package org.orbeon.saxon.expr;

import org.orbeon.saxon.om.SequenceIterator;
import org.orbeon.saxon.om.Item;
import org.orbeon.saxon.trans.XPathException;

/**
 * A SequenceIterator that throws an exception as soon as its next() method is called. Used when
 * the method that returns the iterator isn't allowed to throw a checked exception itself.
 */
public class ErrorIterator implements SequenceIterator {

    private XPathException exception;

    public ErrorIterator(XPathException exception) {
        this.exception = exception;
    }

    /**
     * Get the next item in the sequence. This method changes the state of the
     * iterator, in particular it affects the result of subsequent calls of
     * position() and current().
     *
     * @return the next item, or null if there are no more items. Once a call
     *         on next() has returned null, no further calls should be made. The preferred
     *         action for an iterator if subsequent calls on next() are made is to return
     *         null again, and all implementations within Saxon follow this rule.
     * @throws org.orbeon.saxon.trans.XPathException
     *          if an error occurs retrieving the next item
     * @since 8.4
     */

    public Item next() throws XPathException {
        throw exception;
    }

    /**
     * Get the current value in the sequence (the one returned by the
     * most recent call on next()). This will be null before the first
     * call of next(). This method does not change the state of the iterator.
     *
     * @return the current item, the one most recently returned by a call on
     *         next(). Returns null if next() has not been called, or if the end
     *         of the sequence has been reached.
     * @since 8.4
     */

    public Item current() {
        return null;
    }

    /**
     * Get the current position. This will usually be zero before the first call
     * on next(), otherwise it will be the number of times that next() has
     * been called. Once next() has returned null, the preferred action is
     * for subsequent calls on position() to return -1, but not all existing
     * implementations follow this practice. (In particular, the EmptyIterator
     * is stateless, and always returns 0 as the value of position(), whether
     * or not next() has been called.)
     * <p/>
     * This method does not change the state of the iterator.
     *
     * @return the current position, the position of the item returned by the
     *         most recent call of next(). This is 1 after next() has been successfully
     *         called once, 2 after it has been called twice, and so on. If next() has
     *         never been called, the method returns zero. If the end of the sequence
     *         has been reached, the value returned will always be <= 0; the preferred
     *         value is -1.
     * @since 8.4
     */

    public int position() {
        return 0;
    }

    public void close() {

    }

    /**
     * Get another SequenceIterator that iterates over the same items as the original,
     * but which is repositioned at the start of the sequence.
     * <p/>
     * This method allows access to all the items in the sequence without disturbing the
     * current position of the iterator. Internally, its main use is in evaluating the last()
     * function.
     * <p/>
     * This method does not change the state of the iterator.
     *
     * @return a SequenceIterator that iterates over the same items,
     *         positioned before the first item
     * @throws org.orbeon.saxon.trans.XPathException
     *          if any error occurs
     * @since 8.4
     */

    public SequenceIterator getAnother() throws XPathException {
        return this;
    }

    /**
     * Get properties of this iterator, as a bit-significant integer.
     *
     * @return the properties of this iterator. This will be some combination of
     *         properties such as {@link #GROUNDED}, {@link #LAST_POSITION_FINDER},
     *         and {@link #LOOKAHEAD}. It is always
     *         acceptable to return the value zero, indicating that there are no known special properties.
     *         It is acceptable for the properties of the iterator to change depending on its state.
     * @since 8.6
     */

    public int getProperties() {
        return 0; 
    }

}

//
// The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
// you may not use this file except in compliance with the License. You may obtain a copy of the
// License at http://www.mozilla.org/MPL/
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or implied.
// See the License for the specific language governing rights and limitations under the License.
//
// The Original Code is: all this file
//
// The Initial Developer of the Original Code is Michael H. Kay.
//
// Contributor(s):
//

