//! Loopback JSON-lines control server: one request per line, one reply per line.
//! Agents and tests drive the app through it (adapted from CADCraft, MIT OR Apache-2.0).

use std::io::{BufRead, BufReader, Write};
use std::net::{TcpListener, TcpStream};
use std::sync::mpsc::{Receiver, Sender, channel};
use std::time::Duration;

use serde_json::{Value, json};
use solvecraft_ui_egui::ControlRequest;

pub fn start(port: u16, ctx: egui::Context) -> Receiver<ControlRequest> {
    let (tx, rx) = channel::<ControlRequest>();
    let listener = match TcpListener::bind(("127.0.0.1", port)) {
        Ok(l) => l,
        Err(e) => {
            eprintln!("solvecraft: control server failed to bind 127.0.0.1:{port}: {e}");
            return rx;
        }
    };
    eprintln!("solvecraft: control server listening on 127.0.0.1:{port}");
    std::thread::spawn(move || {
        for stream in listener.incoming().flatten() {
            let tx = tx.clone();
            let ctx = ctx.clone();
            std::thread::spawn(move || serve(stream, tx, ctx));
        }
    });
    rx
}

fn serve(stream: TcpStream, tx: Sender<ControlRequest>, ctx: egui::Context) {
    let Ok(read) = stream.try_clone() else { return };
    let mut out = stream;
    for line in BufReader::new(read).lines() {
        let Ok(line) = line else { break };
        if line.trim().is_empty() {
            continue;
        }
        let reply = match serde_json::from_str::<Value>(&line) {
            Ok(msg) => {
                let id = msg.get("id").cloned().unwrap_or(Value::Null);
                let method = msg.get("method").and_then(Value::as_str).unwrap_or("").to_string();
                let params = msg.get("params").cloned().unwrap_or(json!({}));
                let (req, rrx) = ControlRequest::new(method, params);
                if tx.send(req).is_err() {
                    break;
                }
                ctx.request_repaint();
                let mut r = rrx.recv_timeout(Duration::from_secs(60)).unwrap_or_else(|_| json!({"ok": false, "error": "timeout"}));
                if let Some(o) = r.as_object_mut() {
                    o.insert("id".into(), id);
                }
                r
            }
            Err(e) => json!({"ok": false, "error": format!("bad JSON: {e}")}),
        };
        if writeln!(out, "{reply}").is_err() {
            break;
        }
    }
}