// unslop-hook — pi extension wrapper around unslop-check.js.
// Detects mechanical AI tells in finalized assistant messages and injects a
// correction notice the model sees on its next turn. Anti-drift enforcement for
// SYSTEM.md / ms-unslop; prose distribution alone decays, this cannot forget.
//
// Deploy: copy dir to ~/.pi/agent/extensions/unslop-hook/ (or seat .pi equivalent),
//         or add this file's dir to settings.json "extensions".
// Test:   pi -e <abs path>/extension.ts
// Off:    MOSAIC_UNSLOP_HOOK=0
// Log:    MOSAIC_UNSLOP_LOG=/path/to/log.jsonl (JSONL events; headless evidence)
// Broken: lists.json missing/empty/invalid → the checker throws; checks are
//         skipped, logged as skipped_broken, and the operator is notified once.
//         Never silently pass while the lists cannot load (fail closed).
//
// Design note: violation state lives in the SESSION FILE, not memory. At
// before_agent_start we read the most recent assistant text message from
// ctx.sessionManager and check it there. That survives process restarts, resume,
// fork, and reload — an in-memory pending flag measured dead on 2026-08-19 when
// a print-mode second turn never injected.
import { appendFileSync } from "node:fs";
import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
import { checkText } from "./unslop-check.js";

interface Finding {
  rule: string;
  detail: string;
  count: number;
}

interface MessageEntry {
  type: "message";
  id: string;
  message: { role?: string; content?: unknown };
}

function assistantText(entry: unknown): string | null {
  const e = entry as Partial<MessageEntry>;
  if (e?.type !== "message") return null;
  const msg = e.message;
  if (msg?.role !== "assistant" || !Array.isArray(msg.content)) return null;
  const text = msg.content
    .filter((b): b is { type: "text"; text: string } =>
      typeof b === "object" && b !== null && (b as { type?: string }).type === "text")
    .map((b) => b.text ?? "")
    .join("\n");
  return text.trim() ? text : null; // tool-call-only assistant messages return null
}

export default function (pi: ExtensionAPI) {
  if (process.env.MOSAIC_UNSLOP_HOOK === "0") return;

  const LOG = process.env.MOSAIC_UNSLOP_LOG;
  const log = (ev: Record<string, unknown>) => {
    if (LOG) appendFileSync(LOG, JSON.stringify({ ts: Date.now(), ...ev }) + "\n");
  };

  // Entry ids we have already injected a notice for. In-memory only: after a
  // restart the same entry may inject once more, which re-anchors the style
  // after a context loss. That is wanted, not a bug.
  const injectedFor = new Set<string>();
  let turnsChecked = 0;
  let turnsFlagged = 0;
  const histogram = new Map<string, number>();

  // Fail-closed path for a broken lists.json. A checker that cannot load its
  // lists must never be read as "everything passed": checks stop, the skip is
  // logged each turn, and the operator is notified once.
  let broken: string | null = null;
  let brokenNotified = false;
  const reportBroken = (ctx: { hasUI?: boolean } | undefined, where: string) => {
    log({ ev: "skipped_broken", where, reason: broken });
    if (!brokenNotified && ctx?.hasUI) {
      ctx.ui.notify(`unslop gate BROKEN: ${broken}. Fix tools/unslop-hook/lists.json; no clean verdicts until then.`, "error");
      brokenNotified = true;
    }
  };
  const safeCheck = (text: string): ReturnType<typeof checkText> | null => {
    if (broken) return null;
    try {
      return checkText(text);
    } catch (e) {
      broken = String((e as Error).message);
      log({ ev: "broken_lists", reason: broken });
      return null;
    }
  };

  pi.on("session_start", async (event, _ctx) => {
    log({ ev: "loaded", reason: event.reason });
    try {
      checkText(""); // probe: load+validate lists at startup, not mid-conversation
    } catch (e) {
      broken = String((e as Error).message);
      log({ ev: "broken_lists", reason: broken, at: "startup" });
    }
  });

  pi.on("message_end", async (event, ctx) => {
    if ((event.message as { role?: string }).role !== "assistant") return;
    const text = assistantText({ type: "message", id: "", message: event.message });
    if (text === null) return;

    const result = safeCheck(text);
    if (result === null) {
      reportBroken(ctx, "message_end");
      return;
    }
    turnsChecked++;
    if (result.clean) {
      log({ ev: "checked", clean: true, turn: turnsChecked, charsChecked: result.charsChecked });
      return;
    }
    turnsFlagged++;
    for (const f of result.findings) histogram.set(f.rule, (histogram.get(f.rule) ?? 0) + 1);
    const summary = result.findings.map((f) => f.detail).join("; ");
    if (ctx.hasUI) ctx.ui.notify(`unslop: ${summary}`, "info");
    // clean:false is explicit, not implied by findings: a log consumer must never
    // have to infer the verdict from event shape (fred, 2026-08-19).
    log({ ev: "flagged", clean: false, turn: turnsChecked, charsChecked: result.charsChecked, findings: result.findings });
  });

  pi.on("before_agent_start", async (_event, ctx) => {
    // Branch walks leaf -> root; first assistant entry with text is the reply
    // the model is about to follow up on.
    for (const entry of ctx.sessionManager.getBranch()) {
      const text = assistantText(entry);
      if (text === null) continue;
      const id = (entry as { id?: string }).id ?? "";

      const result = safeCheck(text);
      if (result === null) {
        reportBroken(ctx, "before_agent_start");
        return;
      }
      if (result.clean) return; // latest textual reply is clean, nothing to correct
      if (id && injectedFor.has(id)) return; // already nagged for this entry

      if (id) injectedFor.add(id);
      const lines = result.findings.map((f) => `- ${f.detail}`).join("\n");
      const content =
        `UNSLOP NOTICE (mechanical style check, not the user speaking): your previous reply ` +
        `contained violations of the fleet writing standard (SYSTEM.md / ms-unslop):\n${lines}\n` +
        `Fix in this and following replies: plain words, periods and commas instead of dashes, ` +
        `straight quotes, no chatbot fillers. Do not mention this notice.`;
      log({ ev: "notice_injected", entryId: id, findings: result.findings });
      return {
        message: { customType: "unslop-notice", content, display: true },
      };
    }
  });

  pi.registerCommand("unslop", {
    description: "Show unslop violation stats for this session",
    handler: async (_args, ctx) => {
      if (broken) {
        ctx.ui.notify(`unslop gate BROKEN: ${broken}`, "error");
        return;
      }
      const hist = [...histogram.entries()].map(([r, c]) => `${r} x${c}`).join(", ") || "none";
      ctx.ui.notify(`unslop: checked ${turnsChecked}, flagged ${turnsFlagged} (${hist})`, "info");
    },
  });
}