nuxt-app/app/composables/useFavorite.ts

import { useAuthSession } from "./useAuthSession";

// Module-level singleton state — shared across all components that call useFavorite().
const favoritedCardIds = ref<Set<number>>(new Set())
const loadingIds = ref<Set<number>>(new Set())

/**
 * Favorite management composable.
 * Provides a reactive set of favorited card IDs and toggle function.
 */
export function useFavorite() {
  const { loggedIn } = useAuthSession()
  const { $toast } = useNuxtApp()

  /**
   * Check if a card is favorited.
   */
  function isFavorited(cardId: number): boolean {
    return favoritedCardIds.value.has(cardId)
  }

  /**
   * Toggle favorite for a card.
   * Optimistically updates local state.
   */
  async function toggle(cardId: number): Promise<boolean> {
    if (!loggedIn.value) {
      $toast.info('请先登录')
      return false
    }
    if (loadingIds.value.has(cardId)) return isFavorited(cardId)

    const wasFavorited = favoritedCardIds.value.has(cardId)
    // Optimistic update
    const next = new Set(favoritedCardIds.value)
    if (wasFavorited) {
      next.delete(cardId)
    } else {
      next.add(cardId)
    }
    favoritedCardIds.value = next
    loadingIds.value = new Set(loadingIds.value).add(cardId)

    try {
      const raw = await $fetch<{ code: number; data: { favorited: boolean } }>(
        `/api/cards/${cardId}/favorite`,
        { method: 'POST' },
      )
      if (raw.code !== 0 || !raw.data.favorited) {
        // Server says unfavorited — ensure it's removed
        const corrected = new Set(favoritedCardIds.value)
        corrected.delete(cardId)
        favoritedCardIds.value = corrected
      }
      return raw.data.favorited
    } catch {
      // Revert optimistic update
      const reverted = new Set(favoritedCardIds.value)
      if (wasFavorited) {
        reverted.add(cardId)
      } else {
        reverted.delete(cardId)
      }
      favoritedCardIds.value = reverted
      $toast.error('操作失败，请稍后重试')
      return wasFavorited
    } finally {
      const next = new Set(loadingIds.value)
      next.delete(cardId)
      loadingIds.value = next
    }
  }

  /**
   * Sync favorited status from server response (batch).
   */
  function syncFromCards(cards: Array<{ id: number; isFavorited?: boolean }>) {
    const next = new Set(favoritedCardIds.value)
    for (const card of cards) {
      if (card.isFavorited) {
        next.add(card.id)
      } else {
        next.delete(card.id)
      }
    }
    favoritedCardIds.value = next
  }

  return {
    favoritedCardIds,
    loadingIds,
    isFavorited,
    toggle,
    syncFromCards,
  }
}