//! Whom neighbours reach (`swarm::reach`): told in STATUSes, as measured, and kept for
//! the session; and the writers' trees built on it (`swarm::tree`), which changes go
//! along however they came.

use std::time::Duration;

use super::Sim;
use crate::state::AppState;
use crate::swarm::bootstrap::Start;
use crate::swarm::{reach, topology, tree};

const SOON: Duration = Duration::from_secs(30);

/// Whether `node` reaches `member`, as `node` measured and told it.
fn reaches(node: &AppState, member: &AppState) -> bool {
    reach::published(node).contains(&topology::pair_key(member.local_id()))
}

/// Whether `node` heard from `neighbour` that it reaches `member`.
async fn heard(node: &AppState, neighbour: &AppState, member: &AppState) -> bool {
    let Some(peer_state) = node.get_peer_state(neighbour.local_id()).await else {
        return false;
    };
    let said = peer_state.lock().await.reaches.clone();
    reach::of(said.as_ref())
        .is_some_and(|keys| keys.contains(&topology::pair_key(member.local_id())))
}

/// x, b and c on one net, all members of one full mesh, but nothing passes between x
/// and c: b reaches both and says so; c learns from b that b reaches x, which c itself
/// doesn't.
#[tokio::test(flavor = "multi_thread", worker_threads = 4)]
async fn neighbours_tell_whom_they_reach() {
    let sim = Sim::with_identity(66);
    let cut = crate::transport::sim::LinkParams {
        loss: 1.0,
        ..Default::default()
    };
    sim.net.set_link("x", "c", cut.clone());
    sim.net.set_link("c", "x", cut);
    let b = sim.start_on("b", &["sim"], &[], Start::Genesis);
    let c = sim.start_on("c", &["sim"], &["b"], Start::Join);
    let x = sim.start_on("x", &["sim"], &["b"], Start::Join);
    sim.wait_ready(&[&b, &c, &x], SOON).await;
    let (b, c, x) = (&b, &c, &x);
    sim.wait_until(
        "c heard from b that b reaches x, and c doesn't reach x",
        SOON,
        move || async move {
            reaches(b, x) && reaches(b, c) && !reaches(c, x) && heard(c, b, x).await
        },
    )
    .await;
}

/// The same three: in x's tree (`swarm::tree`), c can't take x as its parent (it
/// doesn't reach it), so it takes b, which comes before it: as far from x, but it
/// reaches x. So x's only child is b, and b's is c.
#[tokio::test(flavor = "multi_thread", worker_threads = 4)]
async fn writer_trees_go_around_links_down() {
    let sim = Sim::with_identity(67);
    let cut = crate::transport::sim::LinkParams {
        loss: 1.0,
        ..Default::default()
    };
    sim.net.set_link("x", "c", cut.clone());
    sim.net.set_link("c", "x", cut);
    let b = sim.start_on("b", &["sim"], &[], Start::Genesis);
    let c = sim.start_on("c", &["sim"], &["b"], Start::Join);
    let x = sim.start_on("x", &["sim"], &["b"], Start::Join);
    sim.wait_ready(&[&b, &c, &x], SOON).await;
    let (b, c, x) = (&b, &c, &x);
    let writer = topology::pair_key(x.local_id());
    sim.wait_until(
        "x's tree: b under x, and c under b",
        SOON,
        move || async move {
            let of_x = tree::children(x, writer).await;
            let of_b = tree::children(b, writer).await;
            heard(c, b, x).await
                && of_x == [b.local_id().to_owned()]
                && of_b == [c.local_id().to_owned()]
        },
    )
    .await;
}

/// What `node` counted: pulls started, changes passed on along writers' trees.
fn counted(node: &AppState) -> (u64, u64) {
    let relay = node.stats.snapshot().relay;
    (relay.pulls, relay.tree_forwards)
}

/// x, b, c and d, one full mesh, but nothing passes between c and x, nor between c and
/// d: c's parent in x's tree is b, the only member it reaches. And x's sync messages to
/// b are lost, so b gets x's write pulled from d (after d's slow round), not along the
/// tree: pulled, it says nothing of whose; its author does, so b passes it on to c along
/// x's tree all the same, and c pulls nothing.
#[tokio::test(flavor = "multi_thread", worker_threads = 4)]
async fn pulled_changes_go_along_their_writers_trees() {
    // Long, so x's own STATUS (every third keepalive) doesn't make b pull from x, whose
    // answers are lost, before d's slow round.
    let slow = |config: &mut crate::node::NodeConfig| {
        config.timing = crate::state::Timing::new(
            Duration::from_secs(5),
            super::SYNC_REPLY_TIMEOUT,
            crate::transport::sim::DELIVERY_LIMIT,
        );
    };
    let sim = Sim::with_identity(68);
    let cut = crate::transport::sim::LinkParams {
        loss: 1.0,
        ..Default::default()
    };
    for (from, to) in [("x", "c"), ("c", "x"), ("d", "c"), ("c", "d")] {
        sim.net.set_link(from, to, cut.clone());
    }
    sim.net.set_link(
        "x",
        "b",
        crate::transport::sim::LinkParams {
            drop: vec![crate::transport::MessageKind::Sync],
            ..Default::default()
        },
    );
    let b = sim.start_on_with("b", &["sim"], &[], Start::Genesis, slow);
    let c = sim.start_on_with("c", &["sim"], &["b"], Start::Join, slow);
    let d = sim.start_on_with("d", &["sim"], &["b"], Start::Join, slow);
    let x = sim.start_on_with("x", &["sim"], &["b"], Start::Join, slow);
    sim.wait_ready(&[&b, &c, &d, &x], SOON).await;
    sim.wait_converged(&[&b, &c, &d, &x], SOON * 2).await;
    let (b, c, d, x) = (&b, &c, &d, &x);
    let writer = topology::pair_key(x.local_id());
    sim.wait_until("c under b in x's tree", SOON, move || async move {
        tree::children(b, writer).await == [c.local_id().to_owned()]
    })
    .await;

    let (c_pulls, _) = counted(c);
    let (_, b_forwards) = counted(b);
    // What b and c send and receive from now on, to show should c pull.
    b.traffic.log.watch(true);
    c.traffic.log.watch(true);
    super::write(x, "y", serde_json::json!(1)).await;
    let written = super::heads(x).await;
    sim.wait_until("c has x's write", SOON, move || async move {
        super::read(c, "y").await == Some(serde_json::json!(1))
    })
    .await;
    assert!(counted(b).1 > b_forwards, "b passed it on along x's tree");
    assert_eq!(
        counted(c).0,
        c_pulls,
        "c pulled nothing; x's write is {written:?}; what b and c sent and received meanwhile:\n{}",
        logged(
            &[("b", b), ("c", c)],
            &[("b", b), ("c", c), ("d", d), ("x", x)]
        )
    );
}

/// What `nodes` sent and received, as their logs kept them (`MessageLog`), in order,
/// peers by their names in `names`: STATUSes and SYNCs written out, the others by type.
fn logged(nodes: &[(&str, &AppState)], names: &[(&str, &AppState)]) -> String {
    let name = |id: &str| {
        names
            .iter()
            .find(|(_, node)| node.local_id() == id)
            .map_or(id.to_owned(), |(name, _)| (*name).to_owned())
    };
    let mut lines: Vec<(u64, String)> = Vec::new();
    for (node_name, node) in nodes {
        for logged in node.traffic.log.after(0, 1000) {
            let text = if logged.kind.starts_with("STATUS") || logged.kind == "SYNC" {
                format!("\n{}", logged.text)
            } else {
                String::new()
            };
            lines.push((
                logged.at,
                format!(
                    "{} {node_name} {} {} {} {}{text}",
                    logged.at,
                    logged.way,
                    logged.kind,
                    if logged.way == "sent" { "to" } else { "from" },
                    name(&logged.peer),
                ),
            ));
        }
    }
    lines.sort_by_key(|(at, _)| *at);
    lines
        .into_iter()
        .map(|(_, line)| line)
        .collect::<Vec<_>>()
        .join("\n")
}

/// x, b and c, nothing between x and c: x's changes reach c through b, along x's tree.
/// x writes every 100 ms for 4 s, many keepalive intervals: the pairs are busy, so no
/// keepalive goes, and no STATUS. b still knows whom c reaches (it said so once, and
/// nothing changed), and passes every write on to c: c pulls none.
#[tokio::test(flavor = "multi_thread", worker_threads = 4)]
async fn trees_hold_through_continuous_writes() {
    let sim = Sim::with_identity(69);
    let cut = crate::transport::sim::LinkParams {
        loss: 1.0,
        ..Default::default()
    };
    sim.net.set_link("x", "c", cut.clone());
    sim.net.set_link("c", "x", cut);
    let b = sim.start_on("b", &["sim"], &[], Start::Genesis);
    let c = sim.start_on("c", &["sim"], &["b"], Start::Join);
    let x = sim.start_on("x", &["sim"], &["b"], Start::Join);
    sim.wait_ready(&[&b, &c, &x], SOON).await;
    sim.wait_converged(&[&b, &c, &x], SOON).await;
    let (b, c, x) = (&b, &c, &x);
    let writer = topology::pair_key(x.local_id());
    sim.wait_until("c under b in x's tree", SOON, move || async move {
        heard(b, c, b).await && tree::children(b, writer).await == [c.local_id().to_owned()]
    })
    .await;

    let (c_pulls, _) = counted(c);
    let (_, b_forwards) = counted(b);
    let writes = 40;
    for i in 0..writes {
        super::write(x, &format!("w/{i}"), serde_json::json!(i)).await;
        tokio::time::sleep(Duration::from_millis(100)).await;
    }
    sim.wait_until("c has x's last write", SOON, move || async move {
        super::read(c, &format!("w/{}", writes - 1)).await == Some(serde_json::json!(writes - 1))
    })
    .await;
    // Some may go together, if b had several to pass on at once.
    assert!(
        counted(b).1 >= b_forwards + writes as u64 / 2,
        "b passed the writes on along x's tree"
    );
    assert_eq!(counted(c).0, c_pulls, "c pulled nothing");
}