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package ftbsc.lll.mapper;

import ftbsc.lll.exceptions.InvalidResourceException;

import java.io.*;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.charset.StandardCharsets;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * The main class of the mapper library. It loads all the
 * valid {@link IMappingFormat}s and gets information from them.
 */
public class MapperProvider {
   /**
    * The static instance of the provider.
    */
   private static MapperProvider INSTANCE = null;

   /**
    * @return the static instance of the provider
    */
   private static MapperProvider getInstance() {
      return INSTANCE == null ? (INSTANCE = new MapperProvider()) : INSTANCE;
   }

   /**
    * A {@link Set} containing all the loaded mapper classes.
    */
   private Set<Class<? extends IMappingFormat>> loadedMappers = null;

   /**
    * Loads the mapper classes into a {@link Set}.
    */
   private void loadMappers() {
      this.loadedMappers = new HashSet<>();
      for(IMappingFormat mapper: ServiceLoader.load(IMappingFormat.class))
         this.loadedMappers.add(mapper.getClass());
      if(this.loadedMappers.isEmpty())
         throw new RuntimeException("Something went wrong: no mapper types were loaded successfully!");
   }

   /**
    * Loads all valid parsers available in the classpath (via the Java Service API),
    * attempts to load the resource at given location and to populate a mapper with
    * its data.
    * @param data the file as a list of strings
    * @return a {@link IMappingFormat} (populating it is left to the user)
    */
   public static IMappingFormat getMapper(List<String> data) {
      if(getInstance().loadedMappers == null)
         getInstance().loadMappers();
      return getInstance().loadedMappers.stream()
         .flatMap(clazz -> {
            try {
               return Stream.of(clazz.newInstance());
            } catch(ReflectiveOperationException ignored) {}
            return Stream.empty();
         }).filter(m -> m.claim(data))
         .max(Comparator.comparingInt(IMappingFormat::priority))
         .orElseThrow(InvalidResourceException::new);
   }

   /**
    * Gets a resource and parses it into a {@link List} of {@link String}s.
    * @param location either a URL or a local path
    * @return a {@link List} containing the lines of the resource
    * @throws InvalidResourceException if provided an invalid resource
    */
   public static List<String> fetchFromLocalOrRemote(String location) {
      InputStream targetStream;
      try {
         URI target = new URI(location);
         targetStream = target.toURL().openStream();
      } catch(URISyntaxException | IllegalArgumentException | IOException e) {
         //may be a local file path
         File f = new File(location);
         try {
            targetStream = new FileInputStream(f);
         } catch(FileNotFoundException ex) {
            throw new InvalidResourceException(location);
         }
      }

      return new BufferedReader(new InputStreamReader(targetStream,
         StandardCharsets.UTF_8)).lines().collect(Collectors.toList());
   }
}