import { onScopeDispose, ref, toValue, watch, type MaybeRefOrGetter, type Ref } from 'vue'
import { errorMessage } from '../lib/http'

/** 串行轮询：请求完成后才计时；切换项目立即取消，过期响应不会覆盖新项目。 */
export function usePolling<T>(
    key: Ref<string>,
    loader: (key: string, signal: AbortSignal) => Promise<T>,
    interval: MaybeRefOrGetter<number | false> = 6000
) {
    const data = ref<T | null>(null) as Ref<T | null>
    const loading = ref(false)
    const error = ref('')
    const updatedAt = ref('')
    let generation = 0
    let controller: AbortController | undefined
    let timer: ReturnType<typeof setTimeout> | undefined
    let disposed = false

    /** 隐藏页面只安排下一次检查，不继续拉取完整 checkpoint。 */
    function schedule() {
        const delay = toValue(interval)
        if (disposed || delay === false) return
        timer = setTimeout(() => {
            if (toValue(interval) === false) return
            if (document.visibilityState === 'hidden') schedule()
            else void refresh()
        }, delay)
    }

    /** 手动刷新也取消上一次查询，避免同时存在多个轮询链。 */
    async function refresh() {
        if (disposed) return
        const current = ++generation
        clearTimeout(timer)
        controller?.abort()
        controller = new AbortController()
        const signal = controller.signal
        loading.value = true
        try {
            const result = await loader(key.value, signal)
            if (current !== generation || disposed) return
            data.value = result
            error.value = ''
            updatedAt.value = new Date().toISOString()
        } catch (cause) {
            if (current === generation && !signal.aborted && !disposed) error.value = errorMessage(cause)
        } finally {
            if (current === generation && !disposed) {
                loading.value = false
                schedule()
            }
        }
    }

    // 页面可关闭定时刷新；首次读取、切换查询目标和手动刷新仍然有效。
    watch(
        () => toValue(interval),
        () => {
            clearTimeout(timer)
            if (!loading.value) schedule()
        }
    )
    watch(
        key,
        () => {
            data.value = null
            error.value = ''
            updatedAt.value = ''
            void refresh()
        },
        { immediate: true }
    )
    onScopeDispose(() => {
        disposed = true
        generation++
        clearTimeout(timer)
        controller?.abort()
    })
    return { data, loading, error, updatedAt, refresh }
}