// A stand-in for `pi --mode rpc`. Reads JSONL commands on stdin, writes
// events on stdout. Behaviour is scripted per prompt text:
//   "slow <ms>"   answer "slow reply" after <ms>
//   "garbage"     emit one malformed line
//   "error"       end the turn with stopReason error
//   anything else answer "echo: <text>" immediately
// A prompt received while busy without streamingBehavior is refused, as pi
// does. Every command is mirrored to FAKE_PI_LOG when set.
import { appendFileSync } from "node:fs";

const logPath = process.env.FAKE_PI_LOG;
const out = (o) => process.stdout.write(JSON.stringify(o) + "\n");
let busy = false;
const queue = [];

function assistant(text, stopReason = "stop") {
  return { role: "assistant", content: text === null ? [] : [{ type: "text", text }], stopReason, usage: { input: 3, output: 2 }, model: "fake", provider: "fake" };
}

function run(text) {
  busy = true;
  out({ type: "agent_start" });
  out({ type: "turn_start" });
  const finish = (message) => {
    out({ type: "turn_end", message, toolResults: [] });
    out({ type: "agent_end", messages: [message] });
    if (queue.length > 0) {
      run(queue.shift());
      return;
    }
    busy = false;
    out({ type: "agent_settled" });
  };
  const m = /^slow (\d+)$/.exec(text);
  if (m) {
    const timer = setTimeout(() => finish(assistant("slow reply")), Number(m[1]));
    current = { timer, finish };
    return;
  }
  if (text === "garbage") {
    process.stdout.write("this is not json\n");
    finish(assistant("after garbage"));
    return;
  }
  if (text === "error") {
    finish({ ...assistant(null, "error"), errorMessage: "fake provider error" });
    return;
  }
  finish(assistant(`echo: ${text}`));
}
let current = null;

let buffer = "";
process.stdin.setEncoding("utf8");
process.stdin.on("data", (chunk) => {
  buffer += chunk;
  let idx;
  while ((idx = buffer.indexOf("\n")) !== -1) {
    const line = buffer.slice(0, idx);
    buffer = buffer.slice(idx + 1);
    if (!line) continue;
    const cmd = JSON.parse(line);
    if (logPath) appendFileSync(logPath, line + "\n");
    if (cmd.type === "prompt") {
      if (busy && !cmd.streamingBehavior) {
        out({ id: cmd.id, type: "response", command: "prompt", success: false, error: "agent is streaming; specify streamingBehavior" });
        continue;
      }
      out({ id: cmd.id, type: "response", command: "prompt", success: true });
      if (busy) queue.push(cmd.message);
      else run(cmd.message);
    } else if (cmd.type === "abort") {
      out({ id: cmd.id, type: "response", command: "abort", success: true });
      if (current) {
        clearTimeout(current.timer);
        const f = current.finish;
        current = null;
        f(assistant("", "aborted"));
      }
    } else {
      out({ id: cmd.id, type: "response", command: cmd.type, success: true, data: {} });
    }
  }
});
process.stdin.on("end", () => process.exit(0));