/* @flow */
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/**
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* Original RenderStream implementation by Sasha Aickin (@aickin)
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* Licensed under the Apache License, Version 2.0
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Modified by Evan You (@yyx990803)
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*/
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const stream = require('stream')
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import { isTrue, isUndef } from 'shared/util'
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import { createWriteFunction } from './write'
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export default class RenderStream extends stream.Readable {
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buffer: string;
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render: (write: Function, done: Function) => void;
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expectedSize: number;
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write: Function;
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next: Function;
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end: Function;
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done: boolean;
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constructor (render: Function) {
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super()
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this.buffer = ''
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this.render = render
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this.expectedSize = 0
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this.write = createWriteFunction((text, next) => {
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const n = this.expectedSize
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this.buffer += text
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if (this.buffer.length >= n) {
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this.next = next
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this.pushBySize(n)
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return true // we will decide when to call next
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}
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return false
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}, err => {
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this.emit('error', err)
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})
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this.end = () => {
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this.emit('beforeEnd')
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// the rendering is finished; we should push out the last of the buffer.
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this.done = true
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this.push(this.buffer)
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}
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}
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pushBySize (n: number) {
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const bufferToPush = this.buffer.substring(0, n)
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this.buffer = this.buffer.substring(n)
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this.push(bufferToPush)
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}
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tryRender () {
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try {
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this.render(this.write, this.end)
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} catch (e) {
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this.emit('error', e)
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}
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}
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tryNext () {
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try {
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this.next()
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} catch (e) {
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this.emit('error', e)
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}
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}
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_read (n: number) {
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this.expectedSize = n
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// it's possible that the last chunk added bumped the buffer up to > 2 * n,
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// which means we will need to go through multiple read calls to drain it
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// down to < n.
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if (isTrue(this.done)) {
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this.push(null)
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return
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}
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if (this.buffer.length >= n) {
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this.pushBySize(n)
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return
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}
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if (isUndef(this.next)) {
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// start the rendering chain.
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this.tryRender()
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} else {
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// continue with the rendering.
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this.tryNext()
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}
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}
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}
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