// Row S0 probe gate for Pi: a `tool_call` handler that guards the `write`
// tool. GATE_MODE picks the behaviour; GATE_LOG records each invocation, so
// a run shows whether the gate ran at all.
import { appendFileSync } from "node:fs";

const mode = process.env.GATE_MODE ?? "block";
const note = (s: string) => appendFileSync(process.env.GATE_LOG ?? "/dev/null", `${new Date().toISOString()} ${s}\n`);

export default function (pi: any) {
  note(`loaded mode=${mode}`);
  pi.on("tool_call", async (event: any) => {
    note(`invoked tool=${event.toolName} mode=${mode}`);
    if (event.toolName !== "write") return undefined;
    if (mode === "block") return { block: true, reason: "PROBE-GATE: write is blocked by policy" };
    if (mode === "throw") throw new Error("PROBE-GATE crashed (throw)");
    if (mode === "throw-string") throw "PROBE-GATE crashed (non-Error throw)";
    // "hang" never settles and holds nothing open; "slow" holds a timer, as a
    // gate waiting on I/O would, and blocks only after an hour.
    if (mode === "hang") return new Promise(() => {});
    if (mode === "slow") return new Promise((r) => setTimeout(() => r({ block: true, reason: "PROBE-GATE: blocked after a delay" }), 3_600_000));
    if (mode === "exit") process.exit(3);
    return undefined;
  });
}