//  Copyright 2010 Todd Ditchendorf
//
//  Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.

#import <Foundation/Foundation.h>
#if PEGKIT
#import <PEGKit/PKTypes.h>
#else
#import <ParseKit/PKTypes.h>
#endif

/*!
    @class      PKSymbolNode 
    @brief      A <tt>PKSymbolNode</tt> object is a member of a tree that contains all possible prefixes of allowable symbols.
    @details    A <tt>PKSymbolNode</tt> object is a member of a tree that contains all possible prefixes of allowable symbols. Multi-character symbols appear in a <tt>PKSymbolNode</tt> tree with one node for each character. For example, the symbol <tt>=:~</tt> will appear in a tree as three nodes. The first node contains an equals sign, and has a child; that child contains a colon and has a child; this third child contains a tilde, and has no children of its own. If the colon node had another child for a dollar sign character, then the tree would contain the symbol <tt>=:$</tt>. A tree of <tt>PKSymbolNode</tt> objects collaborate to read a (potentially multi-character) symbol from an input stream. A root node with no character of its own finds an initial node that represents the first character in the input. This node looks to see if the next character in the stream matches one of its children. If so, the node delegates its reading task to its child. This approach walks down the tree, pulling symbols from the input that match the path down the tree. When a node does not have a child that matches the next character, we will have read the longest possible symbol prefix. This prefix may or may not be a valid symbol. Consider a tree that has had <tt>=:~</tt> added and has not had <tt>=:</tt> added. In this tree, of the three nodes that contain =:~, only the first and third contain complete symbols. If, say, the input contains <tt>=:a</tt>, the colon node will not have a child that matches the <tt>'a'</tt> and so it will stop reading. The colon node has to "unread": it must push back its character, and ask its parent to unread. Unreading continues until it reaches an ancestor that represents a valid symbol.
*/
@interface PKSymbolNode : NSObject {
    NSString *ancestry;
    PKSymbolNode *parent;
    NSMutableDictionary *children;
    PKUniChar character;
    NSString *string;
}

/*!
    @brief      Initializes a <tt>PKSymbolNode</tt> with the given parent, representing the given character.
    @param      p the parent of this node
    @param      c the character for this node
    @result     An initialized <tt>PKSymbolNode</tt>
*/
- (id)initWithParent:(PKSymbolNode *)p character:(PKUniChar)c;

/*!
    @property   ancestry
    @brief      The string of the mulit-character symbol this node represents.
*/
@property (nonatomic, readonly, retain) NSString *ancestry;
@end
