use super::{Limits, Runtime, Socket, net};
use bytes::BufMut;
use std::{io::ErrorKind, time::Instant};
use tokio::{io::AsyncWriteExt, net::TcpStream};

async fn independent_read(socket: &TcpStream, limit: usize) -> Option<Vec<u8>> {
    socket.readable().await.unwrap();
    let mut bytes = Vec::new();
    bytes.try_reserve_exact(limit).unwrap();
    loop {
        let result = socket.try_read_buf(&mut (&mut bytes).limit(limit));
        match result {
            Ok(count) => return (count != 0).then_some(bytes),
            Err(error) if error.kind() == ErrorKind::WouldBlock => {
                socket.readable().await.unwrap();
            }
            Err(error) => panic!("independent TCP read failed: {error}"),
        }
    }
}

async fn sample(
    peer: &mut TcpStream,
    payload: &[u8],
    limit: usize,
    iterations: usize,
    mut read: impl AsyncFnMut() -> Option<Vec<u8>>,
) -> (u128, usize, usize) {
    let mut elapsed = 0;
    let mut reads = 0;
    let mut total = 0;
    for _ in 0..iterations {
        peer.write_all(payload).await.unwrap();
        let mut received = 0;
        loop {
            let started = Instant::now();
            let bytes = read().await;
            elapsed += started.elapsed().as_nanos();
            reads += 1;
            let Some(bytes) = bytes else {
                assert!(payload.is_empty());
                break;
            };
            assert!(!bytes.is_empty() && bytes.len() <= limit);
            assert!(received + bytes.len() <= payload.len());
            assert_eq!(bytes, payload[received..received + bytes.len()]);
            received += bytes.len();
            total += bytes.len();
            if received == payload.len() {
                break;
            }
        }
    }
    assert_eq!(total, payload.len() * iterations);
    (elapsed, reads, total)
}

#[test]
#[ignore = "explicit release performance probe; http enables the independent bytes/io-util peer"]
fn tcp_read_buffer_cost() {
    let runtime = Runtime::new(Limits {
        threads: 1,
        workers: 1,
        tasks: 8,
    })
    .unwrap();
    runtime
        .run(async |scope| {
            eprintln!(
                "tcp_read_buffer: 15 fixed rounds; one async worker; two persistent loopback pairs; \
                 peer writes, byte verification and result drops excluded from read timing; \
                 rust_independent uses Tokio try_read_buf and bytes::BufMut::limit directly; \
                 no shared Dever read implementation; direct peer excludes alias-close and read-lock checks; \
                 actual read counts are retained; empty payload cases measure established EOF"
            );
            println!("\ncase,sample,implementation,iterations,elapsed_ns,reads,bytes");
            for (limit, payload_size, iterations) in [
                (64, 64, 4096),
                (65_536, 64, 2048),
                (1_048_576, 64, 512),
                (65_536, 65_536, 256),
                (1_048_576, 65_536, 128),
                (65_536, 0, 512),
                (1_048_576, 0, 128),
            ] {
                let listener = net::listen("127.0.0.1", 0, scope).await.unwrap();
                let mut dever_peer =
                    TcpStream::connect(("127.0.0.1", listener.port().unwrap() as u16))
                        .await
                        .unwrap();
                let socket: Socket = listener.accept().await.unwrap();
                listener.close().unwrap();
                let listener = tokio::net::TcpListener::bind(("127.0.0.1", 0)).await.unwrap();
                let mut independent_peer = TcpStream::connect(listener.local_addr().unwrap())
                    .await
                    .unwrap();
                let independent = listener.accept().await.unwrap().0;
                independent.set_nodelay(true).unwrap();
                dever_peer.set_nodelay(true).unwrap();
                independent_peer.set_nodelay(true).unwrap();
                drop(listener);
                if payload_size == 0 {
                    dever_peer.shutdown().await.unwrap();
                    independent_peer.shutdown().await.unwrap();
                }
                let payload = (0..payload_size)
                    .map(|position| (position % 251) as u8)
                    .collect::<Vec<_>>();
                sample(&mut dever_peer, &payload, limit, 16, async || {
                    socket.read(limit as i64).await.unwrap()
                })
                .await;
                sample(&mut independent_peer, &payload, limit, 16, async || {
                    independent_read(&independent, limit).await
                })
                .await;
                for round in 0..15 {
                    let mut order = ["dever", "rust_independent", "control"];
                    order.rotate_left(round % 3);
                    for label in order {
                        let (elapsed, reads, total) = if label == "rust_independent" {
                            sample(&mut independent_peer, &payload, limit, iterations, async || {
                                independent_read(&independent, limit).await
                            })
                            .await
                        } else {
                            sample(&mut dever_peer, &payload, limit, iterations, async || {
                                socket.read(limit as i64).await.unwrap()
                            })
                            .await
                        };
                        println!(
                            "tcp_read_{limit}_{payload_size},{round},{label},{iterations},{elapsed},{reads},{total}"
                        );
                    }
                }
                socket.close().unwrap();
            }
        })
        .unwrap();
}