package org.daisy.pipeline.braille.pef;
   
   import java.util.Collection;
   import java.util.Collections;
   import java.util.HashMap;
   import java.util.Iterator;
   import java.util.Map;
   import java.util.NoSuchElementException;
   
  import com.google.common.base.Optional;
  
  import org.daisy.dotify.api.factory.FactoryProperties;
  import org.daisy.dotify.api.table.Table;
  import org.daisy.pipeline.braille.common.Query;
  import org.daisy.pipeline.braille.common.Query.MutableQuery;
  import static org.daisy.pipeline.braille.common.Query.util.mutableQuery;
  
  public abstract class AbstractTableProvider implements TableProvider {
  	
  	protected abstract Iterable<Table> _get(Query query);
  	
  	private final Map<String,Table> tablesFromId = new HashMap<String,Table>();
  
  	@Override
  	public Collection<FactoryProperties> list() {
  		// only list cached tables in preview-table option
  		return Collections.unmodifiableCollection(tablesFromId.values());
  	}
  
  	@Override
  	public Table newFactory(String identifier) {
  		MutableQuery q = mutableQuery();
  		q.add("id", identifier);
  		try {
  			return get(q).iterator().next(); }
  		catch (NoSuchElementException e) {
  			return null; }
  	}
  
  	@Override
  	public final Iterable<Table> get(Query query) {
  		MutableQuery q = mutableQuery(query);
  		if (q.containsKey("id")) {
  			String id = q.removeOnly("id").getValue().get();
  			if (q.isEmpty()) {
  				Table table = tablesFromId.get(id);
  				if (table != null)
  					return Collections.singleton(table); }
  			else
  				return empty; }
  		return cache(_get(query));
  	}
  	
  	private final static Iterable<Table> empty = Optional.<Table>absent().asSet();
  	
  	private Iterable<Table> cache(final Iterable<Table> tables) {
  		return new Iterable<Table>() {
  			public Iterator<Table> iterator() {
  				return new Iterator<Table>() {
  					Iterator<Table> i = null;
  					public boolean hasNext() {
  						if (i == null) i = tables.iterator();
  						return i.hasNext();
  					}
  					public Table next() {
  						Table t;
  						if (i == null) i = tables.iterator();
  						t = i.next();
  						tablesFromId.put(t.getIdentifier(), t);
  						return t;
  					}
  					public void remove() {
  						if (i == null) i = tables.iterator();
  						i.remove();
  					}
  				};
  			}
  		};
  	}
  }