// SPDX-FileCopyrightText: Copyright (c) 2024-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
// SPDX-License-Identifier: Apache-2.0

use async_once_cell::OnceCell as AsyncOnceCell;
use libc::c_char;
use once_cell::sync::OnceCell;
use std::borrow::Cow;
use std::ffi::CStr;
use std::ptr;
use std::sync::Arc;
use std::sync::atomic::{AtomicU32, Ordering};
use std::time::Duration;

use dynamo_kv_router::{
    config::{KvRouterConfig, RouterConfigOverride},
    protocols::*,
};
use dynamo_llm::kv_router::publisher::KvEventPublisher;
use dynamo_llm::model_card::ModelDeploymentCard;
use dynamo_llm::preprocessor::OpenAIPreprocessor;
use dynamo_runtime::discovery::{DiscoveryQuery, hash_pod_name};
use dynamo_runtime::{DistributedRuntime, Worker};

use dynamo_runtime::Runtime;

use dynamo_llm::discovery::{ModelManager, WORKER_TYPE_DECODE};
use dynamo_llm::kv_router::{KvRouter, PrefillRouter};
use dynamo_runtime::pipeline::RouterMode;

use std::collections::HashSet;

static WK: OnceCell<Worker> = OnceCell::new();
static DRT: AsyncOnceCell<DistributedRuntime> = AsyncOnceCell::new();
// [FIXME] shouldn't the publisher be instance passing between API calls?
static KV_PUB: OnceCell<KvEventPublisher> = OnceCell::new();

struct DiscoveredModelBootstrap {
    preprocessor: Arc<OpenAIPreprocessor>,
    card: ModelDeploymentCard,
    actual_namespace: String,
}

/// Convert a C string pointer to a Rust string, falling back to a default when:
/// - the pointer is NULL,
/// - the bytes are not valid UTF-8,
/// - or the resulting string is empty/whitespace.
#[inline]
unsafe fn cstr_or_default<'a>(ptr: *const c_char, default_val: &'a str) -> Cow<'a, str> {
    if ptr.is_null() {
        return Cow::from(default_val);
    }
    match unsafe { CStr::from_ptr(ptr) }
        .to_str()
        .ok()
        .map(|s| s.trim())
    {
        Some(s) if !s.is_empty() => Cow::from(s.to_owned()),
        _ => Cow::from(default_val),
    }
}

fn initialize_tracing() {
    // Sets up RUST_LOG environment variable for logging while KV Publishing
    // Example: os.environ["RUST_LOG"] = "debug"
    let subscriber = tracing_subscriber::fmt()
        .with_env_filter(tracing_subscriber::EnvFilter::from_default_env())
        .finish();

    if tracing::subscriber::set_global_default(subscriber).is_ok() {
        tracing::debug!("Tracing initialized");
    }
}

#[repr(u32)]
pub enum DynamoLlmResult {
    OK = 0,
    ERR = 1,
}

// Wait for the discovery daemon to sync indefinitely and return at least one instance.
// This is because the Model info is registered by workers and it may take up to 30 min for the model weights to load and for the worker to register itself.
// The waiting timeout is implemented in the Kubernetes StartupProbe. The EPP waiting loops runs indefinitely, the Probe is a single source of truth with when to kill the EPP if discovery fails.
// If workers are not found within the probe's failureThreshold × periodSeconds, the pod will be killed and restarted.
// Users can adjust the StartupProbe waiting timed in the DGD for large models.
async fn wait_for_discovery_sync(drt: &DistributedRuntime) -> usize {
    tracing::info!(
        "Waiting for discovery to sync (no timeout - controlled by K8s StartupProbe)..."
    );
    let discovery = drt.discovery();

    loop {
        match discovery.list(DiscoveryQuery::AllModels).await {
            Ok(instances) if !instances.is_empty() => {
                return instances.len();
            }
            Ok(_) => {
                tracing::debug!("No instances yet, waiting...");
                tokio::time::sleep(std::time::Duration::from_millis(500)).await;
            }
            Err(e) => {
                // Log and continue - transient errors shouldn't stop the wait
                tracing::warn!("Discovery list error: {}, retrying...", e);
                tokio::time::sleep(std::time::Duration::from_millis(500)).await;
            }
        }
    }
}

/// # Safety
/// the namespace_c_str and component_c_str are passed as pointers to C strings
#[unsafe(no_mangle)]
pub unsafe extern "C" fn dynamo_llm_init(
    namespace_c_str: *const c_char,
    component_c_str: *const c_char,
    kv_block_size: u32,
) -> DynamoLlmResult {
    initialize_tracing();
    let wk = match WK.get_or_try_init(Worker::from_settings) {
        Ok(wk) => wk.clone(),
        Err(e) => {
            tracing::error!(error = ?e, "Failed to initialize runtime (Worker::from_settings)");
            return DynamoLlmResult::ERR;
        }
    };
    let rt = wk.runtime();
    let secondary = rt.secondary().clone();
    let result = secondary.block_on(async {
        // Initialize the distributed runtime
        match DRT
            .get_or_try_init(async { DistributedRuntime::from_settings(rt.clone()).await })
            .await
        {
            Ok(drt) => {
                // Wait for discovery to sync before returning.
                // This is needed because dynamo_create_worker_selection_pipeline() is called
                // immediately after, and it needs discovery.list() to return data.
                // The discovery daemon takes time to query K8s and returns async, so we need to wait.
                // Note: This waits indefinitely - the K8s StartupProbe is the timeout mechanism.
                wait_for_discovery_sync(drt).await;
                Ok(())
            }
            Err(e) => {
                tracing::error!(error = ?e, "Failed to initialize distributed runtime");
                Err(DynamoLlmResult::ERR)
            }
        }
    });
    let namespace = match unsafe { CStr::from_ptr(namespace_c_str) }.to_str() {
        Ok(s) => s.to_string(),
        Err(e) => {
            tracing::error!(error = ?e, "Failed to convert C string to Rust string (namespace)");
            return DynamoLlmResult::ERR;
        }
    };

    let component_cow = unsafe { cstr_or_default(component_c_str, "backend") };
    if let Cow::Borrowed("backend") = &component_cow {
        tracing::info!("defaulting to \"backend\" for component");
    }
    let component: String = component_cow.into_owned();

    match result {
        Ok(_) => match KV_PUB.get_or_try_init(move || {
            dynamo_create_kv_publisher(namespace, component, kv_block_size)
        }) {
            Ok(_) => DynamoLlmResult::OK,
            Err(e) => {
                tracing::error!(error = ?e, "Failed to initialize distributed runtime");
                DynamoLlmResult::ERR
            }
        },
        Err(e) => e,
    }
}

#[unsafe(no_mangle)]
pub extern "C" fn dynamo_llm_shutdown() -> DynamoLlmResult {
    let wk = match WK.get() {
        Some(wk) => wk,
        None => {
            tracing::error!("Runtime not initialized");
            return DynamoLlmResult::ERR;
        }
    };

    wk.runtime().shutdown();

    DynamoLlmResult::OK
}

#[unsafe(no_mangle)]
pub extern "C" fn dynamo_llm_load_publisher_create() -> DynamoLlmResult {
    DynamoLlmResult::OK
}

// instantiate a kv publisher
// this will bring up the task to publish and the channels to await publishing events
// the [`dynamo_kv_publish_store_event`] call will use a handle to the publisher to send events
// store and the [`dynamo_kv_event_create_removed`] will create remove events
// these call mus be driving by external c++ threads that are consuming the kv events from the
// c++ executor api

fn dynamo_create_kv_publisher(
    namespace: String,
    component: String,
    kv_block_size: u32,
) -> Result<KvEventPublisher, anyhow::Error> {
    tracing::info!("Creating KV Publisher for model: {}", component);
    match DRT
        .get()
        .ok_or(anyhow::Error::msg("Could not get Distributed Runtime"))
    {
        Ok(drt) => {
            let backend = drt.namespace(namespace)?.component(component)?;
            KvEventPublisher::new(backend, kv_block_size, None)
        }
        Err(e) => Err(e),
    }
}

fn kv_event_create_stored_block_from_parts(
    block_hash: u64,
    token_ids: *const u32,
    num_tokens: usize,
    kv_block_size: u32,
    lora_name: Option<&str>,
) -> KvCacheStoredBlockData {
    let tokens_hash = compute_block_hash_for_seq(
        unsafe { std::slice::from_raw_parts(token_ids, num_tokens) },
        kv_block_size,
        BlockHashOptions {
            lora_name,
            ..Default::default()
        },
    )[0];
    KvCacheStoredBlockData {
        block_hash: ExternalSequenceBlockHash(block_hash),
        tokens_hash,
        mm_extra_info: None,
    }
}
static WARN_COUNT: AtomicU32 = AtomicU32::new(0);

fn kv_event_create_stored_from_parts(
    kv_params: DynamoKvStoredEventParams,
    kv_block_size: u32,
) -> KvCacheEvent {
    let mut blocks: Vec<KvCacheStoredBlockData> = Vec::new();

    let mut token_offset: usize = 0;
    for block_idx in 0..kv_params.num_blocks {
        let block_hash = unsafe { *kv_params.block_ids.offset(block_idx.try_into().unwrap()) };
        let tokens = unsafe { kv_params.token_ids.offset(token_offset.try_into().unwrap()) };
        let num_toks = unsafe {
            *kv_params
                .num_block_tokens
                .offset(block_idx.try_into().unwrap())
        };

        if num_toks != (kv_block_size as usize) {
            if WARN_COUNT
                .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |c| {
                    if c < 3 { Some(c + 1) } else { None }
                })
                .is_ok()
            {
                tracing::warn!(
                    "Block not published. Block size must be {} tokens to be published. Block size is: {}",
                    kv_block_size,
                    num_toks
                );
            }
            break;
        }
        token_offset += num_toks;
        blocks.push(kv_event_create_stored_block_from_parts(
            block_hash,
            tokens,
            num_toks,
            kv_block_size,
            kv_params.lora_name.as_deref(),
        ));
    }

    KvCacheEvent {
        data: KvCacheEventData::Stored(KvCacheStoreData {
            blocks,
            parent_hash: kv_params.parent_hash.map(ExternalSequenceBlockHash),
        }),
        event_id: kv_params.event_id,
        dp_rank: 0,
    }
}

fn kv_event_create_removed_from_parts(
    event_id: u64,
    block_ids: *const u64,
    num_blocks: usize,
) -> KvCacheEvent {
    let block_hashes: Vec<ExternalSequenceBlockHash> =
        unsafe { std::slice::from_raw_parts(block_ids, num_blocks) }
            .to_vec()
            .iter()
            .map(|&v| ExternalSequenceBlockHash(v))
            .collect();
    KvCacheEvent {
        event_id,
        data: KvCacheEventData::Removed(KvCacheRemoveData { block_hashes }),
        dp_rank: 0,
    }
}

pub struct DynamoKvStoredEventParams {
    pub event_id: u64,
    pub token_ids: *const u32,
    pub num_block_tokens: *const usize,
    pub block_ids: *const u64,
    pub num_blocks: usize,
    pub parent_hash: Option<u64>,
    pub lora_name: Option<String>,
}

/// # Safety
/// parent_hash is passed as pointer to indicate whether the blocks
/// has a parent hash or not. nullptr is used to represent no parent hash.
/// lora_name is an optional null-terminated C string; pass nullptr for base model.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn dynamo_kv_event_publish_stored(
    event_id: u64,
    token_ids: *const u32,
    num_block_tokens: *const usize,
    block_ids: *const u64,
    num_blocks: usize,
    parent_hash: *const u64,
    lora_name: *const c_char,
) -> DynamoLlmResult {
    let parent_hash = {
        if parent_hash.is_null() {
            None
        } else {
            Some(unsafe { *parent_hash })
        }
    };
    let lora_name = if lora_name.is_null() {
        None
    } else {
        match unsafe { CStr::from_ptr(lora_name) }.to_str() {
            Ok(s) => Some(s.to_owned()),
            Err(e) => {
                tracing::error!(error = ?e, "Failed to convert C string to Rust string (lora_name)");
                return DynamoLlmResult::ERR;
            }
        }
    };
    let kv_params = DynamoKvStoredEventParams {
        event_id,
        token_ids,
        num_block_tokens,
        block_ids,
        num_blocks,
        parent_hash,
        lora_name,
    };
    let publisher = KV_PUB.get().unwrap();
    let event = kv_event_create_stored_from_parts(kv_params, publisher.kv_block_size());
    match publisher.publish(event) {
        Ok(_) => DynamoLlmResult::OK,
        Err(e) => {
            eprintln!("Error publishing stored kv event {:?}", e);
            DynamoLlmResult::ERR
        }
    }
}

#[unsafe(no_mangle)]
pub extern "C" fn dynamo_kv_event_publish_removed(
    event_id: u64,
    block_ids: *const u64,
    num_blocks: usize,
) -> DynamoLlmResult {
    let publisher = KV_PUB.get().unwrap();
    let event = kv_event_create_removed_from_parts(event_id, block_ids, num_blocks);
    match publisher.publish(event) {
        Ok(_) => DynamoLlmResult::OK,
        Err(e) => {
            eprintln!("Error publishing removed kv event {:?}", e);
            DynamoLlmResult::ERR
        }
    }
}

/* ------------------------------------------------------------------------
 *  Router Bindings for GAIE EPP
 * ------------------------------------------------------------------------ */

// Default timeout for bookkeeping operations
const BOOKKEEPING_TIMEOUT_SEC: u64 = 5;
/// Complete routing result for a chat completion request (C-compatible)
#[repr(C)]
pub struct CRoutingResult {
    /// Whether disaggregated mode is active
    pub is_disaggregated: bool,
    /// Prefill worker ID (only valid if is_disaggregated is true)
    pub prefill_worker_id: u64,
    /// Decode worker ID
    pub decode_worker_id: u64,
    /// Data parallel rank selected for the prefill worker
    pub prefill_dp_rank: u32,
    /// Data parallel rank selected for the decode worker
    pub decode_dp_rank: u32,
    /// Token IDs (needed for add_request callback)
    pub token_ids: *mut u32,
    /// Number of tokens in the request
    pub token_count: usize,
}

impl Default for CRoutingResult {
    fn default() -> Self {
        Self {
            is_disaggregated: false,
            prefill_worker_id: 0,
            decode_worker_id: 0,
            prefill_dp_rank: 0,
            decode_dp_rank: 0,
            token_ids: ptr::null_mut(),
            token_count: 0,
        }
    }
}

/// Container holding routers and preprocessor for query routing
pub struct RouterHandles {
    prefill_router: Arc<PrefillRouter>,
    decode_router: Arc<KvRouter>,
    #[allow(dead_code)]
    model_manager: Arc<ModelManager>,
    #[allow(dead_code)]
    namespace: String,
    /// Cached runtime for executing async operations (avoids creating new runtime per call)
    runtime: Runtime,
    /// Preprocessor for tokenization and template application (fetched via discovery)
    preprocessor: Option<Arc<OpenAIPreprocessor>>,
}

impl RouterHandles {
    /// Query optimal prefill worker for a request.
    ///
    /// When `allowed_worker_ids` is Some, only workers in that set are considered.
    /// Returns worker_id on success.
    async fn query_prefill_worker(
        &self,
        tokens: &[u32],
        block_mm_infos: Option<&[Option<dynamo_kv_router::protocols::BlockExtraInfo>]>,
        update_states: bool,
        lora_name: Option<String>,
        priority_jump: f64,
        allowed_worker_ids: Option<HashSet<WorkerId>>,
    ) -> Result<(u64, Option<u32>), QueryRouterResult> {
        if let Some(ref ids) = allowed_worker_ids {
            self.prefill_router.register_workers(ids);
        }

        self.prefill_router
            .query_prefill_worker(
                tokens,
                block_mm_infos,
                update_states,
                lora_name,
                priority_jump,
                allowed_worker_ids,
            )
            .await
            .map_err(|e| {
                tracing::error!(error = ?e, "Prefill query failed");
                QueryRouterResult::ErrQueryFailed
            })
    }

    /// Query optimal decode worker for a request.
    /// For disaggregated mode, set `is_disaggregated` to true to use overlap_score_weight=0
    /// (since KV cache is being transferred from prefill, not reused).
    ///
    /// When `allowed_worker_ids` is Some, only workers in that set are considered.
    /// This does NOT overwrite the router's internal worker state — it only filters this decision.
    ///
    /// Note: The C bindings are query-only and must not mutate router state during worker
    /// selection. State updates require a `context_id` (request id) and are managed via the
    /// explicit bookkeeping APIs (`add_request`, `mark_prefill_complete`, `free_request`).
    /// Returns (worker, overlap_blocks) on success.
    async fn query_decode_worker(
        &self,
        tokens: &[u32],
        is_disaggregated: bool,
        allowed_worker_ids: Option<HashSet<WorkerId>>,
    ) -> Result<(WorkerWithDpRank, u32), QueryRouterResult> {
        if let Some(ref ids) = allowed_worker_ids {
            self.decode_router.register_workers(ids);
        }

        // For decode phase in disaggregated mode, use overlap_score_weight=0
        // This matches prefill_router.rs
        let config_override = if is_disaggregated {
            Some(RouterConfigOverride {
                overlap_score_weight: Some(0.0),
                assume_kv_reuse: Some(false),
                track_prefill_tokens: Some(false),
                ..Default::default()
            })
        } else {
            None
        };

        self.decode_router
            .find_best_match(
                None,
                tokens,
                None,
                config_override.as_ref(),
                false,
                None,
                0.0,
                None,
                None,
                allowed_worker_ids,
            )
            .await
            .map_err(|e| {
                tracing::error!(error = ?e, "Decode query failed");
                QueryRouterResult::ErrQueryFailed
            })
    }
}

/// Opaque handle for the router pair
pub type RouterHandlesPtr = *mut RouterHandles;

/// Result codes for query router C FFI
#[repr(u32)]
pub enum QueryRouterResult {
    Ok = 0,
    ErrInvalidHandle = 1,
    ErrInvalidParam = 2,
    ErrInitFailed = 3,
    ErrQueryFailed = 4,
    ErrDisaggEnforced = 5,
    ErrTimeout = 6,
}

/// Build a `KvRouterConfig` from defaults, overridden by optional `DYN_*` environment variables.
fn kv_router_config_from_env() -> KvRouterConfig {
    let mut cfg = KvRouterConfig::default();

    fn env_f64(key: &str) -> Option<f64> {
        std::env::var(key).ok().and_then(|v| v.parse().ok())
    }
    fn env_bool(key: &str) -> Option<bool> {
        std::env::var(key)
            .ok()
            .and_then(|v| match v.to_lowercase().as_str() {
                "true" | "1" | "yes" | "on" => Some(true),
                "false" | "0" | "no" | "off" => Some(false),
                _ => None,
            })
    }

    if let Some(v) = env_f64("DYN_OVERLAP_SCORE_WEIGHT") {
        cfg.overlap_score_weight = v;
    }
    if let Some(v) = env_f64("DYN_ROUTER_TEMPERATURE") {
        cfg.router_temperature = v;
    }
    if let Some(v) = env_bool("DYN_USE_KV_EVENTS") {
        cfg.use_kv_events = v;
    }
    if let Some(v) = env_bool("DYN_ROUTER_REPLICA_SYNC") {
        cfg.router_replica_sync = v;
    }
    if let Some(v) = env_bool("DYN_ROUTER_TRACK_ACTIVE_BLOCKS") {
        cfg.router_track_active_blocks = v;
    }
    if let Some(v) = env_bool("DYN_ROUTER_TRACK_OUTPUT_BLOCKS") {
        cfg.router_track_output_blocks = v;
    }
    if let Some(v) = env_bool("DYN_ROUTER_TRACK_PREFILL_TOKENS") {
        cfg.router_track_prefill_tokens = v;
    }
    if let Some(v) = env_f64("DYN_ROUTER_QUEUE_THRESHOLD") {
        cfg.router_queue_threshold = Some(v);
    }

    tracing::info!(
        overlap_score_weight = cfg.overlap_score_weight,
        router_temperature = cfg.router_temperature,
        use_kv_events = cfg.use_kv_events,
        router_replica_sync = cfg.router_replica_sync,
        router_track_active_blocks = cfg.router_track_active_blocks,
        router_track_output_blocks = cfg.router_track_output_blocks,
        router_track_prefill_tokens = cfg.router_track_prefill_tokens,
        router_queue_threshold = ?cfg.router_queue_threshold,
        "KvRouterConfig initialized (DYN_* env overrides applied)"
    );

    cfg
}

/// Create router handles for query-only routing
///
/// This function waits for at least one decode worker to be discovered before returning.
/// It auto-detects disaggregated mode by checking if prefill workers are present.
/// The KV cache block size is automatically fetched from the model card via discovery.
///
/// # Arguments
/// - `namespace`: Namespace for the model
/// - `component`: Component name (defaults to "backend" if NULL or empty)
/// - `enforce_disagg`: If true, requires prefill workers to be present at init time
/// - `out_handle`: Output handle
///
/// # Safety
/// - All string parameters must be valid null-terminated C strings
/// - The returned handle must be freed with `destroy`
#[unsafe(no_mangle)]
pub unsafe extern "C" fn create_routers(
    namespace: *const c_char,
    component: *const c_char,
    enforce_disagg: bool,
    out_handle: *mut RouterHandlesPtr,
) -> QueryRouterResult {
    initialize_tracing();

    if namespace.is_null() || out_handle.is_null() {
        return QueryRouterResult::ErrInvalidParam;
    }

    let namespace_str = match unsafe { CStr::from_ptr(namespace) }.to_str() {
        Ok(s) => s.to_owned(),
        Err(_) => return QueryRouterResult::ErrInvalidParam,
    };

    let component_str = if component.is_null() {
        "backend".to_string()
    } else {
        match unsafe { CStr::from_ptr(component) }.to_str() {
            Ok(s) if !s.is_empty() => s.to_owned(),
            _ => "backend".to_string(),
        }
    };

    // Create the runtime once - it will be stored in RouterHandles and reused
    let runtime = match Runtime::from_settings() {
        Ok(rt) => rt,
        Err(e) => {
            tracing::error!(error = ?e, "Failed to create runtime");
            return QueryRouterResult::ErrInitFailed;
        }
    };

    // Clone for use inside the async block (the original will be moved into handles)
    let runtime_for_async = runtime.clone();

    let result = runtime_for_async.secondary().block_on(async {
        let drt = match DistributedRuntime::from_settings(runtime_for_async.clone()).await {
            Ok(drt) => drt,
            Err(e) => {
                tracing::error!(error = ?e, "Failed to create distributed runtime");
                return Err(QueryRouterResult::ErrInitFailed);
            }
        };

        let DiscoveredModelBootstrap {
            preprocessor,
            card,
            actual_namespace,
        } = match init_preprocessor(&drt, &namespace_str).await {
            Ok(result) => result,
            Err(e) => {
                tracing::error!(error = %e, "Failed to initialize preprocessor");
                return Err(QueryRouterResult::ErrInitFailed);
            }
        };
        let block_size = card.kv_cache_block_size;
        let model_name = card.display_name.clone();
        let enable_eagle = card.runtime_config.enable_eagle;

        if actual_namespace != namespace_str {
            tracing::info!(
                base_namespace = %namespace_str,
                actual_namespace = %actual_namespace,
                "Worker namespace has rolling-update suffix"
            );
        }

        let mut kv_router_config = kv_router_config_from_env();
        kv_router_config.skip_initial_worker_wait = true;

        // Build endpoint using the actual namespace discovered from workers,
        // which may include a rolling-update hash suffix.
        let component_handle = match drt.namespace(&actual_namespace) {
            Ok(ns) => match ns.component(&component_str) {
                Ok(c) => c,
                Err(e) => {
                    tracing::error!(error = ?e, "Failed to get component");
                    return Err(QueryRouterResult::ErrInitFailed);
                }
            },
            Err(e) => {
                tracing::error!(error = ?e, "Failed to get namespace");
                return Err(QueryRouterResult::ErrInitFailed);
            }
        };
        let endpoint = component_handle.endpoint("generate");

        let model_manager = Arc::new(ModelManager::new());

        // Create decode router
        let decode_router = match model_manager
            .kv_chooser_for(
                &endpoint,
                block_size,
                Some(kv_router_config.clone()),
                None,
                WORKER_TYPE_DECODE,
                Some(model_name.clone()),
                enable_eagle,
            )
            .await
        {
            Ok(r) => r,
            Err(e) => {
                tracing::error!(error = ?e, "Failed to create decode router");
                return Err(QueryRouterResult::ErrInitFailed);
            }
        };

        // Wait for the runtime config watch to be populated with at least one
        // decode worker's ModelRuntimeConfig. skip_initial_worker_wait=true
        // skips this inside KvRouter::new, but the selector needs workers in
        // workers_with_configs to avoid NoEndpoints on the first request.
        // discovery sync already confirmed workers exist; this just waits for
        // the async join of instance IDs + configs to complete in the watch.
        {
            let mut config_watch = model_manager
                .get_or_create_runtime_config_watcher(&endpoint)
                .await
                .map_err(|e| {
                    tracing::error!(error = ?e, "Failed to get runtime config watcher");
                    QueryRouterResult::ErrInitFailed
                })?;
            tracing::info!(
                "Waiting for decode workers to register ModelRuntimeConfig \
                 (no timeout - controlled by K8s StartupProbe)..."
            );
            let wait_result = config_watch.wait_for(|m| !m.is_empty()).await.map(|_| ());
            match wait_result {
                Ok(()) => {
                    let count = config_watch.borrow().len();
                    tracing::info!(
                        worker_count = count,
                        "Runtime config watch populated with decode workers"
                    );
                }
                Err(_) => {
                    tracing::error!(
                        "Runtime config watch closed before any workers appeared. \
                         Decode routing will fail. \
                         Verify workers are running and publishing to discovery."
                    );
                    return Err(QueryRouterResult::ErrInitFailed);
                }
            }
        }

        // Create PrefillRouter with a pending activation channel.
        // A background task watches discovery for prefill workers and activates
        // the router when one appears. Before activation, requests gracefully
        // fallback to decode-only routing.
        let mut prefill_config = kv_router_config;
        prefill_config.router_track_active_blocks = false;

        let (prefill_tx, prefill_rx) = tokio::sync::oneshot::channel();
        let prefill_router = PrefillRouter::new(
            prefill_rx,
            model_manager.clone(),
            RouterMode::KV,
            block_size,
            Some(prefill_config),
            None,
            enforce_disagg,
            model_name.clone(),
            actual_namespace.clone(),
            enable_eagle,
        );

        // Spawn background discovery watcher for prefill workers.
        // Polls discovery until a prefill-only worker appears in the same
        // rolling-update namespace, then sends its endpoint through the channel
        // to activate the PrefillRouter.
        spawn_prefill_discovery_watcher(drt.clone(), actual_namespace.clone(), prefill_tx);

        Ok((
            prefill_router,
            decode_router,
            model_manager,
            namespace_str,
            Some(preprocessor),
        ))
    });

    match result {
        Ok((prefill_router, decode_router, model_manager, namespace_str, preprocessor)) => {
            let handles = RouterHandles {
                prefill_router,
                decode_router,
                model_manager,
                namespace: namespace_str,
                runtime, // Store the runtime for reuse
                preprocessor,
            };
            unsafe { *out_handle = Box::into_raw(Box::new(handles)) };
            QueryRouterResult::Ok
        }
        Err(code) => code,
    }
}

/// Add a request to the router's bookkeeping after worker selection.
///
/// Register the request with the KvRouter's scheduler for tracking active blocks
/// and managing prefill/decode lifecycle. Call this after `query_decode` returns
/// worker IDs and before sending the request to the worker.
///
/// # Safety
/// - `handle` must be a valid RouterHandles handle
/// - `request_id` must be a valid null-terminated C string
/// - `token_ids` must point to at least `token_count` valid u32 values
#[unsafe(no_mangle)]
pub unsafe extern "C" fn add_request(
    handle: RouterHandlesPtr,
    request_id: *const c_char,
    token_ids: *const u32,
    token_count: usize,
    worker_id: u64,
    dp_rank: u32,
) -> QueryRouterResult {
    if handle.is_null() || request_id.is_null() {
        return QueryRouterResult::ErrInvalidParam;
    }

    let handles = unsafe { &*handle };
    let request_id_str = match unsafe { CStr::from_ptr(request_id) }.to_str() {
        Ok(s) => s.to_owned(),
        Err(_) => return QueryRouterResult::ErrInvalidParam,
    };

    let tokens: Vec<u32> = if token_count > 0 && !token_ids.is_null() {
        unsafe { std::slice::from_raw_parts(token_ids, token_count) }.to_vec()
    } else {
        Vec::new()
    };

    let decode_router = handles.decode_router.clone();

    let result = handles.runtime.secondary().block_on(async {
        let timeout_duration = Duration::from_secs(BOOKKEEPING_TIMEOUT_SEC);

        tokio::time::timeout(timeout_duration, async {
            let worker = WorkerWithDpRank::new(worker_id, dp_rank);
            let router_config_override = RouterConfigOverride {
                overlap_score_weight: Some(0.0),
                assume_kv_reuse: Some(false),
                track_prefill_tokens: Some(false),
                ..Default::default()
            };

            // Compute overlap_blocks using the public method
            let overlap_blocks = match decode_router
                .get_overlap_blocks(&tokens, None, worker, None)
                .await
            {
                Ok(overlap) => overlap,
                Err(e) => {
                    tracing::warn!(error = ?e, "Failed to compute overlap, using 0");
                    0
                }
            };

            decode_router
                .add_request(
                    request_id_str.clone(),
                    &tokens,
                    None,
                    overlap_blocks,
                    None,
                    worker,
                    None, // lora_name
                    Some(&router_config_override),
                )
                .await;

            tracing::debug!(
                request_id = %request_id_str,
                worker_id = worker_id,
                dp_rank = dp_rank,
                overlap_blocks = overlap_blocks,
                token_count = tokens.len(),
                "add_request completed"
            );
        })
        .await
    });

    match result {
        Ok(()) => QueryRouterResult::Ok,
        Err(_elapsed) => {
            tracing::warn!(
                request_id = %request_id_str,
                timeout_secs = BOOKKEEPING_TIMEOUT_SEC,
                "add_request timed out"
            );
            QueryRouterResult::ErrTimeout
        }
    }
}

/// Mark prefill as completed for a request.
///
/// Call when the first token is generated to release prefill tokens from decode worker's load
///
/// # Safety
/// - `handle` must be a valid RouterHandles handle
/// - `request_id` must be a valid null-terminated C string
#[unsafe(no_mangle)]
pub unsafe extern "C" fn mark_prefill_complete(
    handle: RouterHandlesPtr,
    request_id: *const c_char,
) -> QueryRouterResult {
    if handle.is_null() || request_id.is_null() {
        return QueryRouterResult::ErrInvalidParam;
    }

    let handles = unsafe { &*handle };
    let request_id_str = match unsafe { CStr::from_ptr(request_id) }.to_str() {
        Ok(s) => s.to_owned(),
        Err(_) => return QueryRouterResult::ErrInvalidParam,
    };

    let decode_router = handles.decode_router.clone();

    let result = handles.runtime.secondary().block_on(async {
        let timeout_duration = Duration::from_secs(BOOKKEEPING_TIMEOUT_SEC);

        tokio::time::timeout(timeout_duration, async {
            if let Err(e) = decode_router.mark_prefill_completed(&request_id_str).await {
                tracing::warn!(
                    request_id = %request_id_str,
                    error = %e,
                    "Failed to mark prefill complete"
                );
            } else {
                tracing::debug!(
                    request_id = %request_id_str,
                    "mark_prefill_complete completed"
                );
            }
        })
        .await
    });

    match result {
        Ok(()) => QueryRouterResult::Ok,
        Err(_elapsed) => {
            tracing::warn!(
                request_id = %request_id_str,
                timeout_secs = BOOKKEEPING_TIMEOUT_SEC,
                "mark_prefill_complete timed out"
            );
            QueryRouterResult::ErrTimeout
        }
    }
}

/// Free a request from the router's bookkeeping.
///
/// Call this when the stream is closed (completed or cancelled) to release all resources.
///
/// # Safety
/// - `handle` must be a valid RouterHandles handle
/// - `request_id` must be a valid null-terminated C string
#[unsafe(no_mangle)]
pub unsafe extern "C" fn free_request(
    handle: RouterHandlesPtr,
    request_id: *const c_char,
) -> QueryRouterResult {
    if handle.is_null() || request_id.is_null() {
        return QueryRouterResult::ErrInvalidParam;
    }

    let handles = unsafe { &*handle };
    let request_id_str = match unsafe { CStr::from_ptr(request_id) }.to_str() {
        Ok(s) => s.to_owned(),
        Err(_) => return QueryRouterResult::ErrInvalidParam,
    };

    let decode_router = handles.decode_router.clone();

    let result = handles.runtime.secondary().block_on(async {
        let timeout_duration = Duration::from_secs(BOOKKEEPING_TIMEOUT_SEC);

        tokio::time::timeout(timeout_duration, async {
            if let Err(e) = decode_router.free(&request_id_str).await {
                tracing::warn!(
                    request_id = %request_id_str,
                    error = %e,
                    "Failed to free request"
                );
            } else {
                tracing::debug!(
                    request_id = %request_id_str,
                    "free_request completed"
                );
            }
        })
        .await
    });

    match result {
        Ok(()) => QueryRouterResult::Ok,
        Err(_elapsed) => {
            tracing::warn!(
                request_id = %request_id_str,
                timeout_secs = BOOKKEEPING_TIMEOUT_SEC,
                "free_request timed out"
            );
            QueryRouterResult::ErrTimeout
        }
    }
}

/// Destroy router handles
///
/// # Safety
/// - `handle` must be a valid RouterHandles handle or null
/// - After this call, `handle` must not be used
#[unsafe(no_mangle)]
pub unsafe extern "C" fn destroy(handle: RouterHandlesPtr) {
    if !handle.is_null() {
        drop(unsafe { Box::from_raw(handle) });
    }
}

/// Free a routing result.
///
/// # Safety
/// - `result` must be a valid pointer to a CRoutingResult previously returned by route functions
#[unsafe(no_mangle)]
pub unsafe extern "C" fn free_routing_result(result: *mut CRoutingResult) {
    if result.is_null() {
        return;
    }

    let res = unsafe { &mut *result };

    // Free token IDs
    if !res.token_ids.is_null() && res.token_count > 0 {
        drop(unsafe {
            Box::from_raw(std::ptr::slice_from_raw_parts_mut(
                res.token_ids,
                res.token_count,
            ))
        });
        res.token_ids = ptr::null_mut();
        res.token_count = 0;
    }
}

/// Parse a JSON request string, apply the chat template, and tokenize.
/// Returns the token IDs on success, or a `QueryRouterResult` error code.
unsafe fn preprocess_request(
    handles: &RouterHandles,
    request_json: *const c_char,
) -> Result<Vec<u32>, QueryRouterResult> {
    let preprocessor = match &handles.preprocessor {
        Some(p) => p,
        None => {
            tracing::error!("Preprocessor not available");
            return Err(QueryRouterResult::ErrInitFailed);
        }
    };

    let json_str = match unsafe { CStr::from_ptr(request_json) }.to_str() {
        Ok(s) => s,
        Err(_) => return Err(QueryRouterResult::ErrInvalidParam),
    };

    let request: dynamo_llm::types::openai::chat_completions::NvCreateChatCompletionRequest =
        match serde_json::from_str(json_str) {
            Ok(req) => req,
            Err(e) => {
                tracing::error!(error = ?e, "Failed to parse request JSON");
                return Err(QueryRouterResult::ErrInvalidParam);
            }
        };

    let formatted_prompt = match preprocessor.apply_template(&request) {
        Ok(Some(prompt)) => prompt,
        Ok(None) => String::new(),
        Err(e) => {
            tracing::error!(error = ?e, "Failed to apply chat template");
            return Err(QueryRouterResult::ErrQueryFailed);
        }
    };

    let encoding = match preprocessor.tokenize(&formatted_prompt) {
        Ok(enc) => enc,
        Err(e) => {
            tracing::error!(error = ?e, "Failed to tokenize");
            return Err(QueryRouterResult::ErrQueryFailed);
        }
    };

    Ok(encoding.token_ids().to_vec())
}

/// Parse pods JSON into an optional set of allowed worker IDs.
unsafe fn parse_pods_filter(pods_json: *const c_char) -> Option<HashSet<WorkerId>> {
    if pods_json.is_null() {
        return None;
    }
    match unsafe { CStr::from_ptr(pods_json) }.to_str() {
        Ok(s) if !s.is_empty() => match serde_json::from_str::<Vec<serde_json::Value>>(s) {
            Ok(pods) => {
                let mut worker_ids = HashSet::new();
                for pod in &pods {
                    let pod_name = pod
                        .get("pod")
                        .and_then(|p| p.get("podName"))
                        .or_else(|| pod.get("podName"))
                        .and_then(|v| v.as_str());
                    if let Some(name) = pod_name {
                        let worker_id = hash_pod_name(name);
                        tracing::debug!(
                            pod_name = name,
                            worker_id = format!("{:x}", worker_id),
                            "Mapped EPP pod to worker_id"
                        );
                        worker_ids.insert(worker_id);
                    }
                }
                tracing::info!(
                    pod_count = pods.len(),
                    unique_worker_ids = worker_ids.len(),
                    "Parsed EPP pods into allowed_worker_ids filter"
                );
                if worker_ids.is_empty() {
                    None
                } else {
                    Some(worker_ids)
                }
            }
            Err(e) => {
                tracing::error!(error = ?e, "Failed to parse pods JSON");
                None
            }
        },
        _ => None,
    }
}

/// Write token IDs into a `CRoutingResult`, transferring ownership to the caller.
fn write_tokens_to_result(tokens: &[u32], out: &mut CRoutingResult) {
    let token_vec: Vec<u32> = tokens.to_vec();
    let mut tokens_boxed = token_vec.into_boxed_slice();
    out.token_ids = tokens_boxed.as_mut_ptr();
    out.token_count = tokens.len();
    std::mem::forget(tokens_boxed);
}

/// Route a request to select the best **prefill** worker only.
///
/// This is used in disaggregated mode where the EPP runs separate prefill and decode
/// scoring profiles.  It tokenizes the request and queries only the prefill router.
///
/// The returned `CRoutingResult` contains:
/// - `prefill_worker_id`: the selected prefill worker
/// - `decode_worker_id`: 0 (unused — decode is handled by `route_decode_request`)
/// - `is_disaggregated`: always true (this function is only called in disagg mode)
/// - `token_ids` / `token_count`: the tokenized request (caller must free via `free_routing_result`)
///
/// # Safety
/// - `handle` must be a valid RouterHandles handle
/// - `request_json` must be a valid null-terminated C string containing JSON
/// - `pods_json` must be a valid null-terminated C string containing JSON, or null
/// - `out_result` must be a valid pointer
#[unsafe(no_mangle)]
pub unsafe extern "C" fn route_prefill_request(
    handle: RouterHandlesPtr,
    request_json: *const c_char,
    pods_json: *const c_char,
    out_result: *mut CRoutingResult,
) -> QueryRouterResult {
    if handle.is_null() || request_json.is_null() || out_result.is_null() {
        return QueryRouterResult::ErrInvalidParam;
    }

    let handles = unsafe { &*handle };

    let tokens = match unsafe { preprocess_request(handles, request_json) } {
        Ok(t) => t,
        Err(code) => return code,
    };

    let allowed_worker_ids = unsafe { parse_pods_filter(pods_json) };

    let result = handles.runtime.secondary().block_on(async {
        let (prefill_worker_id, prefill_dp_rank) = handles
            .query_prefill_worker(&tokens, None, false, None, 0.0, allowed_worker_ids)
            .await?;

        let prefill_dp_rank = prefill_dp_rank.unwrap_or(u32::MAX);

        tracing::info!(
            prefill_worker_id = prefill_worker_id,
            prefill_dp_rank = prefill_dp_rank,
            token_count = tokens.len(),
            "Routed prefill request"
        );

        Ok((prefill_worker_id, prefill_dp_rank))
    });

    match result {
        Ok((prefill_worker_id, prefill_dp_rank)) => {
            let out = unsafe { &mut *out_result };
            *out = CRoutingResult::default();
            out.is_disaggregated = true;
            out.prefill_worker_id = prefill_worker_id;
            out.prefill_dp_rank = prefill_dp_rank;
            write_tokens_to_result(&tokens, out);
            QueryRouterResult::Ok
        }
        Err(code) => code,
    }
}

/// Route a request to select the best **decode** worker only.
///
/// This is used in both aggregated and disaggregated modes.
/// - When `is_disaggregated` is true, the decode router uses `overlap_score_weight=0`
///   (KV cache is being transferred from prefill, not reused locally).
/// - When `is_disaggregated` is false, normal KV-aware scoring is used.
///
/// The returned `CRoutingResult` contains:
/// - `decode_worker_id`: the selected decode worker
/// - `prefill_worker_id`: 0 (unused — prefill is handled by `route_prefill_request`)
/// - `is_disaggregated`: mirrors the input parameter
/// - `token_ids` / `token_count`: the tokenized request (caller must free via `free_routing_result`)
///
/// # Safety
/// - `handle` must be a valid RouterHandles handle
/// - `request_json` must be a valid null-terminated C string containing JSON
/// - `pods_json` must be a valid null-terminated C string containing JSON, or null
/// - `out_result` must be a valid pointer
#[unsafe(no_mangle)]
pub unsafe extern "C" fn route_decode_request(
    handle: RouterHandlesPtr,
    request_json: *const c_char,
    pods_json: *const c_char,
    is_disaggregated: bool,
    out_result: *mut CRoutingResult,
) -> QueryRouterResult {
    if handle.is_null() || request_json.is_null() || out_result.is_null() {
        return QueryRouterResult::ErrInvalidParam;
    }

    let handles = unsafe { &*handle };

    let tokens = match unsafe { preprocess_request(handles, request_json) } {
        Ok(t) => t,
        Err(code) => return code,
    };

    let allowed_worker_ids = unsafe { parse_pods_filter(pods_json) };

    let result = handles.runtime.secondary().block_on(async {
        let (decode_worker, _overlap_blocks) = handles
            .query_decode_worker(&tokens, is_disaggregated, allowed_worker_ids)
            .await?;

        tracing::info!(
            is_disaggregated = is_disaggregated,
            decode_worker_id = decode_worker.worker_id,
            decode_dp_rank = decode_worker.dp_rank,
            token_count = tokens.len(),
            "Routed decode request"
        );

        Ok(decode_worker)
    });

    match result {
        Ok(decode_worker) => {
            let out = unsafe { &mut *out_result };
            *out = CRoutingResult::default();
            out.is_disaggregated = is_disaggregated;
            out.decode_worker_id = decode_worker.worker_id;
            out.decode_dp_rank = decode_worker.dp_rank;
            write_tokens_to_result(&tokens, out);
            QueryRouterResult::Ok
        }
        Err(code) => code,
    }
}

/// Initialize the preprocessor and fetch the model card used for routing.
///
/// Waits for discovery to sync (model card must be available for tokenization),
/// then creates the preprocessor from the model card. Router settings are
/// derived directly from the returned card by the caller.
async fn init_preprocessor(
    drt: &DistributedRuntime,
    target_namespace: &str,
) -> anyhow::Result<DiscoveredModelBootstrap> {
    let instance_count = wait_for_discovery_sync(drt).await;
    if instance_count == 0 {
        anyhow::bail!("Discovery sync failed: no worker instances found. Is the backend running?");
    }
    tracing::info!(
        "Discovery sync complete, {} worker(s) found",
        instance_count
    );

    // Retry fetching the preprocessor: model card metadata may arrive after
    // worker endpoints are registered.
    let bootstrap = loop {
        match fetch_preprocessor_from_discovery(drt, target_namespace).await {
            Ok(result) => break result,
            Err(e) => {
                tracing::warn!(
                    error = %e,
                    target_namespace,
                    "Model card not available yet, retrying in 5s..."
                );
                tokio::time::sleep(std::time::Duration::from_secs(5)).await;
            }
        }
    };

    tracing::info!(
        kv_cache_block_size = bootstrap.card.kv_cache_block_size,
        model_name = %bootstrap.card.display_name,
        actual_namespace = %bootstrap.actual_namespace,
        enable_eagle = bootstrap.card.runtime_config.enable_eagle,
        "Preprocessor initialized from model card"
    );

    Ok(bootstrap)
}

/// Spawn a background task that watches discovery for a prefill-only worker
/// in the given namespace. When found, sends its endpoint through `tx` to
/// activate the PrefillRouter. Polls every 1 second until a match is found.
fn spawn_prefill_discovery_watcher(
    drt: DistributedRuntime,
    target_namespace: String,
    tx: tokio::sync::oneshot::Sender<dynamo_runtime::component::Endpoint>,
) {
    use dynamo_llm::model_card::ModelDeploymentCard;
    use dynamo_runtime::discovery::DiscoveryInstance;

    tokio::spawn(async move {
        let discovery = drt.discovery();
        tracing::info!(
            namespace = target_namespace,
            "Background task: watching for prefill workers to register..."
        );

        loop {
            if let Ok(instances) = discovery.list(DiscoveryQuery::AllModels).await {
                for instance in instances {
                    if let DiscoveryInstance::Model {
                        namespace,
                        component,
                        endpoint,
                        ..
                    } = &instance
                    {
                        if namespace != &target_namespace {
                            continue;
                        }

                        let card = match instance.deserialize_model::<ModelDeploymentCard>() {
                            Ok(card) => card,
                            Err(_) => continue,
                        };

                        if !card.model_type.supports_prefill()
                            || card.model_type.supports_chat()
                            || card.model_type.supports_completions()
                        {
                            continue;
                        }

                        tracing::info!(
                            model_name = card.name(),
                            namespace = namespace.as_str(),
                            "Prefill worker discovered, activating PrefillRouter"
                        );

                        if let Ok(ns) = drt.namespace(namespace)
                            && let Ok(comp) = ns.component(component)
                        {
                            let ep = comp.endpoint(endpoint);
                            if tx.send(ep).is_err() {
                                tracing::debug!("PrefillRouter activation channel already closed");
                            }
                            return;
                        }
                    }
                }
            }

            tokio::time::sleep(Duration::from_secs(1)).await;
        }
    });
}

/// Fetch model card via discovery and create preprocessor.
///
/// This function:
/// 1. Lists all models via discovery
/// 2. Finds the first model in the target namespace (decode workers only)
/// 3. Downloads the model config (tokenizer files) if needed
/// 4. Creates an OpenAIPreprocessor from the model card
/// 5. Returns the preprocessor, the model card, and the resolved worker namespace
async fn fetch_preprocessor_from_discovery(
    drt: &DistributedRuntime,
    target_namespace: &str,
) -> anyhow::Result<DiscoveredModelBootstrap> {
    use dynamo_runtime::discovery::DiscoveryInstance;

    let discovery = drt.discovery();

    // List all models
    let instances = discovery.list(DiscoveryQuery::AllModels).await?;

    // Find first model card in the target namespace (decode workers only).
    // Use prefix matching because workers may append a rolling-update hash
    // suffix to the base namespace (e.g. "ns-dgd-58908edc" vs "ns-dgd").
    let mut model_card: Option<(ModelDeploymentCard, String)> = None;

    for instance in instances {
        if let DiscoveryInstance::Model { namespace, .. } = &instance {
            if !namespace.starts_with(target_namespace) {
                continue;
            }

            let actual_namespace = namespace.clone();
            match instance.deserialize_model::<ModelDeploymentCard>() {
                Ok(card) => {
                    // Skip prefill-only workers, we want decode workers for routing
                    if card.model_type.supports_prefill()
                        && !card.model_type.supports_chat()
                        && !card.model_type.supports_completions()
                    {
                        continue;
                    }
                    model_card = Some((card, actual_namespace));
                    break;
                }
                Err(e) => {
                    tracing::debug!(error = %e, "Failed to deserialize model card, skipping");
                    continue;
                }
            }
        }
    }

    let (mut card, actual_namespace) = model_card.ok_or_else(|| {
        anyhow::anyhow!(
            "No model found in namespace '{}' via discovery",
            target_namespace
        )
    })?;

    tracing::info!(
        model_name = %card.display_name,
        kv_cache_block_size = card.kv_cache_block_size,
        actual_namespace = %actual_namespace,
        enable_eagle = card.runtime_config.enable_eagle,
        "Found model card via discovery"
    );

    // Download config (tokenizer files) if not local
    card.download_config().await?;

    // Create preprocessor
    let preprocessor = OpenAIPreprocessor::new(card.clone())?;
    Ok(DiscoveredModelBootstrap {
        preprocessor,
        card,
        actual_namespace,
    })
}
