// Pi extension for a managed session, loaded with `-e` by adapters/pi.
// Three jobs:
//   - register the session's typed tools, which call the runner's tool socket;
//   - gate every tool call with gate.mjs (S0 lines 1 and 2: a block or a
//     throw stops the tool);
//   - write the turn marker on agent_end, so the runner can tell a finished
//     turn from a pi that exited 0 mid-turn (S0 line 4).
// Missing or unreadable configuration throws here, which fails pi's start
// (S0 line 3): nothing is defaulted.

import { readFileSync, writeFileSync } from "node:fs";
import { decide } from "./gate.mjs";
import { callTool } from "./tools.mjs";

function need(name) {
  const value = process.env[name];
  if (typeof value !== "string" || !value) throw new Error(`mosaic extension: ${name} is not set`);
  return value;
}

export default function (pi) {
  const policy = JSON.parse(readFileSync(need("MOSAIC_POLICY_FILE"), "utf8"));
  const tools = JSON.parse(readFileSync(need("MOSAIC_TOOLS_FILE"), "utf8"));
  const socket = need("MOSAIC_TOOL_SOCKET");
  const marker = need("MOSAIC_TURN_MARKER");
  if (policy.harness !== "pi" || !Array.isArray(policy.tools) || !Array.isArray(policy.typed)) throw new Error("mosaic extension: policy file is not a pi policy");

  pi.on("tool_call", async (event) => {
    const verdict = decide(policy, event.toolName, event.input);
    return verdict.allow ? undefined : { block: true, reason: verdict.reason };
  });
  pi.on("agent_end", async () => {
    writeFileSync(marker, `${new Date().toISOString()}\n`);
  });

  for (const t of tools) {
    pi.registerTool({
      name: t.name,
      label: t.name,
      description: t.description,
      parameters: t.parameters,
      async execute(_toolCallId, params) {
        // A refusal throws, which pi reports to the model as a tool error.
        const result = await callTool(socket, t.name, params ?? {});
        return { content: [{ type: "text", text: JSON.stringify(result, null, 2) }], details: {} };
      },
    });
  }
}