Example1.scala

import java.util.UUID

import doobie._
import doobie.implicits._
import doobie.postgres.implicits._

class Points(dao: Dao) {
  def increase(userId: UUID): ConnectionIO[Unit] =
    for {
      current <- dao.currentPoints(userId)
      updated = calculatePointsIncrease(current)
      _ <- dao.updatePoints(userId, updated)
    } yield ()

  private def calculatePointsIncrease(points: Int): Int = {
    if (points % 2 == 0) points + 3 else points + 1
  }
}

trait Dao {
  def currentPoints(userId: UUID): ConnectionIO[Int]
  def updatePoints(userId: UUID, value: Int): ConnectionIO[Unit]
}

object DefaultDao extends Dao {
  override def currentPoints(userId: UUID): doobie.ConnectionIO[Int] =
    sql"SELECT points FROM user_points WHERE user_id = $userId"
      .query[Int].unique

  override def updatePoints(userId: UUID, value: Int): doobie.ConnectionIO[Unit] =
    sql"UPDATE user_points SET points = $value WHERE user_id = $userId"
      .update.run.map(_ => ())
}