const qs = require('querystring');

const spliceString = (string, index, removals = 0, insert = '') => {
  return (
    string.slice(0, index) + insert + string.slice(index + Math.abs(removals))
  );
};

const DBUC_REGEX = /^[0-9a-fA-F]{2}$/;
const decodeComponent = (string) => {
  let percentIndex;
  while ((percentIndex = string.indexOf('%')) !== -1) {
    const encodedByte = string.substr(percentIndex + 1, 2);
    if (!DBUC_REGEX.test(encodedByte)) {
      throw new Error('Invalid input (not URI encoded?)');
    }
    string = spliceString(
      string,
      percentIndex,
      3,
      String.fromCharCode(parseInt(encodedByte, 16)),
    );
  }
  return string;
};

const parse = (query, maxKeys = 12) => {
  return qs.parse(query, '&', '=', {
    decodeURIComponent: decodeComponent,
    maxKeys,
  });
};

const fromUrl = (url, max) => {
  const splitUrl = url.split('?');
  if (splitUrl.length > 2) {
    throw new Error('Invalid URL');
  }
  if (splitUrl.length === 1) {
    return {};
  }
  return parse(splitUrl[1]);
};

module.exports = {
  decodeURIComponent: decodeComponent,
  decodeUriComponent: decodeComponent,
  parse,
  fromUrl,
  __test: (cb) => {
    cb({
      spliceString,
      DBUC_REGEX,
      decodeComponent,
      parse,
      fromUrl,
    });
  },
};