//! FlashDNS authoritative DNS server binary

use flashdns_api::{RecordServiceServer, ZoneServiceServer};
use flashdns_server::{
    config::{MetadataBackend, ServerConfig},
    dns::DnsHandler,
    metadata::DnsMetadataStore,
    RecordServiceImpl,
    ZoneServiceImpl,
};
use chainfire_client::Client as ChainFireClient;
use iam_service_auth::AuthService;
use metrics_exporter_prometheus::PrometheusBuilder;
use std::sync::Arc;
use tonic::transport::{Certificate, Identity, Server, ServerTlsConfig};
use tonic::{Request, Status};
use tonic_health::server::health_reporter;
use tracing_subscriber::EnvFilter;
use anyhow::Result;
use clap::Parser;
use std::path::PathBuf;
use std::time::{SystemTime, UNIX_EPOCH};

use config::{Config as Cfg, Environment, File, FileFormat};

/// Command-line arguments for FlashDNS server.
#[derive(Parser, Debug)]
#[command(author, version, about, long_about = None)]
struct CliArgs {
    /// Configuration file path
    #[arg(short, long, default_value = "flashdns.toml")]
    config: PathBuf,

    /// gRPC management API address (overrides config)
    #[arg(long)]
    grpc_addr: Option<String>,

    /// DNS UDP address (overrides config)
    #[arg(long)]
    dns_addr: Option<String>,

    /// ChainFire endpoint for cluster coordination (overrides config)
    #[arg(long, env = "FLASHDNS_CHAINFIRE_ENDPOINT")]
    chainfire_endpoint: Option<String>,

    /// FlareDB endpoint for metadata and tenant data storage (overrides config)
    #[arg(long, env = "FLASHDNS_FLAREDB_ENDPOINT")]
    flaredb_endpoint: Option<String>,

    /// Metadata backend (flaredb, postgres, sqlite)
    #[arg(long, env = "FLASHDNS_METADATA_BACKEND")]
    metadata_backend: Option<String>,

    /// SQL database URL for metadata (required for postgres/sqlite backend)
    #[arg(long, env = "FLASHDNS_METADATA_DATABASE_URL")]
    metadata_database_url: Option<String>,

    /// Run in single-node mode (required when metadata backend is SQLite)
    #[arg(long, env = "FLASHDNS_SINGLE_NODE")]
    single_node: bool,

    /// Log level (overrides config)
    #[arg(short, long)]
    log_level: Option<String>,

    /// Metrics port for Prometheus scraping
    #[arg(long, default_value = "9097")]
    metrics_port: u16,
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let cli_args = CliArgs::parse();

    // Load configuration using config-rs
    let mut settings = Cfg::builder()
        // Layer 1: Application defaults. Serialize ServerConfig::default() into TOML.
        .add_source(File::from_str(
            toml::to_string(&ServerConfig::default())?.as_str(),
            FileFormat::Toml,
        ))
        // Layer 2: Environment variables (e.g., FLASHDNS_GRPC_ADDR, FLASHDNS_LOG_LEVEL)
        .add_source(
            Environment::with_prefix("FLASHDNS")
                .separator("__") // Use double underscore for nested fields
        );

    // Layer 3: Configuration file (if specified)
    if cli_args.config.exists() {
        tracing::info!("Loading config from file: {}", cli_args.config.display());
        settings = settings.add_source(File::from(cli_args.config.as_path()));
    } else {
        tracing::info!("Config file not found, using defaults and environment variables.");
    }

    let mut config: ServerConfig = settings
        .build()?
        .try_deserialize()
        .map_err(|e| anyhow::anyhow!("Failed to load configuration: {}", e))?;

    // Apply command line overrides (Layer 4: highest precedence)
    if let Some(grpc_addr_str) = cli_args.grpc_addr {
        config.grpc_addr = grpc_addr_str.parse()?;
    }
    if let Some(dns_addr_str) = cli_args.dns_addr {
        config.dns_addr = dns_addr_str.parse()?;
    }
    if let Some(chainfire_endpoint) = cli_args.chainfire_endpoint {
        config.chainfire_endpoint = Some(chainfire_endpoint);
    }
    if let Some(flaredb_endpoint) = cli_args.flaredb_endpoint {
        config.flaredb_endpoint = Some(flaredb_endpoint);
    }
    if let Some(metadata_backend) = cli_args.metadata_backend {
        config.metadata_backend = parse_metadata_backend(&metadata_backend)?;
    }
    if let Some(metadata_database_url) = cli_args.metadata_database_url {
        config.metadata_database_url = Some(metadata_database_url);
    }
    if cli_args.single_node {
        config.single_node = true;
    }
    if let Some(log_level) = cli_args.log_level {
        config.log_level = log_level;
    }

    // Initialize tracing
    tracing_subscriber::fmt()
        .with_env_filter(
            EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new(&config.log_level)),
        )
        .init();

    tracing::info!("Starting FlashDNS server");
    tracing::info!("  gRPC: {}", config.grpc_addr);
    tracing::info!("  DNS UDP: {}", config.dns_addr);

    // Initialize Prometheus metrics exporter
    let metrics_addr = format!("0.0.0.0:{}", cli_args.metrics_port);
    let builder = PrometheusBuilder::new();
    builder
        .with_http_listener(metrics_addr.parse::<std::net::SocketAddr>()?)
        .install()
        .expect("Failed to install Prometheus metrics exporter");

    tracing::info!(
        "Prometheus metrics available at http://{}/metrics",
        metrics_addr
    );

    if let Some(endpoint) = &config.chainfire_endpoint {
        tracing::info!("  Cluster coordination: ChainFire at {}", endpoint);
        let endpoint = endpoint.clone();
        let addr = config.grpc_addr.to_string();
        tokio::spawn(async move {
            if let Err(error) = register_chainfire_membership(&endpoint, "flashdns", addr).await {
                tracing::warn!(error = %error, "Failed to register ChainFire membership");
            }
        });
    }

    // Create metadata store from explicitly selected backend.
    let metadata = match config.metadata_backend {
        MetadataBackend::FlareDb => {
            if let Some(endpoint) = config.flaredb_endpoint.as_deref() {
                tracing::info!("  Metadata backend: FlareDB @ {}", endpoint);
            } else {
                tracing::info!("  Metadata backend: FlareDB");
            }
            Arc::new(
                DnsMetadataStore::new_flaredb_with_pd(
                    config.flaredb_endpoint.clone(),
                    config.chainfire_endpoint.clone(),
                )
                    .await
                    .map_err(|e| anyhow::anyhow!("Failed to initialize FlareDB metadata store: {}", e))?,
            )
        }
        MetadataBackend::Postgres | MetadataBackend::Sqlite => {
            let database_url = config
                .metadata_database_url
                .as_deref()
                .ok_or_else(|| {
                    anyhow::anyhow!(
                        "metadata_database_url is required when metadata_backend={} (env: FLASHDNS_METADATA_DATABASE_URL)",
                        metadata_backend_name(config.metadata_backend)
                    )
                })?;
            ensure_sql_backend_matches_url(config.metadata_backend, database_url)?;
            tracing::info!(
                "  Metadata backend: {} @ {}",
                metadata_backend_name(config.metadata_backend),
                database_url
            );
            Arc::new(
                DnsMetadataStore::new_sql(database_url, config.single_node)
                    .await
                    .map_err(|e| anyhow::anyhow!("Failed to initialize SQL metadata store: {}", e))?,
            )
        }
    };

    // Initialize IAM authentication service
    tracing::info!("Connecting to IAM server at {}", config.auth.iam_server_addr);
    let auth_service = AuthService::new(&config.auth.iam_server_addr)
        .await
        .map_err(|e| anyhow::anyhow!("Failed to connect to IAM server: {}", e))?;
    let auth_service = Arc::new(auth_service);

    // Dedicated runtime for auth interceptors to avoid blocking the main async runtime
    let auth_runtime = Arc::new(tokio::runtime::Runtime::new()?);
    let make_interceptor = |auth: Arc<AuthService>| {
        let rt = auth_runtime.clone();
        move |mut req: Request<()>| -> Result<Request<()>, Status> {
            let auth = auth.clone();
            tokio::task::block_in_place(|| {
                rt.block_on(async move {
                    let tenant_context = auth.authenticate_request(&req).await?;
                    req.extensions_mut().insert(tenant_context);
                    Ok(req)
                })
            })
        }
    };

    // Create gRPC services
    let zone_service = ZoneServiceImpl::new(metadata.clone(), auth_service.clone());
    let record_service = RecordServiceImpl::new(metadata.clone(), auth_service.clone());

    // Setup health service
    let (mut health_reporter, health_service) = health_reporter();
    health_reporter
        .set_serving::<ZoneServiceServer<ZoneServiceImpl>>()
        .await;
    health_reporter
        .set_serving::<RecordServiceServer<RecordServiceImpl>>()
        .await;

    // Start DNS handler
    let dns_handler = DnsHandler::bind(config.dns_addr, metadata.clone()).await?;
    let dns_task = tokio::spawn(async move {
        dns_handler.run().await;
    });

    // Configure TLS if enabled
    let mut server = Server::builder();

    if let Some(tls_config) = &config.tls {
        tracing::info!("TLS enabled, loading certificates...");
        let cert = tokio::fs::read(&tls_config.cert_file).await?;
        let key = tokio::fs::read(&tls_config.key_file).await?;
        let server_identity = Identity::from_pem(cert, key);

        let tls = if tls_config.require_client_cert {
            tracing::info!("mTLS enabled");
            let ca_cert = tokio::fs::read(
                tls_config
                    .ca_file
                    .as_ref()
                    .ok_or("ca_file required for mTLS")?,
            )
            .await?;
            let ca = Certificate::from_pem(ca_cert);
            ServerTlsConfig::new()
                .identity(server_identity)
                .client_ca_root(ca)
        } else {
            ServerTlsConfig::new().identity(server_identity)
        };

        server = server.tls_config(tls)?;
    }

    // Start gRPC server
    tracing::info!("gRPC server listening on {}", config.grpc_addr);
    let grpc_server = server
        .add_service(health_service)
        .add_service(tonic::codegen::InterceptedService::new(
            ZoneServiceServer::new(zone_service),
            make_interceptor(auth_service.clone()),
        ))
        .add_service(tonic::codegen::InterceptedService::new(
            RecordServiceServer::new(record_service),
            make_interceptor(auth_service.clone()),
        ))
        .serve(config.grpc_addr);

    // Run both servers
    tokio::select! {
        result = grpc_server => {
            if let Err(e) = result {
                tracing::error!("gRPC server error: {}", e);
            }
        }
        _ = dns_task => {
            tracing::error!("DNS handler unexpectedly terminated");
        }
    }

    Ok(())
}

fn parse_metadata_backend(value: &str) -> Result<MetadataBackend> {
    match value.trim().to_ascii_lowercase().as_str() {
        "flaredb" => Ok(MetadataBackend::FlareDb),
        "postgres" => Ok(MetadataBackend::Postgres),
        "sqlite" => Ok(MetadataBackend::Sqlite),
        other => Err(anyhow::anyhow!(
            "invalid metadata backend '{}'; expected one of: flaredb, postgres, sqlite",
            other
        )),
    }
}

fn metadata_backend_name(backend: MetadataBackend) -> &'static str {
    match backend {
        MetadataBackend::FlareDb => "flaredb",
        MetadataBackend::Postgres => "postgres",
        MetadataBackend::Sqlite => "sqlite",
    }
}

fn ensure_sql_backend_matches_url(backend: MetadataBackend, database_url: &str) -> Result<()> {
    let normalized = database_url.trim().to_ascii_lowercase();
    match backend {
        MetadataBackend::Postgres => {
            if normalized.starts_with("postgres://") || normalized.starts_with("postgresql://") {
                Ok(())
            } else {
                Err(anyhow::anyhow!(
                    "metadata_backend=postgres requires postgres:// or postgresql:// URL"
                ))
            }
        }
        MetadataBackend::Sqlite => {
            if normalized.starts_with("sqlite:") {
                Ok(())
            } else {
                Err(anyhow::anyhow!(
                    "metadata_backend=sqlite requires sqlite: URL"
                ))
            }
        }
        MetadataBackend::FlareDb => Ok(()),
    }
}

async fn register_chainfire_membership(
    endpoint: &str,
    service: &str,
    addr: String,
) -> Result<()> {
    let node_id =
        std::env::var("HOSTNAME").unwrap_or_else(|_| format!("{}-{}", service, std::process::id()));
    let ts = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap_or_default()
        .as_secs();
    let key = format!("/cluster/{}/members/{}", service, node_id);
    let value = format!(r#"{{"addr":"{}","ts":{}}}"#, addr, ts);
    let deadline = tokio::time::Instant::now() + std::time::Duration::from_secs(120);
    let mut attempt = 0usize;
    let mut last_error = String::new();

    loop {
        attempt += 1;
        match ChainFireClient::connect(endpoint).await {
            Ok(mut client) => match client.put_str(&key, &value).await {
                Ok(_) => return Ok(()),
                Err(error) => last_error = format!("put failed: {}", error),
            },
            Err(error) => last_error = format!("connect failed: {}", error),
        }

        if tokio::time::Instant::now() >= deadline {
            break;
        }

        tracing::warn!(
            attempt,
            endpoint,
            service,
            error = %last_error,
            "retrying ChainFire membership registration"
        );
        tokio::time::sleep(std::time::Duration::from_secs(2)).await;
    }

    anyhow::bail!(
        "failed to register ChainFire membership for {} via {} after {} attempts: {}",
        service,
        endpoint,
        attempt,
        last_error
    )
}