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package internal.sdmxdl.file.spi;

import java.lang.Iterable;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.ServiceLoader;
import java.util.function.Predicate;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;
import sdmxdl.file.spi.Reader;

/**
 * Custom service loader for {@link sdmxdl.file.spi.Reader}.
 * 
This class is thread-safe.
 * Properties:
 * 

 * Quantifier: MULTIPLE
 * Fallback: null
 * Preprocessing: wrapper: none filters:[isReaderAvailable] sorters:[getReaderRank]
 * Mutability: NONE
 * Singleton: false
 * Name: internal.{{canonicalName}}Loader
 * Backend: null
 * Cleaner: null
 * Batch: false
 * Batch name: null
 * 
 */
public final class ReaderLoader {
  public static final Pattern ID_PATTERN = Pattern.compile("^[A-Z0-9]+(?:_[A-Z0-9]+)*$");

  private final Iterable source = ServiceLoader.load(Reader.class);

  private final Predicate filter = ((Predicate)o -> ID_PATTERN.matcher(o.getReaderId()).matches()).and(Reader::isReaderAvailable);

  private final Comparator sorter = Collections.reverseOrder(Comparator.comparingInt(Reader::getReaderRank));

  private final List resource = doLoad();

  private List doLoad() {
    return StreamSupport.stream(source.spliterator(), false)
        .filter(filter)
        .sorted(sorter)
        .collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList));
  }

  /**
   * Gets a list of {@link sdmxdl.file.spi.Reader} instances.
   * 
This method is thread-safe.
   * @return the current non-null value
   */
  public List get() {
    return resource;
  }

  /**
   * Gets a list of {@link sdmxdl.file.spi.Reader} instances.
   * 
This is equivalent to the following code: new ReaderLoader().get()
   * 
Therefore, the returned value might be different at each call.
   * 
This method is thread-safe.
   * @return a non-null value
   */
  public static List load() {
    return new ReaderLoader().get();
  }
}