//! Pipeline stages for gRPC router request processing
//!
//! This module defines the core pipeline abstraction and individual processing stages
//! that transform a RequestContext through its lifecycle.

use async_trait::async_trait;
use axum::response::{IntoResponse, Response};
use tracing::{debug, error, warn};

use super::context::*;
use super::processing;
use super::streaming;
use super::utils;
use crate::core::{ConnectionMode, WorkerRegistry, WorkerType};
use crate::grpc_client::proto;
use crate::policies::PolicyRegistry;
use crate::protocols::spec::{
    ChatCompletionRequest, ChatCompletionResponse, GenerateRequest, InputIds, Usage,
};
use rand::Rng;
use std::sync::Arc;
use std::time::{SystemTime, UNIX_EPOCH};
use uuid::Uuid;

// ============================================================================
// Pipeline Trait
// ============================================================================

/// Trait for pipeline stages that process requests
#[async_trait]
pub trait PipelineStage: Send + Sync {
    /// Execute this stage, mutating the context
    ///
    /// Returns:
    /// - `Ok(None)` - Continue to next stage
    /// - `Ok(Some(response))` - Pipeline complete, return this response (e.g., streaming)
    /// - `Err(response)` - Error occurred, return this error response
    async fn execute(&self, ctx: &mut RequestContext) -> Result<Option<Response>, Response>;

    /// Stage name for logging
    fn name(&self) -> &'static str;
}

// ============================================================================
// Stage 1: Preparation
// ============================================================================

/// Preparation stage: Filter tools, process messages, tokenize, build constraints
pub struct PreparationStage;

#[async_trait]
impl PipelineStage for PreparationStage {
    async fn execute(&self, ctx: &mut RequestContext) -> Result<Option<Response>, Response> {
        debug!("Stage {}: Processing request", self.name());

        // Clone the request to avoid borrowing issues
        match &ctx.input.request_type {
            RequestType::Chat(request) => {
                let request_clone = request.clone();
                self.prepare_chat(ctx, &request_clone).await?;
            }
            RequestType::Generate(request) => {
                let request_clone = request.clone();
                self.prepare_generate(ctx, &request_clone).await?;
            }
        }

        Ok(None)
    }

    fn name(&self) -> &'static str {
        "Preparation"
    }
}

impl PreparationStage {
    async fn prepare_chat(
        &self,
        ctx: &mut RequestContext,
        request: &ChatCompletionRequest,
    ) -> Result<(), Response> {
        // Step 1: Filter tools if needed
        let body_ref = utils::filter_tools_for_request(request);

        // Step 2: Process messages and apply chat template
        let processed_messages =
            match utils::process_chat_messages(&body_ref, &*ctx.components.tokenizer) {
                Ok(msgs) => msgs,
                Err(e) => {
                    return Err(utils::bad_request_error(e));
                }
            };

        // Step 3: Tokenize the processed text
        let encoding = match ctx.components.tokenizer.encode(&processed_messages.text) {
            Ok(encoding) => encoding,
            Err(e) => {
                return Err(utils::internal_error_message(format!(
                    "Tokenization failed: {}",
                    e
                )));
            }
        };

        let token_ids = encoding.token_ids().to_vec();
        debug!("Tokenized {} tokens from input", token_ids.len());

        // Step 4: Build tool constraints if needed
        let tool_call_constraint = body_ref.tools.as_ref().and_then(|tools| {
            utils::generate_tool_constraints(tools, &request.tool_choice, &request.model)
        });

        // Step 5: Create stop sequence decoder (build once, reuse in non-stream)
        let stop_decoder = utils::create_stop_decoder(
            &ctx.components.tokenizer,
            request.stop.as_ref(),
            request.stop_token_ids.as_ref(),
            request.skip_special_tokens,
            request.no_stop_trim,
        );

        // Store results in context
        ctx.state.preparation = Some(PreparationOutput {
            original_text: Some(processed_messages.text.clone()),
            token_ids,
            processed_messages: Some(processed_messages),
            tool_constraints: tool_call_constraint,
            filtered_request: if matches!(body_ref, std::borrow::Cow::Owned(_)) {
                Some(body_ref.into_owned())
            } else {
                None
            },
        });

        // Store stop decoder for reuse in response processing
        ctx.state.response.stop_decoder = Some(stop_decoder);

        Ok(())
    }

    async fn prepare_generate(
        &self,
        ctx: &mut RequestContext,
        request: &GenerateRequest,
    ) -> Result<(), Response> {
        // Resolve input (text, prompt, or input_ids)
        let (original_text, token_ids) = match self.resolve_generate_input(ctx, request) {
            Ok(res) => res,
            Err(msg) => {
                return Err(utils::bad_request_error(msg));
            }
        };

        debug!("Resolved input with {} tokens", token_ids.len());

        // Create stop sequence decoder for generate requests
        let params = request.sampling_params.as_ref();
        let stop_decoder = utils::create_stop_decoder(
            &ctx.components.tokenizer,
            params.and_then(|p| p.stop.as_ref()),
            params.and_then(|p| p.stop_token_ids.as_ref()),
            params.and_then(|p| p.skip_special_tokens).unwrap_or(true),
            params.and_then(|p| p.no_stop_trim).unwrap_or(false),
        );

        ctx.state.preparation = Some(PreparationOutput {
            original_text,
            token_ids,
            processed_messages: None,
            tool_constraints: None,
            filtered_request: None,
        });

        // Store stop decoder
        ctx.state.response.stop_decoder = Some(stop_decoder);

        Ok(())
    }

    fn resolve_generate_input(
        &self,
        ctx: &RequestContext,
        request: &GenerateRequest,
    ) -> Result<(Option<String>, Vec<u32>), String> {
        if let Some(text) = &request.text {
            return self
                .tokenize_single_text(&ctx.components.tokenizer, text)
                .map(|(original, ids)| (Some(original), ids));
        }

        // Handle input_ids - validate and convert
        if let Some(input_ids) = &request.input_ids {
            return match input_ids {
                InputIds::Single(ids) => ids
                    .iter()
                    .map(|&id| u32::try_from(id))
                    .collect::<Result<Vec<u32>, _>>()
                    .map(|converted| (None, converted))
                    .map_err(|_| "input_ids must be non-negative".to_string()),
                InputIds::Batch(_) => {
                    Err("Batch input_ids are not supported over gRPC generate yet".to_string())
                }
            };
        }

        Err("Either `text` or `input_ids` must be provided".to_string())
    }

    fn tokenize_single_text(
        &self,
        tokenizer: &Arc<dyn crate::tokenizer::traits::Tokenizer>,
        text: &str,
    ) -> Result<(String, Vec<u32>), String> {
        let encoding = tokenizer
            .encode(text)
            .map_err(|e| format!("Tokenization failed: {}", e))?;
        Ok((text.to_string(), encoding.token_ids().to_vec()))
    }
}

// ============================================================================
// Stage 2: Worker Selection
// ============================================================================

/// Worker selection stage: Select appropriate worker(s) based on routing mode
pub struct WorkerSelectionStage {
    worker_registry: Arc<WorkerRegistry>,
    policy_registry: Arc<PolicyRegistry>,
    mode: WorkerSelectionMode,
}

pub enum WorkerSelectionMode {
    /// Regular mode: select single worker
    Regular,
    /// PD mode: select prefill + decode workers
    PrefillDecode,
}

impl WorkerSelectionStage {
    pub fn new(
        worker_registry: Arc<WorkerRegistry>,
        policy_registry: Arc<PolicyRegistry>,
        mode: WorkerSelectionMode,
    ) -> Self {
        Self {
            worker_registry,
            policy_registry,
            mode,
        }
    }
}

#[async_trait]
impl PipelineStage for WorkerSelectionStage {
    async fn execute(&self, ctx: &mut RequestContext) -> Result<Option<Response>, Response> {
        debug!("Stage {}: Selecting workers", self.name());

        let prep = ctx
            .state
            .preparation
            .as_ref()
            .ok_or_else(|| utils::internal_error_static("Preparation stage not completed"))?;

        let text = prep.original_text.as_deref();

        let workers = match self.mode {
            WorkerSelectionMode::Regular => {
                match self.select_single_worker(ctx.input.model_id.as_deref(), text) {
                    Some(w) => WorkerSelection::Single { worker: w },
                    None => {
                        return Err(utils::service_unavailable_error(format!(
                            "No available workers for model: {:?}",
                            ctx.input.model_id
                        )));
                    }
                }
            }
            WorkerSelectionMode::PrefillDecode => {
                match self.select_pd_pair(ctx.input.model_id.as_deref(), text) {
                    Some((prefill, decode)) => WorkerSelection::Dual { prefill, decode },
                    None => {
                        return Err(utils::service_unavailable_error(format!(
                            "No available PD worker pairs for model: {:?}",
                            ctx.input.model_id
                        )));
                    }
                }
            }
        };

        ctx.state.workers = Some(workers);
        Ok(None)
    }

    fn name(&self) -> &'static str {
        "WorkerSelection"
    }
}

impl WorkerSelectionStage {
    fn select_single_worker(
        &self,
        model_id: Option<&str>,
        text: Option<&str>,
    ) -> Option<Arc<dyn crate::core::Worker>> {
        // Get workers for the specified model, filtered by connection mode
        let workers = self.worker_registry.get_workers_filtered(
            model_id,
            Some(WorkerType::Regular),
            Some(ConnectionMode::Grpc { port: None }),
            false, // get all workers, we'll filter by is_available() next
        );

        // Filter by availability (health + circuit breaker)
        let available: Vec<Arc<dyn crate::core::Worker>> = workers
            .iter()
            .filter(|w| w.is_available())
            .cloned()
            .collect();

        if available.is_empty() {
            return None;
        }

        // Get the appropriate policy for this model
        let policy = match model_id {
            Some(model) => self.policy_registry.get_policy_or_default(model),
            None => self.policy_registry.get_default_policy(),
        };

        // Select worker using the policy
        let idx = policy.select_worker(&available, text)?;
        Some(available[idx].clone())
    }

    fn select_pd_pair(
        &self,
        model_id: Option<&str>,
        text: Option<&str>,
    ) -> Option<(Arc<dyn crate::core::Worker>, Arc<dyn crate::core::Worker>)> {
        // Get prefill workers - use None for WorkerType filter to get all types,
        // then filter manually (since Prefill is a struct variant)
        let all_workers = self.worker_registry.get_workers_filtered(
            model_id,
            None, // Get all types
            Some(ConnectionMode::Grpc { port: None }),
            false,
        );

        let prefill_workers: Vec<_> = all_workers
            .iter()
            .filter(|w| matches!(w.metadata().worker_type, WorkerType::Prefill { .. }))
            .cloned()
            .collect();

        let available_prefill: Vec<_> = prefill_workers
            .iter()
            .filter(|w| w.is_available())
            .cloned()
            .collect();

        if available_prefill.is_empty() {
            warn!("No available prefill workers");
            return None;
        }

        // Get decode workers from the same all_workers list
        let decode_workers: Vec<_> = all_workers
            .iter()
            .filter(|w| matches!(w.metadata().worker_type, WorkerType::Decode))
            .cloned()
            .collect();

        let available_decode: Vec<_> = decode_workers
            .iter()
            .filter(|w| w.is_available())
            .cloned()
            .collect();

        if available_decode.is_empty() {
            warn!("No available decode workers");
            return None;
        }

        // Select using policies
        let policy = match model_id {
            Some(model) => self.policy_registry.get_policy_or_default(model),
            None => self.policy_registry.get_default_policy(),
        };

        let prefill_idx = policy.select_worker(&available_prefill, text)?;
        let decode_idx = policy.select_worker(&available_decode, text)?;

        Some((
            available_prefill[prefill_idx].clone(),
            available_decode[decode_idx].clone(),
        ))
    }
}

// ============================================================================
// Stage 3: Client Acquisition
// ============================================================================

/// Client acquisition stage: Get gRPC clients from selected workers
pub struct ClientAcquisitionStage;

#[async_trait]
impl PipelineStage for ClientAcquisitionStage {
    async fn execute(&self, ctx: &mut RequestContext) -> Result<Option<Response>, Response> {
        debug!("Stage {}: Acquiring gRPC clients", self.name());

        let workers = ctx
            .state
            .workers
            .as_ref()
            .ok_or_else(|| utils::internal_error_static("Worker selection not completed"))?;

        let clients = match workers {
            WorkerSelection::Single { worker } => {
                let client = utils::get_grpc_client_from_worker(worker).await?;
                ClientSelection::Single { client }
            }
            WorkerSelection::Dual { prefill, decode } => {
                let prefill_client = utils::get_grpc_client_from_worker(prefill).await?;
                let decode_client = utils::get_grpc_client_from_worker(decode).await?;
                ClientSelection::Dual {
                    prefill: prefill_client,
                    decode: decode_client,
                }
            }
        };

        ctx.state.clients = Some(clients);
        Ok(None)
    }

    fn name(&self) -> &'static str {
        "ClientAcquisition"
    }
}

// ============================================================================
// Stage 4: Request Building
// ============================================================================

/// Request building stage: Build proto GenerateRequest
pub struct RequestBuildingStage {
    inject_pd_metadata: bool,
}

impl RequestBuildingStage {
    pub fn new(inject_pd_metadata: bool) -> Self {
        Self { inject_pd_metadata }
    }
}

#[async_trait]
impl PipelineStage for RequestBuildingStage {
    async fn execute(&self, ctx: &mut RequestContext) -> Result<Option<Response>, Response> {
        debug!("Stage {}: Building proto request", self.name());

        let prep = ctx
            .state
            .preparation
            .as_ref()
            .ok_or_else(|| utils::internal_error_static("Preparation not completed"))?;

        let clients = ctx
            .state
            .clients
            .as_ref()
            .ok_or_else(|| utils::internal_error_static("Client acquisition not completed"))?;

        // Get client for building request (use prefill client if PD mode)
        let builder_client = match clients {
            ClientSelection::Single { client } => client,
            ClientSelection::Dual { prefill, .. } => prefill,
        };

        let mut proto_request = match &ctx.input.request_type {
            RequestType::Chat(request) => {
                let request_id = format!("chatcmpl-{}", Uuid::new_v4());
                let body_ref = prep.filtered_request.as_ref().unwrap_or(request);

                builder_client
                    .build_generate_request(
                        request_id,
                        body_ref,
                        prep.processed_messages.as_ref().unwrap().text.clone(),
                        prep.token_ids.clone(),
                        prep.processed_messages
                            .as_ref()
                            .unwrap()
                            .multimodal_inputs
                            .clone(),
                        prep.tool_constraints.clone(),
                    )
                    .map_err(|e| {
                        utils::bad_request_error(format!("Invalid request parameters: {}", e))
                    })?
            }
            RequestType::Generate(request) => {
                let request_id = request
                    .rid
                    .clone()
                    .unwrap_or_else(|| format!("gen-{}", Uuid::new_v4()));

                builder_client
                    .build_plain_generate_request(
                        request_id,
                        request,
                        prep.original_text.clone(),
                        prep.token_ids.clone(),
                    )
                    .map_err(utils::bad_request_error)?
            }
        };

        // Inject PD metadata if needed
        if self.inject_pd_metadata {
            if let WorkerSelection::Dual { prefill, .. } = ctx.state.workers.as_ref().unwrap() {
                self.inject_bootstrap_metadata(&mut proto_request, prefill);
            }
        }

        ctx.state.proto_request = Some(proto_request);
        Ok(None)
    }

    fn name(&self) -> &'static str {
        "RequestBuilding"
    }
}

impl RequestBuildingStage {
    fn inject_bootstrap_metadata(
        &self,
        request: &mut proto::GenerateRequest,
        prefill_worker: &Arc<dyn crate::core::Worker>,
    ) {
        use proto::DisaggregatedParams;

        let hostname = prefill_worker.bootstrap_host();
        let bootstrap_port = prefill_worker.bootstrap_port().unwrap_or(8998);

        // Generate room ID for bootstrap
        let room_id = rand::rng().random_range(0..i32::MAX);

        // Create DisaggregatedParams
        let disagg_params = DisaggregatedParams {
            bootstrap_host: hostname.to_string(),
            bootstrap_port: bootstrap_port as i32,
            bootstrap_room: room_id,
        };

        // Inject metadata directly into request
        request.disaggregated_params = Some(disagg_params);

        debug!(
            "Injected bootstrap metadata: host={}, port={}, room={}",
            hostname, bootstrap_port, room_id
        );
    }
}

// ============================================================================
// Stage 5: Dispatch Metadata
// ============================================================================

/// Dispatch metadata stage: Prepare metadata for dispatch
pub struct DispatchMetadataStage;

#[async_trait]
impl PipelineStage for DispatchMetadataStage {
    async fn execute(&self, ctx: &mut RequestContext) -> Result<Option<Response>, Response> {
        debug!("Stage {}: Preparing dispatch metadata", self.name());

        let proto_request = ctx
            .state
            .proto_request
            .as_ref()
            .ok_or_else(|| utils::internal_error_static("Proto request not built"))?;

        let request_id = proto_request.request_id.clone();
        let model = match &ctx.input.request_type {
            RequestType::Chat(req) => req.model.clone(),
            RequestType::Generate(_req) => {
                // Generate requests don't have a model field
                // Use model_id from input or default
                ctx.input
                    .model_id
                    .clone()
                    .unwrap_or_else(|| "default".to_string())
            }
        };

        let weight_version = ctx
            .state
            .workers
            .as_ref()
            .map(|w| match w {
                WorkerSelection::Single { worker } => worker,
                WorkerSelection::Dual { decode, .. } => decode,
            })
            .and_then(|w| w.metadata().labels.get("weight_version").cloned())
            .unwrap_or_else(|| "default".to_string());

        let created = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or_default()
            .as_secs();

        ctx.state.dispatch = Some(DispatchMetadata {
            request_id,
            model,
            created,
            weight_version: Some(weight_version),
            is_streaming: ctx.is_streaming(),
        });

        Ok(None)
    }

    fn name(&self) -> &'static str {
        "DispatchMetadata"
    }
}

// ============================================================================
// Stage 6: Request Execution
// ============================================================================

/// Request execution stage: Execute gRPC requests (single or dual dispatch)
pub struct RequestExecutionStage {
    mode: ExecutionMode,
}

pub enum ExecutionMode {
    /// Regular mode: single worker execution
    Single,
    /// PD mode: dual dispatch to prefill + decode workers
    DualDispatch,
}

impl RequestExecutionStage {
    pub fn new(mode: ExecutionMode) -> Self {
        Self { mode }
    }
}

#[async_trait]
impl PipelineStage for RequestExecutionStage {
    async fn execute(&self, ctx: &mut RequestContext) -> Result<Option<Response>, Response> {
        debug!("Stage {}: Executing gRPC request", self.name());

        let proto_request = ctx
            .state
            .proto_request
            .take()
            .ok_or_else(|| utils::internal_error_static("Proto request not built"))?;

        let clients = ctx
            .state
            .clients
            .as_mut()
            .ok_or_else(|| utils::internal_error_static("Client acquisition not completed"))?;

        let result = match self.mode {
            ExecutionMode::Single => self.execute_single(proto_request, clients).await?,
            ExecutionMode::DualDispatch => {
                self.execute_dual_dispatch(proto_request, clients).await?
            }
        };

        // Store result in context for ResponseProcessingStage
        ctx.state.response.execution_result = Some(result);
        Ok(None)
    }

    fn name(&self) -> &'static str {
        "RequestExecution"
    }
}

impl RequestExecutionStage {
    async fn execute_single(
        &self,
        proto_request: proto::GenerateRequest,
        clients: &mut ClientSelection,
    ) -> Result<ExecutionResult, Response> {
        let client = clients
            .single_mut()
            .ok_or_else(|| utils::internal_error_static("Expected single client but got dual"))?;

        let stream = client.generate(proto_request).await.map_err(|e| {
            utils::internal_error_message(format!("Failed to start generation: {}", e))
        })?;

        Ok(ExecutionResult::Single { stream })
    }

    async fn execute_dual_dispatch(
        &self,
        proto_request: proto::GenerateRequest,
        clients: &mut ClientSelection,
    ) -> Result<ExecutionResult, Response> {
        let (prefill_client, decode_client) = clients
            .dual_mut()
            .ok_or_else(|| utils::internal_error_static("Expected dual clients but got single"))?;

        debug!("Sending concurrent requests to prefill and decode workers");

        let prefill_request = proto_request.clone();
        let decode_request = proto_request;

        let (prefill_result, decode_result) = tokio::join!(
            prefill_client.generate(prefill_request),
            decode_client.generate(decode_request)
        );

        // Handle prefill result
        let prefill_stream = match prefill_result {
            Ok(s) => s,
            Err(e) => {
                return Err(utils::internal_error_message(format!(
                    "Prefill worker failed to start: {}",
                    e
                )));
            }
        };

        // Handle decode result
        let decode_stream = match decode_result {
            Ok(s) => s,
            Err(e) => {
                return Err(utils::internal_error_message(format!(
                    "Decode worker failed to start: {}",
                    e
                )));
            }
        };

        Ok(ExecutionResult::Dual {
            prefill: prefill_stream,
            decode: Box::new(decode_stream),
        })
    }
}

// ============================================================================
// Stage 7: Response Processing
// ============================================================================

/// Response processing stage: Handles both streaming and non-streaming responses
///
/// - For streaming: Spawns background task and returns SSE response (early exit)
/// - For non-streaming: Collects all responses and builds final ChatCompletionResponse
pub struct ResponseProcessingStage {
    processor: processing::ResponseProcessor,
    streaming_processor: Arc<streaming::StreamingProcessor>,
}

impl ResponseProcessingStage {
    pub fn new(
        processor: processing::ResponseProcessor,
        streaming_processor: Arc<streaming::StreamingProcessor>,
    ) -> Self {
        Self {
            processor,
            streaming_processor,
        }
    }
}

#[async_trait]
impl PipelineStage for ResponseProcessingStage {
    async fn execute(&self, ctx: &mut RequestContext) -> Result<Option<Response>, Response> {
        debug!("Stage {}: Processing response", self.name());

        // Delegate to request-type specific processing
        match &ctx.input.request_type {
            RequestType::Chat(_) => return self.process_chat_response(ctx).await,
            RequestType::Generate(_) => return self.process_generate_response(ctx).await,
        }
    }

    fn name(&self) -> &'static str {
        "ResponseProcessing"
    }
}

impl ResponseProcessingStage {
    async fn process_chat_response(
        &self,
        ctx: &mut RequestContext,
    ) -> Result<Option<Response>, Response> {
        let is_streaming = ctx.is_streaming();

        // Extract execution result
        let execution_result = ctx
            .state
            .response
            .execution_result
            .take()
            .ok_or_else(|| utils::internal_error_static("No execution result"))?;

        if is_streaming {
            // Get dispatch metadata for consistent response fields
            let dispatch = ctx
                .state
                .dispatch
                .as_ref()
                .ok_or_else(|| utils::internal_error_static("Dispatch metadata not set"))?;

            // Streaming: Use StreamingProcessor and return SSE response (done)
            return Ok(Some(
                self.streaming_processor.clone().process_streaming_response(
                    execution_result,
                    ctx.chat_request().clone(),
                    dispatch.clone(),
                ),
            ));
        }

        // Non-streaming: Extract chat request details before mutable borrows
        let request_logprobs = match &ctx.input.request_type {
            RequestType::Chat(req) => req.logprobs,
            _ => false,
        };

        // Collect all responses from the execution result
        let all_responses = match execution_result {
            ExecutionResult::Single { stream } => {
                utils::collect_stream_responses(stream, "Single").await?
            }
            ExecutionResult::Dual { prefill, decode } => {
                // Collect prefill for input_logprobs
                let prefill_responses = utils::collect_stream_responses(prefill, "Prefill").await?;

                // Collect decode for actual output
                let mut decode_responses =
                    utils::collect_stream_responses(*decode, "Decode").await?;

                // Merge prefill input_logprobs if requested
                if request_logprobs {
                    if let Some(prefill_input_logprobs) = prefill_responses
                        .first()
                        .and_then(|r| r.input_logprobs.clone())
                    {
                        for response in &mut decode_responses {
                            response.input_logprobs = Some(prefill_input_logprobs.clone());
                        }
                    }
                }

                decode_responses
            }
        };

        if all_responses.is_empty() {
            return Err(utils::internal_error_static("No responses from server"));
        }

        // Clone chat_request to avoid borrow checker conflict
        // (ctx.chat_request() borrows ctx, preventing mutable borrow of ctx.state.response.stop_decoder)
        let chat_request = ctx.chat_request().clone();
        let history_tool_calls_count = utils::get_history_tool_calls_count(&chat_request);

        let stop_decoder = ctx
            .state
            .response
            .stop_decoder
            .as_mut()
            .ok_or_else(|| utils::internal_error_static("Stop decoder not initialized"))?;

        let mut choices = Vec::new();
        for (index, complete) in all_responses.iter().enumerate() {
            match self
                .processor
                .process_single_choice(
                    complete,
                    index,
                    &chat_request,
                    stop_decoder,
                    history_tool_calls_count,
                )
                .await
            {
                Ok(choice) => choices.push(choice),
                Err(e) => {
                    return Err(utils::internal_error_message(format!(
                        "Failed to process choice {}: {}",
                        index, e
                    )));
                }
            }
        }

        // Build usage
        let total_prompt_tokens: u32 = all_responses.iter().map(|r| r.prompt_tokens as u32).sum();
        let total_completion_tokens: u32 = all_responses
            .iter()
            .map(|r| r.completion_tokens as u32)
            .sum();
        let usage = Usage {
            prompt_tokens: total_prompt_tokens,
            completion_tokens: total_completion_tokens,
            total_tokens: total_prompt_tokens + total_completion_tokens,
            completion_tokens_details: None,
        };

        // Build final ChatCompletionResponse
        let dispatch = ctx
            .state
            .dispatch
            .as_ref()
            .ok_or_else(|| utils::internal_error_static("Dispatch metadata not set"))?;

        let response = ChatCompletionResponse {
            id: dispatch.request_id.clone(),
            object: "chat.completion".to_string(),
            created: dispatch.created,
            model: dispatch.model.clone(),
            choices,
            usage: Some(usage),
            system_fingerprint: dispatch.weight_version.clone(),
        };

        // Store the final response
        ctx.state.response.final_response = Some(FinalResponse::Chat(response));

        Ok(None)
    }

    async fn process_generate_response(
        &self,
        _ctx: &mut RequestContext,
    ) -> Result<Option<Response>, Response> {
        // TODO(generate): Implement generate response processing
        //
        // Required implementation:
        // 1. Extract execution_result from ctx
        // 2. Check is_streaming flag
        // 3. For streaming:
        //    - Add StreamingProcessor::process_streaming_generate() method
        //    - Similar to process_streaming_response but WITHOUT tool/reasoning parsing
        //    - Return Err(sse_response) for early exit
        // 4. For non-streaming:
        //    - Collect stream responses using utils::collect_stream_responses()
        //    - Process through stop decoder (sequential with reset for n>1, like chat)
        //    - Build GenerateResponse struct (see TODO in protocols/spec.rs)
        //    - Set ctx.state.response.final_response = Some(FinalResponse::Generate(response))
        //
        // Reference implementation: router.rs:297-595
        // Key differences from chat:
        //   - No tool parsing
        //   - No reasoning parsing
        //   - Different response format (GenerateResponse instead of ChatCompletionResponse)
        //   - Still needs: stop decoder, logprobs, finish_reason, matched_stop
        Err((
            axum::http::StatusCode::NOT_IMPLEMENTED,
            axum::Json(serde_json::json!({
                "error": {
                    "message": "Generate response processing not yet implemented in pipeline",
                    "type": "not_implemented",
                    "code": 501
                }
            })),
        )
            .into_response())
    }
}

// ============================================================================
// Pipeline Orchestrator
// ============================================================================

/// Complete chat completion pipeline
///
/// Orchestrates all stages from request preparation to response delivery.
/// Configured differently for regular vs PD mode.
#[derive(Clone)]
pub struct ChatCompletionPipeline {
    stages: Arc<Vec<Box<dyn PipelineStage>>>,
}

impl ChatCompletionPipeline {
    /// Create a regular (single-worker) pipeline
    pub fn new_regular(
        worker_registry: Arc<WorkerRegistry>,
        policy_registry: Arc<PolicyRegistry>,
        processor: processing::ResponseProcessor,
        streaming_processor: Arc<streaming::StreamingProcessor>,
    ) -> Self {
        let stages: Vec<Box<dyn PipelineStage>> = vec![
            Box::new(PreparationStage),
            Box::new(WorkerSelectionStage::new(
                worker_registry,
                policy_registry,
                WorkerSelectionMode::Regular,
            )),
            Box::new(ClientAcquisitionStage),
            Box::new(RequestBuildingStage::new(false)), // No PD metadata
            Box::new(DispatchMetadataStage),
            Box::new(RequestExecutionStage::new(ExecutionMode::Single)),
            Box::new(ResponseProcessingStage::new(
                processor,
                streaming_processor.clone(),
            )),
        ];

        Self {
            stages: Arc::new(stages),
        }
    }

    /// Create a PD (prefill-decode) pipeline
    pub fn new_pd(
        worker_registry: Arc<WorkerRegistry>,
        policy_registry: Arc<PolicyRegistry>,
        processor: processing::ResponseProcessor,
        streaming_processor: Arc<streaming::StreamingProcessor>,
    ) -> Self {
        let stages: Vec<Box<dyn PipelineStage>> = vec![
            Box::new(PreparationStage),
            Box::new(WorkerSelectionStage::new(
                worker_registry,
                policy_registry,
                WorkerSelectionMode::PrefillDecode,
            )),
            Box::new(ClientAcquisitionStage),
            Box::new(RequestBuildingStage::new(true)), // Inject PD metadata
            Box::new(DispatchMetadataStage),
            Box::new(RequestExecutionStage::new(ExecutionMode::DualDispatch)),
            Box::new(ResponseProcessingStage::new(
                processor,
                streaming_processor.clone(),
            )),
        ];

        Self {
            stages: Arc::new(stages),
        }
    }

    /// Execute the complete pipeline for a chat request
    pub async fn execute_chat(
        &self,
        request: ChatCompletionRequest,
        headers: Option<axum::http::HeaderMap>,
        model_id: Option<String>,
        components: Arc<SharedComponents>,
    ) -> Response {
        let mut ctx = RequestContext::for_chat(request, headers, model_id, components);

        // Execute each stage in sequence
        for (idx, stage) in self.stages.iter().enumerate() {
            debug!("Executing stage {}: {}", idx + 1, stage.name());
            match stage.execute(&mut ctx).await {
                Ok(Some(response)) => {
                    // Stage completed successfully with a response (e.g., streaming)
                    debug!(
                        "Stage {} ({}) completed with response",
                        idx + 1,
                        stage.name()
                    );
                    return response;
                }
                Ok(None) => {
                    // Continue to next stage
                    continue;
                }
                Err(response) => {
                    // Error occurred
                    error!(
                        "Stage {} ({}) failed with status {}",
                        idx + 1,
                        stage.name(),
                        response.status()
                    );
                    return response;
                }
            }
        }

        // Extract final response
        match ctx.state.response.final_response {
            Some(FinalResponse::Chat(response)) => axum::Json(response).into_response(),
            Some(FinalResponse::Generate(_)) => {
                utils::internal_error_static("Internal error: wrong response type")
            }
            None => utils::internal_error_static("No response produced"),
        }
    }

    /// Execute the complete pipeline for a generate request
    pub async fn execute_generate(
        &self,
        request: GenerateRequest,
        headers: Option<axum::http::HeaderMap>,
        model_id: Option<String>,
        components: Arc<SharedComponents>,
    ) -> Response {
        let mut ctx = RequestContext::for_generate(request, headers, model_id, components);

        // Execute each stage in sequence
        for (idx, stage) in self.stages.iter().enumerate() {
            debug!("Executing stage {}: {}", idx + 1, stage.name());
            match stage.execute(&mut ctx).await {
                Ok(Some(response)) => {
                    // Stage completed successfully with a response (e.g., streaming)
                    debug!(
                        "Stage {} ({}) completed with response",
                        idx + 1,
                        stage.name()
                    );
                    return response;
                }
                Ok(None) => {
                    // Continue to next stage
                    continue;
                }
                Err(response) => {
                    // Error occurred
                    error!(
                        "Stage {} ({}) failed with status {}",
                        idx + 1,
                        stage.name(),
                        response.status()
                    );
                    return response;
                }
            }
        }

        // Extract final response
        match ctx.state.response.final_response {
            Some(FinalResponse::Generate(response)) => axum::Json(*response).into_response(),
            Some(FinalResponse::Chat(_)) => {
                utils::internal_error_static("Internal error: wrong response type")
            }
            None => utils::internal_error_static("No response produced"),
        }
    }
}
