import { STMRetryException } from "@effect/core/stm/STM/definition/primitives"
import { concreteTPriorityQueue } from "@effect/core/stm/TPriorityQueue/operations/_internal/InternalTPriorityQueue"

/**
 * Peeks at the first value in the queue without removing it, retrying until a
 * value is in the queue.
 *
 * @tsplus getter effect/core/stm/TPriorityQueue peek
 */
export function peek<A>(self: TPriorityQueue<A>): USTM<A> {
  return STM.Effect((journal) => {
    concreteTPriorityQueue(self)

    const result = self.map.unsafeGet(journal).headMaybe
      .map((tuple) => tuple[1])
      .flatMap((chunk) => chunk.head)

    if (result._tag === "None") {
      throw new STMRetryException()
    }

    return result.value
  })
}