using System;
using System.Linq;

namespace Stack
{
    class Program
    {
        // INT? = NULLABLE INT, CAN SET VALUE TO NULL
        static int?[] numbers = new int?[6];
        static int t = -1;

        static void Main(string[] args)
        {
            bool quit = false; // ENDS PROGRAM WHEN TRUE

            while (!quit) // KEEP RUNNING
            {
                // UI STUFF
                Console.Clear();
                Console.WriteLine("Stack Simulator");
                Console.WriteLine(" -----------------------");
                Console.Write("| ");
                print(numbers);
                Console.WriteLine(" -----------------------");
                Console.WriteLine("1) Peek");
                Console.WriteLine("2) Pop");
                Console.WriteLine("3) Push");
                Console.WriteLine("4) QUIT");

                try
                {
                    int choice = Convert.ToInt32(Console.ReadLine()); // TAKE USER CHOICE

                    switch (choice)
                    {
                        case 1:
                            peek(numbers);
                            break;

                        case 2:
                            pop(numbers);
                            break;

                        case 3:
                            push(numbers);
                            break;

                        case 4: // END PROGRAM
                            quit = true;
                            break;

                    }
                }
                catch
                {
                    // IF THE USER ENTERS ANYTHING WHICH ISNT AN INT, IT WILL THROW AN ERROR BECAUSE THIS USES A SWITCH STATEMENT
                    // THIS JUST IGNORES THAT
                    continue;
                }

            }
        }

        static void print(int?[] stack)
        {
            // A BEAUTIFULLY FORMATTED PREVIEW OF THE STACK
            for (int i = 0; i < stack.Length; i++)
            {
                Console.Write("{0} | ", stack[i]);
            }
            Console.WriteLine();
        }

        static bool overflow(int?[] stack)
        {
            if (t >= stack.Length - 1)
            {
                // CHECKS IF TOP OF STACK IS LARGER THAN THE STACK ITSELF
                return true;
            }
            else
            {
                return false;
            }
        }

        static bool underflow(int?[] stack)
        {
            if (t < 0)
            {
                // CHECKS IF THE TOP OF THE ARRAY IS LESS THAN 0
                return true;
            }
            else
            {
                return false;
            }
        }

        static void push(int?[] stack)
        {
            if (overflow(numbers) == true)
            {
                Console.Clear();
                Console.WriteLine("Stack Overflow error");
                if (stack[t] == 0)
                {
                    Console.WriteLine("0 still counts as a value, remove it first");
                }
                Console.WriteLine("Press any key to continue...");
                Console.ReadKey();
            }
            else
            {
                Console.Clear();

                int val;

                Console.WriteLine("Value to be pushed: ");
                val = Convert.ToInt32(Console.ReadLine());

                t++; // INCREASE THE TOP POINTER BY ONE
                stack[t] = val; // AND SET IT TO THE VALUE

                Console.Clear();
                Console.WriteLine("{0} successfully added to stack", val);
                Console.WriteLine("Press any key to continue...");
                Console.ReadKey();
            }
        }

        static void pop(int?[] stack)
        {
            if (underflow(numbers) == true)
            {
                Console.Clear();
                Console.WriteLine("Stack Underflow error");
                Console.WriteLine("Press any key to continue...");
                Console.ReadKey();
            }
            else
            {
                stack[t] = null; // SET THE TOP VALUE TO NULL
                t = t - 1; // AND INDICATE THAT THE TOP VALUE HAS MOVED DOWN

                Console.Clear();
                Console.WriteLine("Top value removed from stack");
                Console.WriteLine("Press any key to continue...");
                Console.ReadKey();
            }

        }

        static void peek(int?[] stack)
        {
            Console.Clear();
            Console.WriteLine("Top Value: {0}", stack[t]);
            Console.WriteLine("Press any key to continue...");
            Console.ReadKey();
        }
    }
}