using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace Dining_Philosophers
{
    class Program
    {
        private const int DinerCount = 5;
        private static List<Diner> Diners = new List<Diner>();
        private static List<Fork> Forks = new List<Fork>();
        private static DateTime TimeToStop;

        static void Main(string[] args)
        {
            Initialize();
            WriteHeaderLine();

            do
            {
                WriteStatusLine();
                Thread.Sleep(1000);
            }
            while (DateTime.Now < TimeToStop);

            TearDown();
        }

        private static void Initialize()
        {
            for (int i = 0; i < DinerCount; i++)
                Forks.Add(new Fork());
            for (int i = 0; i < DinerCount; i++)
                Diners.Add(new Diner(i, Forks[i], Forks[(i + 1) % DinerCount]));

            TimeToStop = DateTime.Now.AddSeconds(60);
        }

        private static void TearDown()
        {
            foreach (var diner in Diners)
                diner.Dispose();
        }

        private static void WriteHeaderLine()
        {
            Console.Write("|");

            foreach (Diner d in Diners)
                Console.Write("D " + d.ID + "|");

            Console.Write("    |");

            for (int i = 0; i < DinerCount; i++)
                Console.Write("F" + i + "|");

            Console.WriteLine();
        }

        private static void WriteStatusLine()
        {
            Console.Write("|");

            foreach (Diner d in Diners)
                Console.Write(FormatDinerState(d) + "|");

            Console.Write("    |");

            foreach (Fork f in Forks)
                Console.Write(FormatForkState(f) + "|");

            Console.WriteLine();
        }

        private static string FormatDinerState(Diner diner)
        {
            switch (diner.State)
            {
                case Diner.DinerState.Eating:
                    return "Eat";
                case Diner.DinerState.Pondering:
                    return "Pon";
                case Diner.DinerState.TryingToGetForks:
                    return "Get";
                default:
                    throw new Exception("Unknown diner state.");
            }
        }

        private static string FormatForkState(Fork fork)
        {
            return (!ForkIsBeingUsed(fork) ? "  " : "D" + GetForkHolder(fork));
        }

        private static bool ForkIsBeingUsed(Fork fork)
        {
            return Diners.Count(d => d.CurrentlyHeldForks.Contains(fork)) > 0;
        }

        private static int GetForkHolder(Fork fork)
        {
            return Diners.Single(d => d.CurrentlyHeldForks.Contains(fork)).ID;
        }
    }

    class Diner : IDisposable
    {
        private bool IsCurrentlyHoldingLeftFork = false;
        private bool IsCurrentlyHoldingRightFork = false;
        private const int MaximumWaitTime = 100;
        private static Random Randomizer = new Random();
        private bool ShouldStopEating = false;

        public int ID { get; private set; }
        public Fork LeftFork { get; private set; }
        public Fork RightFork { get; private set; }
        public DinerState State { get; private set; }

        public IEnumerable<Fork> CurrentlyHeldForks
        {
            get
            {
                var forks = new List<Fork>();
                if (IsCurrentlyHoldingLeftFork)
                    forks.Add(LeftFork);
                if (IsCurrentlyHoldingRightFork)
                    forks.Add(RightFork);
                return forks;
            }
        }

        public Diner(int id, Fork leftFork, Fork rightFork)
        {
            InitializeDinerState(id, leftFork, rightFork);
            BeginDinerActivity();
        }

        private void KeepTryingToEat()
        {
            do
                if (State == DinerState.TryingToGetForks)
                {
                    TryToGetLeftFork();
                    if (IsCurrentlyHoldingLeftFork)
                    {
                        TryToGetRightFork();
                        if (IsCurrentlyHoldingRightFork)
                        {
                            Eat();
                            DropForks();
                            Ponder();
                        }
                        else
                        {
                            DropForks();
                            WaitForAMoment();
                        }
                    }
                    else
                        WaitForAMoment();
                }
                else
                    State = DinerState.TryingToGetForks;
            while (!ShouldStopEating);
        }

        private void InitializeDinerState(int id, Fork leftFork, Fork rightFork)
        {
            ID = id;
            LeftFork = leftFork;
            RightFork = rightFork;
            State = DinerState.TryingToGetForks;
        }

        private async void BeginDinerActivity()
        {
            await Task.Run(() => KeepTryingToEat());
        }

        private void TryToGetLeftFork()
        {
            Monitor.TryEnter(LeftFork, ref IsCurrentlyHoldingLeftFork);
        }

        private void TryToGetRightFork()
        {
            Monitor.TryEnter(RightFork, ref IsCurrentlyHoldingRightFork);
        }

        private void DropForks()
        {
            DropLeftFork();
            DropRightFork();
        }

        private void DropLeftFork()
        {
            if (IsCurrentlyHoldingLeftFork)
            {
                IsCurrentlyHoldingLeftFork = false;
                Monitor.Exit(LeftFork);
            }
        }

        private void DropRightFork()
        {
            if (IsCurrentlyHoldingRightFork)
            {
                IsCurrentlyHoldingRightFork = false;
                Monitor.Exit(RightFork);
            }
        }

        private void Eat()
        {
            State = DinerState.Eating;
            WaitForAMoment();
        }

        private void Ponder()
        {
            State = DinerState.Pondering;
            WaitForAMoment();
        }

        private static void WaitForAMoment()
        {
            Thread.Sleep(Randomizer.Next(MaximumWaitTime));
        }

        public void Dispose()
        {
            ShouldStopEating = true;
        }

        public enum DinerState
        {
            Eating,
            TryingToGetForks,
            Pondering
        }
    }

    class Fork { }
}