import { computed, reactive } from 'vue'
import { readerApi } from '../api'

// 一篇文章的评论区状态。
// 刻意做成「每个文章实例化一份」而不是像 site.js 那样的单例 ——
// 换文章必须重新来过，单例会在路由切换时残留上一条的数据。
//
// 后端契约（见 README / 方案文档）：
//   GET /api/comments?post_id=&sort=&page=&size=
//     -> { items:[Comment], total, page, pages, has_more }
//   Comment = { id, parent_id, root_id, body_html, state, created_at, edited_at,
//               is_deleted, reply_count, replies:[Comment], author:{...} }
// total / has_more 只统计顶层评论；回复挂在各自的 replies 里。

const PAGE_SIZE = 10

export function useComments(postId) {
  const s = reactive({
    items: [],
    total: 0,
    page: 0,
    sort: 'default', // default | newest | oldest
    loading: false,
    loadingMore: false,
    error: '',
    replyTo: null, // 正在回复的那条（顶层或回复都可能是）
    editing: null, // 正在编辑的那条
    submitting: false
  })

  const remaining = computed(() => Math.max(0, s.total - s.items.length))

  async function load(reset = true) {
    if (s.loading || s.loadingMore) return
    if (reset) {
      s.loading = true
      s.error = ''
    } else {
      s.loadingMore = true
    }
    try {
      const page = reset ? 1 : s.page + 1
      const data = await readerApi.comments(postId, { sort: s.sort, page, size: PAGE_SIZE })
      const items = (data && data.items) || []
      s.items = reset ? items : s.items.concat(items)
      s.page = page
      s.total = (data && data.total) || 0
    } catch (e) {
      s.error = e.message || '评论加载失败'
    } finally {
      s.loading = false
      s.loadingMore = false
    }
  }

  function setSort(sort) {
    if (sort === s.sort) return
    s.sort = sort
    load(true)
  }

  // SSE 触发的静默刷新：回到第一页按当前排序重拉，不亮加载态——
  // 别人发了新评论时页面只是「悄悄长出」新内容，不该闪一下。
  // 返回 true 表示列表真的变了（顶层条数有差异）。
  async function refresh() {
    try {
      const data = await readerApi.comments(postId, { sort: s.sort, page: 1, size: PAGE_SIZE })
      if (s.loading || s.loadingMore || s.replyTo || s.editing) return false
      const items = (data && data.items) || []
      const changed = (data && data.total) !== s.total || items.some((c, i) => !s.items[i] || s.items[i].id !== c.id || s.items[i].edited_at !== c.edited_at)
      s.items = items
      s.page = 1
      s.total = (data && data.total) || 0
      return changed
    } catch {
      return false
    }
  }

  // 发表 / 回复。成功后直接插进列表，不整页重拉 —— 位置按当前排序决定，
  // 用户刚发的东西必须马上看得见。
  async function submit(bodyMd, parent = null) {
    s.submitting = true
    s.error = ''
    try {
      const created = await readerApi.create(postId, bodyMd, parent ? parent.id : 0)
      s.total += 1
      if (parent) {
        const root = rootOf(parent)
        if (root) {
          root.replies = (root.replies || []).concat(created)
          root.reply_count = (root.reply_count || 0) + 1
        }
      } else if (s.sort === 'oldest') {
        s.items.push(created)
      } else {
        s.items.unshift(created)
      }
      return created
    } catch (e) {
      s.error = e.message || '发表失败'
      return null
    } finally {
      s.submitting = false
    }
  }

  async function saveEdit(comment, bodyMd) {
    s.submitting = true
    s.error = ''
    try {
      const updated = await readerApi.edit(comment.id, bodyMd)
      // 后端会把新的 body_html / edited_at 一起回来，就地替换
      comment.body_html = updated.body_html
      comment.edited_at = updated.edited_at
      s.editing = null
      return true
    } catch (e) {
      s.error = e.message || '保存失败'
      return false
    } finally {
      s.submitting = false
    }
  }

  async function remove(comment) {
    s.error = ''
    try {
      await readerApi.remove(comment.id)
      comment.is_deleted = true
      comment.body_html = ''
      // 顶层评论软删后总数要减；回复只改自身
      if (!comment.parent_id) s.total = Math.max(0, s.total - 1)
      else {
        const root = rootOf(comment)
        if (root) root.reply_count = Math.max(0, (root.reply_count || 0) - 1)
      }
      return true
    } catch (e) {
      s.error = e.message || '删除失败'
      return false
    }
  }

  // 回复折叠时按需拉取（GET /api/comments/{rootId}/thread）
  async function loadMoreReplies(root) {
    if (root.__threadLoading) return
    root.__threadLoading = true
    try {
      const data = await readerApi.thread(root.id, root.__cursor || '')
      const more = (data && data.items) || []
      root.replies = (root.replies || []).concat(more)
      root.__cursor = (data && data.cursor) || ''
      root.reply_count = (data && data.reply_count) || (root.replies || []).length
    } catch (e) {
      s.error = e.message || '回复加载失败'
    } finally {
      root.__threadLoading = false
    }
  }

  // 顶层评论列表里找出某条回复所属的根
  function rootOf(comment) {
    if (comment.root_id) {
      const byRoot = s.items.find((c) => c.id === comment.root_id)
      if (byRoot) return byRoot
    }
    return s.items.find((c) => (c.replies || []).some((r) => r.id === comment.id)) || null
  }

  function startReply(comment) {
    s.editing = null
    s.replyTo = comment
  }
  function startEdit(comment) {
    s.replyTo = null
    s.editing = comment
  }
  function cancel() {
    s.replyTo = null
    s.editing = null
  }

  return {
    s,
    remaining,
    load,
    refresh,
    setSort,
    submit,
    saveEdit,
    remove,
    loadMoreReplies,
    startReply,
    startEdit,
    cancel
  }
}