import { ref } from 'vue'

const STORAGE_KEY = 'pub_search_history'
const MAX_ENTRIES = 50

export interface HistoryEntry {
  id: string
  query: string
  expanded_query: string
  result_count: number | null
  timestamp: string
}

function loadAll(): HistoryEntry[] {
  try {
    const raw = localStorage.getItem(STORAGE_KEY)
    return raw ? JSON.parse(raw) : []
  } catch {
    return []
  }
}

function saveAll(entries: HistoryEntry[]) {
  localStorage.setItem(STORAGE_KEY, JSON.stringify(entries))
}

/** 把 #N 引用替换为 expanded_query（加括号保护优先级） */
export function resolveQuery(query: string, entries: HistoryEntry[]): string {
  return query.replace(/#(\d+)/g, (_m, num) => {
    const found = entries.find(e => e.id === `#${num}`)
    return found ? `(${found.expanded_query})` : _m
  })
}

/** 递归展开所有 #N 引用为纯查询，带循环引用检测 */
export function expandQuery(query: string, entries: HistoryEntry[]): string {
  const seen = new Set<string>()
  let prev = ''
  let current = query
  for (let i = 0; i < 10; i++) {
    if (current === prev) break
    const refs = current.match(/#(\d+)/g)
    if (refs) {
      const uniqueRefs = [...new Set(refs)]
      for (const ref of uniqueRefs) {
        if (seen.has(ref)) return prev  // 循环引用 → 返回上次安全结果
        seen.add(ref)
      }
    }
    prev = current
    current = resolveQuery(current, entries)
  }
  return current
}

/** 重新计算所有条目的 expanded_query，在删除/淘汰后保证一致性 */
function recomputeExpanded(entries: HistoryEntry[]) {
  const ids = new Set(entries.map(e => e.id))
  for (const entry of entries) {
    entry.expanded_query = expandQuery(entry.query, entries)
      .replace(/#(\d+)/g, (m) => ids.has(m) ? m : '(deleted)')
  }
}

export function useSearchHistory() {
  const entries = ref<HistoryEntry[]>(loadAll())

  function getAll(): HistoryEntry[] {
    return [...entries.value]
  }

  function add(query: string, resultCount?: number | null): HistoryEntry {
    const all = loadAll()
    const nextNum = all.length > 0
      ? Math.max(...all.map(e => parseInt(e.id.slice(1), 10))) + 1
      : 1
    const id = `#${nextNum}`
    const expanded = expandQuery(query, all)
    const entry: HistoryEntry = {
      id,
      query,
      expanded_query: expanded,
      result_count: resultCount ?? null,
      timestamp: new Date().toISOString(),
    }

    if (all.length >= MAX_ENTRIES) {
      all.sort((a, b) => a.timestamp.localeCompare(b.timestamp))
      all.shift()
      recomputeExpanded(all)  // 清除悬空 #N 引用
    }

    all.push(entry)
    saveAll(all)
    entries.value = [...all]
    return entry
  }

  function remove(id: string) {
    const all = loadAll().filter(e => e.id !== id)
    recomputeExpanded(all)  // 重新展开，清除悬空 #N 引用
    saveAll(all)
    entries.value = all
  }

  function clear() {
    localStorage.removeItem(STORAGE_KEY)
    entries.value = []
  }

  function download() {
    const all = loadAll()
    /** 转义 TSV 特殊字符：制表符/换行/回车 → 空格 */
    const escapeTsv = (s: string) => s.replace(/[\t\n\r]/g, ' ')
    const lines = all.map(e =>
      `${e.id}\t${e.result_count ?? ''}\t${e.timestamp}\t${escapeTsv(e.query)}`
    )
    const blob = new Blob([lines.join('\n')], { type: 'text/plain;charset=utf-8' })
    const url = URL.createObjectURL(blob)
    const a = document.createElement('a')
    a.href = url
    a.download = `pubmed-search-history-${new Date().toISOString().slice(0, 10)}.tsv`
    a.click()
    // 延迟回收 blob URL，确保浏览器已开始下载
    setTimeout(() => URL.revokeObjectURL(url), 1000)
  }

  return {
    entries,
    getAll,
    add,
    remove,
    clear,
    download,
  }
}