// 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);

/**
 * Bumped every time the backend's downloads-only gate *settles* into a new
 * state. Library pages watch it and re-query.
 *
 * The gate lives in Rust and is only consulted when a query runs, so flipping
 * it changes nothing already on screen. Without this signal the toggle merely
 * greyed cards — `MediaCard.isServerOnly` is a pure frontend derivation and
 * updates instantly — while the item list stayed as first loaded. That is the
 * "shows everything until I filter" behaviour: the listing had never been
 * re-queried under the closed gate. Going offline had the same problem, since
 * nothing reloads on the online → offline transition either.
 *
 * It bumps *after* the command resolves, never before: a reload racing the push
 * would re-query under the old gate and undo itself.
 *
 * TRACES: UR-052 | DR-143
 */
export const catalogFilterVersion: Writable<number> = writable(0);

// 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;
async function pushCatalogVisibility(connected: boolean, showCatalog: boolean): Promise<void> {
  const include = connected || showCatalog;
  if (include === lastIncludeCatalog) return;
  lastIncludeCatalog = include;

  try {
    await commands.setShowServerCatalog(include);
  } catch (err) {
    console.warn("[OfflineCatalog] Failed to set catalog visibility:", err);
    // The backend is still on the old gate, so forget that we sent this —
    // otherwise the next identical transition is skipped as a no-op and the
    // frontend and backend disagree about the filter for the rest of the
    // session. No version bump: there is nothing new to re-query under.
    lastIncludeCatalog = null;
    return;
  }

  catalogFilterVersion.update((n) => n + 1);
}

let connectedNow = true;
let showCatalogNow = false;
// Fire-and-forget on purpose: the push handles its own failure, and subscribers
// must not block. Consumers wait on `catalogFilterVersion` instead.
isConnected.subscribe((v) => {
  connectedNow = v;
  void pushCatalogVisibility(connectedNow, showCatalogNow);
});
showServerCatalog.subscribe((v) => {
  showCatalogNow = v;
  void 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
  }
}

/**
 * Force a full re-index now, ignoring freshness.
 *
 * Routine scheduling is the Rust indexer's job (DR-109) — this is the manual
 * override, for a "re-index now" affordance. It is deliberately *not* called on
 * startup or reconnect any more: doing so forced a full crawl on every launch
 * regardless of how fresh the index was.
 *
 * The backend refuses overlapping passes, so this is safe to call at any time.
 */
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();
  // Re-indexing on reconnect is the Rust indexer's job (DR-109) — it re-checks
  // staleness every tick, so it picks this up without a nudge from here. Queued
  // downloads still need resolving from the frontend, which is why this
  // function remains.
}
