const fs = require('fs');

/** [OPTIONAL] To add custom methods to String */
String.prototype.contains = String.prototype.includes;
String.prototype.lines = function lines() { return this.split(/\r?\n/); };

class Config {
  constructor(args) {
    /** Node.js needs to call .next() twice */
    args.next();
    args.next();

    let query = args.next().value;

    if (!query) {
      throw new Error(`Didn't get a query string`);
    }

    let filename = args.next().value;

    if (!filename) {
      throw new Error(`Didn't get a file name`);
    }

    this.query = query;
    this.filename = filename;
    this.caseSensitive = !('CASE_INSENSITIVE' in process.env);
  }
}

function search(query, contents) {
  return contents.lines()
    .filter(line => line.contains(query));
}

function searchCaseInsensitive(query, contents) {
  const lowercasedQuery = query.toLowerCase();

  return contents.lines()
    .filter(line => line.toLowerCase().contains(lowercasedQuery));
}

function run(config) {
  try {
    const contents = fs.readFileSync(config.filename, 'utf8');
    const results = config.caseSensitive ?
      search(config.query, contents) :
      searchCaseInsensitive(config.query, contents);

    for (const line of results) {
      console.log(`${line}`);
    }
  }
  catch (e) {
    console.error(`Application error: ${e.message}\n`);
  }
}

module.exports = {
  Config,
  run,
};

/** No standard library for testing in Node.js */