/**
 * Newline-delimited JSON-RPC framing over the ACP agent's stdio.
 * Parses incoming lines and emits typed messages; writes outgoing messages.
 * Used by the persistent `grok agent stdio` process.
 */
import type { ChildProcessWithoutNullStreams } from "node:child_process";
import { EventEmitter } from "node:events";
import type { JsonRpcMessage } from "./types.js";
import { createLogger } from "../logger.js";

const log = createLogger("grok:transport");

export class JsonRpcTransport extends EventEmitter {
  private buffer = "";

  constructor(private readonly proc: ChildProcessWithoutNullStreams) {
    super();
    proc.stdout.setEncoding("utf-8");
    proc.stdout.on("data", (chunk: string) => this.onData(chunk));
    proc.stderr.setEncoding("utf-8");
    proc.stderr.on("data", (chunk: string) => {
      const msg = chunk.trim();
      if (msg) log.debug("[grok stderr]", msg.slice(0, 500));
    });
  }

  private onData(chunk: string): void {
    this.buffer += chunk;
    let idx: number;
    while ((idx = this.buffer.indexOf("\n")) !== -1) {
      const line = this.buffer.slice(0, idx).trim();
      this.buffer = this.buffer.slice(idx + 1);
      if (!line) continue;
      let parsed: JsonRpcMessage;
      try {
        parsed = JSON.parse(line) as JsonRpcMessage;
      } catch {
        log.debug("non-JSON line ignored:", line.slice(0, 200));
        continue;
      }
      this.emit("message", parsed);
    }
  }

  send(msg: object): void {
    if (!this.proc.stdin.writable) {
      throw new Error("ACP process stdin is not writable");
    }
    this.proc.stdin.write(JSON.stringify(msg) + "\n");
  }
}