'use strict';

const JSON2CSVBase = require('./JSON2CSVBase');

class JSON2CSVParser extends JSON2CSVBase {
  /**
   * Main function that converts json to csv.
   *
   * @param {Array|Object} data Array of JSON objects to be converted to CSV
   * @returns {String} The CSV formated data as a string
   */
  parse(data) {
    const processedData = this.preprocessData(data);

    if (!this.opts.fields) {
      const dataFields = processedData
        .map(item => Object.keys(item))
        .reduce((tempData, rows) => tempData.concat(rows), []);

      this.opts.fields = dataFields
        .filter((field, pos, arr) => arr.indexOf(field) == pos);
    }

    const header = this.opts.header ? this.getHeader() : '';
    const rows = this.processData(processedData);
    const csv = (this.opts.withBOM ? '\ufeff' : '')
      + header
      + ((header && rows) ? this.opts.eol : '')
      + rows;

    return csv;
  }

  /**
   * Preprocess the data according to the give opts (unwind, flatten, etc.)
    and calculate the fields and field names if they are not provided.
   *
   * @param {Array|Object} data Array or object to be converted to CSV
   */
  preprocessData(data) {
    const processedData = Array.isArray(data) ? data : [data];

    if (!this.opts.fields && (processedData.length === 0 || typeof processedData[0] !== 'object')) {
      throw new Error('Data should not be empty or the "fields" option should be included');
    }

    return processedData
      .map(row => this.preprocessRow(row))
      .reduce((tempData, rows) => tempData.concat(rows), []);
  }

  /**
   * Create the content row by row below the header
   *
   * @param {Array} data Array of JSON objects to be converted to CSV
   * @returns {String} CSV string (body)
   */
  processData(data) {
    return data
      .map(row => this.processRow(row))
      .filter(row => row) // Filter empty rows
      .join(this.opts.eol);
  }
}

module.exports = JSON2CSVParser;