/* @flow */
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import VNode from '../vnode'
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import { createFnInvoker } from './update-listeners'
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import { remove, isDef, isUndef, isTrue } from 'shared/util'
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export function mergeVNodeHook (def: Object, hookKey: string, hook: Function) {
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if (def instanceof VNode) {
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def = def.data.hook || (def.data.hook = {})
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}
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let invoker
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const oldHook = def[hookKey]
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function wrappedHook () {
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hook.apply(this, arguments)
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// important: remove merged hook to ensure it's called only once
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// and prevent memory leak
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remove(invoker.fns, wrappedHook)
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}
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if (isUndef(oldHook)) {
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// no existing hook
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invoker = createFnInvoker([wrappedHook])
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} else {
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/* istanbul ignore if */
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if (isDef(oldHook.fns) && isTrue(oldHook.merged)) {
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// already a merged invoker
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invoker = oldHook
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invoker.fns.push(wrappedHook)
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} else {
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// existing plain hook
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invoker = createFnInvoker([oldHook, wrappedHook])
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}
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}
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invoker.merged = true
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def[hookKey] = invoker
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}
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