/*
    * SPDX-FileCopyrightText: none
    * SPDX-License-Identifier: CC0-1.0
    */
   
   package gov.nist.secauto.metaschema.cli.processor.command;
   
   import gov.nist.secauto.metaschema.core.util.ObjectUtils;
   
  import java.util.List;
  import java.util.ServiceLoader;
  import java.util.ServiceLoader.Provider;
  import java.util.stream.Collectors;
  
  import edu.umd.cs.findbugs.annotations.NonNull;
  import nl.talsmasoftware.lazy4j.Lazy;
  
  /**
   * A service that loads commands using SPI.
   * <p>
   * This class implements the singleton pattern to ensure a single instance of
   * the command service is used throughout the application.
   *
   * @see ServiceLoader for more information
   */
  public final class CommandService {
    private static final Lazy<CommandService> INSTANCE = Lazy.lazy(CommandService::new);
    @NonNull
    private final ServiceLoader<ICommand> loader;
  
    /**
     * Get the singleton instance of the function service.
     *
     * @return the service instance
     */
    public static CommandService getInstance() {
      return INSTANCE.get();
    }
  
    /**
     * Construct a new service.
     * <p>
     * Initializes the ServiceLoader for ICommand implementations.
     * <p>
     * This constructor is private to enforce the singleton pattern.
     */
    private CommandService() {
      ServiceLoader<ICommand> loader = ServiceLoader.load(ICommand.class);
      assert loader != null;
      this.loader = loader;
    }
  
    /**
     * Get the function service loader instance.
     *
     * @return the service loader instance.
     */
    @NonNull
    private ServiceLoader<ICommand> getLoader() {
      return loader;
    }
  
    /**
     * Get the loaded commands.
     *
     * @return the list of loaded commands
     */
    @NonNull
    public List<ICommand> getCommands() {
      return ObjectUtils.notNull(getLoader().stream()
          .map(Provider<ICommand>::get)
          .collect(Collectors.toUnmodifiableList()));
    }
  }