// Offline catalog service - "browse & queue" for offline mode.
//
// Two responsibilities:
//  1. Full-catalog pre-sync: while online, walk every library and persist all
//     items to the offline cache so the whole catalog is browsable (greyed out)
//     offline. Backed by the `syncFullCatalog` Rust command.
//  2. Resume-on-reconnect: when the server becomes reachable again, resolve the
//     stream URLs of downloads that were queued while offline and let the pump
//     start them. Backed by `resumeQueuedDownloads`.
//
// It also owns the `showServerCatalog` UI flag (the offline banner toggle that
// reveals greyed-out, non-downloaded server media).
//
// TRACES: UR-002, UR-052 | DR-078

import { writable, type Writable } from "svelte/store";
import { commands } from "$lib/api/bindings";
import { auth } from "$lib/stores/auth";
import { isConnected } from "$lib/stores/connectivity";

/**
 * When true (and offline), library grids reveal greyed-out versions of media
 * that exists on the server but isn't downloaded, each with a button to queue
 * a download for the next reconnect. Toggled from the offline banner.
 */
export const showServerCatalog: Writable<boolean> = writable(false);

// Keep the backend's offline library queries in sync with the UI toggle. The
// offline cache holds the whole synced catalog, so `get_items` would otherwise
// return every server item even offline with the toggle off. Include the
// non-downloaded catalog only when online (fast browsing reads the same cache)
// or when the "Show all server media" toggle is on.
let lastIncludeCatalog: boolean | null = null;
function pushCatalogVisibility(connected: boolean, showCatalog: boolean): void {
  const include = connected || showCatalog;
  if (include === lastIncludeCatalog) return;
  lastIncludeCatalog = include;
  commands.setShowServerCatalog(include).catch((err) => {
    console.warn("[OfflineCatalog] Failed to set catalog visibility:", err);
  });
}

let connectedNow = true;
let showCatalogNow = false;
isConnected.subscribe((v) => {
  connectedNow = v;
  pushCatalogVisibility(connectedNow, showCatalogNow);
});
showServerCatalog.subscribe((v) => {
  showCatalogNow = v;
  pushCatalogVisibility(connectedNow, showCatalogNow);
});

/** Last time a full catalog sync completed, for a UI hint. */
export const lastCatalogSync: Writable<string | null> = writable(null);

// Guard against overlapping syncs (they can be slow on large libraries).
let syncInProgress = false;

function currentHandle(): string | null {
  try {
    return auth.getRepository().getHandle();
  } catch {
    return null; // not connected yet
  }
}

/**
 * Walk every library and cache the full catalog. Best-effort and non-blocking:
 * safe to call on startup (while online) and on reconnect. No-ops if not
 * connected or a sync is already running.
 */
export async function syncCatalog(): Promise<void> {
  if (syncInProgress) return;
  const handle = currentHandle();
  if (!handle) return;

  syncInProgress = true;
  try {
    const result = await commands.syncFullCatalog(handle);
    console.info(
      `[OfflineCatalog] Synced ${result.itemsCached} items (${result.librariesFailed} libraries failed)`
    );
    await refreshSyncStatus();
  } catch (err) {
    console.warn("[OfflineCatalog] Full catalog sync failed:", err);
  } finally {
    syncInProgress = false;
  }
}

/**
 * Resolve URLs for downloads queued while offline and pump them. Call on
 * reconnect. No-ops if not connected.
 */
export async function resumeQueued(): Promise<void> {
  const handle = currentHandle();
  if (!handle) return;
  try {
    const result = await commands.resumeQueuedDownloads(handle);
    if (result.resolved > 0 || result.failed > 0) {
      console.info(
        `[OfflineCatalog] Resumed queued downloads: ${result.resolved} resolved, ${result.failed} failed`
      );
    }
  } catch (err) {
    console.warn("[OfflineCatalog] Failed to resume queued downloads:", err);
  }
}

/** Refresh the last-synced timestamp from the backend. */
export async function refreshSyncStatus(): Promise<void> {
  try {
    const status = await commands.catalogSyncStatus();
    lastCatalogSync.set(status.lastSyncedAt ?? null);
  } catch (err) {
    console.debug("[OfflineCatalog] Failed to fetch sync status:", err);
  }
}

/**
 * Called when the server becomes reachable again: resume queued downloads first
 * (fast, user-visible), then refresh the catalog in the background.
 */
export async function onReconnected(): Promise<void> {
  await resumeQueued();
  // Fire-and-forget: don't block reconnection handling on a potentially long walk.
  void syncCatalog();
}
