FetchConcurrent.scala

package com.redbubble.util.fetch

import cats.data.NonEmptyList
import cats.free.Free
import fetch._

object FetchConcurrent {
  def multipleConcurrently[I, A](i: I, is: I*)(implicit ds: DataSource[I, A]): Fetch[List[A]] = {
    val idsAsNel = NonEmptyList(i, is.toList)
    val queries = NonEmptyList.of(FetchMany(idsAsNel, ds).asInstanceOf[FetchQuery[Any, Any]])
    concurrently(queries).map { imc =>
      idsAsNel.foldLeft(List[A]()) { (acc, id) =>
        val key = ds.identity(id)
        imc.get(key).fold(acc)((v: A) => acc.:+(v))
      }
    }
  }

  private def concurrently(queries: NonEmptyList[FetchQuery[Any, Any]]): Fetch[InMemoryCache] =
    Free.liftF(Concurrent(queries))
}