import { reactive, computed } from 'vue'
import { fetchCurrentMenu } from '@/api/menu'
import router from '@/router'
import { useAuth } from '@/store/auth'

// 上边栏最多支持的层级数；超出部分只把最后一层放到侧边栏
const MAX_TOPBAR_LEVELS = 3

const state = reactive({
  loaded: false,
  loading: false,
  error: null,
  topMenus: [],
  activeId: null,
})

function bySort(a, b) {
  return (a?.sort ?? 0) - (b?.sort ?? 0)
}

function sortTree(list) {
  if (!Array.isArray(list)) return []
  return list
    .slice()
    .sort(bySort)
    .map((m) => ({ ...m, children: Array.isArray(m.children) ? sortTree(m.children) : [] }))
}

function pathMatches(item, path) {
  if (!item?.route) return false
  return path === item.route || path.startsWith(`${item.route}/`)
}

// 判断 item 是否“拥有”该路径，即自身匹配，或任意后代匹配
function ownsRoute(item, path) {
  if (pathMatches(item, path)) return true
  if (!Array.isArray(item.children)) return false
  return item.children.some((c) => ownsRoute(c, path))
}

function findNode(list, path) {
  if (!Array.isArray(list)) return null
  for (const node of list) {
    if (pathMatches(node, path)) return node
    if (Array.isArray(node.children)) {
      const hit = findNode(node.children, path)
      if (hit) return node
    }
  }
  return null
}

// 计算整棵菜单树的最大深度
function treeDepth(list, current = 1) {
  if (!Array.isArray(list) || list.length === 0) return 0
  let max = current
  for (const node of list) {
    if (Array.isArray(node.children) && node.children.length) {
      const d = treeDepth(node.children, current + 1)
      if (d > max) max = d
    }
  }
  return max
}

// 从顶层往下逐级选中（未命中的层级用第一个子项补齐）
function buildCascade(items, path) {
  const result = []
  let current = items
  while (Array.isArray(current) && current.length) {
    // 用 ownsRoute 判断：路由可能在当前项上，也可能在后代上
    let hit = current.find((m) => ownsRoute(m, path))
    if (!hit) hit = current[0]
    result.push(hit)
    current = hit.children
  }
  return result
}

function findFirstDescendantRoute(item) {
  let cur = item
  while (cur) {
    if (cur.route) return cur.route
    cur = Array.isArray(cur.children) && cur.children.length ? cur.children[0] : null
  }
  return null
}

export function useMenu() {
  async function load(force = false) {
    if (state.loading) return
    if (state.loaded && !force) return
    state.loading = true
    state.error = null
    try {
      const data = await fetchCurrentMenu()
      const list = Array.isArray(data) ? data : []
      state.topMenus = sortTree(list)
      state.loaded = true
      if (!state.topMenus.some((m) => m.id === state.activeId)) {
        state.activeId = state.topMenus[0]?.id ?? null
      }
    } catch (err) {
      state.error = err
      useAuth().logout()
      const redirect = router.currentRoute.value.fullPath
      if (router.currentRoute.value.name !== 'login') {
        router.replace({ name: 'login', query: { redirect } })
      }
    } finally {
      state.loading = false
    }
  }

  function setActive(id) {
    if (state.activeId === id) return
    state.activeId = id
  }

  // 根据当前路径同步选中的一级菜单(及一级菜单下的二级高亮)
  function syncActiveFromPath(path) {
    if (!Array.isArray(state.topMenus) || !state.topMenus.length) return
    const hit = findNode(state.topMenus, path)
    if (hit && state.activeId !== hit.id) {
      state.activeId = hit.id
    }
  }

  function reset() {
    state.loaded = false
    state.loading = false
    state.error = null
    state.topMenus = []
    state.activeId = null
  }

  const activeTopMenu = computed(
    () => state.topMenus.find((m) => m.id === state.activeId) ?? null,
  )

  const subMenus = computed(() => {
    const cur = activeTopMenu.value
    return cur && Array.isArray(cur.children) ? cur.children : []
  })

  // ===== 多级菜单：上边栏最多展示 N-1 层（≤3），侧边栏只展示最后一层 =====
  // 深度按当前激活的一级菜单所在分支计算，而非整棵树

  const activeBranchRoot = computed(() => cascadeSelection.value[0] ?? null)

  // 当前激活一级菜单分支的深度
  const activeBranchDepth = computed(() => {
    const root = activeBranchRoot.value
    if (!root) return 0
    return treeDepth([root])
  })

  // 上边栏要渲染的层级数：
  //   深度=1 → 1；深度=2 → 1；深度=3 → 2；深度=4 → 3；深度 >4 同样最多 3
  const topBarLevelCount = computed(() => {
    const depth = activeBranchDepth.value
    if (depth <= 0) return 0
    return Math.max(1, Math.min(depth - 1, MAX_TOPBAR_LEVELS))
  })

  // 侧边栏要展示的层级（当前分支最后一层）；深度=1 时为 0（不展示侧边栏）
  const sidebarDepth = computed(() => Math.max(0, activeBranchDepth.value - topBarLevelCount.value))

  // 当前路由对应的级联选中项，顶层到深层依次排列；缺失层级用第一个子项补齐
  const cascadeSelection = computed(() => {
    const path = router.currentRoute.value.path
    return buildCascade(state.topMenus, path)
  })

  // 上边栏各层级要渲染的菜单项（数组的每一项对应一行）
  const topBarLevelItems = computed(() => {
    const sel = cascadeSelection.value
    const rows = [state.topMenus]
    for (let i = 0; i < topBarLevelCount.value - 1; i++) {
      const parent = sel[i]
      if (!parent) {
        rows.push([])
        continue
      }
      rows.push(Array.isArray(parent.children) ? parent.children : [])
    }
    return rows
  })

  // 侧边栏要展示的项 = 上边栏最后一行选中项的子项（即整棵树的最后一层）
  const sidebarItems = computed(() => {
    if (sidebarDepth.value <= 0) return []
    const sel = cascadeSelection.value
    const parent = sel[topBarLevelCount.value - 1]
    if (!parent) return []
    return Array.isArray(parent.children) ? parent.children : []
  })

  // 当前激活的层级项（高亮用）：按层级取 cascadeSelection 中对应下标
  const activeByLevel = computed(() => cascadeSelection.value.slice())

  // 点击某层某项：定位该层为选中项，并跳转到该项目（或首个后代）的路由
  function selectLevel(level, item) {
    if (!item) return
    // L1 仅为分组目录（无 route 且有子项）时，不更新 activeId 也不导航，
    // 真正的导航要交给二级 / 三级菜单触发
    if (level === 1 && !item.route && Array.isArray(item.children) && item.children.length > 0) {
      return
    }
    if (level === 1) {
      state.activeId = item.id
    }
    const target = findFirstDescendantRoute(item)
    if (target && router.currentRoute.value.path !== target) {
      router.push(target)
    }
  }

  return {
    state,
    load,
    setActive,
    syncActiveFromPath,
    reset,
    activeTopMenu,
    subMenus,
    activeBranchRoot,
    activeBranchDepth,
    topBarLevelCount,
    sidebarDepth,
    cascadeSelection,
    topBarLevelItems,
    sidebarItems,
    activeByLevel,
    selectLevel,
  }
}