//! IPC round-trip latency benchmark (#342, D-020)
//!
//! Measures end-to-end latency from client send (write_framed) to client receive
//! (read_framed) over the real subprocess IPC channel. Reports p50/p95/p99.
//!
//! Latency budget: p99 must be <= 5ms (D-020: "~1-5ms serialization latency per tick").
//!
//! Run with:
//!   cargo test --release --test ipc_bench -- --ignored --nocapture
//!
//! Output: IPC_BENCH_RESULT:{json} on a single line for tooling to parse.
//!
//!
//! Spec references: D-020 (subprocess IPC, 5ms budget), D-030 (Layer 3)

use settled_reach_server::bridge::framing::{read_framed, write_framed};
use settled_reach_server::bridge::types::*;
use std::io::{BufRead, BufReader, BufWriter};
use std::net::TcpStream;
use std::process::{Command, Stdio};
use std::time::{Duration, Instant};

/// Number of warmup round-trips before timing begins.
const WARMUP_ROUNDS: usize = 10;

/// Number of timed round-trips (N in the spec).
const MEASURE_ROUNDS: usize = 100;

/// Latency threshold (p99 must be below this). D-020: "~1-5ms per tick".
const THRESHOLD_MS: f64 = 5.0;

/// Timeout for the server to emit LISTENING:{port} on stdout.
const LISTEN_TIMEOUT: Duration = Duration::from_secs(15);

/// Timeout per round-trip read.
const ROUND_TRIP_TIMEOUT: Duration = Duration::from_secs(5);

fn percentile(sorted: &[f64], p: f64) -> f64 {
    if sorted.is_empty() {
        return 0.0;
    }
    let idx = ((sorted.len() - 1) as f64 * p).floor() as usize;
    sorted[idx.min(sorted.len() - 1)]
}

#[test]
#[ignore]
fn ipc_round_trip_latency() {
    // 1. Spawn server binary with --test-mode --port 0
    let server_bin = env!("CARGO_BIN_EXE_settled-reach-server");
    let mut child = Command::new(server_bin)
        .args(["--test-mode", "--port", "0"])
        .stdout(Stdio::piped())
        .stderr(Stdio::piped())
        .spawn()
        .expect("failed to spawn server binary");

    let stdout = child.stdout.take().expect("stdout not captured");
    let mut stdout_reader = BufReader::new(stdout);

    // 2. Parse LISTENING:{port} from stdout
    let port = {
        let deadline = Instant::now() + LISTEN_TIMEOUT;
        let mut line = String::new();
        loop {
            line.clear();
            match stdout_reader.read_line(&mut line) {
                Ok(0) => panic!("server stdout closed before LISTENING signal"),
                Ok(_) => {
                    let trimmed = line.trim();
                    if let Some(port_str) = trimmed.strip_prefix("LISTENING:") {
                        break port_str
                            .parse::<u16>()
                            .unwrap_or_else(|e| panic!("invalid port '{}': {}", port_str, e));
                    }
                }
                Err(e) => panic!("failed to read server stdout: {}", e),
            }
            assert!(
                Instant::now() < deadline,
                "timed out waiting for LISTENING signal"
            );
        }
    };

    // 3. Connect via TCP
    let addr = format!("127.0.0.1:{}", port);
    let stream = TcpStream::connect(&addr)
        .unwrap_or_else(|e| panic!("failed to connect to {}: {}", addr, e));
    stream
        .set_read_timeout(Some(ROUND_TRIP_TIMEOUT))
        .expect("set read timeout");

    let mut reader = BufReader::new(stream.try_clone().expect("clone stream"));
    let mut writer = BufWriter::new(stream);

    // 4. Handshake: read and validate HandshakeMessage before timing (#555/#556).
    // Server sends HandshakeMessage { protocol_version } as the very first framed message.
    let handshake_bytes = read_framed(&mut reader)
        .expect("read handshake")
        .expect("server closed before sending HandshakeMessage");
    // D-192: HandshakeMessage carries no version field. Verify it deserialises cleanly.
    let _handshake: HandshakeMessage =
        rmp_serde::from_slice(&handshake_bytes).expect("deserialize HandshakeMessage");

    let make_input = |tick: u64| PlayerInput {
        tick,
        action: PlayerAction::MoveNorth,
    };

    let mut round_trip_ms: Vec<f64> = Vec::with_capacity(WARMUP_ROUNDS + MEASURE_ROUNDS);

    // 5. Warmup rounds (not timed)
    for tick in 0..WARMUP_ROUNDS as u64 {
        let payload =
            rmp_serde::to_vec_named(&vec![make_input(tick)]).expect("serialize PlayerInput");
        write_framed(&mut writer, &payload).expect("send warmup input");
        let _ = read_framed(&mut reader)
            .expect("read warmup snapshot")
            .expect("server closed during warmup");
    }

    // 6. Timed measurement rounds
    for tick in WARMUP_ROUNDS as u64..(WARMUP_ROUNDS + MEASURE_ROUNDS) as u64 {
        let payload =
            rmp_serde::to_vec_named(&vec![make_input(tick)]).expect("serialize PlayerInput");

        let t_send = Instant::now();
        write_framed(&mut writer, &payload).expect("send timed input");
        let response = read_framed(&mut reader)
            .expect("read timed snapshot")
            .expect("server closed during measurement");
        let elapsed_ms = t_send.elapsed().as_secs_f64() * 1000.0;

        // Verify we received a valid snapshot (not just noise)
        let _snapshot: ObserverSnapshot =
            rmp_serde::from_slice(&response).expect("deserialize ObserverSnapshot");

        round_trip_ms.push(elapsed_ms);
    }

    // 7. Clean up
    drop(reader);
    drop(writer);
    let exit_deadline = Instant::now() + Duration::from_secs(5);
    loop {
        match child.try_wait() {
            Ok(Some(_)) => break,
            Ok(None) => {
                if Instant::now() > exit_deadline {
                    child.kill().ok();
                    child.wait().ok();
                    break;
                }
                std::thread::sleep(Duration::from_millis(50));
            }
            Err(_) => {
                child.kill().ok();
                break;
            }
        }
    }

    // 8. Compute percentiles
    let mut sorted = round_trip_ms.clone();
    sorted.sort_by(|a, b| a.partial_cmp(b).unwrap());

    let p50 = percentile(&sorted, 0.50);
    let p95 = percentile(&sorted, 0.95);
    let p99 = percentile(&sorted, 0.99);
    let passed = p99 <= THRESHOLD_MS;

    let result = serde_json::json!({
        "p50_ms": (p50 * 100.0).round() / 100.0,
        "p95_ms": (p95 * 100.0).round() / 100.0,
        "p99_ms": (p99 * 100.0).round() / 100.0,
        "threshold_ms": THRESHOLD_MS,
        "passed": passed,
        "rounds": MEASURE_ROUNDS,
    });

    println!(
        "IPC_BENCH_RESULT:{}",
        serde_json::to_string(&result).unwrap()
    );

    // Fail the test if we exceed the latency budget
    assert!(
        passed,
        "IPC latency budget exceeded: p99={:.2}ms > threshold={}ms",
        p99, THRESHOLD_MS
    );
}