downloader.rb

require 'csv'
require 'json'
require 'open-uri'

class Downloader
  SCRIPT_URL = 'SCRIPT_URL'

  attr_reader :uri

  def initialize
    @uri = "#{SCRIPT_URL}?token=#{ENV['TOKEN']}"
  end

  def data
    @data ||= open(uri).read
  end

  alias perform data
end

class Generator
  def initialize(json)
    @data = JSON.parse(json)
  end

  def perform
    @data['files']&.each do |file|
      create(file['name'], file['rows'])
    end
  end

  private

  def create(name, rows)
    CSV.open(name, 'wb') do |csv|
      rows.each { |row| csv << row }
    end
  end
end

desc 'Update fixtures from Google Spreadsheet'
task :update do
  downloader = Downloader.new
  generator = Generator.new(downloader.data)
  generator.perform
end

exporter.gs

var TOKEN = 'API_TOKEN';
var SPREADSHEET = 'SPREADSHEET_ID'

function doGet(e) {
  var response = {}
  
  // Block no access users
  if (e.parameter.token !== TOKEN) {
    response = {
      error: {
        code: '401',
        message: 'Invalid Token: ' + e.parameter.token 
      }
    }
  } else {
    var SpreadSheet = SpreadsheetApp.openById(SPREADSHEET);
    response['name'] = SpreadSheet.getName();
    response['files'] = export(SpreadSheet.getSheets());
  }
  
  Logger.log(response);
  return ContentService.createTextOutput(JSON.stringify(response))
                       .setMimeType(ContentService.MimeType.JSON);
}

function export(sheets) {
  return sheets
  .filter(function(sheet) {
    return sheet.getName().indexOf('_') !== 0;  
  })
  .map(function(sheet) {
    var rows = sheet.getLastRow();
    return {
      name: sheet.getName() + ".csv",
      rows: exportRows(sheet)
    };
  });
}

function exportRows(sheet) {
 var rows = sheet.getLastRow();
 var columns = sheet.getLastColumn();
  
 return sheet
 .getSheetValues(1, 1, rows, columns);
}