/**
 * useNavContext
 *
 * Provides prev/next artwork IDs scoped to the same author via API.
 */
import { useCallback } from 'react';

// Module-level cache for API calls
const fallbackCache = new Map();

function normalizeNavigation(data) {
  if (!data || typeof data !== 'object') return null;
  const hasPrev = data.prev_id == null || (data.prev_url && data.prev_slug);
  const hasNext = data.next_id == null || (data.next_url && data.next_slug);
  if (!hasPrev || !hasNext) return null;

  return {
    prevId: data.prev_id ?? null,
    nextId: data.next_id ?? null,
    prevUrl: data.prev_url ?? null,
    nextUrl: data.next_url ?? null,
    prevPreview: data.prev_preview ?? null,
    nextPreview: data.next_preview ?? null,
  };
}

async function fetchFallback(artworkId) {
  const key = String(artworkId);
  if (fallbackCache.has(key)) return fallbackCache.get(key);

  try {
    const res = await fetch(`/api/artworks/navigation/${artworkId}`, {
      headers: { Accept: 'application/json' },
    });
    if (!res.ok) return { prevId: null, nextId: null, prevUrl: null, nextUrl: null, prevPreview: null, nextPreview: null };
    const data = await res.json();
    const result = normalizeNavigation(data) || { prevId: null, nextId: null, prevUrl: null, nextUrl: null, prevPreview: null, nextPreview: null };
    fallbackCache.set(key, result);
    return result;
  } catch {
    return { prevId: null, nextId: null, prevUrl: null, nextUrl: null, prevPreview: null, nextPreview: null };
  }
}

export function useNavContext(currentArtworkId, embeddedNavigation = null) {
  /**
   * Always resolve via API to guarantee same-user navigation.
   */
  const getNeighbors = useCallback(async () => {
    const embedded = normalizeNavigation(embeddedNavigation);
    if (embedded) return embedded;
    return fetchFallback(currentArtworkId);
  }, [currentArtworkId, embeddedNavigation]);

  return { getNeighbors };
}