/**
 * useAutoSave Hook
 *
 * 表单内容变化后自动保存草稿到 localStorage。
 * 使用 debounce 避免频繁写入，提供保存状态指示器。
 *
 * 用法：
 *   const { isSaving, lastSaved, hasUnsavedChanges, saveNow } = useAutoSave({
 *     key: 'consultation_draft',
 *     data: formData,
 *     debounceMs: 3000,
 *     onSave: async (data) => { await api.saveDraft(data) },
 *   })
 *
 *   // 显示保存状态
 *   {isSaving && '正在保存...'}
 *   {lastSaved && !isSaving && `上次保存：${lastSaved}`}
 */

import { useState, useEffect, useCallback, useRef } from 'react'

// ================================================================
// 类型定义
// ================================================================

interface UseAutoSaveOptions<T> {
  /** localStorage 存储键 */
  key: string
  /** 需要自动保存的数据 */
  data: T
  /** 防抖延迟（ms），默认 2000 */
  debounceMs?: number
  /** 自定义保存函数（如保存到后端），返回 true 表示成功 */
  onSave?: (data: T) => Promise<boolean>
  /** 是否启用，默认 true */
  enabled?: boolean
}

interface UseAutoSaveReturn<T> {
  /** 是否正在保存 */
  isSaving: boolean
  /** 上次成功保存的时间字符串 */
  lastSaved: string | null
  /** 是否有未保存的更改（自上次保存后） */
  hasUnsavedChanges: boolean
  /** 手动触发保存 */
  saveNow: () => Promise<void>
  /** 清除已保存的草稿 */
  clearDraft: () => void
  /** 从 localStorage 恢复草稿数据 */
  restoreDraft: () => T | null
}

// ================================================================
// Hook
// ================================================================

const DRAFT_PREFIX = 'vetcopilot_autosave_'

export function useAutoSave<T>(options: UseAutoSaveOptions<T>): UseAutoSaveReturn<T> {
  const { key, data, debounceMs = 2000, onSave, enabled = true } = options

  const [isSaving, setIsSaving] = useState(false)
  const [lastSaved, setLastSaved] = useState<string | null>(null)
  const [hasUnsavedChanges, setHasUnsavedChanges] = useState(false)
  const timerRef = useRef<ReturnType<typeof setTimeout> | null>(null)
  const storageKey = `${DRAFT_PREFIX}${key}`
  const dataRef = useRef(data)
  dataRef.current = data

  const doSave = useCallback(async () => {
    setIsSaving(true)
    try {
      const currentData = dataRef.current
      // 保存到 localStorage
      localStorage.setItem(
        storageKey,
        JSON.stringify({
          data: currentData,
          timestamp: Date.now(),
        })
      )

      // 调用自定义保存函数
      if (onSave) {
        const success = await onSave(currentData)
        if (!success) throw new Error('Save failed')
      }

      const now = new Date().toLocaleTimeString()
      setLastSaved(now)
      setHasUnsavedChanges(false)
    } catch {
      // 保存失败时不清除 hasUnsavedChanges
    } finally {
      setIsSaving(false)
    }
  }, [storageKey, onSave])

  // 数据变化时标记未保存，并启动防抖定时器
  useEffect(() => {
    if (!enabled) return

    setHasUnsavedChanges(true)

    if (timerRef.current) {
      clearTimeout(timerRef.current)
    }

    timerRef.current = setTimeout(() => {
      doSave()
    }, debounceMs)

    return () => {
      if (timerRef.current) {
        clearTimeout(timerRef.current)
      }
    }
  }, [data, debounceMs, enabled, doSave])

  const saveNow = useCallback(async () => {
    if (timerRef.current) {
      clearTimeout(timerRef.current)
      timerRef.current = null
    }
    await doSave()
  }, [doSave])

  const clearDraft = useCallback(() => {
    try {
      localStorage.removeItem(storageKey)
    } catch {
      // ignore
    }
    setHasUnsavedChanges(false)
  }, [storageKey])

  const restoreDraft = useCallback((): T | null => {
    try {
      const raw = localStorage.getItem(storageKey)
      if (!raw) return null
      const parsed = JSON.parse(raw)
      return parsed.data as T
    } catch {
      return null
    }
  }, [storageKey])

  return {
    isSaving,
    lastSaved,
    hasUnsavedChanges,
    saveNow,
    clearDraft,
    restoreDraft,
  }
}