shortener.js

const dbClient = require('./db_client');
class Shortener extends dbClient {
  async init() {
    this._init();
  }

  async last(n) {
    const res = await this._db.query('SELECT * FROM links ORDER BY updated DESC LIMIT $1', [n]);
    return res.rows;
  }

  async lookup(key) {
    // todo: fill in query
    const res = await this._db.query('SELECT $1', [key]);
    return res.rows.length ? res.rows[0] : null;
  }

  async exists(url) {
    // todo: fill in query
    const res = await this._db.query('SELECT $1', [key]);
    return res.rows.length ? res.rows[0] : null;
  }

  async nextKey(url) {
    // url is passed in, but it doesn't need to be used
    const query = `SELECT nextval('key_serial')`;
    const res = await this._db.query(query);

    return res.rows[0].nextval;
  }

  async insert(url, key = null) {
    // check if a record exists
    // - if it does, then this.update() the record
    // - if it doesn't
    //   - generate a new key using this.nextKey()
    //   - using the key, insert a new record into the database
    
   key = await this.nextKey(null);

    // "RETURNING *" is specific to postgres and will let you return the new values you just inserted
    const res = await this._db.query('INSERT INTO links(key,url) VALUES ($1, $2) GRETURNING *', [key, url]);
    return res.rows.length ? res.rows[0] : null;
  }

  async update(key) {
    // CURRENT_TIMESTAMP is a postgres function that returns the current time
    // - e.g. try "SELECT CURRENT_TIMESTAMP"
    const res = await this._db.query('UPDATE links SET updated = CURRENT_TIMESTAMP  <fill in condition>', [key]);
    return res.rows.length ? res.rows[0] : null;
  }

  async remove(key) {
    // check if the key exists
    // - if it does, DELETE the key
    // - if it doesn't, you don't need to do anything
    // In either case, it may be helpful to return something
    const res = await this._db.query('DELETE FROM <complete the query>', [key]);
    return exists;
  }
}

module.exports = Shortener;