// app/composables/useArticleNavContext.js
// 维护文章列表上下文（顺序、当前位置）供详情页/抽屉使用
import { computed } from 'vue'

const STORAGE_KEY = 'article:list:context'

function useStorage () {
  if (process.server) return null
  return window.sessionStorage
}

function readPersisted () {
  try {
    const store = useStorage()
    if (!store) return null
    const raw = store.getItem(STORAGE_KEY)
    if (!raw) return null
    return JSON.parse(raw)
  } catch (err) {
    console.warn('[ArticleNav] read persist failed', err)
    return null
  }
}

function writePersisted (payload) {
  try {
    const store = useStorage()
    if (!store) return
    store.setItem(STORAGE_KEY, JSON.stringify(payload))
  } catch (err) {
    console.warn('[ArticleNav] write persist failed', err)
  }
}

function uniqSlugs (slugs = []) {
  const seen = new Set()
  const res = []
  for (const s of slugs) {
    if (!s || seen.has(s)) continue
    seen.add(s)
    res.push(s)
  }
  return res
}

export function useArticleNavContext () {
  const state = useState('article:nav', () => {
    // SSR 时返回空状态，客户端会在下面恢复
    if (process.server) {
      return {
        listId: '',
        slugs: [],
        current: ''
      }
    }
    // 客户端首次初始化时从 sessionStorage 恢复
    return readPersisted() || {
      listId: '',
      slugs: [],
      current: ''
    }
  })

  // 客户端挂载时，确保从 sessionStorage 恢复状态
  if (process.client) {
    const persisted = readPersisted()
    if (persisted && persisted.slugs && persisted.slugs.length > 0) {
      // 如果 sessionStorage 中有数据，但 state 是空的，则恢复
      if (!state.value.slugs || state.value.slugs.length === 0) {
        console.log('[ArticleNav] 从 sessionStorage 恢复导航上下文:', persisted)
        state.value = persisted
      }
    }
  }

  const index = computed(() => {
    if (!state.value.current) return -1
    return state.value.slugs.findIndex((s) => s === state.value.current)
  })

  const prevSlug = computed(() => {
    const i = index.value
    return i > 0 ? state.value.slugs[i - 1] : ''
  })

  const nextSlug = computed(() => {
    const i = index.value
    return i >= 0 && i < state.value.slugs.length - 1 ? state.value.slugs[i + 1] : ''
  })

  const hasNav = computed(() => Boolean(state.value.slugs.length))

  function setList (listId, slugs) {
    if (!Array.isArray(slugs)) return
    state.value.listId = listId || ''
    state.value.slugs = uniqSlugs(slugs.filter(Boolean))
    writePersisted(state.value)
  }

  function setCurrent (slug) {
    const s = slug || ''
    state.value.current = s
    if (s && !state.value.slugs.includes(s)) {
      state.value.slugs = uniqSlugs([...(state.value.slugs || []), s])
    }
    writePersisted(state.value)
  }

  return {
    state,
    index,
    prevSlug,
    nextSlug,
    hasNav,
    setList,
    setCurrent
  }
}