// SPDX-FileCopyrightText: Copyright (c) 2024-2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
// SPDX-License-Identifier: Apache-2.0
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

pub use crate::component::Component;
use crate::transports::nats::DRTNatsPrometheusMetrics;
use crate::{
    component::{self, ComponentBuilder, Endpoint, InstanceSource, Namespace},
    discovery::DiscoveryClient,
    metrics::MetricsRegistry,
    service::ServiceClient,
    transports::{etcd, nats, tcp},
    ErrorContext, RuntimeCallback,
};

use super::{error, Arc, DistributedRuntime, OnceCell, Result, Runtime, SystemHealth, Weak, OK};
use std::sync::OnceLock;

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

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

    fn parent_hierarchy(&self) -> Vec<String> {
        vec![] // drt is the root, so no parent hierarchy
    }
}

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

        let runtime_clone = runtime.clone();

        let etcd_client = if is_static {
            None
        } else {
            Some(etcd::Client::new(etcd_config.clone(), runtime_clone).await?)
        };

        let nats_client = 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(std::sync::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();

        let distributed_runtime = Self {
            runtime,
            etcd_client,
            nats_client,
            tcp_server: Arc::new(OnceCell::new()),
            system_status_server: Arc::new(OnceLock::new()),
            component_registry: component::Registry::new(),
            is_static,
            instance_sources: Arc::new(Mutex::new(HashMap::new())),
            hierarchy_to_metricsregistry: Arc::new(std::sync::RwLock::new(HashMap::<
                String,
                crate::MetricsRegistryEntry,
            >::new())),
            system_health,
        };

        let sys_nats_metrics = DRTNatsPrometheusMetrics::new(
            &distributed_runtime,
            nats_client_for_metrics.client().clone(),
        )?;
        let mut drt_hierarchies = distributed_runtime.parent_hierarchy();
        drt_hierarchies.push(distributed_runtime.hierarchy());
        // Register a callback to update NATS client metrics
        let nats_metrics_callback = Arc::new({
            let sys_nats_metrics_clone = sys_nats_metrics.clone();
            move || {
                sys_nats_metrics_clone.set_from_client_stats();
                Ok(())
            }
        });
        distributed_runtime.register_metrics_callback(drt_hierarchies, nats_metrics_callback);

        // Start system status server if enabled
        if let Some(cancel_token) = cancel_token {
            let host = config.system_host.clone();
            let port = config.system_port;

            // Start system status server (it spawns its own task 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 {
            tracing::debug!("Health and system status server is disabled via DYN_SYSTEM_ENABLED");
        }

        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()
    }

    /// The etcd lease all our components will be attached to.
    /// Not available for static workers.
    pub fn primary_lease(&self) -> Option<etcd::Lease> {
        self.etcd_client.as_ref().map(|c| c.primary_lease())
    }

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

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

    // /// Create a [`Component`]
    // pub fn component(
    //     &self,
    //     name: impl Into<String>,
    //     namespace: impl Into<String>,
    // ) -> Result<Component> {
    //     Ok(ComponentBuilder::from_runtime(self.clone())
    //         .name(name.into())
    //         .namespace(namespace.into())
    //         .build()?)
    // }

    pub(crate) fn discovery_client(&self, namespace: impl Into<String>) -> DiscoveryClient {
        DiscoveryClient::new(
            namespace.into(),
            self.etcd_client
                .clone()
                .expect("Attempt to get discovery_client on static DistributedRuntime"),
        )
    }

    pub(crate) fn service_client(&self) -> ServiceClient {
        ServiceClient::new(self.nats_client.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(server)
            })
            .await?
            .clone())
    }

    pub fn nats_client(&self) -> nats::Client {
        self.nats_client.clone()
    }

    /// 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
    pub fn etcd_client(&self) -> Option<etcd::Client> {
        self.etcd_client.clone()
    }

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

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

    /// Add a Prometheus metric to a specific hierarchy's registry
    pub fn add_prometheus_metric(
        &self,
        hierarchy: &str,
        metric_name: &str,
        prometheus_metric: Box<dyn prometheus::core::Collector>,
    ) -> anyhow::Result<()> {
        let mut registries = self.hierarchy_to_metricsregistry.write().unwrap();
        let entry = registries.entry(hierarchy.to_string()).or_default();

        // If a metric with this name already exists for the hierarchy, warn and skip registration
        if entry.has_metric_named(metric_name) {
            tracing::warn!(
                hierarchy = ?hierarchy,
                metric_name = ?metric_name,
                "Metric already exists in registry; skipping registration"
            );
            return Ok(());
        }

        // Try to register the metric and provide better error information
        match entry.prometheus_registry.register(prometheus_metric) {
            Ok(_) => Ok(()),
            Err(e) => {
                let error_msg = e.to_string();
                tracing::error!(
                    hierarchy = ?hierarchy,
                    error = ?error_msg,
                    metric_name = ?metric_name,
                    "Metric registration failed"
                );
                Err(e.into())
            }
        }
    }

    /// Add a callback function to metrics registries for the given hierarchies
    pub fn register_metrics_callback(&self, hierarchies: Vec<String>, callback: RuntimeCallback) {
        let mut registries = self.hierarchy_to_metricsregistry.write().unwrap();
        for hierarchy in hierarchies {
            registries
                .entry(hierarchy)
                .or_default()
                .add_callback(callback.clone());
        }
    }

    /// Execute all callbacks for a given hierarchy key and return their results
    pub fn execute_metrics_callbacks(&self, hierarchy: &str) -> Vec<anyhow::Result<()>> {
        // Clone callbacks while holding read lock (fast operation)
        let callbacks = {
            let registries = self.hierarchy_to_metricsregistry.read().unwrap();
            registries
                .get(hierarchy)
                .map(|entry| entry.runtime_callbacks.clone())
        }; // Read lock released here

        // Execute callbacks without holding the lock
        match callbacks {
            Some(callbacks) => callbacks.iter().map(|callback| callback()).collect(),
            None => Vec::new(),
        }
    }

    /// Get all registered hierarchy keys. Private because it is only used for testing.
    fn get_registered_hierarchies(&self) -> Vec<String> {
        let registries = self.hierarchy_to_metricsregistry.read().unwrap();
        registries.keys().cloned().collect()
    }
}

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

impl DistributedConfig {
    pub fn from_settings(is_static: bool) -> DistributedConfig {
        DistributedConfig {
            etcd_config: etcd::ClientOptions::default(),
            nats_config: nats::ClientOptions::default(),
            is_static,
        }
    }

    pub fn for_cli() -> DistributedConfig {
        let mut config = DistributedConfig {
            etcd_config: etcd::ClientOptions::default(),
            nats_config: nats::ClientOptions::default(),
            is_static: false,
        };

        config.etcd_config.attach_lease = false;

        config
    }
}