/*******************************************************************************
 * Copyright (c) 2009-2013 CWI
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:

 *   * Jurgen J. Vinju - Jurgen.Vinju@cwi.nl - CWI
*******************************************************************************/
package org.rascalmpl.interpreter.types;

import java.util.HashSet;
import java.util.Set;

import org.rascalmpl.interpreter.env.Environment;
import org.rascalmpl.value.type.Type;
import org.rascalmpl.value.type.TypeFactory;

public class TypeReachability {
	public static boolean mayOccurIn(Type small, Type large, Environment env) {
		return mayOccurIn(small, large, new HashSet<Type>(), env);
	}

	static private boolean mayOccurIn(final Type small, final Type large, final Set<Type> seen, final Environment env) {
		// TODO: this should probably be a visitor as well
	  if (small.isBottom() && !large.isBottom()) {
	    return false;
	  }
	  
	  if (small.comparable(large)) {
      return true;
	  }
	  
	  return large.accept(new DefaultRascalTypeVisitor<Boolean, RuntimeException>(false) {
	    @Override
	    public Boolean visitList(Type type)  {
	      return mayOccurIn(small, large.getElementType(), seen, env);
	    }
	    
	    @Override
      public Boolean visitSet(Type type)  {
        return mayOccurIn(small, large.getElementType(), seen, env);
      }
	    
	    @Override
      public Boolean visitMap(Type type)  {
        return mayOccurIn(small, large.getKeyType(), seen, env)
            ||  mayOccurIn(small, large.getValueType(), seen, env);
      }
	    
	    @Override
	    public Boolean visitTuple(Type type)  {
	      for (int i = 0; i < large.getArity(); i++) {
	        if (mayOccurIn(small, large.getFieldType(i), seen, env)) {
	          return true;
	        }
	      }
	      return false;
	    }
	    
	    @Override
	    public Boolean visitFunction(RascalType type)  {
	      return false;
	    }

	    @Override
	    public Boolean visitOverloadedFunction(RascalType type) throws RuntimeException {
	      return false;
	    }

	    @Override
	    public Boolean visitReified(RascalType type) throws RuntimeException {
	      // TODO: we can be more precise here because we know only Symbols and Definitions can occur in 
	      // reified types
	      return true;
	    }

	    @Override
	    public Boolean visitNonTerminal(RascalType type) throws RuntimeException {
	      // TODO: Until we have more precise info about the types in the
	      // concrete syntax
	      // we just return true here.
	      return true;
	    }
	    
	    @Override
	    public Boolean visitConstructor(Type type)  {
	      for (int i = 0; i < type.getArity(); i++) {
	        if (mayOccurIn(small, type.getFieldType(i), seen, env)) {
	          return true;
	        }
	      }
	      return false;
	    }
	    
	    
	    @Override
	    public Boolean visitAbstractData(Type type)  {
	      if (small.equivalent(TypeFactory.getInstance().nodeType())) {
	        return true;
	      }
	      
	      seen.add(large);
	      
	      for (Type alt : env.lookupAlternatives(large)) {
	        for (int i = 0; i < alt.getArity(); i++) {
	          Type fType = alt.getFieldType(i);
	          if (seen.add(fType) && mayOccurIn(small, fType, seen, env)) {
	            return true;
	          }
	        }
	      }
	      return false;
	    }
    });
	}

}