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Tooling for reactive Domain-Driven Design projects that are highly concurrent. Includes compute grid, actor caching, spaces, cross-node cluster messaging, CQRS, and Event Sourcing support.

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// Copyright © 2012-2020 VLINGO LABS. All rights reserved.
//
// This Source Code Form is subject to the terms of the
// Mozilla Public License, v. 2.0. If a copy of the MPL
// was not distributed with this file, You can obtain
// one at https://mozilla.org/MPL/2.0/.

package io.vlingo.lattice.model;

import java.util.function.Supplier;

import io.vlingo.actors.CompletesEventually;

/**
 * Supports providing a latent {@code Completes} outcome by way of {@code CompletesEventually}.
 * Used by {@code Sourced}, {@code ObjectEntity}, and {@code StateEntity} to provide answers
 * from methods that complete asynchronously to the original message delivery.
 * @param  the return value type of the internal {@code Supplier}.
 */
public class CompletionSupplier {
  private final Supplier supplier;
  private final CompletesEventually completes;

  /**
   * Answer a new instance of {@code CompletionSupplier} if the {@code supplier} is not {@code null};
   * otherwise answer null.
   * @param supplier the {@code Supplier} of the eventual outcome, or null if none is provided
   * @param completes the CompletesEventually through which the eventual outcome is sent
   * @param  the return type of the given supplier, if any
   * @return {@code CompletionSupplier}
   */
  public static  CompletionSupplier supplierOrNull(final Supplier supplier, final CompletesEventually completes) {
    if (supplier == null) {
      return null;
    }

    return new CompletionSupplier(supplier, completes);
  }

  /**
   * Completes the outcome by executing the {@code Supplier} for its answer.
   */
  public void complete() {
    completes.with(supplier.get());
  }

  /**
   * Construct my default state.
   * @param supplier the {@code Supplier} to supply the eventual outcome with which to complete
   * @param completes the {@code CompletesEventually} used to complete the eventual outcome
   */
  private CompletionSupplier(final Supplier supplier, final CompletesEventually completes) {
    this.supplier = supplier;
    this.completes = completes;
  }
}