// SPDX-FileCopyrightText: Copyright (c) 2024-2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
// SPDX-License-Identifier: Apache-2.0

use crate::component::Component;
use crate::pipeline::PipelineError;
use crate::storage::key_value_store::{
    EtcdStore, KeyValueStore, KeyValueStoreEnum, KeyValueStoreManager, KeyValueStoreSelect,
    MemoryStore,
};
use crate::transports::nats::DRTNatsClientPrometheusMetrics;
use crate::{
    component::{self, ComponentBuilder, Endpoint, InstanceSource, Namespace},
    discovery::Discovery,
    metrics::PrometheusUpdateCallback,
    metrics::{MetricsHierarchy, MetricsRegistry},
    service::ServiceClient,
    transports::{etcd, nats, tcp},
};
use crate::{discovery, system_status_server, transports};

use super::utils::GracefulShutdownTracker;
use crate::SystemHealth;
use crate::runtime::Runtime;

use async_once_cell::OnceCell;
use std::sync::{Arc, OnceLock, Weak};

use anyhow::Result;
use derive_getters::Dissolve;
use figment::error;
use std::collections::HashMap;
use tokio::sync::Mutex;
use tokio_util::sync::CancellationToken;

/// Distributed [Runtime] which provides access to shared resources across the cluster, this includes
/// communication protocols and transports.
#[derive(Clone)]
pub struct DistributedRuntime {
    // local runtime
    runtime: Runtime,

    // we might consider a unifed transport manager here
    etcd_client: Option<transports::etcd::Client>,
    nats_client: Option<transports::nats::Client>,
    store: KeyValueStoreManager,
    tcp_server: Arc<OnceCell<Arc<transports::tcp::server::TcpStreamServer>>>,
    system_status_server: Arc<OnceLock<Arc<system_status_server::SystemStatusServerInfo>>>,

    // Service discovery client
    discovery_client: Arc<dyn discovery::Discovery>,

    // local registry for components
    // the registry allows us to use share runtime resources across instances of the same component object.
    // take for example two instances of a client to the same remote component. The registry allows us to use
    // a single endpoint watcher for both clients, this keeps the number background tasking watching specific
    // paths in etcd to a minimum.
    component_registry: component::Registry,

    // Will only have static components that are not discoverable via etcd, they must be know at
    // startup. Will not start etcd.
    is_static: bool,

    instance_sources: Arc<tokio::sync::Mutex<HashMap<Endpoint, Weak<InstanceSource>>>>,

    // Health Status
    system_health: Arc<parking_lot::Mutex<SystemHealth>>,

    // This hierarchy's own metrics registry
    metrics_registry: MetricsRegistry,
}

impl MetricsHierarchy for DistributedRuntime {
    fn basename(&self) -> String {
        "".to_string() // drt has no basename. Basename only begins with the Namespace.
    }

    fn parent_hierarchies(&self) -> Vec<&dyn MetricsHierarchy> {
        vec![] // drt is the root, so no parent hierarchies
    }

    fn get_metrics_registry(&self) -> &MetricsRegistry {
        &self.metrics_registry
    }
}

impl std::fmt::Debug for DistributedRuntime {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "DistributedRuntime")
    }
}

impl DistributedRuntime {
    pub async fn new(runtime: Runtime, config: DistributedConfig) -> Result<Self> {
        let (selected_kv_store, nats_config, is_static) = config.dissolve();

        let runtime_clone = runtime.clone();

        let (etcd_client, store) = match (is_static, selected_kv_store) {
            (false, KeyValueStoreSelect::Etcd(etcd_config)) => {
                let etcd_client = etcd::Client::new(*etcd_config, runtime_clone).await.inspect_err(|err|
                    // The returned error doesn't show because of a dropped runtime error, so
                    // log it first.
                    tracing::error!(%err, "Could not connect to etcd. Pass `--store-kv ..` to use a different backend or start etcd."))?;
                let store = KeyValueStoreManager::etcd(etcd_client.clone());
                (Some(etcd_client), store)
            }
            (false, KeyValueStoreSelect::File(root)) => (None, KeyValueStoreManager::file(root)),
            (true, _) | (false, KeyValueStoreSelect::Memory) => {
                (None, KeyValueStoreManager::memory())
            }
        };

        let nats_client = Some(nats_config.clone().connect().await?);

        // Start system status server for health and metrics if enabled in configuration
        let config = crate::config::RuntimeConfig::from_settings().unwrap_or_default();
        // IMPORTANT: We must extract cancel_token from runtime BEFORE moving runtime into the struct below.
        // This is because after moving, runtime is no longer accessible in this scope (ownership rules).
        let cancel_token = if config.system_server_enabled() {
            Some(runtime.clone().child_token())
        } else {
            None
        };
        let starting_health_status = config.starting_health_status.clone();
        let use_endpoint_health_status = config.use_endpoint_health_status.clone();
        let health_endpoint_path = config.system_health_path.clone();
        let live_endpoint_path = config.system_live_path.clone();
        let system_health = Arc::new(parking_lot::Mutex::new(SystemHealth::new(
            starting_health_status,
            use_endpoint_health_status,
            health_endpoint_path,
            live_endpoint_path,
        )));

        let nats_client_for_metrics = nats_client.clone();

        // Initialize discovery backed by KV store
        let discovery_client = {
            use crate::discovery::KVStoreDiscovery;
            Arc::new(KVStoreDiscovery::new(
                store.clone(),
                runtime.primary_token(),
            )) as Arc<dyn Discovery>
        };

        let distributed_runtime = Self {
            runtime,
            etcd_client,
            store,
            nats_client,
            tcp_server: Arc::new(OnceCell::new()),
            system_status_server: Arc::new(OnceLock::new()),
            discovery_client,
            component_registry: component::Registry::new(),
            is_static,
            instance_sources: Arc::new(Mutex::new(HashMap::new())),
            metrics_registry: crate::MetricsRegistry::new(),
            system_health,
        };

        if let Some(nats_client_for_metrics) = nats_client_for_metrics {
            let nats_client_metrics = DRTNatsClientPrometheusMetrics::new(
                &distributed_runtime,
                nats_client_for_metrics.client().clone(),
            )?;
            // Register a callback to update NATS client metrics on the DRT's metrics registry
            let nats_client_callback = Arc::new({
                let nats_client_clone = nats_client_metrics.clone();
                move || {
                    nats_client_clone.set_from_client_stats();
                    Ok(())
                }
            });
            distributed_runtime
                .metrics_registry
                .add_update_callback(nats_client_callback);
        }

        // Initialize the uptime gauge in SystemHealth
        distributed_runtime
            .system_health
            .lock()
            .initialize_uptime_gauge(&distributed_runtime)?;

        // Handle system status server initialization
        if let Some(cancel_token) = cancel_token {
            // System server is enabled - start both the state and HTTP server
            let host = config.system_host.clone();
            let port = config.system_port as u16;

            // Start system status server (it creates SystemStatusState internally)
            match crate::system_status_server::spawn_system_status_server(
                &host,
                port,
                cancel_token,
                Arc::new(distributed_runtime.clone()),
            )
            .await
            {
                Ok((addr, handle)) => {
                    tracing::info!("System status server started successfully on {}", addr);

                    // Store system status server information
                    let system_status_server_info =
                        crate::system_status_server::SystemStatusServerInfo::new(
                            addr,
                            Some(handle),
                        );

                    // Initialize the system_status_server field
                    distributed_runtime
                        .system_status_server
                        .set(Arc::new(system_status_server_info))
                        .expect("System status server info should only be set once");
                }
                Err(e) => {
                    tracing::error!("System status server startup failed: {}", e);
                }
            }
        } else {
            // System server HTTP is disabled, but uptime metrics are still being tracked via SystemHealth
            tracing::debug!(
                "System status server HTTP endpoints disabled, but uptime metrics are being tracked"
            );
        }

        // Start health check manager if enabled
        if config.health_check_enabled {
            let health_check_config = crate::health_check::HealthCheckConfig {
                canary_wait_time: std::time::Duration::from_secs(config.canary_wait_time_secs),
                request_timeout: std::time::Duration::from_secs(
                    config.health_check_request_timeout_secs,
                ),
            };

            // Start the health check manager (spawns per-endpoint monitoring tasks)
            match crate::health_check::start_health_check_manager(
                distributed_runtime.clone(),
                Some(health_check_config),
            )
            .await
            {
                Ok(()) => tracing::info!(
                    "Health check manager started (canary_wait_time: {}s, request_timeout: {}s)",
                    config.canary_wait_time_secs,
                    config.health_check_request_timeout_secs
                ),
                Err(e) => tracing::error!("Health check manager failed to start: {}", e),
            }
        }

        Ok(distributed_runtime)
    }

    pub async fn from_settings(runtime: Runtime) -> Result<Self> {
        let config = DistributedConfig::from_settings(false);
        Self::new(runtime, config).await
    }

    // Call this if you are using static workers that do not need etcd-based discovery.
    pub async fn from_settings_without_discovery(runtime: Runtime) -> Result<Self> {
        let config = DistributedConfig::from_settings(true);
        Self::new(runtime, config).await
    }

    pub fn runtime(&self) -> &Runtime {
        &self.runtime
    }

    pub fn primary_token(&self) -> CancellationToken {
        self.runtime.primary_token()
    }

    // TODO: Don't hand out pointers, instead have methods to use the registry in friendly ways
    // (without being aware of async locks and so on)
    pub fn component_registry(&self) -> &component::Registry {
        &self.component_registry
    }

    // TODO: Don't hand out pointers, instead provide system health related services.
    pub fn system_health(&self) -> Arc<parking_lot::Mutex<SystemHealth>> {
        self.system_health.clone()
    }

    pub fn connection_id(&self) -> u64 {
        self.store.connection_id()
    }

    pub fn shutdown(&self) {
        self.runtime.shutdown();
        self.store.shutdown();
    }

    /// Create a [`Namespace`]
    pub fn namespace(&self, name: impl Into<String>) -> Result<Namespace> {
        Namespace::new(self.clone(), name.into(), self.is_static)
    }

    /// Returns the discovery interface for service registration and discovery
    pub fn discovery(&self) -> Arc<dyn Discovery> {
        self.discovery_client.clone()
    }

    pub(crate) fn service_client(&self) -> Option<ServiceClient> {
        self.nats_client().map(|nc| ServiceClient::new(nc.clone()))
    }

    pub async fn tcp_server(&self) -> Result<Arc<tcp::server::TcpStreamServer>> {
        Ok(self
            .tcp_server
            .get_or_try_init(async move {
                let options = tcp::server::ServerOptions::default();
                let server = tcp::server::TcpStreamServer::new(options).await?;
                Ok::<_, PipelineError>(server)
            })
            .await?
            .clone())
    }

    pub fn nats_client(&self) -> Option<&nats::Client> {
        self.nats_client.as_ref()
    }

    /// Get system status server information if available
    pub fn system_status_server_info(
        &self,
    ) -> Option<Arc<crate::system_status_server::SystemStatusServerInfo>> {
        self.system_status_server.get().cloned()
    }

    // todo(ryan): deprecate this as we move to Discovery traits and Component Identifiers
    //
    // Try to use `store()` instead of this. Only use this if you have not been able to migrate
    // yet, or if you require etcd-specific features like distributed locking (rare).
    pub fn etcd_client(&self) -> Option<etcd::Client> {
        self.etcd_client.clone()
    }

    /// An interface to store things. Will eventually replace `etcd_client`.
    /// Currently does key-value, but will grow to include whatever we need to store.
    pub fn store(&self) -> &KeyValueStoreManager {
        &self.store
    }

    pub fn child_token(&self) -> CancellationToken {
        self.runtime.child_token()
    }

    pub(crate) fn graceful_shutdown_tracker(&self) -> Arc<GracefulShutdownTracker> {
        self.runtime.graceful_shutdown_tracker()
    }

    pub fn instance_sources(&self) -> Arc<Mutex<HashMap<Endpoint, Weak<InstanceSource>>>> {
        self.instance_sources.clone()
    }
}

#[derive(Dissolve)]
pub struct DistributedConfig {
    pub store_backend: KeyValueStoreSelect,
    pub nats_config: nats::ClientOptions,
    pub is_static: bool,
}

impl DistributedConfig {
    pub fn from_settings(is_static: bool) -> DistributedConfig {
        DistributedConfig {
            store_backend: KeyValueStoreSelect::Etcd(Box::default()),
            nats_config: nats::ClientOptions::default(),
            is_static,
        }
    }

    pub fn for_cli() -> DistributedConfig {
        let etcd_config = etcd::ClientOptions {
            attach_lease: false,
            ..Default::default()
        };
        DistributedConfig {
            store_backend: KeyValueStoreSelect::Etcd(Box::new(etcd_config)),
            nats_config: nats::ClientOptions::default(),
            is_static: false,
        }
    }
}

pub mod distributed_test_utils {
    //! Common test helper functions for DistributedRuntime tests
    // TODO: Use in-memory DistributedRuntime for tests instead of full runtime when available.

    /// Helper function to create a DRT instance for integration-only tests.
    /// Uses from_current to leverage existing tokio runtime
    /// Note: Settings are read from environment variables inside DistributedRuntime::from_settings_without_discovery
    #[cfg(feature = "integration")]
    pub async fn create_test_drt_async() -> crate::DistributedRuntime {
        let rt = crate::Runtime::from_current().unwrap();
        crate::DistributedRuntime::from_settings_without_discovery(rt)
            .await
            .unwrap()
    }
}

#[cfg(all(test, feature = "integration"))]
mod tests {
    use super::distributed_test_utils::create_test_drt_async;

    #[tokio::test]
    async fn test_drt_uptime_after_delay_system_disabled() {
        // Test uptime with system status server disabled
        temp_env::async_with_vars([("DYN_SYSTEM_ENABLED", Some("false"))], async {
            // Start a DRT
            let drt = create_test_drt_async().await;

            // Wait 50ms
            tokio::time::sleep(tokio::time::Duration::from_millis(50)).await;

            // Check that uptime is 50+ ms
            let uptime = drt.system_health.lock().uptime();
            assert!(
                uptime >= std::time::Duration::from_millis(50),
                "Expected uptime to be at least 50ms, but got {:?}",
                uptime
            );

            println!(
                "✓ DRT uptime test passed (system disabled): uptime = {:?}",
                uptime
            );
        })
        .await;
    }

    #[tokio::test]
    async fn test_drt_uptime_after_delay_system_enabled() {
        // Test uptime with system status server enabled
        temp_env::async_with_vars([("DYN_SYSTEM_PORT", Some("8081"))], async {
            // Start a DRT
            let drt = create_test_drt_async().await;

            // Wait 50ms
            tokio::time::sleep(tokio::time::Duration::from_millis(50)).await;

            // Check that uptime is 50+ ms
            let uptime = drt.system_health.lock().uptime();
            assert!(
                uptime >= std::time::Duration::from_millis(50),
                "Expected uptime to be at least 50ms, but got {:?}",
                uptime
            );

            println!(
                "✓ DRT uptime test passed (system enabled): uptime = {:?}",
                uptime
            );
        })
        .await;
    }
}
