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package edu.isi.nlp.io;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.base.Optional;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import edu.isi.nlp.files.KeyValueSource;
import edu.isi.nlp.symbols.Symbol;
import java.io.IOException;
import java.util.concurrent.ExecutionException;

/**
 * This should be merged into the newer {@link KeyValueSource} code.
 *
 * @author Ryan Gabbard
 */
public final class CachingOriginalTextSource implements OriginalTextSource {

  private final LoadingCache cache;

  private CachingOriginalTextSource(final LoadingCache cache) {
    this.cache = checkNotNull(cache);
  }

  public static OriginalTextSource from(final OriginalTextSource baseSource, int maxToCache) {
    return new CachingOriginalTextSource(
        CacheBuilder.newBuilder()
            .maximumSize(maxToCache)
            .build(
                new CacheLoader() {
                  @Override
                  public String load(final Symbol key) throws Exception {
                    final Optional baseRet = baseSource.getOriginalText(key);
                    if (baseRet.isPresent()) {
                      return baseRet.get();
                    } else {
                      return null;
                    }
                  }
                }));
  }

  @Override
  public Optional getOriginalText(final Symbol docID) throws IOException {
    try {
      return Optional.fromNullable(cache.get(docID));
    } catch (final ExecutionException e) {
      if (e.getCause() instanceof IOException) {
        throw (IOException) e.getCause();
      } else {
        throw new RuntimeException(e);
      }
    }
  }
}