pd_router.rs

use super::pd_types::api_path;
use crate::config::types::RetryConfig;
use crate::core::{
    is_retryable_status, ConnectionMode, RetryExecutor, Worker, WorkerLoadGuard, WorkerRegistry,
    WorkerType,
};
use crate::metrics::RouterMetrics;
use crate::policies::{LoadBalancingPolicy, PolicyRegistry};
use crate::protocols::spec::{
    ChatCompletionRequest, ChatMessage, CompletionRequest, GenerateRequest, RerankRequest,
    ResponsesGetParams, ResponsesRequest, StringOrArray, UserMessageContent,
};
use crate::routers::header_utils;
use crate::routers::RouterTrait;
use async_trait::async_trait;
use axum::{
    body::Body,
    extract::Request,
    http::{header::CONTENT_TYPE, HeaderMap, HeaderValue, StatusCode},
    response::{IntoResponse, Response},
    Json,
};
use futures_util::StreamExt;
use reqwest::Client;
use serde::Serialize;
use serde_json::{json, Value};
use std::collections::HashMap;
use std::sync::Arc;
use std::time::{Duration, Instant};
use tokio_stream::wrappers::UnboundedReceiverStream;
use tracing::{debug, error, info, warn};

#[derive(Debug)]
pub struct PDRouter {
    pub worker_registry: Arc<WorkerRegistry>,
    pub policy_registry: Arc<PolicyRegistry>,
    pub worker_loads: Arc<tokio::sync::watch::Receiver<HashMap<String, isize>>>,
    pub load_monitor_handle: Option<Arc<tokio::task::JoinHandle<()>>>,
    pub client: Client,
    pub retry_config: RetryConfig,
    pub api_key: Option<String>,
    pub enable_igw: bool,
}

#[derive(Clone)]
struct PDRequestContext<'a> {
    route: &'static str,
    batch_size: Option<usize>,
    is_stream: bool,
    return_logprob: bool,
    request_text: Option<String>,
    model_id: Option<&'a str>,
}

impl PDRouter {
    fn _get_worker_url_and_key(&self, w: &Arc<dyn Worker>) -> (String, Option<String>) {
        (w.url().to_string(), w.api_key().clone())
    }

    fn get_prefill_worker_urls_with_api_key(&self) -> Vec<(String, Option<String>)> {
        self.worker_registry
            .get_prefill_workers()
            .iter()
            .map(|w| self._get_worker_url_and_key(w))
            .collect()
    }

    fn get_decode_worker_urls_with_api_key(&self) -> Vec<(String, Option<String>)> {
        self.worker_registry
            .get_decode_workers()
            .iter()
            .map(|w| self._get_worker_url_and_key(w))
            .collect()
    }

    async fn proxy_to_first_prefill_worker(
        &self,
        endpoint: &str,
        headers: Option<Vec<(String, String)>>,
    ) -> Response {
        let workers = self.worker_registry.get_prefill_workers();
        let first_worker_url = workers.first().map(|w| w.url().to_string());

        if let Some(worker_url) = first_worker_url {
            self.proxy_to_worker(worker_url, endpoint, headers).await
        } else {
            (
                StatusCode::SERVICE_UNAVAILABLE,
                "No prefill servers available".to_string(),
            )
                .into_response()
        }
    }

    async fn proxy_to_worker(
        &self,
        worker_url: String,
        endpoint: &str,
        headers: Option<Vec<(String, String)>>,
    ) -> Response {
        let url = format!("{}/{}", worker_url, endpoint);
        let mut request_builder = self.client.get(&url);

        if let Some(headers) = headers {
            for (name, value) in headers {
                request_builder = request_builder.header(name, value);
            }
        }

        match request_builder.send().await {
            Ok(res) if res.status().is_success() => {
                let response_headers = header_utils::preserve_response_headers(res.headers());

                match res.bytes().await {
                    Ok(body) => {
                        let mut response = Response::new(axum::body::Body::from(body));
                        *response.status_mut() = StatusCode::OK;
                        *response.headers_mut() = response_headers;
                        response
                    }
                    Err(e) => {
                        error!("Failed to read response body: {}", e);
                        (
                            StatusCode::INTERNAL_SERVER_ERROR,
                            format!("Failed to read response body: {}", e),
                        )
                            .into_response()
                    }
                }
            }
            Ok(res) => {
                let status = StatusCode::from_u16(res.status().as_u16())
                    .unwrap_or(StatusCode::INTERNAL_SERVER_ERROR);
                (status, format!("{} server returned status: ", res.status())).into_response()
            }
            Err(e) => {
                error!("Failed to proxy request server: {}", e);
                (
                    StatusCode::INTERNAL_SERVER_ERROR,
                    format!("Failed to proxy request: {}", e),
                )
                    .into_response()
            }
        }
    }

    pub async fn new(ctx: &Arc<crate::server::AppContext>) -> Result<Self, String> {
        let prefill_workers = ctx.worker_registry.get_workers_filtered(
            None, // any model
            Some(WorkerType::Prefill {
                bootstrap_port: None,
            }),
            Some(ConnectionMode::Http),
            false, // include all workers
        );

        let decode_workers = ctx.worker_registry.get_workers_filtered(
            None, // any model
            Some(WorkerType::Decode),
            Some(ConnectionMode::Http),
            false, // include all workers
        );

        let all_urls: Vec<String> = prefill_workers
            .iter()
            .chain(decode_workers.iter())
            .map(|w| w.url().to_string())
            .collect();
        let all_api_keys: Vec<Option<String>> = prefill_workers
            .iter()
            .chain(decode_workers.iter())
            .map(|w| w.api_key().clone())
            .collect();

        let (tx, rx) = tokio::sync::watch::channel(HashMap::new());
        let worker_loads = Arc::new(rx);

        let prefill_policy = ctx.policy_registry.get_prefill_policy();
        let decode_policy = ctx.policy_registry.get_decode_policy();

        let load_monitor_handle =
            if prefill_policy.name() == "power_of_two" || decode_policy.name() == "power_of_two" {
                let monitor_urls = all_urls.clone();
                let monitor_api_keys = all_api_keys.clone();
                let monitor_interval = ctx.router_config.worker_startup_check_interval_secs;
                let monitor_client = ctx.client.clone();
                let prefill_policy_clone = Arc::clone(&prefill_policy);
                let decode_policy_clone = Arc::clone(&decode_policy);

                Some(Arc::new(tokio::spawn(async move {
                    Self::monitor_worker_loads_with_client(
                        monitor_urls,
                        monitor_api_keys,
                        tx,
                        monitor_interval,
                        monitor_client,
                        prefill_policy_clone,
                        decode_policy_clone,
                    )
                    .await;
                })))
            } else {
                None
            };

        // No longer need prefill drain channel - we'll wait for both responses

        Ok(PDRouter {
            worker_registry: Arc::clone(&ctx.worker_registry),
            policy_registry: Arc::clone(&ctx.policy_registry),
            worker_loads,
            load_monitor_handle,
            client: ctx.client.clone(),
            retry_config: ctx.router_config.effective_retry_config(),
            api_key: ctx.router_config.api_key.clone(),
            enable_igw: ctx.router_config.enable_igw,
        })
    }

    fn handle_server_selection_error(error: String) -> Response {
        error!("Failed to select PD pair error={}", error);
        RouterMetrics::record_pd_error("server_selection");
        (
            StatusCode::SERVICE_UNAVAILABLE,
            format!("No available servers: {}", error),
        )
            .into_response()
    }

    fn handle_serialization_error(error: impl std::fmt::Display) -> Response {
        error!("Failed to serialize request error={}", error);
        (
            StatusCode::INTERNAL_SERVER_ERROR,
            "Failed to serialize request",
        )
            .into_response()
    }

    fn get_generate_batch_size(req: &GenerateRequest) -> Option<usize> {
        if let Some(StringOrArray::Array(arr)) = &req.prompt {
            if !arr.is_empty() {
                return Some(arr.len());
            }
        }
        if let Some(text) = &req.text {
            if text.contains("[") && text.contains("]") {
                return None;
            }
        }
        None
    }

    fn get_chat_batch_size(req: &ChatCompletionRequest) -> Option<usize> {
        if let Some(n) = req.n {
            if n > 1 {
                return Some(n as usize);
            }
        }
        None
    }

    fn get_completion_batch_size(req: &CompletionRequest) -> Option<usize> {
        if let StringOrArray::Array(arr) = &req.prompt {
            if !arr.is_empty() {
                return Some(arr.len());
            }
        }
        None
    }

    fn inject_bootstrap_into_value(
        mut original: Value,
        prefill_worker: &dyn Worker,
        batch_size: Option<usize>,
    ) -> Result<Value, String> {
        let bootstrap_port = match prefill_worker.worker_type() {
            crate::core::WorkerType::Prefill { bootstrap_port } => bootstrap_port,
            _ => None,
        };
        let hostname = super::pd_types::get_hostname(prefill_worker.url());

        let obj = original
            .as_object_mut()
            .ok_or_else(|| "Request must be a JSON object".to_string())?;

        if let Some(n) = batch_size {
            let mut hosts = Vec::with_capacity(n);
            let mut ports = Vec::with_capacity(n);
            let mut rooms = Vec::with_capacity(n);
            for _ in 0..n {
                hosts.push(hostname.clone());
                ports.push(bootstrap_port);
                rooms.push(super::pd_types::generate_room_id());
            }
            obj.insert(
                "bootstrap_host".to_string(),
                Value::Array(hosts.into_iter().map(serde_json::Value::from).collect()),
            );
            obj.insert(
                "bootstrap_port".to_string(),
                Value::Array(
                    ports
                        .into_iter()
                        .map(|p| match p {
                            Some(v) => serde_json::Value::from(v),
                            None => Value::Null,
                        })
                        .collect(),
                ),
            );
            obj.insert(
                "bootstrap_room".to_string(),
                Value::Array(rooms.into_iter().map(serde_json::Value::from).collect()),
            );
        } else {
            obj.insert(
                "bootstrap_host".to_string(),
                serde_json::Value::from(hostname),
            );
            obj.insert(
                "bootstrap_port".to_string(),
                match bootstrap_port {
                    Some(v) => serde_json::Value::from(v),
                    None => Value::Null,
                },
            );
            obj.insert(
                "bootstrap_room".to_string(),
                serde_json::Value::from(super::pd_types::generate_room_id()),
            );
        }
        Ok(original)
    }

    async fn execute_dual_dispatch<T: Serialize + Clone>(
        &self,
        headers: Option<&HeaderMap>,
        original_request: &T,
        context: PDRequestContext<'_>,
    ) -> Response {
        let start_time = Instant::now();

        let route = context.route;
        RetryExecutor::execute_response_with_retry(
            &self.retry_config,
            {
                let original_request = original_request.clone();
                move |attempt: u32| {
                    let original_request = original_request.clone();
                    let context = context.clone();
                    async move {
                        let (prefill, decode) = match self
                            .select_pd_pair(context.request_text.as_deref(), context.model_id)
                            .await
                        {
                            Ok(pair) => pair,
                            Err(e) => {
                                RouterMetrics::record_pd_error("server_selection");
                                return Self::handle_server_selection_error(e);
                            }
                        };

                        debug!(
                            "PD retry attempt {} using prefill={} decode={}",
                            attempt,
                            prefill.url(),
                            decode.url()
                        );

                        let mut json_request = match serde_json::to_value(&original_request) {
                            Ok(v) => v,
                            Err(e) => return Self::handle_serialization_error(e),
                        };

                        json_request = match Self::inject_bootstrap_into_value(
                            json_request,
                            prefill.as_ref(),
                            context.batch_size,
                        ) {
                            Ok(v) => v,
                            Err(e) => return Self::handle_serialization_error(e),
                        };

                        let response = self
                            .execute_dual_dispatch_internal(
                                headers,
                                json_request,
                                context,
                                prefill.as_ref(),
                                decode.as_ref(),
                                start_time,
                            )
                            .await;

                        let _status = response.status();
                        let not_error = _status.is_success() || _status.is_client_error();
                        prefill.record_outcome(not_error);
                        decode.record_outcome(not_error);

                        response
                    }
                }
            },
            |res, _attempt| is_retryable_status(res.status()),
            |delay, attempt| {
                RouterMetrics::record_retry(route);
                RouterMetrics::record_retry_backoff_duration(delay, attempt);
            },
            || RouterMetrics::record_retries_exhausted(route),
        )
        .await
    }

    async fn handle_decode_error_response(
        &self,
        res: reqwest::Response,
        context: &PDRequestContext<'_>,
        prefill: &dyn Worker,
        decode: &dyn Worker,
    ) -> Response {
        let status = res.status();

        if context.is_stream {
            // Handle streaming error response
            let response_headers = header_utils::preserve_response_headers(res.headers());
            let error_payload = match res.bytes().await {
                Ok(error_body) => {
                    if let Ok(error_json) = serde_json::from_slice::<Value>(&error_body) {
                        json!({ "message": error_json, "status": status.as_u16() })
                    } else {
                        json!({ "message": String::from_utf8_lossy(&error_body).to_string(), "status": status.as_u16() })
                    }
                }
                Err(e) => {
                    json!({ "message": format!("Decode server error: {}", e), "status": status.as_u16() })
                }
            };

            let sse_data = format!(
                "data: {{'error': {}}}",
                serde_json::to_string(&error_payload).unwrap_or_default()
            );
            let error_stream = tokio_stream::once(Ok(axum::body::Bytes::from(sse_data)));

            let decode_url = decode.url().to_string();
            self.create_streaming_response(
                error_stream,
                status,
                None,
                context.return_logprob,
                Some(decode_url),
                Some(response_headers),
                prefill,
                decode,
            )
        } else {
            // Handle non-streaming error response
            match res.bytes().await {
                Ok(error_body) => (status, error_body).into_response(),
                Err(e) => (status, format!("Decode server error: {}", e)).into_response(),
            }
        }
    }

    // Internal method that performs the actual dual dispatch (without retry logic)
    async fn execute_dual_dispatch_internal(
        &self,
        headers: Option<&HeaderMap>,
        json_request: Value,
        context: PDRequestContext<'_>,
        prefill: &dyn Worker,
        decode: &dyn Worker,
        start_time: Instant,
    ) -> Response {
        // For non-streaming: use guard for automatic load management
        // For streaming: load will be managed in create_streaming_response
        let _guard = if !context.is_stream {
            Some(WorkerLoadGuard::new_multi(vec![prefill, decode]))
        } else {
            None
        };

        // Build both requests
        let prefill_request = self.build_post_with_headers(
            &self.client,
            prefill.url(),
            context.route,
            &json_request,
            headers,
            false,
        );
        let decode_request = self.build_post_with_headers(
            &self.client,
            decode.url(),
            context.route,
            &json_request,
            headers,
            false,
        );

        // Send both requests concurrently and wait for both
        debug!(
            "Sending concurrent requests to prefill={} decode={}",
            prefill.url(),
            decode.url()
        );

        let (prefill_result, decode_result) =
            tokio::join!(prefill_request.send(), decode_request.send());
        debug!("Received responses from both servers");

        let duration = start_time.elapsed();
        RouterMetrics::record_pd_request_duration(context.route, duration);
        RouterMetrics::record_pd_request(context.route);
        RouterMetrics::record_pd_prefill_request(prefill.url());
        RouterMetrics::record_pd_decode_request(decode.url());

        // Process decode response
        match decode_result {
            Ok(res) => {
                let status = StatusCode::from_u16(res.status().as_u16())
                    .unwrap_or(StatusCode::INTERNAL_SERVER_ERROR);
                debug!("Decode response status: {}", status);

                if !status.is_success() {
                    RouterMetrics::record_pd_decode_error(decode.url());
                    error!(
                        "Decode server returned error status decode_url={} status={}",
                        decode.url(),
                        status
                    );

                    return self
                        .handle_decode_error_response(res, &context, prefill, decode)
                        .await;
                }

                // Process prefill response
                let prefill_body = if context.return_logprob {
                    match self
                        .process_prefill_response(
                            prefill_result,
                            prefill.url(),
                            context.return_logprob,
                        )
                        .await
                    {
                        Ok((_, body)) => body,
                        Err(error_response) => return error_response,
                    }
                } else {
                    // Even if we don't need logprobs, we should check prefill status
                    match self
                        .process_prefill_response(prefill_result, prefill.url(), false)
                        .await
                    {
                        Ok((_, body)) => body,
                        Err(error_response) => return error_response,
                    }
                };

                if context.is_stream {
                    // Streaming response
                    let prefill_logprobs = if context.return_logprob {
                        prefill_body
                            .as_ref()
                            .and_then(|body| serde_json::from_slice::<Value>(body).ok())
                            .and_then(|json| {
                                json.pointer("/meta_info/input_token_logprobs").cloned()
                            })
                    } else {
                        None
                    };

                    let response_headers = header_utils::preserve_response_headers(res.headers());

                    self.create_streaming_response(
                        res.bytes_stream(),
                        status,
                        prefill_logprobs,
                        context.return_logprob,
                        None,
                        Some(response_headers),
                        prefill,
                        decode,
                    )
                } else {
                    // Non-streaming response
                    if context.return_logprob {
                        self.process_non_streaming_response(
                            res,
                            status,
                            context.return_logprob,
                            prefill_body,
                        )
                        .await
                    } else {
                        // Direct passthrough when no logprobs needed
                        let response_headers =
                            header_utils::preserve_response_headers(res.headers());

                        match res.bytes().await {
                            Ok(decode_body) => {
                                let mut response =
                                    Response::new(axum::body::Body::from(decode_body));
                                *response.status_mut() = status;
                                *response.headers_mut() = response_headers;
                                response
                            }
                            Err(e) => {
                                error!("Failed to read decode response: {}", e);
                                (StatusCode::INTERNAL_SERVER_ERROR, "Failed to read response")
                                    .into_response()
                            }
                        }
                    }
                }
            }
            Err(e) => {
                error!(
                    decode_url = %decode.url(),
                    error = %e,
                    "Decode request failed"
                );
                RouterMetrics::record_pd_decode_error(decode.url());
                (
                    StatusCode::BAD_GATEWAY,
                    format!("Decode server error: {}", e),
                )
                    .into_response()
            }
        }
    }

    fn policies_need_request_text(&self) -> bool {
        let prefill_policy = self.policy_registry.get_prefill_policy();
        let decode_policy = self.policy_registry.get_decode_policy();
        prefill_policy.needs_request_text() || decode_policy.needs_request_text()
    }

    async fn select_pd_pair(
        &self,
        request_text: Option<&str>,
        model_id: Option<&str>,
    ) -> Result<(Arc<dyn Worker>, Arc<dyn Worker>), String> {
        let effective_model_id = if !self.enable_igw { None } else { model_id };

        debug!(
            "Selecting PD pair: enable_igw={}, model_id={:?}, effective_model_id={:?}",
            self.enable_igw, model_id, effective_model_id
        );

        let prefill_workers = if let Some(model) = effective_model_id {
            self.worker_registry
                .get_by_model_fast(model)
                .into_iter()
                .filter(|w| matches!(w.worker_type(), WorkerType::Prefill { .. }))
                .collect()
        } else {
            self.worker_registry.get_prefill_workers()
        };

        let decode_workers = if let Some(model) = effective_model_id {
            self.worker_registry
                .get_by_model_fast(model)
                .into_iter()
                .filter(|w| matches!(w.worker_type(), WorkerType::Decode))
                .collect()
        } else {
            self.worker_registry.get_decode_workers()
        };

        let prefill_policy = self.policy_registry.get_prefill_policy();
        let decode_policy = self.policy_registry.get_decode_policy();

        let prefill = Self::pick_worker_by_policy_arc(
            &prefill_workers,
            &*prefill_policy,
            request_text,
            "prefill",
        )?;

        let decode = Self::pick_worker_by_policy_arc(
            &decode_workers,
            &*decode_policy,
            request_text,
            "decode",
        )?;

        Ok((prefill, decode))
    }

    fn pick_worker_by_policy_arc(
        workers: &[Arc<dyn Worker>],
        policy: &dyn LoadBalancingPolicy,
        request_text: Option<&str>,
        worker_type: &str,
    ) -> Result<Arc<dyn Worker>, String> {
        if workers.is_empty() {
            return Err(format!(
                "No {} workers available. Please check if {} servers are configured and healthy.",
                worker_type, worker_type
            ));
        }

        let available_workers: Vec<Arc<dyn Worker>> = workers
            .iter()
            .filter(|w| w.is_available())
            .cloned()
            .collect();

        if available_workers.is_empty() {
            return Err(format!(
                "No available {} workers (all circuits open or unhealthy)",
                worker_type
            ));
        }

        let selected_idx = policy
            .select_worker(&available_workers, request_text)
            .ok_or_else(|| {
                format!(
                    "Policy {} failed to select a {} worker",
                    policy.name(),
                    worker_type
                )
            })?;

        Ok(available_workers[selected_idx].clone())
    }

    async fn monitor_worker_loads_with_client(
        worker_urls: Vec<String>,
        worker_api_keys: Vec<Option<String>>,
        tx: tokio::sync::watch::Sender<HashMap<String, isize>>,
        interval_secs: u64,
        client: Client,
        prefill_policy: Arc<dyn LoadBalancingPolicy>,
        decode_policy: Arc<dyn LoadBalancingPolicy>,
    ) {
        loop {
            let mut loads = HashMap::new();

            let futures: Vec<_> = worker_urls
                .iter()
                .zip(worker_api_keys.iter())
                .map(|(url, api_key)| {
                    let client = client.clone();
                    let url = url.clone();
                    let api_key = api_key.clone();
                    async move {
                        let load = get_worker_load(&client, &url, &api_key).await.unwrap_or(0);
                        (url, load)
                    }
                })
                .collect();

            let results = futures_util::future::join_all(futures).await;

            for (url, load) in results {
                loads.insert(url, load);
            }

            debug!("Worker loads updated: {:?}", loads);

            prefill_policy.update_loads(&loads);
            decode_policy.update_loads(&loads);

            if tx.send(loads).is_err() {
                info!("Load monitor receiver dropped, shutting down monitor task");
                break;
            }

            tokio::time::sleep(Duration::from_secs(interval_secs)).await;
        }
    }

    #[allow(clippy::too_many_arguments)]
    fn create_streaming_response(
        &self,
        stream: impl futures_util::Stream<Item = Result<bytes::Bytes, reqwest::Error>> + Send + 'static,
        status: StatusCode,
        prefill_logprobs: Option<Value>,
        return_logprob: bool,
        decode_url: Option<String>,
        headers: Option<HeaderMap>,
        prefill: &dyn Worker,
        decode: &dyn Worker,
    ) -> Response {
        prefill.increment_load();
        decode.increment_load();

        let prefill_url = prefill.url().to_string();
        let decode_url_str = decode.url().to_string();

        let (tx, rx) = tokio::sync::mpsc::unbounded_channel();

        let registry = self.worker_registry.clone();

        tokio::spawn(async move {
            let mut stream_completed = false;

            futures_util::pin_mut!(stream);
            while let Some(chunk_result) = stream.next().await {
                match chunk_result {
                    Ok(chunk) => {
                        let is_done = chunk
                            .as_ref()
                            .windows(12)
                            .any(|window| window == b"data: [DONE]");

                        let result = if return_logprob && prefill_logprobs.is_some() {
                            Self::merge_streaming_logprobs(prefill_logprobs.clone(), &chunk)
                                .unwrap_or(chunk)
                        } else {
                            chunk
                        };

                        if tx.send(Ok(result)).is_err() {
                            break;
                        }

                        if is_done {
                            stream_completed = true;
                            break;
                        }
                    }
                    Err(e) => {
                        if let Some(ref url) = decode_url {
                            error!("Stream error from decode server {}: {}", url, e);
                            RouterMetrics::record_pd_stream_error(url);
                        }
                        let _ = tx.send(Err(format!("Stream error: {}", e)));
                        break;
                    }
                }
            }

            if let Some(worker) = registry.get_by_url(&prefill_url) {
                worker.decrement_load();
                debug!(
                    "Decremented load for prefill worker: {} (stream_completed: {})",
                    prefill_url, stream_completed
                );
            }

            if let Some(worker) = registry.get_by_url(&decode_url_str) {
                worker.decrement_load();
                debug!(
                    "Decremented load for decode worker: {} (stream_completed: {})",
                    decode_url_str, stream_completed
                );
            }
        });

        let stream = UnboundedReceiverStream::new(rx);
        let body = Body::from_stream(stream);

        let mut response = Response::new(body);
        *response.status_mut() = status;

        let mut headers = headers.unwrap_or_default();
        headers.insert(CONTENT_TYPE, HeaderValue::from_static("text/event-stream"));
        *response.headers_mut() = headers;

        response
    }

    // Helper to process non-streaming decode response with logprob merging
    async fn process_non_streaming_response(
        &self,
        res: reqwest::Response,
        status: StatusCode,
        return_logprob: bool,
        prefill_body: Option<bytes::Bytes>,
    ) -> Response {
        let response = res.bytes().await;
        let decode_body = match response {
            Ok(decode_body) => decode_body,
            Err(e) => {
                error!("Failed to read decode response: {}", e);
                return (StatusCode::INTERNAL_SERVER_ERROR, "Failed to read response")
                    .into_response();
            }
        };

        if !return_logprob {
            return (status, decode_body).into_response();
        }

        let Some(prefill_body) = prefill_body else {
            return (status, decode_body).into_response();
        };

        // Merge logprobs from prefill and decode
        let (Ok(prefill_json), Ok(mut decode_json)) = (
            serde_json::from_slice::<Value>(&prefill_body),
            serde_json::from_slice::<Value>(&decode_body),
        ) else {
            warn!("Failed to parse responses for logprob merging");
            return (status, decode_body).into_response();
        };

        Self::merge_logprobs_in_json(&prefill_json, &mut decode_json);

        // Return merged response
        match serde_json::to_vec(&decode_json) {
            Ok(body) => (status, body).into_response(),
            Err(e) => {
                error!("Failed to serialize merged response: {}", e);
                (status, decode_body).into_response()
            }
        }
    }

    // Helper to process prefill response and extract body if needed for logprobs
    async fn process_prefill_response(
        &self,
        prefill_result: Result<reqwest::Response, reqwest::Error>,
        prefill_url: &str,
        return_logprob: bool,
    ) -> Result<(StatusCode, Option<bytes::Bytes>), Response> {
        // Check prefill result first - it's critical for disaggregated mode
        let prefill_response = match prefill_result {
            Ok(response) => response,
            Err(e) => {
                RouterMetrics::record_pd_prefill_error(prefill_url);
                error!(
                    "Prefill server failed (CRITICAL) prefill_url={} error={}. Decode will timeout without prefill KV cache.",
                    prefill_url,
                    e
                );

                // Return error immediately - don't wait for decode to timeout
                return Err((
                    StatusCode::BAD_GATEWAY,
                    format!(
                        "Prefill server error: {}. This will cause decode timeout.",
                        e
                    ),
                )
                    .into_response());
            }
        };

        let prefill_status = StatusCode::from_u16(prefill_response.status().as_u16())
            .unwrap_or(StatusCode::INTERNAL_SERVER_ERROR);

        // Check if prefill succeeded
        if !prefill_status.is_success() {
            RouterMetrics::record_pd_prefill_error(prefill_url);

            // Get error body from prefill
            let error_msg = prefill_response
                .text()
                .await
                .unwrap_or_else(|_| "Unknown prefill error".to_string());

            error!(
                "Prefill server returned error status prefill_url={} status={} body={}",
                prefill_url, prefill_status, error_msg
            );

            return Err((
                prefill_status,
                format!("Prefill server error ({}): {}", prefill_status, error_msg),
            )
                .into_response());
        }

        // Read prefill body if needed for logprob merging
        let prefill_body = if return_logprob {
            match prefill_response.bytes().await {
                Ok(body) => Some(body),
                Err(e) => {
                    warn!("Failed to read prefill response body for logprobs: {}", e);
                    None
                }
            }
        } else {
            // For non-logprob requests, just consume the response without storing
            debug!("Consuming prefill response body (non-logprob request)");
            match prefill_response.bytes().await {
                Ok(_) => debug!("Prefill response consumed successfully"),
                Err(e) => warn!("Error consuming prefill response: {}", e),
            }
            None
        };

        Ok((prefill_status, prefill_body))
    }

    fn build_post_with_headers(
        &self,
        client: &Client,
        url: &str,
        route: &str,
        json_request: &Value,
        headers: Option<&HeaderMap>,
        connection_close: bool,
    ) -> reqwest::RequestBuilder {
        let mut request = client.post(api_path(url, route)).json(json_request);
        if connection_close {
            request = request.header("Connection", "close");
        }
        if let Some(headers) = headers {
            for (name, value) in headers.iter() {
                let name_lc = name.as_str().to_ascii_lowercase();
                // Whitelist important end-to-end headers, skip hop-by-hop
                let forward = matches!(
                    name_lc.as_str(),
                    "authorization" | "x-request-id" | "x-correlation-id"
                ) || name_lc.starts_with("x-request-id-");
                if forward {
                    if let Ok(val) = value.to_str() {
                        request = request.header(name, val);
                    }
                }
            }
        }
        request
    }

    // Helper to merge logprobs from prefill and decode responses
    fn merge_logprobs_in_json(prefill_json: &Value, decode_json: &mut Value) -> bool {
        if let (Some(prefill_meta), Some(decode_meta)) = (
            prefill_json.get("meta_info"),
            decode_json.get_mut("meta_info"),
        ) {
            if let (Some(prefill_logprobs), Some(decode_logprobs)) = (
                prefill_meta.get("input_token_logprobs"),
                decode_meta.get_mut("input_token_logprobs"),
            ) {
                if let (Some(prefill_arr), Some(decode_arr)) =
                    (prefill_logprobs.as_array(), decode_logprobs.as_array_mut())
                {
                    let mut merged = prefill_arr.clone();
                    merged.extend(decode_arr.clone());
                    decode_meta["input_token_logprobs"] = Value::Array(merged);
                    return true;
                }
            }
        }
        false
    }

    // Simple helper to merge logprobs in streaming responses
    fn merge_streaming_logprobs(
        prefill_logprobs: Option<Value>,
        decode_chunk: &[u8],
    ) -> Result<bytes::Bytes, ()> {
        // Skip non-data chunks
        let chunk_str = std::str::from_utf8(decode_chunk).map_err(|_| ())?;
        if !chunk_str.starts_with("data: ") || chunk_str.contains("[DONE]") {
            return Err(());
        }

        // Parse JSON from chunk
        let json_str = chunk_str.trim_start_matches("data: ").trim();
        let mut decode_json: Value = serde_json::from_str(json_str).map_err(|_| ())?;

        // Merge prefill logprobs if available
        if let Some(ref p_logprobs) = prefill_logprobs {
            if let Some(meta) = decode_json.get_mut("meta_info") {
                if let Some(d_logprobs) = meta.get_mut("input_token_logprobs") {
                    if let (Some(p_arr), Some(d_arr)) =
                        (p_logprobs.as_array(), d_logprobs.as_array())
                    {
                        let mut merged = p_arr.clone();
                        merged.extend(d_arr.clone());
                        *d_logprobs = Value::Array(merged);
                    }
                }
            }
        }

        // Re-serialize
        let merged_str = format!(
            "data: {}\n\n",
            serde_json::to_string(&decode_json).unwrap_or_default()
        );
        Ok(bytes::Bytes::from(merged_str))
    }
}

// Helper functions

async fn get_worker_load(
    client: &Client,
    worker_url: &str,
    api_key: &Option<String>,
) -> Option<isize> {
    let mut req_builder = client.get(format!("{}/get_load", worker_url));
    if let Some(key) = api_key {
        req_builder = req_builder.bearer_auth(key);
    }
    match req_builder.send().await {
        Ok(res) if res.status().is_success() => match res.bytes().await {
            Ok(bytes) => match serde_json::from_slice::<Value>(&bytes) {
                Ok(data) => data
                    .get("load")
                    .and_then(|v| v.as_i64())
                    .map(|v| v as isize),
                Err(e) => {
                    debug!("Failed to parse load response from {}: {}", worker_url, e);
                    None
                }
            },
            Err(e) => {
                debug!("Failed to read load response from {}: {}", worker_url, e);
                None
            }
        },
        Ok(res) => {
            debug!(
                "Worker {} returned non-success status: {}",
                worker_url,
                res.status()
            );
            None
        }
        Err(e) => {
            debug!("Failed to get load from {}: {}", worker_url, e);
            None
        }
    }
}

#[async_trait]
impl RouterTrait for PDRouter {
    fn as_any(&self) -> &dyn std::any::Any {
        self
    }

    async fn health_generate(&self, _req: Request<Body>) -> Response {
        // Test model generation capability by selecting a random pair and testing them
        // Note: This endpoint actually causes the model to generate tokens, so we only test one pair

        // Select a random worker pair using the policy
        let (prefill, decode) = match self.select_pd_pair(None, None).await {
            Ok(pair) => pair,
            Err(e) => {
                return (
                    StatusCode::SERVICE_UNAVAILABLE,
                    format!("No healthy worker pair available: {}", e),
                )
                    .into_response();
            }
        };

        // Test prefill server's health_generate
        let prefill_url = format!("{}/health_generate", prefill.url());
        let (prefill_result, decode_result) = tokio::join!(
            self.client.get(&prefill_url).send(),
            self.client
                .get(format!("{}/health_generate", decode.url()))
                .send()
        );

        // Check results
        let mut errors = Vec::new();

        match prefill_result {
            Ok(res) if res.status().is_success() => {
                debug!(
                    "Health generate passed for prefill server: {}",
                    prefill.url()
                );
            }
            Ok(res) => {
                errors.push(format!(
                    "Prefill {} returned status {}",
                    prefill.url(),
                    res.status()
                ));
            }
            Err(e) => {
                errors.push(format!("Prefill {} error: {}", prefill.url(), e));
            }
        }

        match decode_result {
            Ok(res) if res.status().is_success() => {
                debug!("Health generate passed for decode server: {}", decode.url());
            }
            Ok(res) => {
                errors.push(format!(
                    "Decode {} returned status {}",
                    decode.url(),
                    res.status()
                ));
            }
            Err(e) => {
                errors.push(format!("Decode {} error: {}", decode.url(), e));
            }
        }

        if errors.is_empty() {
            (
                StatusCode::OK,
                format!(
                    "Health generate passed on selected pair: prefill={}, decode={}",
                    prefill.url(),
                    decode.url()
                ),
            )
                .into_response()
        } else {
            (
                StatusCode::SERVICE_UNAVAILABLE,
                format!("Health generate failed: {:?}", errors),
            )
                .into_response()
        }
    }

    async fn get_server_info(&self, _req: Request<Body>) -> Response {
        // Get info from the first decode server to match sglang's server info format
        // Note: We use decode workers for server info to match expected format
        self.proxy_to_first_prefill_worker("get_server_info", None)
            .await
    }

    async fn get_models(&self, req: Request<Body>) -> Response {
        // Extract headers first to avoid Send issues
        let headers = header_utils::copy_request_headers(&req);

        // Proxy to first prefill worker
        self.proxy_to_first_prefill_worker("v1/models", Some(headers))
            .await
    }

    async fn get_model_info(&self, req: Request<Body>) -> Response {
        // Extract headers first to avoid Send issues
        let headers = header_utils::copy_request_headers(&req);

        // Proxy to first prefill worker
        self.proxy_to_first_prefill_worker("get_model_info", Some(headers))
            .await
    }

    async fn route_generate(
        &self,
        headers: Option<&HeaderMap>,
        body: &GenerateRequest,
        model_id: Option<&str>,
    ) -> Response {
        let is_stream = body.stream;
        let return_logprob = body.return_logprob;

        let request_text = if self.policies_need_request_text() {
            body.text
                .as_deref()
                .or_else(|| {
                    body.prompt.as_ref().and_then(|p| match p {
                        StringOrArray::String(s) => Some(s.as_str()),
                        StringOrArray::Array(v) => v.first().map(|s| s.as_str()),
                    })
                })
                .map(|s| s.to_string())
        } else {
            None
        };

        let batch_size = Self::get_generate_batch_size(body);

        let context = PDRequestContext {
            route: "/generate",
            batch_size,
            is_stream,
            return_logprob,
            request_text,
            model_id,
        };

        self.execute_dual_dispatch(headers, body, context).await
    }

    async fn route_chat(
        &self,
        headers: Option<&HeaderMap>,
        body: &ChatCompletionRequest,
        model_id: Option<&str>,
    ) -> Response {
        let is_stream = body.stream;
        let return_logprob = body.logprobs;

        let request_text = if self.policies_need_request_text() {
            body.messages.first().and_then(|msg| match msg {
                ChatMessage::User { content, .. } => match content {
                    UserMessageContent::Text(text) => Some(text.clone()),
                    UserMessageContent::Parts(_) => None,
                },
                ChatMessage::System { content, .. } => Some(content.clone()),
                _ => None,
            })
        } else {
            None
        };

        // Calculate batch size
        let batch_size = Self::get_chat_batch_size(body);

        let context = PDRequestContext {
            route: "/v1/chat/completions",
            batch_size,
            is_stream,
            return_logprob,
            request_text,
            model_id,
        };

        self.execute_dual_dispatch(headers, body, context).await
    }

    async fn route_completion(
        &self,
        headers: Option<&HeaderMap>,
        body: &CompletionRequest,
        model_id: Option<&str>,
    ) -> Response {
        let is_stream = body.stream;
        let return_logprob = body.logprobs.is_some();

        let request_text = if self.policies_need_request_text() {
            match &body.prompt {
                StringOrArray::String(s) => Some(s.clone()),
                StringOrArray::Array(v) => v.first().map(|s| s.to_string()),
            }
        } else {
            None
        };

        // Calculate batch size
        let batch_size = Self::get_completion_batch_size(body);

        let context = PDRequestContext {
            route: "/v1/completions",
            batch_size,
            is_stream,
            return_logprob,
            request_text,
            model_id,
        };

        self.execute_dual_dispatch(headers, body, context).await
    }

    async fn route_responses(
        &self,
        _headers: Option<&HeaderMap>,
        _body: &ResponsesRequest,
        _model_id: Option<&str>,
    ) -> Response {
        (
            StatusCode::NOT_IMPLEMENTED,
            "Responses endpoint not implemented for PD router",
        )
            .into_response()
    }

    async fn get_response(
        &self,
        _headers: Option<&HeaderMap>,
        _response_id: &str,
        _params: &ResponsesGetParams,
    ) -> Response {
        (
            StatusCode::NOT_IMPLEMENTED,
            "Responses retrieve endpoint not implemented for PD router",
        )
            .into_response()
    }

    async fn cancel_response(&self, _headers: Option<&HeaderMap>, _response_id: &str) -> Response {
        (
            StatusCode::NOT_IMPLEMENTED,
            "Responses cancel endpoint not implemented for PD router",
        )
            .into_response()
    }

    async fn route_embeddings(
        &self,
        _headers: Option<&HeaderMap>,
        _body: &crate::protocols::spec::EmbeddingRequest,
        _model_id: Option<&str>,
    ) -> Response {
        (
            StatusCode::NOT_IMPLEMENTED,
            "Embeddings endpoint not implemented for PD router",
        )
            .into_response()
    }

    async fn route_rerank(
        &self,
        headers: Option<&HeaderMap>,
        body: &RerankRequest,
        model_id: Option<&str>,
    ) -> Response {
        // Extract text for cache-aware routing
        let req_text = if self.policies_need_request_text() {
            Some(body.query.clone())
        } else {
            None
        };

        let context = PDRequestContext {
            route: "/v1/rerank",
            batch_size: None,
            is_stream: false,
            return_logprob: false,
            request_text: req_text,
            model_id,
        };

        self.execute_dual_dispatch(headers, body, context).await
    }

    async fn get_worker_loads(&self) -> Response {
        let mut loads = HashMap::new();
        let mut errors = Vec::new();

        // Process prefill workers
        let prefill_urls_with_key = self.get_prefill_worker_urls_with_api_key();
        for (worker_url, api_key) in prefill_urls_with_key {
            match get_worker_load(&self.client, &worker_url, &api_key).await {
                Some(load) => {
                    loads.insert(format!("prefill_{}", worker_url), load);
                }
                None => {
                    errors.push(format!("Failed to get load from prefill {}", worker_url));
                }
            }
        }

        // Process decode workers
        let decode_urls_with_key = self.get_decode_worker_urls_with_api_key();
        for (worker_url, api_key) in decode_urls_with_key {
            match get_worker_load(&self.client, &worker_url, &api_key).await {
                Some(load) => {
                    loads.insert(format!("decode_{}", worker_url), load);
                }
                None => {
                    errors.push(format!("Failed to get load from decode {}", worker_url));
                }
            }
        }

        let response_data = serde_json::json!({
            "loads": loads,
            "errors": errors
        });

        (StatusCode::OK, Json(response_data)).into_response()
    }

    fn router_type(&self) -> &'static str {
        "pd"
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::core::{BasicWorkerBuilder, WorkerType};

    fn create_test_pd_router() -> PDRouter {
        let worker_registry = Arc::new(WorkerRegistry::new());
        let policy_registry =
            Arc::new(PolicyRegistry::new(crate::config::PolicyConfig::RoundRobin));

        PDRouter {
            worker_registry,
            policy_registry,
            worker_loads: Arc::new(tokio::sync::watch::channel(HashMap::new()).1),
            load_monitor_handle: None,
            client: Client::new(),
            retry_config: RetryConfig::default(),
            api_key: Some("test_api_key".to_string()),
            enable_igw: false,
        }
    }

    fn create_test_worker(url: String, worker_type: WorkerType, healthy: bool) -> Box<dyn Worker> {
        let worker = BasicWorkerBuilder::new(url)
            .worker_type(worker_type)
            .build();
        worker.set_healthy(healthy);
        Box::new(worker)
    }

    #[tokio::test]
    async fn test_select_healthy_prefill_worker() {
        let router = create_test_pd_router();

        let healthy_worker = create_test_worker(
            "http://healthy".to_string(),
            WorkerType::Prefill {
                bootstrap_port: None,
            },
            true,
        );
        let unhealthy_worker = create_test_worker(
            "http://unhealthy".to_string(),
            WorkerType::Prefill {
                bootstrap_port: None,
            },
            false,
        );
        let decode_worker =
            create_test_worker("http://decode".to_string(), WorkerType::Decode, true);

        router.worker_registry.register(Arc::from(unhealthy_worker));
        router.worker_registry.register(Arc::from(healthy_worker));
        router.worker_registry.register(Arc::from(decode_worker));

        let result = router.select_pd_pair(None, None).await;

        assert!(result.is_ok());
        let (prefill, _decode) = result.unwrap();

        assert_eq!(prefill.url(), "http://healthy");
        assert!(prefill.is_healthy());
    }

    #[tokio::test]
    async fn test_empty_worker_lists() {
        let router = create_test_pd_router();

        let result = router.select_pd_pair(None, None).await;

        assert!(result.is_err());
        assert!(result.unwrap_err().contains("No prefill workers available"));
    }

    #[tokio::test]
    async fn test_load_monitor_updates() {
        let power_of_two_policy = Arc::new(crate::policies::PowerOfTwoPolicy::new());
        let mut router = create_test_pd_router();
        router
            .policy_registry
            .set_prefill_policy(power_of_two_policy.clone());
        router
            .policy_registry
            .set_decode_policy(power_of_two_policy);

        let (tx, rx) = tokio::sync::watch::channel(HashMap::new());
        router.worker_loads = Arc::new(rx);

        let mut loads = HashMap::new();
        loads.insert("http://worker1".to_string(), 10);
        loads.insert("http://worker2".to_string(), 5);

        let _ = tx.send(loads.clone());

        let received = router.worker_loads.borrow().clone();
        assert_eq!(received.get("http://worker1"), Some(&10));
        assert_eq!(received.get("http://worker2"), Some(&5));
    }

    #[test]
    fn test_worker_load_metrics() {
        let prefill_worker = create_test_worker(
            "http://prefill".to_string(),
            WorkerType::Prefill {
                bootstrap_port: None,
            },
            true,
        );
        let decode_worker =
            create_test_worker("http://decode".to_string(), WorkerType::Decode, true);

        let _guard =
            WorkerLoadGuard::new_multi(vec![prefill_worker.as_ref(), decode_worker.as_ref()]);

        assert_eq!(prefill_worker.load(), 1);
        assert_eq!(decode_worker.load(), 1);

        drop(_guard);

        assert_eq!(prefill_worker.load(), 0);
        assert_eq!(decode_worker.load(), 0);
    }

    #[tokio::test]
    async fn test_streaming_load_tracking() {
        use futures_util::StreamExt;
        use tokio::time::{sleep, Duration};

        let router = create_test_pd_router();

        let prefill_worker = create_test_worker(
            "http://prefill".to_string(),
            WorkerType::Prefill {
                bootstrap_port: None,
            },
            true,
        );
        let decode_worker =
            create_test_worker("http://decode".to_string(), WorkerType::Decode, true);

        router.worker_registry.register(Arc::from(prefill_worker));
        router.worker_registry.register(Arc::from(decode_worker));

        let prefill_workers = router.worker_registry.get_prefill_workers();
        let decode_workers = router.worker_registry.get_decode_workers();

        let prefill_ref = prefill_workers[0].clone();
        let decode_ref = decode_workers[0].clone();

        assert_eq!(prefill_ref.load(), 0);
        assert_eq!(decode_ref.load(), 0);

        let (tx, rx) = tokio::sync::mpsc::unbounded_channel();
        let stream = tokio_stream::wrappers::UnboundedReceiverStream::new(rx);

        let _response = router.create_streaming_response(
            stream.map(Ok),
            StatusCode::OK,
            None,
            false,
            None,
            None,
            prefill_ref.as_ref(),
            decode_ref.as_ref(),
        );

        assert_eq!(prefill_ref.load(), 1);
        assert_eq!(decode_ref.load(), 1);

        tx.send(bytes::Bytes::from("test data")).unwrap();

        sleep(Duration::from_millis(10)).await;

        assert_eq!(prefill_ref.load(), 1);
        assert_eq!(decode_ref.load(), 1);

        drop(tx);

        sleep(Duration::from_millis(100)).await;

        assert_eq!(prefill_ref.load(), 0);
        assert_eq!(decode_ref.load(), 0);
    }
}