// **The forge's announcements carry a message id** (novox/hq ADR 0406 §6 and §7, issue 976). A merge, a new head and a
// close are announced by more than one path — the poll, the forge's own event, the merge tool's ask of a check — and
// were kept from being announced twice by files of what had been announced. They are now announced with a message id
// that is the same for the same announcement, whichever path makes it: the runtime makes an event's `x-event-id` header
// the bus's message id (mesh-tools node-tools/internal/bus/bus.go, `nats.MsgId`), and the bus stores a message it has
// seen the id of, within its de-duplication window, once.
//
// They are the seat git's events (design 47 *The seat git*), said through the runtime's seat publish with that id.
//
// The ids: a merge by its merge commit, a head by the head and the trunk commit it was announced against (the check asked
// again against a new trunk commit is another announcement), a close by its head.

import { sayOnSeat } from "./seatevents.js";
import { state as keptState } from "@novox/mesh-sdk/state";

type Said = { owner?: string; repo?: string; number?: number; head_sha?: string; base_sha?: string; merge_commit_sha?: string };

/** The message id of an announcement, or undefined for an event that is not one of these three. */
export function announcementId(type: string, body: unknown): string | undefined {
  const b = (body ?? {}) as Said;
  const pull = `${b.owner}/${b.repo}#${b.number}`;
  switch (type) {
    case "pull.merged":
      return `merged:${pull}@${b.merge_commit_sha ?? ""}`;
    case "pull.updated":
      return `updated:${pull}@${b.head_sha ?? ""}:${b.base_sha ?? ""}`;
    case "pull.closed":
      return `closed:${pull}@${b.head_sha ?? ""}`;
    default:
      return undefined;
  }
}

/** Announce a merge, a head or a close: said on the seat git (seatevents.ts) with its message id. */
export async function announce(type: string, body: unknown): Promise<void> {
  const id = announcementId(type, body);
  if (!id) throw new Error(`${type} is not an announcement with a message id`);
  if (!(await sayOnSeat(type, (body ?? {}) as Record<string, unknown>, id))) throw new Error(`the seat git says no ${type}`);
}

// --- the watermark: the one value of the old files that is not the bus's to remember --------------------------------

/** What the module keeps of how far its poll of merges has looked: a time, in its own state. */
interface Kept {
  get(key: string): Promise<{ value: unknown } | null>;
  put(key: string, value: unknown): Promise<number>;
}

const WATERMARK = "merges-since";

/** The time the poll of merges last looked from, or "" when none is kept or the state cannot be reached: a merge made
 *  before it is history, one after it is announced. */
export async function readWatermark(state: Kept = keptState("announced")): Promise<string> {
  try {
    const entry = await state.get(WATERMARK);
    const since = (entry?.value as { since?: string } | undefined)?.since;
    return typeof since === "string" ? since : "";
  } catch (err) {
    console.error(`[gitea] where the poll of merges last looked from could not be read, so none is kept — ${err instanceof Error ? err.message : err}`);
    return "";
  }
}

/** Keep the time the poll of merges looked from; a state that cannot be reached is said, and the next pass keeps it. */
export async function keepWatermark(since: string, state: Kept = keptState("announced")): Promise<void> {
  try {
    await state.put(WATERMARK, { since });
  } catch (err) {
    console.error(`[gitea] where the poll of merges looked from could not be kept — ${err instanceof Error ? err.message : err}`);
  }
}