mod common;
use common::*;

use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Arc;

// ── Additional actors for edge-case tests ────────────────────────────────

/// Sends a countdown message to itself, then replies Done(0) when remaining hits zero.
/// Tests pending_local self-delivery path.
struct SelfSendActor;

#[derive(Clone)]
struct Countdown {
    remaining: usize,
    reply_to: ActorAddress,
}

impl ActorInterface for SelfSendActor {
    type Incoming = Countdown;
    type Response = Done;
    fn handle(&mut self, ctx: &Ctx, msg: Countdown) {
        if msg.remaining == 0 {
            let _ = ctx.send(msg.reply_to, Done(0));
        } else {
            let _ = ctx.send(
                ctx.self_addr(),
                Countdown { remaining: msg.remaining - 1, reply_to: msg.reply_to },
            );
        }
    }
}

/// Spawns a DoubleActor child, sends it work, then panics.
/// The child should still process the forwarded message.
struct SpawnThenPanicActor;

impl ActorInterface for SpawnThenPanicActor {
    type Incoming = Forward;
    type Response = ();
    fn handle(&mut self, ctx: &Ctx, msg: Forward) {
        let child = ctx.spawn(DoubleActor).unwrap();
        let _ = ctx.send(child, Forward { value: msg.value, reply_to: msg.reply_to });
        panic!("intentional panic after spawn+send");
    }
}

/// Processes `remaining_good` messages, then panics on the next one.
/// Uses a shared counter so the test can observe how many were processed.
struct PanicAfterNActor {
    remaining_good: usize,
    counter: Arc<AtomicUsize>,
}

impl ActorInterface for PanicAfterNActor {
    type Incoming = Ping;
    type Response = ();
    fn handle(&mut self, _ctx: &Ctx, _msg: Ping) {
        if self.remaining_good == 0 {
            panic!("intentional delayed panic");
        }
        self.remaining_good -= 1;
        self.counter.fetch_add(1, Ordering::SeqCst);
    }
}

/// Sends a reply, then panics. Tests that messages sent before the panic
/// are still delivered (they're already in the queue).
struct SendThenPanicActor;

impl ActorInterface for SendThenPanicActor {
    type Incoming = Ping;
    type Response = Pong;
    fn handle(&mut self, ctx: &Ctx, msg: Ping) {
        let _ = ctx.send(msg.reply_to, Pong);
        panic!("intentional panic after send");
    }
}

// ═══════════════════════════════════════════════════════════════════════════
// Actor Lifecycle
// ═══════════════════════════════════════════════════════════════════════════

#[test]
fn actor_receives_message_and_replies() {
    // Given a spawned PingPongActor
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(PingPongActor).unwrap();
    let inbox = rt.new_inbox::<Pong>().unwrap();

    // When I send it a Ping
    rt.send_to(addr, Ping { reply_to: *inbox.addr() }).unwrap();

    // Then my inbox receives a Pong
    let reply = tick_until_recv(&rt, &inbox, 10);
    assert!(reply.is_some(), "actor should have replied with Pong");
}

#[test]
fn actor_maintains_state_across_messages() {
    // Given a CounterActor starting at 0
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(CounterActor { count: 0 }).unwrap();
    let inbox = rt.new_inbox::<Count>().unwrap();

    // When I send 3 Increments
    for _ in 0..3 {
        rt.send_to(addr, Increment { reply_to: *inbox.addr() }).unwrap();
    }

    // Then replies are Count(1), Count(2), Count(3) — state accumulated
    let replies = tick_and_drain(&rt, &inbox, 10);
    assert_eq!(replies, vec![Count(1), Count(2), Count(3)]);
}

#[test]
fn actor_spawns_child_and_child_replies() {
    // Given a DelegatorActor
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(DelegatorActor).unwrap();
    let inbox = rt.new_inbox::<Done>().unwrap();

    // When I ask it to process value 7
    rt.send_to(addr, Forward { value: 7, reply_to: *inbox.addr() }).unwrap();

    // Then the child doubled it — inbox gets Done(14)
    let reply = tick_until_recv(&rt, &inbox, 20);
    assert_eq!(reply, Some(Done(14)), "child should have doubled the value");
}

#[test]
fn three_level_chain_reaches_leaf() {
    // Given a ChainActor that will spawn 2 more levels
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(ChainActor).unwrap();
    let inbox = rt.new_inbox::<Done>().unwrap();

    // When I send remaining=2 (root -> child -> grandchild)
    rt.send_to(addr, ChainMsg { remaining: 2, depth: 0, reply_to: *inbox.addr() }).unwrap();

    // Then the grandchild (depth 2) replies
    let reply = tick_until_recv(&rt, &inbox, 30);
    assert_eq!(reply, Some(Done(2)), "leaf at depth 2 should have replied");
}

#[test]
fn fan_out_distributes_work_to_children() {
    // Given a FanOutActor told to spawn 5 children
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(FanOutActor).unwrap();
    let inbox = rt.new_inbox::<Done>().unwrap();

    // When it spawns 5 children, each doubling their index
    rt.send_to(addr, FanOut { count: 5, reply_to: *inbox.addr() }).unwrap();

    // Then I receive 5 replies whose values are {2, 4, 6, 8, 10}
    let mut replies = tick_and_drain(&rt, &inbox, 20);
    let mut values: Vec<usize> = replies.drain(..).map(|d| d.0).collect();
    values.sort();
    assert_eq!(values, vec![2, 4, 6, 8, 10], "each child should have doubled its index");
}

#[test]
fn actor_knows_its_own_address() {
    // Given a SelfAddrActor
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(SelfAddrActor).unwrap();
    let inbox = rt.new_inbox::<MyAddr>().unwrap();

    // When I ask it for its address
    rt.send_to(addr, WhoAreYou { reply_to: *inbox.addr() }).unwrap();

    // Then the address it reports matches the one from spawn
    let reply = tick_until_recv(&rt, &inbox, 10);
    assert_eq!(reply, Some(MyAddr(addr)), "actor should know its own address");
}

// ═══════════════════════════════════════════════════════════════════════════
// Message Delivery
// ═══════════════════════════════════════════════════════════════════════════

#[test]
fn messages_arrive_in_fifo_order() {
    // Given a CounterActor
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(CounterActor { count: 0 }).unwrap();
    let inbox = rt.new_inbox::<Count>().unwrap();

    // When I send 5 Increments
    for _ in 0..5 {
        rt.send_to(addr, Increment { reply_to: *inbox.addr() }).unwrap();
    }

    // Then replies arrive Count(1)..Count(5) in order
    let replies = tick_and_drain(&rt, &inbox, 10);
    assert_eq!(
        replies,
        vec![Count(1), Count(2), Count(3), Count(4), Count(5)],
        "messages must be processed in FIFO order"
    );
}

#[test]
fn multiple_actors_have_independent_mailboxes() {
    // Given 3 PingPongActors, each with its own inbox
    let rt = std_runtime(RuntimeConfig::default());
    let mut addrs = Vec::new();
    let mut inboxes = Vec::new();
    for _ in 0..3 {
        let addr = rt.spawn(PingPongActor).unwrap();
        let inbox = rt.new_inbox::<Pong>().unwrap();
        rt.send_to(addr, Ping { reply_to: *inbox.addr() }).unwrap();
        addrs.push(addr);
        inboxes.push(inbox);
    }

    // When all messages are processed
    for _ in 0..10 {
        rt.tick();
    }

    // Then each inbox sees exactly one Pong — no cross-contamination
    for (i, inbox) in inboxes.iter().enumerate() {
        assert!(inbox.try_recv().is_some(), "actor {i} should have replied");
        assert!(inbox.try_recv().is_none(), "actor {i} should have only one reply");
    }
}

#[test]
fn multiple_senders_reach_same_actor() {
    // Given 1 CounterActor
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(CounterActor { count: 0 }).unwrap();
    let inbox_a = rt.new_inbox::<Count>().unwrap();
    let inbox_b = rt.new_inbox::<Count>().unwrap();

    // When two different callers each send an Increment
    rt.send_to(addr, Increment { reply_to: *inbox_a.addr() }).unwrap();
    rt.send_to(addr, Increment { reply_to: *inbox_b.addr() }).unwrap();

    // Then both replies arrive and the counter incremented for each
    for _ in 0..10 {
        rt.tick();
    }
    let a = inbox_a.try_recv();
    let b = inbox_b.try_recv();
    assert!(a.is_some(), "first sender should get a reply");
    assert!(b.is_some(), "second sender should get a reply");
    // Second caller sees Count(2), proving both messages were handled
    assert_eq!(b, Some(Count(2)));
}

#[test]
fn send_to_nonexistent_address_returns_error() {
    // Given a runtime with no actors at a random address
    let rt = std_runtime(RuntimeConfig::default());
    let bogus = ActorAddress::new_random();

    // When I try to send to that address
    let result = rt.send_to(bogus, Pong);

    // Then I get an error
    assert!(result.is_err(), "sending to unknown address should fail");
}

#[test]
fn messages_sent_within_handler_are_delivered() {
    // Given a DelegatorActor (spawns child + sends in same handler call)
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(DelegatorActor).unwrap();
    let inbox = rt.new_inbox::<Done>().unwrap();

    // When I trigger the delegator
    rt.send_to(addr, Forward { value: 5, reply_to: *inbox.addr() }).unwrap();

    // Then the child receives the forwarded msg and replies to my inbox
    let reply = tick_until_recv(&rt, &inbox, 20);
    assert!(reply.is_some(), "child spawned during handler should receive its message");
    assert_eq!(reply.unwrap(), Done(10));
}

// ═══════════════════════════════════════════════════════════════════════════
// Threading Model
// ═══════════════════════════════════════════════════════════════════════════

#[test]
fn tick_drives_single_threaded_processing() {
    // Given a single-threaded runtime
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(PingPongActor).unwrap();
    let inbox = rt.new_inbox::<Pong>().unwrap();

    // When I send a message and tick manually
    rt.send_to(addr, Ping { reply_to: *inbox.addr() }).unwrap();

    // Before ticking: nothing received
    assert!(inbox.try_recv().is_none(), "should not receive before tick");

    // After ticking: reply available
    rt.tick();
    rt.tick();
    assert!(inbox.try_recv().is_some(), "tick() should drive processing");
}

#[test]
fn run_processes_messages_in_background() {
    // Given a multi-threaded runtime
    let rt = std_runtime(RuntimeConfig { num_threads: 4, ..Default::default() });
    let addr = rt.spawn(PingPongActor).unwrap();
    let inbox = rt.new_inbox::<Pong>().unwrap();
    rt.send_to(addr, Ping { reply_to: *inbox.addr() }).unwrap();

    // When I call run() (spawns background worker threads)
    let handle = rt.run().unwrap();

    // Then the inbox receives a reply without manual ticking
    let mut received = false;
    for _ in 0..100 {
        if inbox.try_recv().is_some() {
            received = true;
            break;
        }
        std::thread::sleep(std::time::Duration::from_millis(10));
    }
    handle.shutdown();
    handle.join();
    assert!(received, "background workers should process the message");
}

#[test]
fn shutdown_stops_background_workers() {
    // Given a running multi-threaded runtime
    let rt = std_runtime(RuntimeConfig { num_threads: 2, ..Default::default() });
    let handle = rt.run().unwrap();

    // When I call shutdown + join
    handle.shutdown();
    handle.join();

    // Then join returns (threads have stopped) — test passes by not hanging
}

#[test]
fn cross_worker_delegation_delivers_reply() {
    // Given a 2-thread runtime with a DelegatorActor
    let rt = std_runtime(RuntimeConfig { num_threads: 2, ..Default::default() });
    let addr = rt.spawn(DelegatorActor).unwrap();
    let inbox = rt.new_inbox::<Done>().unwrap();
    rt.send_to(addr, Forward { value: 3, reply_to: *inbox.addr() }).unwrap();

    // When processing runs across worker threads
    let handle = rt.run().unwrap();

    // Then the reply reaches the inbox despite potentially crossing workers
    let mut reply = None;
    for _ in 0..100 {
        if let Some(msg) = inbox.try_recv() {
            reply = Some(msg);
            break;
        }
        std::thread::sleep(std::time::Duration::from_millis(10));
    }
    handle.shutdown();
    handle.join();
    assert_eq!(reply, Some(Done(6)), "cross-worker delegation should deliver the reply");
}

// ═══════════════════════════════════════════════════════════════════════════
// Backpressure & Scale
// ═══════════════════════════════════════════════════════════════════════════

#[test]
fn inbox_handles_burst_of_messages() {
    // Given a CounterActor and a small runtime
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(CounterActor { count: 0 }).unwrap();
    let inbox = rt.new_inbox::<Count>().unwrap();

    // When I send a burst of 20 messages
    for _ in 0..20 {
        rt.send_to(addr, Increment { reply_to: *inbox.addr() }).unwrap();
    }

    // Then all 20 are delivered in order
    let replies = tick_and_drain(&rt, &inbox, 30);
    assert_eq!(replies.len(), 20, "all 20 messages should be delivered");
    // Verify ordering: last reply should be Count(20)
    assert_eq!(replies.last(), Some(&Count(20)), "messages should arrive in FIFO order");
}

#[test]
fn hundred_actors_all_receive_messages() {
    // Given 100 PingPongActors
    let rt = std_runtime(RuntimeConfig {
        max_actors: 2000,
        ..Default::default()
    });
    let mut pairs = Vec::new();
    for _ in 0..100 {
        let addr = rt.spawn(PingPongActor).unwrap();
        let inbox = rt.new_inbox::<Pong>().unwrap();
        rt.send_to(addr, Ping { reply_to: *inbox.addr() }).unwrap();
        pairs.push(inbox);
    }

    // When all messages are processed
    for _ in 0..50 {
        rt.tick();
    }

    // Then all 100 inboxes have a Pong
    let received = pairs.iter().filter(|inbox| inbox.try_recv().is_some()).count();
    assert_eq!(received, 100, "all 100 actors should have replied");
}

// ═══════════════════════════════════════════════════════════════════════════
// Panic Safety
// ═══════════════════════════════════════════════════════════════════════════

#[test]
fn panic_in_handler_does_not_kill_other_actors() {
    // Given a PanicActor and a PingPongActor on the same runtime
    let rt = std_runtime(RuntimeConfig::default());
    let panic_addr = rt.spawn(PanicActor).unwrap();
    let good_addr = rt.spawn(PingPongActor).unwrap();
    let inbox = rt.new_inbox::<Pong>().unwrap();

    // When the PanicActor panics (stderr output expected)
    rt.send_to(panic_addr, PanicMsg).unwrap();
    for _ in 0..5 {
        rt.tick();
    }

    // Then PingPongActor still works normally
    rt.send_to(good_addr, Ping { reply_to: *inbox.addr() }).unwrap();
    let reply = tick_until_recv(&rt, &inbox, 10);
    assert!(reply.is_some(), "healthy actor should still work after peer panics");
}

#[test]
fn panic_does_not_corrupt_subsequent_messages() {
    // Given a PanicActor and a CounterActor
    let rt = std_runtime(RuntimeConfig::default());
    let panic_addr = rt.spawn(PanicActor).unwrap();
    let counter_addr = rt.spawn(CounterActor { count: 0 }).unwrap();
    let inbox = rt.new_inbox::<Count>().unwrap();

    // When the PanicActor panics, then the CounterActor handles messages
    rt.send_to(panic_addr, PanicMsg).unwrap();
    rt.send_to(counter_addr, Increment { reply_to: *inbox.addr() }).unwrap();
    rt.send_to(panic_addr, PanicMsg).unwrap(); // panic again
    rt.send_to(counter_addr, Increment { reply_to: *inbox.addr() }).unwrap();

    // Then the CounterActor is unaffected — state accumulates correctly
    let replies = tick_and_drain(&rt, &inbox, 20);
    assert_eq!(replies, vec![Count(1), Count(2)], "counter should be unaffected by peer panics");
}

#[test]
fn panicked_actor_is_poisoned_and_discards_future_messages() {
    let rt = std_runtime(RuntimeConfig::default());
    let panic_addr = rt.spawn(PanicActor).unwrap();
    let good_addr = rt.spawn(CounterActor { count: 0 }).unwrap();
    let inbox = rt.new_inbox::<Count>().unwrap();

    // Send a panic message, then more panic messages — they should be discarded
    rt.send_to(panic_addr, PanicMsg).unwrap();
    rt.send_to(panic_addr, PanicMsg).unwrap();
    rt.send_to(panic_addr, PanicMsg).unwrap();

    // Also send to a healthy actor to prove the system still works
    rt.send_to(good_addr, Increment { reply_to: *inbox.addr() }).unwrap();

    // When messages are processed
    for _ in 0..20 {
        rt.tick();
    }

    // Then: healthy actor still works, and only 1 panic recorded (not 3)
    let reply = inbox.try_recv();
    assert!(reply.is_some(), "healthy actor should still reply after peer is poisoned");

    let s = rt.stats();
    let total_panics: u64 = s.workers.iter().map(|w| w.panics).sum();
    assert_eq!(total_panics, 1, "only the first panic should be recorded; rest are discarded");
}

// ═══════════════════════════════════════════════════════════════════════════
// Observability
// ═══════════════════════════════════════════════════════════════════════════

#[test]
fn stats_report_spawned_actors() {
    // Given 3 spawned actors
    let rt = std_runtime(RuntimeConfig::default());
    for _ in 0..3 {
        rt.spawn(PingPongActor).unwrap();
    }
    rt.tick();

    // When I check stats
    let s = rt.stats();

    // Then the system accounts for every spawned actor
    assert!(
        s.actors.len() >= 3,
        "stats should report at least 3 actors, got {}",
        s.actors.len()
    );
}

#[test]
fn stats_report_message_throughput() {
    // Given 3 actors that each process 10 messages
    let rt = std_runtime(RuntimeConfig::default());
    let counter = Arc::new(AtomicUsize::new(0));
    let inbox = rt.new_inbox::<Pong>().unwrap();
    let inbox_addr = *inbox.addr();

    let mut addrs = Vec::new();
    for _ in 0..3 {
        addrs.push(rt.spawn(CountingPingActor { counter: counter.clone() }).unwrap());
    }

    for addr in &addrs {
        for _ in 0..10 {
            rt.send_to(*addr, Ping { reply_to: inbox_addr }).unwrap();
        }
    }

    // When messages are processed
    for _ in 0..50 {
        rt.tick();
    }

    // Then stats reflect the throughput
    let s = rt.stats();
    let total: u64 = s.workers.iter().map(|w| w.messages_processed).sum();
    assert!(
        total >= 30,
        "at least 30 messages should be processed, got {}",
        total
    );
}

#[test]
fn stats_record_panics() {
    // Given a PanicActor that panics twice
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(PanicActor).unwrap();

    rt.send_to(addr, PanicMsg).unwrap();
    rt.send_to(addr, PanicMsg).unwrap();

    // When messages are processed (stderr output expected)
    for _ in 0..10 {
        rt.tick();
    }

    // Then stats record the panic (second message is discarded — actor is poisoned)
    let s = rt.stats();
    let total_panics: u64 = s.workers.iter().map(|w| w.panics).sum();
    assert!(
        total_panics >= 1,
        "stats should record at least 1 panic, got {}",
        total_panics
    );
}

// ═══════════════════════════════════════════════════════════════════════════
// Edge Cases & Adversarial Tests
// ═══════════════════════════════════════════════════════════════════════════

#[test]
fn wrong_type_to_actor_increments_type_mismatch_counter() {
    // Given a PingPongActor that expects Ping
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(PingPongActor).unwrap();

    // When I send it a Count message (wrong type)
    rt.send_to(addr, Count(42)).unwrap();
    for _ in 0..10 {
        rt.tick();
    }

    // Then stats record the type mismatch
    let s = rt.stats();
    let mismatches: u64 = s.workers.iter().map(|w| w.type_mismatches).sum();
    assert_eq!(mismatches, 1, "sending wrong type should increment type_mismatches");
}

// FIXME dont count dropped messages
#[test]
fn type_mismatch_still_counted_as_processed() {
    // Given a PingPongActor
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(PingPongActor).unwrap();

    // When I send it 3 wrong-type messages
    for _ in 0..3 {
        rt.send_to(addr, Count(0)).unwrap();
    }
    for _ in 0..10 {
        rt.tick();
    }

    // Then all 3 are counted in both type_mismatches AND messages_processed
    let s = rt.stats();
    let mismatches: u64 = s.workers.iter().map(|w| w.type_mismatches).sum();
    let processed: u64 = s.workers.iter().map(|w| w.messages_processed).sum();
    assert_eq!(mismatches, 3);
    assert!(
        processed >= 3,
        "type-mismatched messages count as processed (dequeued+attempted), got {}",
        processed
    );
}

#[test]
fn self_send_chain_completes() {
    // Given a SelfSendActor that will bounce a message to itself 10 times
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(SelfSendActor).unwrap();
    let inbox = rt.new_inbox::<Done>().unwrap();

    // When triggered with remaining=10
    rt.send_to(addr, Countdown { remaining: 10, reply_to: *inbox.addr() }).unwrap();

    // Then after enough ticks the chain completes.
    let reply = tick_until_recv(&rt, &inbox, 50);
    assert_eq!(reply, Some(Done(0)), "self-send chain should complete");
}

#[test]
fn panic_mid_batch_discards_remaining_messages() {
    // Given an actor that processes 2 messages then panics on the 3rd
    let counter = Arc::new(AtomicUsize::new(0));
    let rt = std_runtime(RuntimeConfig::default());
    let dummy = rt.new_inbox::<Pong>().unwrap();
    let addr = rt.spawn(PanicAfterNActor {
        remaining_good: 2,
        counter: counter.clone(),
    }).unwrap();

    // When I queue 5 messages and tick (all arrive before first tick_all)
    for _ in 0..5 {
        rt.send_to(addr, Ping { reply_to: *dummy.addr() }).unwrap();
    }
    for _ in 0..20 {
        rt.tick();
    }

    // Then only 2 messages were processed — the 3rd panicked, 4th+5th discarded
    assert_eq!(
        counter.load(Ordering::SeqCst),
        2,
        "only messages before the panic should be processed"
    );
    let s = rt.stats();
    let panics: u64 = s.workers.iter().map(|w| w.panics).sum();
    assert_eq!(panics, 1, "exactly one panic should be recorded");
}

#[test]
fn spawn_then_panic_child_survives() {
    // Given a SpawnThenPanicActor
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(SpawnThenPanicActor).unwrap();
    let inbox = rt.new_inbox::<Done>().unwrap();

    // When the parent spawns a child, sends it work, then panics
    rt.send_to(addr, Forward { value: 5, reply_to: *inbox.addr() }).unwrap();

    // Then the child still processes the forwarded message and replies Done(10)
    let reply = tick_until_recv(&rt, &inbox, 30);
    assert_eq!(
        reply,
        Some(Done(10)),
        "child spawned before parent panic should still work"
    );
}

#[test]
fn panic_after_send_still_delivers_sent_messages() {
    // Given a SendThenPanicActor (sends Pong, then panics)
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(SendThenPanicActor).unwrap();
    let inbox = rt.new_inbox::<Pong>().unwrap();

    // When it processes a Ping (sends reply, then panics)
    rt.send_to(addr, Ping { reply_to: *inbox.addr() }).unwrap();

    // Then the Pong reply still arrives — sends happen before the panic unwinds
    let reply = tick_until_recv(&rt, &inbox, 20);
    assert!(
        reply.is_some(),
        "message sent before panic should still be delivered"
    );
}

// FIXME: document somewhere this behavior.
#[test]
fn send_to_poisoned_actor_is_a_silent_black_hole() {
    // Given a poisoned actor (panicked on first message)
    let rt = std_runtime(RuntimeConfig::default());
    let panic_addr = rt.spawn(PanicActor).unwrap();
    rt.send_to(panic_addr, PanicMsg).unwrap();
    for _ in 0..5 {
        rt.tick();
    }

    // When I send more messages to it (after cleanup, address is removed)
    let result = rt.send_to(panic_addr, PanicMsg);

    // Then send_to returns an error (actor has been cleaned up and removed)
    assert!(
        result.is_err(),
        "send_to cleaned-up actor should return error"
    );

    // And the original panic was recorded
    let s = rt.stats();
    let panics: u64 = s.workers.iter().map(|w| w.panics).sum();
    assert_eq!(panics, 1, "poisoned actor should have recorded one panic");
}

#[test]
fn tiny_buffer_delivers_all_messages_in_order() {
    // Given a runtime with channel_buffer_size=1
    let rt = std_runtime(RuntimeConfig {
        channel_buffer_size: 1,
        ..Default::default()
    });
    let addr = rt.spawn(CounterActor { count: 0 }).unwrap();
    let inbox = rt.new_inbox::<Count>().unwrap();

    // When I send 50 messages
    for _ in 0..50 {
        rt.send_to(addr, Increment { reply_to: *inbox.addr() }).unwrap();
    }

    // Then all 50 arrive and in FIFO order
    let replies = tick_and_drain(&rt, &inbox, 100);
    assert_eq!(replies.len(), 50, "all messages should arrive despite tiny buffer");
    assert_eq!(
        replies.last(),
        Some(&Count(50)),
        "messages should maintain FIFO order through overflow queue"
    );
}

#[test]
fn empty_runtime_tick_and_stats_are_safe() {
    // Given a runtime with no actors at all
    let rt = std_runtime(RuntimeConfig::default());

    // When I tick and check stats
    for _ in 0..10 {
        rt.tick();
    }
    let s = rt.stats();

    // Then everything reports zeros without panicking
    assert_eq!(s.actors.len(), 0);
    assert_eq!(s.num_workers, 1);
    let total: u64 = s.workers.iter().map(|w| w.messages_processed).sum();
    assert_eq!(total, 0);
}

#[test]
fn stats_stable_after_idle_ticks() {
    // Given an actor that processes a message
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(CounterActor { count: 0 }).unwrap();
    let inbox = rt.new_inbox::<Count>().unwrap();
    rt.send_to(addr, Increment { reply_to: *inbox.addr() }).unwrap();
    for _ in 0..5 {
        rt.tick();
    }
    let _ = inbox.try_recv();
    let s1 = rt.stats();

    // When I tick 100 more times with no messages
    for _ in 0..100 {
        rt.tick();
    }
    let s2 = rt.stats();

    // Then messages_processed doesn't grow during idle ticks
    let total1: u64 = s1.workers.iter().map(|w| w.messages_processed).sum();
    let total2: u64 = s2.workers.iter().map(|w| w.messages_processed).sum();
    assert_eq!(
        total1, total2,
        "idle ticks must not inflate messages_processed"
    );
}

#[test]
fn deep_spawn_chain_completes() {
    // Given a 100-level chain
    let rt = std_runtime(RuntimeConfig {
        max_actors: 2000,
        ..Default::default()
    });
    let addr = rt.spawn(ChainActor).unwrap();
    let inbox = rt.new_inbox::<Done>().unwrap();

    // When chain of depth 100 is triggered
    rt.send_to(
        addr,
        ChainMsg { remaining: 100, depth: 0, reply_to: *inbox.addr() },
    ).unwrap();

    // Then the leaf at depth 100 replies
    let reply = tick_until_recv(&rt, &inbox, 500);
    assert_eq!(
        reply,
        Some(Done(100)),
        "100-level chain should complete"
    );
}

#[test]
fn all_spawned_addresses_are_unique() {
    let rt = std_runtime(RuntimeConfig {
        max_actors: 10_000,
        ..Default::default()
    });
    let mut addrs: Vec<ActorAddress> = (0..1000)
        .map(|_| rt.spawn(PingPongActor).unwrap())
        .collect();

    addrs.sort_by_key(|a| a.0);
    let before = addrs.len();
    addrs.dedup_by_key(|a| a.0);
    assert_eq!(addrs.len(), before, "all 1000 addresses should be unique");
}

#[test]
fn inbox_empty_before_any_tick() {
    // Given a sent message that hasn't been ticked
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(PingPongActor).unwrap();
    let inbox = rt.new_inbox::<Pong>().unwrap();
    rt.send_to(addr, Ping { reply_to: *inbox.addr() }).unwrap();

    // Then inbox is empty — no processing without tick
    assert!(inbox.try_recv().is_none());
}

#[test]
fn interleaved_spawn_and_send_in_handler_all_complete() {
    // Given a FanOutActor that spawns 20 children with interleaved spawn+send
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(FanOutActor).unwrap();
    let inbox = rt.new_inbox::<Done>().unwrap();

    rt.send_to(addr, FanOut { count: 20, reply_to: *inbox.addr() }).unwrap();

    let replies = tick_and_drain(&rt, &inbox, 50);
    assert_eq!(
        replies.len(),
        20,
        "all 20 children spawned+messaged in same handler should reply"
    );
}

#[test]
fn multiple_inbox_types_coexist() {
    // Given two inboxes of different types on the same runtime
    let rt = std_runtime(RuntimeConfig::default());
    let counter = rt.spawn(CounterActor { count: 0 }).unwrap();
    let pinger = rt.spawn(PingPongActor).unwrap();
    let count_inbox = rt.new_inbox::<Count>().unwrap();
    let pong_inbox = rt.new_inbox::<Pong>().unwrap();

    // When both actors reply to their respective inboxes
    rt.send_to(counter, Increment { reply_to: *count_inbox.addr() }).unwrap();
    rt.send_to(pinger, Ping { reply_to: *pong_inbox.addr() }).unwrap();
    for _ in 0..10 {
        rt.tick();
    }

    // Then each inbox gets its correct type — no cross-contamination
    assert_eq!(count_inbox.try_recv(), Some(Count(1)));
    assert_eq!(pong_inbox.try_recv(), Some(Pong));
}

#[test]
fn poisoned_actor_messages_not_counted_as_processed() {
    // Given a poisoned actor that has been cleaned up
    let rt = std_runtime(RuntimeConfig::default());
    let panic_addr = rt.spawn(PanicActor).unwrap();
    rt.send_to(panic_addr, PanicMsg).unwrap();
    for _ in 0..5 {
        rt.tick();
    }
    let s1 = rt.stats();
    let processed_before: u64 = s1.workers.iter().map(|w| w.messages_processed).sum();

    // When I try to send 10 messages to the cleaned-up actor
    let mut send_failures = 0;
    for _ in 0..10 {
        if rt.send_to(panic_addr, PanicMsg).is_err() {
            send_failures += 1;
        }
    }
    for _ in 0..20 {
        rt.tick();
    }
    let s2 = rt.stats();
    let processed_after: u64 = s2.workers.iter().map(|w| w.messages_processed).sum();

    // Then sends fail (actor cleaned up) and processed count unchanged
    assert_eq!(send_failures, 10, "all sends should fail to cleaned-up actor");
    assert_eq!(
        processed_before, processed_after,
        "no additional messages should be processed after cleanup"
    );
}

#[test]
fn rapid_spawn_and_immediate_send() {
    // Given a runtime, spawn an actor and immediately send before any tick
    let rt = std_runtime(RuntimeConfig::default());
    let inbox = rt.new_inbox::<Pong>().unwrap();

    // When I spawn + send in rapid succession, 50 times
    let mut addrs = Vec::new();
    for _ in 0..50 {
        let addr = rt.spawn(PingPongActor).unwrap();
        rt.send_to(addr, Ping { reply_to: *inbox.addr() }).unwrap();
        addrs.push(addr);
    }

    // Then all 50 replies eventually arrive
    let replies = tick_and_drain(&rt, &inbox, 50);
    assert_eq!(replies.len(), 50, "all spawn+send pairs should complete");
}

// ═══════════════════════════════════════════════════════════════════════════
// Configuration
// ═══════════════════════════════════════════════════════════════════════════

#[test]
fn default_config_works_out_of_the_box() {
    // Given the default config — no tuning needed
    let rt = std_runtime(RuntimeConfig::default());
    let addr = rt.spawn(PingPongActor).unwrap();
    let inbox = rt.new_inbox::<Pong>().unwrap();

    // When I do the simplest possible thing
    rt.send_to(addr, Ping { reply_to: *inbox.addr() }).unwrap();

    // Then it just works
    let reply = tick_until_recv(&rt, &inbox, 10);
    assert!(reply.is_some(), "default config should work without tuning");
}

#[test]
fn custom_thread_count_respected() {
    // Given a config requesting 4 threads
    let rt = std_runtime(RuntimeConfig { num_threads: 4, ..Default::default() });
    // Spawn an actor so the runtime has something to report
    rt.spawn(PingPongActor).unwrap();
    let handle = rt.run().unwrap();

    // When I check stats
    let s = handle.runtime.stats();

    handle.shutdown();
    handle.join();

    // Then the runtime created the requested number of workers
    assert_eq!(s.num_workers, 4, "runtime should respect the requested thread count");
}

// ═══════════════════════════════════════════════════════════════════════════
// Fairness (message budget)
// ═══════════════════════════════════════════════════════════════════════════

#[test]
fn hot_actor_does_not_starve_cold_actor() {
    // Given: one "hot" actor with 1000 queued messages and one "cold" actor with 1 message
    let rt = std_runtime(RuntimeConfig::default());
    let hot_counter = Arc::new(AtomicUsize::new(0));
    let cold_inbox = rt.new_inbox::<Pong>().unwrap();

    let hot_addr = rt.spawn(CountingPingActor { counter: hot_counter.clone() }).unwrap();
    let cold_addr = rt.spawn(PingPongActor).unwrap();

    // Load the hot actor with 1000 messages
    let dummy = rt.new_inbox::<Pong>().unwrap();
    for _ in 0..1000 {
        rt.send_to(hot_addr, Ping { reply_to: *dummy.addr() }).unwrap();
    }
    // Send one message to the cold actor
    rt.send_to(cold_addr, Ping { reply_to: *cold_inbox.addr() }).unwrap();

    // When: we tick a limited number of times (default budget = 64 msgs/actor/tick)
    rt.tick();

    // Then: the cold actor replied even though the hot actor had 1000 queued messages
    let cold_reply = cold_inbox.try_recv();
    assert!(
        cold_reply.is_some(),
        "cold actor must not be starved by hot actor; message budget should enforce fairness"
    );
    // And the hot actor only processed its budget, not all 1000
    let hot_processed = hot_counter.load(Ordering::SeqCst);
    assert!(
        hot_processed <= 64,
        "hot actor should process at most the budget (64) per tick, got {hot_processed}"
    );
}

#[test]
fn unlimited_budget_drains_all_messages() {
    // Given: a runtime with unlimited budget (0)
    let rt = std_runtime(RuntimeConfig {
        actor_message_budget: 0,
        ..Default::default()
    });
    let counter = Arc::new(AtomicUsize::new(0));
    let dummy = rt.new_inbox::<Pong>().unwrap();
    let addr = rt.spawn(CountingPingActor { counter: counter.clone() }).unwrap();

    // When: 500 messages are queued and we tick once
    for _ in 0..500 {
        rt.send_to(addr, Ping { reply_to: *dummy.addr() }).unwrap();
    }
    rt.tick();
    rt.tick();

    // Then: all 500 are processed in a single pass (no budget limit)
    let processed = counter.load(Ordering::SeqCst);
    assert_eq!(processed, 500, "unlimited budget should drain all messages");
}

#[test]
fn budget_messages_drain_across_multiple_ticks() {
    // Given: an actor with more messages than the budget
    let rt = std_runtime(RuntimeConfig::default()); // budget=64
    let counter = Arc::new(AtomicUsize::new(0));
    let dummy = rt.new_inbox::<Pong>().unwrap();
    let addr = rt.spawn(CountingPingActor { counter: counter.clone() }).unwrap();

    // When: 200 messages are queued
    for _ in 0..200 {
        rt.send_to(addr, Ping { reply_to: *dummy.addr() }).unwrap();
    }

    // Then: it takes multiple ticks to drain them all
    for _ in 0..10 {
        rt.tick();
    }
    let processed = counter.load(Ordering::SeqCst);
    assert_eq!(processed, 200, "all messages should eventually be processed across ticks");
}

// ═══════════════════════════════════════════════════════════════════════════
// Stress Tests
// ═══════════════════════════════════════════════════════════════════════════

#[test]
fn message_ordering_preserved_under_budget() {
    // Given: a CounterActor processing messages with a small budget
    let rt = std_runtime(RuntimeConfig {
        actor_message_budget: 8,
        ..Default::default()
    });
    let addr = rt.spawn(CounterActor { count: 0 }).unwrap();
    let inbox = rt.new_inbox::<Count>().unwrap();

    // When: 100 messages are sent and processed across many ticks
    for _ in 0..100 {
        rt.send_to(addr, Increment { reply_to: *inbox.addr() }).unwrap();
    }
    for _ in 0..50 {
        rt.tick();
    }

    // Then: replies arrive in FIFO order
    let replies: Vec<_> = std::iter::from_fn(|| inbox.try_recv()).collect();
    assert_eq!(replies.len(), 100, "all 100 messages should be delivered");
    for (i, reply) in replies.iter().enumerate() {
        assert_eq!(
            *reply,
            Count(i + 1),
            "message ordering must be preserved under budget; expected Count({}) at position {i}",
            i + 1
        );
    }
}

#[test]
fn mt_stress_many_senders_one_receiver() {
    // Given: 4 threads, 50 senders each sending 100 messages to one receiver
    let rt = std_runtime(RuntimeConfig {
        num_threads: 4,
        max_actors: 5_000,
        channel_buffer_size: 10_000,
        ..Default::default()
    });
    let total_senders = 50;
    let msgs_per_sender = 100;
    let total_expected = total_senders * msgs_per_sender;

    let counter = Arc::new(AtomicUsize::new(0));
    let inbox = rt.new_inbox::<Pong>().unwrap();
    let receiver = rt.spawn(CountingPingActor { counter: counter.clone() }).unwrap();

    // Spawn senders and send messages
    for _ in 0..total_senders {
        for _ in 0..msgs_per_sender {
            rt.send_to(receiver, Ping { reply_to: *inbox.addr() }).unwrap();
        }
    }

    // When: runtime runs in background
    let handle = rt.run().unwrap();

    // Then: all messages are eventually processed
    let deadline = std::time::Instant::now() + std::time::Duration::from_secs(5);
    loop {
        let processed = counter.load(Ordering::SeqCst);
        if processed >= total_expected {
            break;
        }
        if std::time::Instant::now() > deadline {
            let processed = counter.load(Ordering::SeqCst);
            handle.shutdown();
            handle.join();
            panic!(
                "Timed out: only {processed}/{total_expected} messages processed in 5s"
            );
        }
        std::thread::sleep(std::time::Duration::from_millis(10));
    }

    handle.shutdown();
    handle.join();
    let final_count = counter.load(Ordering::SeqCst);
    assert_eq!(
        final_count, total_expected,
        "all {total_expected} messages should be processed"
    );
}

#[test]
fn mt_stress_concurrent_spawn_and_send() {
    // Given: a multi-threaded runtime
    let rt = std_runtime(RuntimeConfig {
        num_threads: 4,
        max_actors: 5_000,
        channel_buffer_size: 10_000,
        ..Default::default()
    });
    let inbox = rt.new_inbox::<Pong>().unwrap();
    let inbox_addr = *inbox.addr();

    // Spawn 200 actors and immediately send them messages before any ticks
    let mut addrs = Vec::new();
    for _ in 0..200 {
        let addr = rt.spawn(PingPongActor).unwrap();
        rt.send_to(addr, Ping { reply_to: inbox_addr }).unwrap();
        addrs.push(addr);
    }

    // When: runtime processes in background
    let handle = rt.run().unwrap();

    // Then: all 200 replies arrive
    let deadline = std::time::Instant::now() + std::time::Duration::from_secs(5);
    let mut received = 0;
    while received < 200 {
        if inbox.try_recv().is_some() {
            received += 1;
        } else if std::time::Instant::now() > deadline {
            handle.shutdown();
            handle.join();
            panic!("Timed out: only {received}/200 replies received in 5s");
        } else {
            std::thread::sleep(std::time::Duration::from_millis(1));
        }
    }

    handle.shutdown();
    handle.join();
    assert_eq!(received, 200, "all 200 concurrent spawn+send pairs should complete");
}

#[test]
fn mt_chain_spawning_under_load() {
    // Given: a multi-threaded runtime with a chain actor
    let rt = std_runtime(RuntimeConfig {
        num_threads: 2,
        max_actors: 5_000,
        ..Default::default()
    });
    let addr = rt.spawn(ChainActor).unwrap();
    let inbox = rt.new_inbox::<Done>().unwrap();

    // When: we trigger a 50-level chain
    rt.send_to(
        addr,
        ChainMsg { remaining: 50, depth: 0, reply_to: *inbox.addr() },
    )
    .unwrap();
    let handle = rt.run().unwrap();

    // Then: the chain completes despite actors being on different workers
    let deadline = std::time::Instant::now() + std::time::Duration::from_secs(5);
    let mut reply = None;
    while reply.is_none() {
        if let Some(msg) = inbox.try_recv() {
            reply = Some(msg);
        } else if std::time::Instant::now() > deadline {
            handle.shutdown();
            handle.join();
            panic!("Timed out waiting for chain completion");
        } else {
            std::thread::sleep(std::time::Duration::from_millis(1));
        }
    }

    handle.shutdown();
    handle.join();
    assert_eq!(
        reply,
        Some(Done(50)),
        "50-level chain should complete across multiple workers"
    );
}

#[test]
fn mt_panic_isolation_under_load() {
    // Given: a 4-thread runtime with panicking and healthy actors
    let rt = std_runtime(RuntimeConfig {
        num_threads: 4,
        max_actors: 5_000,
        channel_buffer_size: 10_000,
        ..Default::default()
    });
    let counter = Arc::new(AtomicUsize::new(0));
    let dummy = rt.new_inbox::<Pong>().unwrap();

    // Spawn 10 panicking actors and 10 healthy counting actors
    let mut panic_addrs = Vec::new();
    let mut healthy_addrs = Vec::new();
    for _ in 0..10 {
        panic_addrs.push(rt.spawn(PanicActor).unwrap());
        healthy_addrs.push(rt.spawn(CountingPingActor { counter: counter.clone() }).unwrap());
    }

    // Trigger panics and send 100 messages to each healthy actor
    for &addr in &panic_addrs {
        rt.send_to(addr, PanicMsg).unwrap();
    }
    for &addr in &healthy_addrs {
        for _ in 0..100 {
            rt.send_to(addr, Ping { reply_to: *dummy.addr() }).unwrap();
        }
    }

    // When: runtime runs
    let handle = rt.run().unwrap();

    let deadline = std::time::Instant::now() + std::time::Duration::from_secs(5);
    let expected = 10 * 100;
    loop {
        let processed = counter.load(Ordering::SeqCst);
        if processed >= expected {
            break;
        }
        if std::time::Instant::now() > deadline {
            let processed = counter.load(Ordering::SeqCst);
            handle.shutdown();
            handle.join();
            panic!("Timed out: only {processed}/{expected} healthy messages processed");
        }
        std::thread::sleep(std::time::Duration::from_millis(10));
    }

    handle.shutdown();
    handle.join();

    // Then: all healthy actors processed all their messages despite panicking peers
    let final_count = counter.load(Ordering::SeqCst);
    assert_eq!(
        final_count, expected,
        "panicking actors should not affect healthy actors on other workers"
    );
}

#[test]
fn sustained_throughput_does_not_drop_messages() {
    // Given: a runtime processing messages in batches, simulating sustained load
    let rt = std_runtime(RuntimeConfig::default());
    let counter = Arc::new(AtomicUsize::new(0));
    let dummy = rt.new_inbox::<Pong>().unwrap();
    let addr = rt.spawn(CountingPingActor { counter: counter.clone() }).unwrap();

    // When: we send 10 batches of 100 messages, ticking between batches
    for batch in 0..10 {
        for _ in 0..100 {
            rt.send_to(addr, Ping { reply_to: *dummy.addr() }).unwrap();
        }
        // Tick enough to process one budget worth per batch
        for _ in 0..5 {
            rt.tick();
        }
        // Verify progress is being made (not stuck)
        let processed = counter.load(Ordering::SeqCst);
        assert!(
            processed > batch * 50,
            "batch {batch}: should have made progress, only {processed} processed"
        );
    }

    // Drain remaining
    for _ in 0..100 {
        rt.tick();
    }

    // Then: all 1000 messages are eventually processed
    let total = counter.load(Ordering::SeqCst);
    assert_eq!(total, 1000, "sustained load should not drop any messages");
}

#[test]
fn mt_parked_worker_wakes_on_send() {
    // Given: a 2-thread runtime that has been idle (workers are parked)
    let rt = std_runtime(RuntimeConfig {
        num_threads: 2,
        ..Default::default()
    });
    let addr = rt.spawn(PingPongActor).unwrap();
    let inbox = rt.new_inbox::<Pong>().unwrap();

    let handle = rt.run().unwrap();

    // Let workers park (idle for a while)
    std::thread::sleep(std::time::Duration::from_millis(50));

    // When: we send a message to a parked worker
    let before = std::time::Instant::now();
    handle.runtime.send_to(addr, Ping { reply_to: *inbox.addr() }).unwrap();

    // Then: the worker wakes up and processes the message quickly
    let mut received = false;
    for _ in 0..1000 {
        if inbox.try_recv().is_some() {
            received = true;
            break;
        }
        std::thread::sleep(std::time::Duration::from_millis(1));
    }
    let latency = before.elapsed();

    handle.shutdown();
    handle.join();

    assert!(received, "parked worker should wake up and process the message");
    assert!(
        latency.as_millis() < 100,
        "wake-from-park latency should be low, was {:?}",
        latency
    );
}

// ═══════════════════════════════════════════════════════════════════════════
// Competitor Bug-Inspired Tests
// ═══════════════════════════════════════════════════════════════════════════

#[test]
fn stats_snapshot_is_read_only() {
    let rt = std_runtime(RuntimeConfig::default());
    let _addr = rt.spawn(PingPongActor).unwrap();
    rt.tick();

    let s1 = rt.stats();
    let s2 = rt.stats();
    let s3 = rt.stats();

    assert_eq!(s1.actors.len(), s2.actors.len(), "stats() should not mutate state");
    assert_eq!(s2.actors.len(), s3.actors.len(), "repeated stats() calls must be idempotent");
    assert!(s1.actors.len() >= 1, "should report at least 1 actor");
}

#[test]
fn stats_under_load_do_not_interfere_with_processing() {
    let rt = std_runtime(RuntimeConfig::default());
    let counter = Arc::new(AtomicUsize::new(0));
    let dummy = rt.new_inbox::<Pong>().unwrap();
    let addr = rt.spawn(CountingPingActor { counter: counter.clone() }).unwrap();

    for _ in 0..100 {
        rt.send_to(addr, Ping { reply_to: *dummy.addr() }).unwrap();
    }

    // Interleave stats calls with ticks
    for _ in 0..20 {
        rt.tick();
        let _s = rt.stats();
    }

    let processed = counter.load(Ordering::SeqCst);
    assert_eq!(processed, 100, "stats() calls must not interfere with message processing");
}

#[test]
fn shutdown_wakes_parked_workers_immediately() {
    let rt = std_runtime(RuntimeConfig {
        num_threads: 4,
        ..Default::default()
    });
    let handle = rt.run().unwrap();

    // Let workers park
    std::thread::sleep(std::time::Duration::from_millis(50));

    // Shutdown should wake all parked workers
    let before = std::time::Instant::now();
    handle.shutdown();
    handle.join();
    let shutdown_time = before.elapsed();

    assert!(
        shutdown_time.as_millis() < 500,
        "shutdown should complete quickly with parked workers, took {:?}",
        shutdown_time
    );
}

#[test]
fn mt_send_after_run_delivers_to_running_actors() {
    let rt = std_runtime(RuntimeConfig {
        num_threads: 2,
        ..Default::default()
    });
    let addr = rt.spawn(PingPongActor).unwrap();
    let inbox = rt.new_inbox::<Pong>().unwrap();

    // Start the runtime FIRST, then send
    let handle = rt.run().unwrap();

    // Give workers a moment to start
    std::thread::sleep(std::time::Duration::from_millis(10));

    // Send after run()
    handle.runtime.send_to(addr, Ping { reply_to: *inbox.addr() }).unwrap();

    let deadline = std::time::Instant::now() + std::time::Duration::from_secs(5);
    let mut received = false;
    while !received {
        if inbox.try_recv().is_some() {
            received = true;
        } else if std::time::Instant::now() > deadline {
            handle.shutdown();
            handle.join();
            panic!("Message sent after run() was not delivered");
        } else {
            std::thread::sleep(std::time::Duration::from_millis(1));
        }
    }

    handle.shutdown();
    handle.join();
    assert!(received, "messages sent after run() must be delivered");
}

#[test]
fn budget_respected_even_with_self_sends() {
    let rt = std_runtime(RuntimeConfig {
        actor_message_budget: 4,
        ..Default::default()
    });
    let addr = rt.spawn(SelfSendActor).unwrap();
    let inbox = rt.new_inbox::<Done>().unwrap();

    // remaining=20 means 20 self-sends before replying Done(0)
    rt.send_to(addr, Countdown { remaining: 20, reply_to: *inbox.addr() }).unwrap();

    // With budget=4, each tick processes at most 4 messages per actor.
    for _ in 0..30 {
        rt.tick();
    }

    let reply = inbox.try_recv();
    assert_eq!(
        reply,
        Some(Done(0)),
        "self-send chain should complete despite message budget"
    );
}