main.rs

use regex::Regex;
use rmpv::{decode::read_value, encode::write_value, Value};
use std::{net::TcpStream, path::PathBuf, sync::atomic};

macro_rules! rmp_vec {
    () => (Value::Array(Vec::new()));
    ($($x:expr),+$(,)*) => (Value::from([$(Value::from($x)),+].to_vec()));
}

struct Client {
    conn: TcpStream,
    tag_re: Regex,
}

static MSG_ID: atomic::AtomicU8 = atomic::AtomicU8::new(0);

impl Client {
    fn new() -> Option<Self> {
        let conn = TcpStream::connect("127.0.0.1:6969").ok()?;
        let tag_re: Regex = Regex::new(r"\*(.*?)\*").ok()?;
        Some(Self { conn, tag_re })
    }

    fn call(&mut self, method: &str, args: Value) -> Option<Value> {
        write_value(&mut self.conn, &rmp_vec![0, msgid(), method, args]).ok()?;
        read_value(&mut self.conn).ok()
    }

    fn get_help_link(&mut self, topic: &str) -> Option<String> {
        let help_cmd = format!(":h {}", topic);
        self.call("nvim_command", rmp_vec![help_cmd])?;

        let tagpath = self
            .call("nvim_buf_get_name", rmp_vec![0])
            .and_then(|it| it[3].as_str().map(str::to_string))
            .map(|it| PathBuf::from(it).file_stem().map(|it| it.to_owned()))
            .flatten()?;

        let tag = self
            .call("nvim_get_current_line", rmp_vec![])
            .and_then(|it| it[3].as_str().map(str::to_string))
            .map(|it| self.tag_re.captures(&it).map(|c| c[1].to_string()))
            .flatten()?;

        Some(format!(
            "https://neovim.io/doc/user/{}.html#{}",
            tagpath.to_str()?,
            tag
        ))
    }
}

fn msgid() -> u8 {
    MSG_ID.fetch_add(1, atomic::Ordering::SeqCst)
}

fn main() {
    let mut cl = Client::new().unwrap();
    println!("{:?}", cl.get_help_link("highlight"));
}