//! CAN Sync — P2P full-mirror replication agent for CAN Service.
//!
//! Uses iroh for encrypted QUIC transport + NAT traversal,
//! and iroh-gossip for peer discovery via a shared passphrase.
//!
//! Each instance talks to its local CAN Service via the private
//! protobuf sync API (/sync/*), authenticated with an API key.

mod can_client;
mod config;
mod discovery;
mod peer;
mod protocol;

use std::path::Path;

use anyhow::{Context, Result};
use iroh::endpoint::presets::N0;
use iroh::{Endpoint, EndpointAddr, EndpointId};
use iroh_gossip::net::Gossip;
use tokio::sync::mpsc;
use tracing::{error, info, warn};

use crate::can_client::CanSyncClient;
use crate::config::SyncConfig;
use crate::discovery::Discovery;

/// ALPN protocol identifier for CAN sync peer connections.
const SYNC_ALPN: &[u8] = b"can-sync/1";

#[tokio::main]
async fn main() -> Result<()> {
    // Initialize logging
    tracing_subscriber::fmt()
        .with_env_filter(
            tracing_subscriber::EnvFilter::try_from_default_env()
                .unwrap_or_else(|_| "can_sync=info,iroh=warn,iroh_gossip=warn".parse().unwrap()),
        )
        .init();

    // Load config
    let config_path = std::env::args()
        .nth(1)
        .unwrap_or_else(|| "config.yaml".to_string());
    let config = SyncConfig::load(Path::new(&config_path))
        .with_context(|| format!("loading config from {}", config_path))?;

    info!("CAN Sync v2 starting");
    info!("CAN service: {}", config.can_service_url);
    info!("Poll interval: {}s", config.poll_interval_secs);

    // Create HTTP client for local CAN service's sync API
    let can = CanSyncClient::new(&config.can_service_url, &config.sync_api_key);

    // Verify CAN service is reachable
    if can.health_check().await {
        info!("CAN service sync API is healthy");
    } else {
        warn!("CAN service sync API not reachable — will retry on sync");
    }

    // Create iroh endpoint for QUIC transport with n0 defaults (relay + discovery)
    let endpoint = Endpoint::builder()
        .preset(N0)
        .alpns(vec![SYNC_ALPN.to_vec()])
        .bind()
        .await
        .context("creating iroh endpoint")?;

    let node_id = endpoint.id();
    info!("Node ID: {}", node_id);

    let addrs = endpoint.bound_sockets();
    if let Some(addr) = addrs.first() {
        info!("Listening on {}", addr);
    }

    // Write our EndpointAddr to file if configured (for direct peer connection in tests)
    if let Some(ref ticket_path) = config.ticket_file {
        // Wait briefly for the endpoint to register with relay
        tokio::time::sleep(std::time::Duration::from_millis(500)).await;

        let addr = endpoint.addr();
        let addr_json = serde_json::to_string(&addr)
            .context("serializing EndpointAddr")?;
        std::fs::write(ticket_path, &addr_json)
            .with_context(|| format!("writing addr to {}", ticket_path))?;
        info!("Wrote EndpointAddr to {}", ticket_path);
    }

    // Create gossip instance for peer discovery (not async — returns directly)
    let gossip = Gossip::builder().spawn(endpoint.clone());

    // Channel for discovered peers
    let (peer_tx, mut peer_rx) = mpsc::channel::<EndpointId>(32);

    // Spawn discovery via gossip
    let disc = Discovery::new(endpoint.clone(), gossip.clone(), &config.sync_passphrase);
    tokio::spawn(async move {
        if let Err(e) = disc.run(peer_tx.clone()).await {
            error!("Discovery failed: {:#}", e);
        }
    });

    // If a direct connect ticket file is specified, spawn a task to read it and connect
    if let Some(ref ticket_path) = config.connect_ticket_file {
        let ticket_path = ticket_path.clone();
        let endpoint_direct = endpoint.clone();
        let can_direct = can.clone();

        tokio::spawn(async move {
            info!("Waiting for peer addr file: {}", ticket_path);

            // Poll until the file exists and is non-empty
            let addr_json = loop {
                match std::fs::read_to_string(&ticket_path) {
                    Ok(s) if !s.trim().is_empty() => break s.trim().to_string(),
                    _ => tokio::time::sleep(std::time::Duration::from_millis(200)).await,
                }
            };

            info!("Read peer addr from {}", ticket_path);

            let peer_addr: EndpointAddr = match serde_json::from_str(&addr_json) {
                Ok(a) => a,
                Err(e) => {
                    error!("Invalid EndpointAddr JSON: {:#}", e);
                    return;
                }
            };

            let peer_id = peer_addr.id;
            let short = peer_id.fmt_short().to_string();
            info!("Direct connecting to peer: {} (from addr file)", short);

            match endpoint_direct.connect(peer_addr, SYNC_ALPN).await {
                Ok(conn) => {
                    info!("Direct connection to {} established!", short);

                    // Initial reconciliation
                    if let Err(e) = peer::run_sync_session(conn.clone(), can_direct.clone(), true).await {
                        error!("Initial sync with {} failed: {:#}", short, e);
                        return;
                    }

                    info!("Initial sync with {} complete, starting live sync", short);

                    // Live sync: SSE-driven push + accept incoming streams
                    peer::run_live_sync(conn, can_direct).await;
                }
                Err(e) => {
                    error!("Failed to connect to {}: {:#}", short, e);
                }
            }
        });
    }

    // Spawn incoming connection handler
    let endpoint_accept = endpoint.clone();
    let can_accept = can.clone();
    tokio::spawn(async move {
        loop {
            match endpoint_accept.accept().await {
                Some(incoming) => {
                    let can_clone = can_accept.clone();
                    tokio::spawn(async move {
                        match incoming.await {
                            Ok(conn) => {
                                info!("Accepted incoming connection from {}", conn.remote_id().fmt_short());
                                peer::handle_incoming(conn, can_clone, std::time::Duration::from_secs(0)).await;
                            }
                            Err(e) => {
                                warn!("Failed to accept connection: {:#}", e);
                            }
                        }
                    });
                }
                None => {
                    info!("Endpoint closed, stopping accept loop");
                    break;
                }
            }
        }
    });

    // Main loop: connect to discovered peers (from gossip) and sync
    info!("Waiting for peers...");

    while let Some(peer_id) = peer_rx.recv().await {
        let short = peer_id.fmt_short();
        info!("Connecting to discovered peer: {}", short);

        let endpoint_clone = endpoint.clone();
        let can_clone = can.clone();

        tokio::spawn(async move {
            let conn = match endpoint_clone.connect(peer_id, SYNC_ALPN).await {
                Ok(c) => c,
                Err(e) => {
                    error!("Failed to connect to {}: {:#}", short, e);
                    return;
                }
            };

            if let Err(e) = peer::run_sync_session(conn.clone(), can_clone.clone(), true).await {
                error!("Initial sync with {} failed: {:#}", short, e);
                return;
            }

            peer::run_live_sync(conn, can_clone).await;
        });
    }

    info!("CAN Sync shutting down");
    Ok(())
}