(event?);
        }
        Ok(events)
    }

    /// Send a server-sent events model request and return events as they arrive.
    ///
    /// # Errors
    ///
    /// Returns an error when transport setup fails.
    async fn send_event_stream_incremental(
        &self,
        request: HttpRequest,
    ) -> Result<ModelEventStream, ModelError> {
        Err(ModelError::Transport(format!(
            "server-sent event streaming is not implemented for {}",
            request.url
        )))
    }

    /// Send a WebSocket model request and return JSON text-frame events as they arrive.
    ///
    /// # Errors
    ///
    /// Returns an error when WebSocket transport setup fails.
    async fn send_websocket_event_stream_incremental(
        &self,
        request: HttpRequest,
    ) -> Result<ModelEventStream, ModelError> {
        Err(ModelError::Transport(format!(
            "websocket event streaming is not implemented for {}",
            request.url
        )))
    }

    /// Create a session that may reuse WebSocket transport state across sequential requests.
    fn websocket_event_session(&self) -> Box<dyn ModelWebSocketEventSession + '_> {
        Box::new(PerRequestWebSocketEventSession { client: self })
    }
}

/// Run-scoped WebSocket event transport session.
#[async_trait]
pub trait ModelWebSocketEventSession: Send {
    /// Send a WebSocket model request and return JSON text-frame events as they arrive.
    async fn send_websocket_event_stream_incremental(
        &mut self,
        request: HttpRequest,
    ) -> Result<ModelEventStream, ModelError>;

    /// Reset any reusable transport state held by the session.
    async fn reset(&mut self) {}
}

struct PerRequestWebSocketEventSession<'a, C: ModelHttpClient + ?Sized> {
    client: &'a C,
}

#[async_trait]
impl<C> ModelWebSocketEventSession for PerRequestWebSocketEventSession<'_, C>
where
    C: ModelHttpClient + ?Sized,
{
    async fn send_websocket_event_stream_incremental(
        &mut self,
        request: HttpRequest,
    ) -> Result<ModelEventStream, ModelError> {
        self.client
            .send_websocket_event_stream_incremental(request)
            .await
    }
}

/// Receiver for incremental model JSON events.
pub struct ModelEventStream {
    receiver: tokio::sync::mpsc::Receiver<Result<Value, ModelError>>,
    prefetched: VecDeque<Result<Value, ModelError>>,
    cancellation_token: CancellationToken,
    drop_abort_token: Option<CancellationToken>,
}

impl ModelEventStream {
    /// Build a stream from a channel receiver.
    #[must_use]
    pub fn new(receiver: tokio::sync::mpsc::Receiver<Result<Value, ModelError>>) -> Self {
        Self::new_with_cancellation(receiver, CancellationToken::default())
    }

    /// Build a stream from a channel receiver and cancellation token.
    #[must_use]
    pub const fn new_with_cancellation(
        receiver: tokio::sync::mpsc::Receiver<Result<Value, ModelError>>,
        cancellation_token: CancellationToken,
    ) -> Self {
        Self::new_with_cancellation_and_drop_abort(receiver, cancellation_token, None)
    }

    /// Build a stream from a channel receiver, cancellation token, and drop-abort token.
    #[must_use]
    pub const fn new_with_cancellation_and_drop_abort(
        receiver: tokio::sync::mpsc::Receiver<Result<Value, ModelError>>,
        cancellation_token: CancellationToken,
        drop_abort_token: Option<CancellationToken>,
    ) -> Self {
        Self {
            receiver,
            prefetched: VecDeque::new(),
            cancellation_token,
            drop_abort_token,
        }
    }

    pub(crate) fn prepend_events(
        mut self,
        events: impl IntoIterator<Item = Result<Value, ModelError>>,
    ) -> Self {
        let mut prefetched = events.into_iter().collect::<VecDeque<_>>();
        prefetched.append(&mut self.prefetched);
        self.prefetched = prefetched;
        self
    }

    /// Return the transport-local drop-abort token, when the stream owns one.
    #[must_use]
    pub fn drop_abort_token(&self) -> Option<CancellationToken> {
        self.drop_abort_token.clone()
    }

    /// Receive the next JSON event from the stream.
    pub async fn recv(&mut self) -> Option<Result<Value, ModelError>> {
        if self.cancellation_token.is_cancelled() {
            return Some(Err(ModelError::Cancelled {
                reason: "model event stream cancellation requested".to_string(),
            }));
        }
        if let Some(event) = self.prefetched.pop_front() {
            return Some(event);
        }
        tokio::select! {
            biased;
            () = self.cancellation_token.cancelled() => Some(Err(ModelError::Cancelled {
                reason: "model event stream cancellation requested".to_string(),
            })),
            event = self.receiver.recv() => event,
        }
    }
}

impl Drop for ModelEventStream {
    fn drop(&mut self) {
        if let Some(token) = &self.drop_abort_token {
            token.cancel();
        }
    }
}

/// Shared reference to an HTTP client.
pub type DynHttpClient = Arc<dyn ModelHttpClient>;