import type { TimeRecord } from "../shared/record.ts";
import { allRecords, applyRemote, cursor, pendingOperations, removeOperations } from "./store.ts";

export type SyncStatus = "offline" | "syncing" | "synced" | "pending" | "signed-out";
let current: Promise<void> | null = null;
let rerunRequested = false;

class SignedOut extends Error {}

async function api<T>(url: string, init?: RequestInit): Promise<T> {
  const response = await fetch(url, init);
  if (response.status === 401) throw new SignedOut();
  if (!response.ok) throw new Error(`Sync failed (${response.status})`);
  return response.json() as Promise<T>;
}

export function syncNow(onChange: (status: SyncStatus, records?: TimeRecord[]) => void): Promise<void> {
  if (current) {
    rerunRequested = true;
    return current;
  }
  current = (async () => {
    if (!navigator.onLine) { onChange("offline"); return; }
    onChange("syncing");
    try {
      let pending = await pendingOperations();
      while (pending.length) {
        const batch = pending.slice(0, 200);
        const body = await api<{ accepted: string[] }>("/api/operations", {
          method: "POST", headers: { "Content-Type": "application/json" },
          body: JSON.stringify({ operations: batch.map(({ id, record }) => ({ id, record })) }),
        });
        await removeOperations(body.accepted);
        pending = await pendingOperations();
      }
      let since = await cursor();
      for (;;) {
        const body = await api<{ records: TimeRecord[]; cursor: number; hasMore: boolean }>(
          `/api/state?since=${since}`, { cache: "no-store" });
        await applyRemote(body.records, body.cursor);
        since = body.cursor;
        if (!body.hasMore) break;
      }
      onChange("synced", await allRecords());
    } catch (error) {
      if (error instanceof SignedOut) { onChange("signed-out"); return; }
      console.error(error);
      onChange("pending");
    }
  })().finally(() => {
    current = null;
    if (rerunRequested) {
      rerunRequested = false;
      void syncNow(onChange);
    }
  });
  return current;
}