import { useSyncExternalStore } from "react";
import { ApiError, post } from "./api";

/** Messages written without a connection: kept on this device and sent when it is back. */
export interface OutboxItem {
  id: string;
  sessionId: string;
  text: string;
  effort?: string;
  createdAt: number;
}

const KEY = "codecraft.outbox";
const listeners = new Set<() => void>();
let cache: OutboxItem[] | undefined;

function load(): OutboxItem[] {
  if (cache) return cache;
  try {
    const v = JSON.parse(localStorage.getItem(KEY) ?? "[]");
    cache = Array.isArray(v) ? v : [];
  } catch {
    cache = [];
  }
  return cache!;
}

function save(items: OutboxItem[]) {
  cache = items;
  try {
    localStorage.setItem(KEY, JSON.stringify(items));
  } catch {
    // Storage blocked: the list still works until the page is closed.
  }
  listeners.forEach((l) => l());
}

export function addToOutbox(sessionId: string, text: string, effort?: string) {
  save([...load(), { id: `${Date.now()}-${Math.random().toString(36).slice(2, 8)}`, sessionId, text, effort, createdAt: Date.now() }]);
}

export function removeFromOutbox(id: string) {
  save(load().filter((i) => i.id !== id));
}

export function useOutbox(sessionId: string): OutboxItem[] {
  const all = useSyncExternalStore(
    (l) => {
      listeners.add(l);
      return () => listeners.delete(l);
    },
    () => load(),
  );
  return all.filter((i) => i.sessionId === sessionId);
}

/** True for failures of the connection itself (not answers of the server). */
export function isOffline(e: unknown) {
  return !(e instanceof ApiError) && (!navigator.onLine || e instanceof TypeError);
}

let flushing = false;

/** Send the waiting messages of a chat in order; stops at the first connection failure. Returns how many were sent. */
export async function flushOutbox(sessionId: string): Promise<number> {
  if (flushing) return 0;
  flushing = true;
  let sent = 0;
  try {
    for (const item of load().filter((i) => i.sessionId === sessionId)) {
      try {
        await post(`/sessions/${item.sessionId}/prompt`, { text: item.text, effort: item.effort });
        removeFromOutbox(item.id);
        sent++;
      } catch (e) {
        if (isOffline(e)) break;
        // The server refused it (deleted chat, read-only …): it would never go through.
        removeFromOutbox(item.id);
      }
    }
  } finally {
    flushing = false;
  }
  return sent;
}