use std::ffi::OsStr;
use std::os::unix::ffi::OsStrExt;
use std::path::PathBuf;

/// Get the foreground process name for a given child PID.
///
/// Uses `proc_pidinfo(PROC_PIDTBSDINFO)` to read `e_tpgid` — the foreground
/// process group ID of the child's controlling terminal. Then `proc_name()`
/// to resolve that PID to a short command name.
///
/// This is the macOS equivalent of Linux's `/proc/{pid}/stat` → tpgid → `/proc/{tpgid}/comm`.
pub fn foreground_process_name(child_pid: u32) -> Option<String> {
    if child_pid == 0 {
        return None;
    }

    // Get BSD info for the child process — contains e_tpgid
    let mut info: libc::proc_bsdinfo = unsafe { std::mem::zeroed() };
    let size = std::mem::size_of::<libc::proc_bsdinfo>() as libc::c_int;

    let ret = unsafe {
        libc::proc_pidinfo(
            child_pid as libc::c_int,
            libc::PROC_PIDTBSDINFO,
            0,
            &mut info as *mut _ as *mut libc::c_void,
            size,
        )
    };

    if ret != size {
        return None;
    }

    let fg_pid = info.e_tpgid;
    if fg_pid == 0 {
        return None;
    }

    // Resolve the foreground PID to a process name
    let mut buf = [0u8; libc::MAXCOMLEN + 1];
    let len = unsafe {
        libc::proc_name(
            fg_pid as libc::c_int,
            buf.as_mut_ptr() as *mut libc::c_void,
            buf.len() as u32,
        )
    };

    if len <= 0 {
        return None;
    }

    let len = len as usize;
    let end = buf[..len].iter().position(|&b| b == 0).unwrap_or(len);
    Some(String::from_utf8_lossy(&buf[..end]).into_owned())
}

/// Get the current working directory of a process.
///
/// Uses `proc_pidinfo(PROC_PIDVNODEPATHINFO)` to read `pvi_cdir.vip_path`.
pub fn process_cwd(pid: u32) -> Option<PathBuf> {
    if pid == 0 {
        return None;
    }

    let mut pathinfo: libc::proc_vnodepathinfo = unsafe { std::mem::zeroed() };
    let size = std::mem::size_of::<libc::proc_vnodepathinfo>() as libc::c_int;

    let ret = unsafe {
        libc::proc_pidinfo(
            pid as libc::c_int,
            libc::PROC_PIDVNODEPATHINFO,
            0,
            &mut pathinfo as *mut _ as *mut libc::c_void,
            size,
        )
    };

    if ret != size {
        return None;
    }

    // vip_path is [[c_char; 32]; 32] in libc (workaround for old Rust const generics).
    // Reinterpret as flat bytes (total MAXPATHLEN = 1024).
    let vip_path = unsafe {
        std::slice::from_raw_parts(
            pathinfo.pvi_cdir.vip_path.as_ptr() as *const u8,
            libc::MAXPATHLEN as usize,
        )
    };

    let nul = vip_path.iter().position(|&b| b == 0)?;
    if nul == 0 {
        return None;
    }
    Some(PathBuf::from(OsStr::from_bytes(&vip_path[..nul])))
}