/** A generic list of elements tracked in an alternative to be used in
 *  a -> rewrite rule.  We need to subclass to fill in the next() method,
 *  which returns either an AST node wrapped around a token payload or
 *  an existing subtree.
 *
 *  Once you start next()ing, do not try to add more elements.  It will
 *  break the cursor tracking I believe.
 *
 *  @see org.antlr.runtime.tree.RewriteRuleSubtreeStream
 *  @see org.antlr.runtime.tree.RewriteRuleTokenStream
 *
 *  TODO: add mechanism to detect/puke on modification after reading from stream
 */
org.antlr.runtime.tree.RewriteRuleElementStream = function(adaptor, elementDescription, el) {
    /** Cursor 0..n-1.  If singleElement!=null, cursor is 0 until you next(),
     *  which bumps it to 1 meaning no more elements.
     */
    this.cursor = 0;

    /** Once a node / subtree has been used in a stream, it must be dup'd
     *  from then on.  Streams are reset after subrules so that the streams
     *  can be reused in future subrules.  So, reset must set a dirty bit.
     *  If dirty, then next() always returns a dup.
     *
     *  I wanted to use "naughty bit" here, but couldn't think of a way
     *  to use "naughty".
     */
    this.dirty = false;

    this.elementDescription = elementDescription;
    this.adaptor = adaptor;
    if (el) {
        if (org.antlr.lang.isArray(el)) {
            this.singleElement = null;
            this.elements = el;
        } else {
            this.add(el);
        }
    }
};

org.antlr.runtime.tree.RewriteRuleElementStream.prototype = {
    /** Reset the condition of this stream so that it appears we have
     *  not consumed any of its elements.  Elements themselves are untouched.
     *  Once we reset the stream, any future use will need duplicates.  Set
     *  the dirty bit.
     */
    reset: function() {
        this.cursor = 0;
        this.dirty = true;
    },

    add: function(el) {
        if ( !org.antlr.lang.isValue(el) ) {
            return;
        }
        if ( this.elements ) { // if in list, just add
            this.elements.push(el);
            return;
        }
        if ( !org.antlr.lang.isValue(this.singleElement) ) { // no elements yet, track w/o list
            this.singleElement = el;
            return;
        }
        // adding 2nd element, move to list
        this.elements = [];
        this.elements.push(this.singleElement);
        this.singleElement = null;
        this.elements.push(el);
    },

    /** Return the next element in the stream.  If out of elements, throw
     *  an exception unless size()==1.  If size is 1, then return elements[0].
     *  Return a duplicate node/subtree if stream is out of elements and
     *  size==1.  If we've already used the element, dup (dirty bit set).
     */
    nextTree: function() {
        var n = this.size(),
            el;
        if ( this.dirty || (this.cursor>=n && n==1) ) {
            // if out of elements and size is 1, dup
            el = this._next();
            return this.dup(el);
        }
        // test size above then fetch
        el = this._next();
        return el;
    },

    /** do the work of getting the next element, making sure that it's
     *  a tree node or subtree.  Deal with the optimization of single-
     *  element list versus list of size > 1.  Throw an exception
     *  if the stream is empty or we're out of elements and size>1.
     *  protected so you can override in a subclass if necessary.
     */
    _next: function() {
        var n = this.size();
        if (n===0) {
            throw new org.antlr.runtime.tree.RewriteEmptyStreamException(this.elementDescription);
        }
        if ( this.cursor>= n) { // out of elements?
            if ( n===1 ) {  // if size is 1, it's ok; return and we'll dup
                return this.toTree(this.singleElement);
            }
            // out of elements and size was not 1, so we can't dup
            throw new org.antlr.runtime.tree.RewriteCardinalityException(this.elementDescription);
        }
        // we have elements
        if ( org.antlr.lang.isValue(this.singleElement) ) {
            this.cursor++; // move cursor even for single element list
            return this.toTree(this.singleElement);
        }
        // must have more than one in list, pull from elements
        var o = this.toTree(this.elements[this.cursor]);
        this.cursor++;
        return o;
    },

    /** Ensure stream emits trees; tokens must be converted to AST nodes.
     *  AST nodes can be passed through unmolested.
     */
    toTree: function(el) {
        if (el && el.getTree) {
            return el.getTree();
        }
        return el;
    },

    hasNext: function() {
         return (org.antlr.lang.isValue(this.singleElement) && this.cursor < 1) ||
               (this.elements && this.cursor < this.elements.length);
    },

    size: function() {
        var n = 0;
        if ( org.antlr.lang.isValue(this.singleElement) ) {
            n = 1;
        }
        if ( this.elements ) {
            return this.elements.length;
        }
        return n;
    },

    getDescription: function() {
        return this.elementDescription;
    }
};