//template for Stack abstract data type
//Updated 19 May 2012
//Found a bug? Awesome! Let us know via: http://generaldevelopment.net/contact

/*==============================================================================

Copyright (c) 2011 General Development

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==============================================================================*/


#pragma once
#include <exception>
#include <stdexcept>

template <class T> class Stack {
    private:
        template <class U> class StackNode {
            public:
                U element;
                StackNode* next; //next node down. NULL if we're on the bottom.
        };
        
        StackNode<T>* top;

        void copy(Stack& src) {
        //push another complete stack onto this one. If *this is empty initially, it will become a copy of src.
            StackNode<T>* srcNode;
            StackNode<T>* newTop;
            StackNode<T>* newNode;

            //Step 1: duplicate the linked list.
            if(!src.top) return; //nothing to be done.
            newNode = new StackNode<T>;
            newTop = newNode;
            srcNode = src.top; 
            while(true) { //loop condition is a non-null source node, but check it half way through to save code
                newNode->element = srcNode->element;
                srcNode = srcNode->next;
                if(!srcNode) break; //check loop condition here
                newNode->next = new StackNode<T>;
                newNode = newNode->next;
            }
            //Step 2: append the current list's top to the end of the new list
            newNode->next = top;
            //Step 3: place new stack on existing stack
            top = newTop;
        }

    public:
        class StackUnderflow : public std::exception {
            public:
                virtual const char* what() const throw() {
                    return "Stack underflow in Stack ADT";
                }
        };
    
        Stack() {
            top = 0;
        }

        Stack(Stack& src) : Stack() {
        //copy constructor
            copy(src);
        }

        Stack& operator=(Stack& src) {
            clear();
            copy(src);
            return *this; //by C++ convention.
        }

        ~Stack() {
            clear();
        }

        void clear() {
        //clear this stack object
            while(!isEmpty()) pop();
        }
        
        void push(T a) {
            StackNode<T>* n = new StackNode<T>;
            n->next = top;
            n->element = a;
            top = n;
        }
        
        T pop() {
            if(!top) throw StackUnderflow();
            T ret = top->element;
            StackNode<T>* n = top;
            top = n->next;
            delete n;
            return ret;
        }
        
        T peek() {
            if(!top) throw StackUnderflow();
            return top->element;
        }
        
        bool isEmpty() {
            return !top;
        }

        bool isPresent(T a) {
        //Provides a search function for the stack.
        //returns true iff a is present in the stack at all, top or otherwise
            StackNode<T>* n = top;
            while(n) {
                if(n->element == a)
                    return true;
                n = n->next;
            } 
            return false;
        }
};