//! End-to-end tests of route selection: routes for one prefix from several
//! peers, which of them the server chooses, and how that is shown.

use std::net::Ipv4Addr;

use bgp_integration_tests::announcement::{Announcement, withdrawal as withdrawal_of};
use bgp_integration_tests::test_peer::TestPeer;
use bgp_integration_tests::test_server::{RouteChange, TestServer};
use bgp_integration_tests::{TIMEOUT, get_json, prefix};
use bgp_packet::message::{PathAttribute, UpdateMessage};
use bgp_primitives::ip_prefix::{IpPrefix, Nlri};
use eyre::Result;
use serde_json::Value;

const LOCAL_ASN: u32 = 65000;

/// A session from the peer numbered `number`, in AS 65000 + `number`.
async fn peer(server: &TestServer, number: u8) -> Result<TestPeer> {
    server
        .established(
            LOCAL_ASN + u32::from(number),
            Ipv4Addr::new(10, 0, 0, number),
        )
        .await
}

fn announcement(prefixes: &[IpPrefix], as_path: &[u32]) -> Announcement {
    Announcement::of(Nlri::plain(prefixes.iter().copied()), as_path)
}

fn withdrawal(prefixes: &[IpPrefix]) -> UpdateMessage {
    withdrawal_of(Nlri::plain(prefixes.iter().copied()))
}

/// The AS path of the route the server holds as best for `prefix`.
fn best_path(server: &TestServer, prefix: &IpPrefix) -> Option<Vec<u32>> {
    let best = server
        .received_routes()
        .into_iter()
        .find(|route| route.prefix == *prefix && route.best)?;
    best.attributes
        .iter()
        .find_map(|attribute| match attribute {
            PathAttribute::AsPath(path) => Some(path.segments[0].path.clone()),
            _ => None,
        })
}

/// Two peers offer the same prefix. The route with the shorter AS path is
/// chosen; when it goes, the other is.
#[tokio::test]
async fn test_the_best_route_is_chosen_and_replaced_when_it_goes() -> Result<()> {
    let server = TestServer::start(LOCAL_ASN).await?;
    let (base, _http) = server.serve_http().await?;
    let client = reqwest::Client::new();
    let mut changes = server.route_changes();
    let p = prefix("203.0.113.0/24");

    let mut far = peer(&server, 1).await?;
    far.announce(announcement(&[p], &[65001, 64999, 64998]))
        .await?;
    server.wait_for_routes(1).await?;
    assert_eq!(best_path(&server, &p), Some(vec![65001, 64999, 64998]));

    let mut near = peer(&server, 2).await?;
    near.announce(announcement(&[p], &[65002, 64998])).await?;
    server.wait_for_routes(2).await?;
    assert_eq!(best_path(&server, &p), Some(vec![65002, 64998]));

    // Both routes are kept and shown; one is marked.
    let status = get_json(&client, &format!("{base}/api/status")).await?;
    assert_eq!(status["received_routes"], 2);
    assert_eq!(status["received_prefixes"], 1);
    let routes = get_json(&client, &format!("{base}/api/routes/received")).await?["routes"].take();
    let best: Vec<&Value> = routes
        .as_array()
        .unwrap()
        .iter()
        .filter(|route| route["best"] == true)
        .collect();
    assert_eq!(routes.as_array().unwrap().len(), 2);
    assert_eq!(best.len(), 1);
    assert_eq!(best[0]["peer_asn"], 65002);
    // Listed from the best down, each with its place in selection.
    let ranks: Vec<(u64, u64)> = routes
        .as_array()
        .unwrap()
        .iter()
        .map(|route| {
            (
                route["rank"].as_u64().unwrap(),
                route["peer_asn"].as_u64().unwrap(),
            )
        })
        .collect();
    assert_eq!(ranks, vec![(1, 65002), (2, 65001)]);

    // The session with the best route ends: the other route takes over.
    drop(near);
    server.wait_for_routes(1).await?;
    assert_eq!(best_path(&server, &p), Some(vec![65001, 64999, 64998]));

    far.announce(withdrawal(&[p])).await?;
    server.wait_for_routes(0).await?;
    assert_eq!(best_path(&server, &p), None);

    // A follower of the best routes is told of each change: the first
    // route, the better one, back to the first, none.
    let mut seen = Vec::new();
    while seen.last() != Some(&RouteChange::Withdrawn { prefix: p }) {
        seen.push(tokio::time::timeout(TIMEOUT, changes.recv()).await??);
    }
    assert!(
        seen.iter()
            .all(|change| matches!(change, RouteChange::Announced { prefix, .. } | RouteChange::Withdrawn { prefix } if *prefix == p)),
        "{seen:?}"
    );
    Ok(())
}

/// The event stream reports changes of best route, and only those.
#[tokio::test]
async fn test_changes_of_best_route_are_on_the_event_stream() -> Result<()> {
    let server = TestServer::start(LOCAL_ASN).await?;
    let (base, _http) = server.serve_http().await?;
    let p = prefix("203.0.113.0/24");

    // A route that is there before the client connects is not an event.
    let mut first = peer(&server, 1).await?;
    first
        .announce(announcement(&[prefix("198.51.100.0/24")], &[65001]))
        .await?;
    server.wait_for_routes(1).await?;

    let mut stream = reqwest::Client::new()
        .get(format!("{base}/api/events"))
        .send()
        .await?
        .error_for_status()?;

    first.announce(announcement(&[p], &[65001, 64998])).await?;
    server.wait_for_routes(2).await?;
    first.announce(withdrawal(&[p])).await?;
    server.wait_for_routes(1).await?;

    let mut text = String::new();
    let mut events: Vec<Value> = Vec::new();
    tokio::time::timeout(TIMEOUT, async {
        while !events.iter().any(|event| event["type"] == "best_withdrawn") {
            let chunk = stream
                .chunk()
                .await?
                .ok_or_else(|| eyre::eyre!("stream ended"))?;
            text.push_str(std::str::from_utf8(&chunk)?);
            events = text
                .lines()
                .filter_map(|line| line.strip_prefix("data:"))
                .filter_map(|data| serde_json::from_str(data.trim()).ok())
                .collect();
        }
        Ok::<_, eyre::Error>(())
    })
    .await??;

    let about_routes: Vec<&Value> = events
        .iter()
        .filter(|event| {
            event["type"]
                .as_str()
                .is_some_and(|t| t.starts_with("best_"))
        })
        .collect();
    // The announcement and the withdrawal may have been read as one change
    // or as two; either way nothing is said of the route that was there
    // from the start, and the last word is that the prefix is gone.
    assert!(about_routes.len() <= 2, "{about_routes:?}");
    for event in &about_routes {
        let named = event["prefix"]
            .as_str()
            .or(event["route"]["prefix"].as_str());
        assert_eq!(named, Some("203.0.113.0/24"), "{event}");
    }
    assert_eq!(about_routes.last().unwrap()["type"], "best_withdrawn");
    Ok(())
}

/// The table can be far too large to send whole: the API gives a part of
/// it, and says how much there is.
#[tokio::test]
async fn test_received_routes_are_returned_up_to_a_limit() -> Result<()> {
    let server = TestServer::start(LOCAL_ASN).await?;
    let (base, _http) = server.serve_http().await?;
    let client = reqwest::Client::new();

    let prefixes: Vec<IpPrefix> = (0..40).map(|n| prefix(&format!("10.{n}.0.0/16"))).collect();
    let mut peer = peer(&server, 1).await?;
    peer.announce(announcement(&prefixes, &[65001])).await?;
    server.wait_for_routes(40).await?;

    let count = |page: Value| page["routes"].as_array().unwrap().len();
    let url = format!("{base}/api/routes/received");
    assert_eq!(count(get_json(&client, &url).await?), 40);
    assert_eq!(
        count(get_json(&client, &format!("{url}?limit=7")).await?),
        7
    );
    let status = get_json(&client, &format!("{base}/api/status")).await?;
    assert_eq!(status["received_routes"], 40);
    Ok(())
}