package edu.princeton.toy.lang;

/**
 * TExceptionHandler essentially maintains a list of what exceptions to ignore and what exceptions
 * to propagate throughout the virtual machine (halting the TVM).
 *
 * @author btsang
 * @version 7.1
 */

public interface TExceptionHandler
{
    /**
     * An implementation of TExceptionHandler which ignores all exceptions.
     */
    public static final TExceptionHandler PROMISCUOUS_EXCEPTION_HANDLER = new TExceptionHandler()
    {
        public void raise(TExceptionType type) throws TException
        {
            if (type == null)
                throw new NullPointerException();
        }

        public boolean getWillThrow(int index)
        {
            if (index < 0 || index >= TExceptionType.TYPES.length)
                throw new ArrayIndexOutOfBoundsException();
            return false;
        }

        public boolean getWillThrow(TExceptionType type)
        {
            if (type == null)
                throw new NullPointerException();
            return false;
        }
    };

    /**
     * An implementation of TExceptionHandler which throws all exceptions.
     */
    public static final TExceptionHandler PRUDISH_EXCEPTION_HANDLER = new TExceptionHandler()
    {
        public void raise(TExceptionType type) throws TException
        {
            throw new TException(type);
        }

        public boolean getWillThrow(int index)
        {
            if (index < 0 || index >= TExceptionType.TYPES.length)
                throw new ArrayIndexOutOfBoundsException();
            return true;
        }

        public boolean getWillThrow(TExceptionType type)
        {
            if (type == null)
                throw new NullPointerException();
            return true;
        }
    };

    /**
     * Throws a TException with the specified type iff the specified exception was not set to be
     * ignored.  The Virtual Machine should raise all exceptional conditions and let the handler
     * decide wheter or not that exception should be propagated through the rest of the machine.
     * 
     * @param type The type of exceptional condition that was raised in the Virtual Machine.
     */
    public abstract void raise(TExceptionType type) throws TException;

    /**
     * Gets wheter or not the handler should throw a raised exception of the specified type.
     *
     * @param index The index of type (in the TExceptionType.TYPES array) in question.  An invalid
     * value will result in an ArrayIndexOutOfBoundsException.
     * @return True iff the handler will throw exceptions of this type.
     * @see edu.princeton.toy.lang.TExceptionType#TYPES
     */
    public abstract boolean getWillThrow(int index);

    /**
     * Gets wheter or not the handler should throw a raised exception of the specified type.
     *
     * @param type The type in question.  A null value will result in a NullPointerException.
     * @return True iff the handler will throw exceptions of this type.
     * @see edu.princeton.toy.lang.TExceptionType#TYPES
     */
    public abstract boolean getWillThrow(TExceptionType type);
}