import { SaxesOptions, SaxesStream, SaxesStreamChunk } from "saxes-stream";

import { Transform, TransformOptions, TransformCallback } from "stream";
import request from "request";
import fs from "fs";
import stringify from "csv-stringify";

/ Source HTTP XML stream /
const httpStream = request(url);

/ SaxesStream XML parser /
const const saxesOptions: SaxesOptions = {
// ...
}

const streamOptions: TransformOptions = {
// ...
}

const parser = new SaxesStream(saxesOptions, streamOptions);

/ Custom Transform Stream to pick the data from XML /
class BookTransform extends Transform {

item: any = {};

// Stream setting
readableObjectMode = true;
writableObjectMode = true;

_transform(chunk: SaxesStreamChunk, encoding: string, callback: TransformCallback) {

/ Save parts by matching path /
if (chunk.event === "text") {
switch (chunk.path) {
case ".books.book.title": this.item["title"] = chunk.text; break;
case ".books.book.content": this.item["content"] = chunk.text; break;
}
}

/ On ending tag emit the completed book object as data (or piped to a next stream) /
if (chunk.event === "closetag") {
switch (chunk.path) {
case ".books.book":
this.push(this.item);
this.item = {};
break;
}
}

callback();

}

}

const bookTransform = new BookTransform();

/ JSON -> CSV Transform Stream /
const csv = stringify({ delimiter: ',' });

/ File Write Stream /
const file = fs.createWriteStream('./books.csv');

/ PIPE ALL THINGS TOGETHER /
httpStream.pipe(parser).pipe(bookTransform).pipe(csv).pipe(file);