//! ptytest -- checks pseudo-terminals (ptys) and the line discipline.
//!
//! A pty is a pair: the *master* side is held by a terminal emulator (or
//! ssh, tmux, a compositor's terminal window), the *slave* side
//! (/dev/pts/N) looks exactly like a real terminal to the program running
//! on it. Between them sits the line discipline: in *canonical* mode it
//! collects a whole line (with backspace editing) before the program can
//! read it, echoes what's typed, turns ^C into SIGINT; in *raw* mode bytes
//! pass straight through (what editors and games use).
#![no_std]
#![no_main]

#[macro_use]
#[path = "ulib.rs"]
mod ulib;

extern crate alloc;

use alloc::format;
use alloc::string::String;
use ulib::*;

/// Read whatever the other side has (waits up to 1 s for the first byte).
fn read_some(fd: i64, buf: &mut [u8]) -> usize {
    let mut p = [PollFd { fd: fd as i32, events: POLLIN, revents: 0 }];
    if poll(&mut p, 1000) <= 0 {
        return 0;
    }
    read(fd, buf).max(0) as usize
}

/// musl's ttyname(fd), step by step (stage 19): the name is what
/// /proc/self/fd/N points to, but only if stat() of that name is the same
/// file (st_dev and st_ino) as fstat(fd). Otherwise ENODEV.
fn ttyname(fd: i64) -> Result<String, i64> {
    let mut buf = [0u8; 64];
    let n = readlink(&format!("/proc/self/fd/{}", fd), &mut buf);
    if n < 0 {
        return Err(n);
    }
    let name = String::from(core::str::from_utf8(&buf[..n as usize]).map_err(|_| -EINVAL)?);
    let (mut a, mut b) = (Stat::default(), Stat::default());
    if stat(&name, &mut a) != 0 || fstat(fd, &mut b) != 0 {
        return Err(-ENOENT);
    }
    if a.dev != b.dev || a.ino != b.ino {
        return Err(-ENODEV);
    }
    Ok(name)
}

/// Linux's device numbers (`makedev`).
fn makedev(major: u64, minor: u64) -> u64 {
    ((major & 0xffff_f000) << 32) | ((major & 0xfff) << 8) | ((minor & 0xffff_ff00) << 12) | (minor & 0xff)
}

/// Every /dev node has one identity: stat twice, or stat and fstat of an
/// open fd, agree; st_rdev and the mode are Linux's.
fn device_identities(c: &mut Checks, master: i64, slave: i64, n: u32) {
    for (path, major, minor, perm) in [
        ("/dev/null", 1, 3, 0o666),
        ("/dev/zero", 1, 5, 0o666),
        ("/dev/random", 1, 8, 0o666),
        ("/dev/urandom", 1, 9, 0o666),
        ("/dev/tty", 5, 0, 0o666),
        ("/dev/console", 5, 1, 0o600),
        ("/dev/ptmx", 5, 2, 0o666),
    ] {
        let (mut a, mut b, mut f) = (Stat::default(), Stat::default(), Stat::default());
        stat(path, &mut a);
        stat(path, &mut b);
        let fd = if path == "/dev/tty" { -1 } else { open(path, O_RDWR | O_NOCTTY) };
        let fd_same = fd < 0 || (fstat(fd, &mut f) == 0 && f.dev == a.dev && f.ino == a.ino && f.rdev == a.rdev && f.mode == a.mode);
        if fd >= 0 {
            close(fd); // (for /dev/ptmx: a new pty, gone again)
        }
        c.check(
            a.ino == b.ino && a.dev == b.dev && a.rdev == makedev(major, minor) && a.mode == S_IFCHR | perm && fd_same,
            &format!("{}: char device {}:{}, mode {:o}, one inode for stat and fstat", path, major, minor, perm),
        );
    }
    let (mut a, mut m) = (Stat::default(), Stat::default());
    stat(&format!("/dev/pts/{}", n), &mut a);
    c.check(a.rdev == makedev(136, n as u64) && a.mode == S_IFCHR | 0o620, "/dev/pts/N: char device 136:N, mode 620");
    stat("/dev/ptmx", &mut a);
    fstat(master, &mut m);
    c.check(m.ino == a.ino && m.rdev == makedev(5, 2), "a pty master fstats as /dev/ptmx");
    c.check(ttyname(slave) == Ok(format!("/dev/pts/{}", n)), "ttyname(pty slave) = /dev/pts/N");
    let console = open("/dev/console", O_RDWR | O_NOCTTY);
    c.check(ttyname(console).as_deref() == Ok("/dev/console"), "ttyname(console fd) = /dev/console");
    close(console);
    // The console fds the kernel gave us (if stdin is the console).
    if isatty(0) {
        c.check(ttyname(0).is_ok(), "ttyname(0) works for the console the kernel handed us");
    }
    let mut buf = [0u8; 64];
    let r = readlink("/proc/self/cwd", &mut buf);
    let mut cwd = [0u8; 64];
    let k = getcwd(&mut cwd);
    c.check(r > 0 && r == k && buf[..r as usize] == cwd[..k as usize], "/proc/self/cwd links to the current directory");
}

fn main() -> i64 {
    let mut c = Checks::new("ptytest");
    let (master, n) = match openpty() {
        Ok(x) => x,
        Err(e) => {
            println!("ptytest: openpty: {}", strerror(e));
            return 1;
        }
    };
    let path = format!("/dev/pts/{}", n);
    let slave = open(&path, O_RDWR | O_NOCTTY);
    c.check(slave >= 0, &format!("open {} (the slave side)", path));
    device_identities(&mut c, master, slave, n);
    let mut buf = [0u8; 64];

    // Canonical mode: a line is readable only once it's complete.
    write(master, b"hel");
    set_nonblocking(slave, true);
    c.check(read(slave, &mut buf) == -EAGAIN, "canonical: half a line can't be read yet (EAGAIN)");
    write(master, b"lo\x7f\x7fp me\r"); // two backspaces, then Enter ('\r')
    let got = read_some(slave, &mut buf);
    c.check(&buf[..got] == b"help me\n", "canonical: backspace edits the line, Enter ('\\r') ends it as '\\n'");
    let got = read_some(master, &mut buf);
    c.check(got > 0 && buf[..got].ends_with(b"\r\n"), "echo: what's typed comes back to the master");

    // Output processing: the program's '\n' reaches the terminal as "\r\n".
    write(slave, b"out\n");
    let got = read_some(master, &mut buf);
    c.check(&buf[..got] == b"out\r\n", "output: '\\n' becomes \"\\r\\n\" (ONLCR)");

    // Raw mode: every byte at once, no echo, no conversions.
    let saved = tcgetattr(slave).unwrap_or_default();
    let mut raw = saved;
    cfmakeraw(&mut raw);
    c.check(tcsetattr(slave, &raw) == 0, "TCSETS: switch to raw mode");
    write(master, b"x\r\x03");
    let got = read_some(slave, &mut buf);
    c.check(&buf[..got] == b"x\r\x03", "raw: bytes arrive at once, unchanged (even ^C)");
    set_nonblocking(master, true);
    c.check(read(master, &mut buf) == -EAGAIN, "raw: no echo");
    set_nonblocking(master, false);
    tcsetattr(slave, &saved);
    c.check(tcgetattr(slave).map(|t| t.lflag & ICANON != 0).unwrap_or(false), "TCGETS: canonical mode back on");
    // (We keep `slave` open: with no slave open at all, the master reports
    // a hang-up (POLLHUP) instead of waiting for the child to open it.)

    // ^C: a child makes the pty its controlling terminal (setsid + open)
    // and waits; typing ^C on the master must kill it with SIGINT.
    let pid = fork();
    if pid == 0 {
        setsid();
        let fd = open(&path, O_RDWR); // session leader: becomes our ctty
        if fd < 0 {
            exit(3);
        }
        // /dev/tty is "my controlling terminal", whichever that is.
        let me = open("/dev/tty", O_RDWR);
        if me < 0 {
            exit(4);
        }
        write(me, b"ready\n");
        loop {
            pause();
        }
    }
    let got = read_some(master, &mut buf); // "ready\r\n"
    c.check(&buf[..got] == b"ready\r\n", "child opened the pty as its controlling terminal");
    write(master, b"\x03");
    let status = match wait4(pid, 0) {
        Ok((_, s)) => s,
        Err(_) => 0,
    };
    c.check(wifsignaled(status) && wtermsig(status) == SIGINT, "^C on the master: SIGINT for the foreground job");
    let got = read_some(master, &mut buf);
    c.check(got >= 2 && &buf[..2] == b"^C", "^C is echoed as \"^C\"");

    // ^\ is SIGQUIT (it would dump core on Unix).
    let pid = fork();
    if pid == 0 {
        setsid();
        if open(&path, O_RDWR) < 0 {
            exit(3);
        }
        loop {
            pause();
        }
    }
    sleep_ms(100); // let the child open the pty first
    write(master, b"\x1c");
    let status = match wait4(pid, 0) {
        Ok((_, s)) => s,
        Err(_) => 0,
    };
    c.check(wifsignaled(status) && wtermsig(status) == SIGQUIT, "^\\ on the master: SIGQUIT");
    set_nonblocking(master, true);
    while read(master, &mut buf) > 0 {} // drop the "^\\" echo
    set_nonblocking(master, false);
    // Without a controlling terminal, /dev/tty doesn't exist for us.
    let pid = fork();
    if pid == 0 {
        setsid();
        exit(if open("/dev/tty", O_RDWR) < 0 { 0 } else { 1 });
    }
    c.check(matches!(wait4(pid, 0), Ok((_, 0))), "no controlling terminal: /dev/tty fails");

    // Hang-up: closing the master gives the slave end-of-file.
    close(master);
    c.check(read(slave, &mut buf) == 0, "master closed: the slave reads end-of-file");
    close(slave);
    c.done()
}