json-parser-yaml-converter/src/parser.js

Enhanced JSON Parser with verbose error messages and JSON to YAML conversion

/**
 * This module contains the function jsonParse that parses a JSON file.
 *
 * @module parser
 */


'use strict';

import { readFileSync } from 'fs';
import { YELLOW, RESET, BOLD, UNDERLINE } from './colors.js';
import nearley from 'nearley';
import grammar from './grammar.js';

/**
 * Parses a JSON file.
 * @param {string} jsonFile JSON file to parse.
 * @param {boolean} ast If true, returns the AST instead of the object.
 * @returns {Object} The parsed JSON file.
 * @throws {Error} If the JSON file could not be parsed.
 */
function jsonParse(jsonFile, ast = false) {
  const INPUT = readFileSync(jsonFile, 'utf-8');
  const PARSER = new nearley.Parser(nearley.Grammar.fromCompiled(grammar));
  try {
    const RESULT = PARSER.feed(INPUT);
    return ast ? RESULT.results[0] : astToObject(RESULT.results[0]);
  } catch (error) {
    const TOKEN = error.token;
    const EXPECTED = error.message.match(/(?<=A ).*(?= based on:)/g).map(s => s.replace(/\s+token/i, ''));
    if (INPUT.length === 0) {
      TOKEN.line = 0;
      TOKEN.col = 0;
    }
    const FINAL_ERROR = {
      token: TOKEN.value,
      line: TOKEN.line,
      col: TOKEN.col,
      expected: [...new Set(EXPECTED)]
    }
    throw FINAL_ERROR;
  }
}

/**
 * Converts an AST to an object.
 * @param {Object} ast AST to convert.
 * @returns {Object} The object.
 */
function astToObject(ast) {
  if (ast.type === 'object') {
    return ast.properties.reduce((acc, property) => {
      if (property.key in acc) {
        console.warn(YELLOW + 'Warning: Duplicate key ' + RESET + BOLD + UNDERLINE + property.key + RESET + YELLOW + ' found!' + RESET);
      }
      acc[property.key] = astToObject(property.value);
      return acc;
    }, {});
  }
  if (ast.type === 'array') {
    return ast.elements.map(astToObject);
  }
  return ast.value;
}

export { jsonParse, astToObject };