import { env } from "cloudflare:workers";
import { all } from "./db";

/**
 * One-shot data backfills that walk every repository once, a page per cron run, so new indexes can cover rows
 * written before they existed. Progress lives in KV (`backfill:<name>`): the last repository id visited, or
 * DONE. Readers that need the index consult `backfillDone` and keep their old (slower) path until it is.
 */
const DONE = "done";
const PAGE = 50;
const finished = new Set<string>();

function key(name: string): string {
  return `backfill:${name}`;
}

/** False until the backfill has finished, and whenever its state can't be read (callers keep their safe path). */
export async function backfillDone(name: string): Promise<boolean> {
  if (finished.has(name)) return true;
  const state = await Promise.resolve()
    .then(() => env.KV.get(key(name)))
    .catch(() => null);
  if (state === DONE) finished.add(name);
  return state === DONE;
}

async function walk(name: string, table: "repos" | "accounts", visit: (id: string) => Promise<void>): Promise<boolean> {
  if (await backfillDone(name)) return true;
  const cursor = (await env.KV.get(key(name))) ?? "";
  const rows = await all<{ id: string }>(`SELECT id FROM ${table} WHERE id > ? ORDER BY id LIMIT ?`, cursor, PAGE);
  for (const row of rows) await visit(row.id);
  const done = rows.length < PAGE;
  await env.KV.put(key(name), done ? DONE : (rows.at(-1)?.id ?? cursor));
  if (done) finished.add(name);
  return done;
}

/** Visits the next page of repositories in id order; call from the cron until it reports done. */
export function backfillRepos(name: string, visit: (repoId: string) => Promise<void>): Promise<boolean> {
  return walk(name, "repos", visit);
}

/** Visits the next page of accounts (users and organizations) in id order. */
export function backfillAccounts(name: string, visit: (accountId: string) => Promise<void>): Promise<boolean> {
  return walk(name, "accounts", visit);
}