import { computed, ref, watch, type Ref } from 'vue'

/** 默认每页条数 */
export const DEFAULT_PAGE_SIZE = 10

/** 可选每页条数 */
export const PAGE_SIZES = [10, 20, 50]

/**
 * 前端列表分页（对接真实接口前先对本地数组切片）
 * @param source 完整列表 ref，或返回列表的 getter（适合 computed）
 */
function asArray<T>(value: unknown): T[] {
  if (Array.isArray(value)) return value
  if (value && typeof value === 'object') {
    const list = (value as { list?: unknown }).list
    if (Array.isArray(list)) return list as T[]
  }
  return []
}

export function useClientPagination<T>(
  source: Ref<T[]> | (() => T[]),
  options?: { pageSize?: number },
) {
  const page = ref(1)
  const pageSize = ref(options?.pageSize ?? DEFAULT_PAGE_SIZE)

  const sourceList = computed(() =>
    asArray<T>(typeof source === 'function' ? source() : source.value),
  )

  const total = computed(() => sourceList.value.length)

  const pageCount = computed(() =>
    Math.max(1, Math.ceil(total.value / pageSize.value) || 1),
  )

  const pagedList = computed(() => {
    const start = (page.value - 1) * pageSize.value
    return sourceList.value.slice(start, start + pageSize.value)
  })

  function resetPage() {
    page.value = 1
  }

  function goFirst() {
    page.value = 1
  }

  function goLast() {
    page.value = pageCount.value
  }

  // 数据量或每页条数变化时，纠正越界页码
  watch([total, pageSize], () => {
    if (page.value > pageCount.value) {
      page.value = pageCount.value
    }
  })

  return {
    page,
    pageSize,
    total,
    pageCount,
    pagedList,
    resetPage,
    goFirst,
    goLast,
  }
}