var numExp = /^[0-9]+$/;
module.exports = function (params) {
  var _param = {
    constructResult: true, //set to false to not construct result in memory. suitable for big csv data
    delimiter: ',', // change the delimiter of csv columns. It is able to use an array to specify potencial delimiters. e.g. [",","|",";"]
    ignoreColumns: [], // columns to ignore upon input.
    includeColumns: [], // columns to include upon input.
    quote: '"', //quote for a column containing delimiter.
    trim: true, //trim column's space charcters
    checkType: false, //whether check column type
    toArrayString: false, //stream down stringified json array instead of string of json. (useful if downstream is file writer etc)
    ignoreEmpty: false, //Ignore empty value while parsing. if a value of the column is empty, it will be skipped parsing.
    workerNum: getEnv("CSV_WORKER", 1), //number of parallel workers. If multi-core CPU available, increase the number will get better performance for large csv data.
    fork: false, //use another CPU core to convert the csv stream
    noheader: false, //indicate if first line of CSV file is header or not.
    headers: null, //an array of header strings. If noheader is false and headers is array, csv header will be ignored.
    flatKeys: false, // Don't interpret dots and square brackets in header fields as nested object or array identifiers at all.
    maxRowLength: 0, //the max character a csv row could have. 0 means infinite. If max number exceeded, parser will emit "error" of "row_exceed". if a possibly corrupted csv data provided, give it a number like 65535 so the parser wont consume memory. default: 0
    checkColumn: false, //whether check column number of a row is the same as headers. If column number mismatched headers number, an error of "mismatched_column" will be emitted.. default: false
    escape: '"', //escape char for quoted column
    colParser:{}, //flags on columns to alter field processing.

    /**below are internal params */
    _columnConv:[],
    _headerType: [],
    _headerTitle: [],
    _headerFlag: [],
    _headers: null,
    _needFilterRow: false
  };
  if (!params) {
    params = {};
  }
  for (var key in params) {
    if (params.hasOwnProperty(key)) {
      if (Array.isArray(params[key])) {
        _param[key] = [].concat(params[key]);
      } else {
        _param[key] = params[key];
      }
    }
  }
  if (_param.ignoreColumns.length > 0 && !numExp.test(_param.ignoreColumns.join(""))) {
    _param._postIgnoreColumns = true;
  }
  if (_param.includeColumns.length > 0 && !numExp.test(_param.includeColumns.join(""))) {
    _param._postIncludeColumns = true;
  }

  if (_param.ignoreColumns.length || _param.includeColumns.length) {
    _param._needFilterRow = true;
    if (!_param._postIgnoreColumns){
      _param.ignoreColumns.sort(function (a, b) { return b-a;});
    }
  }


  return _param;
};

function getEnv(key, def) {
  if (process.env[key]) {
    return process.env[key];
  } else {
    return def;
  }
}