package ulti;

import java.util.Stack;

public class Main
{
	public static void main(String[] args)
	{
		Stack<String> stack = new Stack<String>();

		String xml = "<foo> some <bar> useless </bar> data </foo>";

		int openStart = xml.indexOf("<"); //find initial start/end values
		int closeStart = xml.indexOf("</");
		int end = xml.indexOf(">");

		while(end != -1) //while end is found
		{
			String tag;

			if(openStart < closeStart) //if "<" comes before "</"
			{
				tag = xml.substring(openStart + 1, end); //push the string onto the stack
				System.out.println("Pushing: " + tag);

				stack.push(tag);
			}
			else //otherwise
			{
				tag = xml.substring(closeStart + 2, end);

				if(stack.peek().equals(tag)) //check to see that the stack's top string equals the closing tag
				{
					System.out.println("Popping: " + tag); //and pop the string
					stack.pop();
				}
				else
				{
					System.out.println("XML Invalid."); //otherwise, xml is invalid

					return;
				}
			}

			xml = xml.substring(end + 1);

			openStart = xml.indexOf("<");
			closeStart = xml.indexOf("</");
			end = xml.indexOf(">");
		}

		if(!stack.isEmpty()) //if anything's left on the stack, then xml is invalid
		{
			System.out.println("XML Invalid.");

			return;
		}
	}
}