#!/usr/bin/env node
// Compile a Vega-Lite spec to Vega

//@ts-check
'use strict';

const helpText = `Compile a Vega-Lite spec to Vega.

Usage: vl2vg [vega_lite_json_file] [output_vega_json_file] [-p]
  If no arguments are provided, reads from stdin.
  If output_vega_json_file is not provided, writes to stdout.
  Passing -p formats the generated Vega spec.`;

// import required libraries
const {createReadStream, createWriteStream} = require('fs');
const vegaLite = require('../build/vega-lite');
const compactStringify = require('json-stringify-pretty-compact');

// arguments
const args = require('yargs')
  .usage(helpText)
  .demand(0);

args
  .boolean('p')
  .alias('p', 'pretty')
  .describe('p', 'Output human readable/pretty spec.');

const argv = args.help().version().argv;

/**
 * Read a file.
 *
 * @param file {string} File path
 */
function read(file) {
  return new Promise((resolve, reject) => {
    const input = file ? createReadStream(file) : process.stdin;
    let text = '';

    input.setEncoding('utf8');
    input.on('error', err => reject(err));
    input.on('data', chunk => (text += chunk));
    input.on('end', () => resolve(text));
  });
}

// load spec, compile vg spec
read(argv._[0]).then(text => compile(JSON.parse(text)));

/**
 * Compile the Vega-Lite spec to Vega.
 *
 * @param vlSpec {import("../src").TopLevelSpec} The Vega-Lite spec.
 */
function compile(vlSpec) {
  // @ts-ignore
  const vgSpec = vegaLite.compile(vlSpec).spec;

  const file = argv._[1] || null;
  const out = file ? createWriteStream(file) : process.stdout;
  if (argv.p) {
    out.write(compactStringify(vgSpec) + '\n');
  } else {
    out.write(JSON.stringify(vgSpec) + '\n');
  }
}