using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;

namespace AppointmentScheduler
{
    class Apointment // this class to define class of Apointment
    {
        public string Title { get; set; } // The title of Apointment
        public DateTime Date { get; set; }  // The date of Apointment
        public string Location { get; set; }// The location of Apointment
    }

    class Program // class to execute what is required
    {
        // this list to add all apointments are added
        static List<Apointment> apointments = new List<Apointment>();

        static void Main(string[] args) // main method
        {
            bool noStopping = true; // to check if the user will be continue
            while (noStopping)     // loop to serve all what user wants
            {
                // All choices
                Console.WriteLine("Welcome to Appointment Scheduler!");
                Console.WriteLine("Menu:");
                Console.WriteLine("1. Schedule Appointment");// to add new apointment
                Console.WriteLine("2. View Appointments"); // to view all apointments
                Console.WriteLine("3. Update Appointment"); // to update an apointment
                Console.WriteLine("4. Delete Appointment"); // to delete an apointment
                Console.WriteLine("5. Exit"); // To exist from program

                Console.Write("Enter your choice (1-5):"); // to allow choicing a choice

                int choice; // save what the user wants
                if (!int.TryParse(Console.ReadLine(), out choice)) //to read choice from console
                {
                    // if user enters an invalid choice
                    Console.WriteLine("Invalid choice. Please enter a number from 1-5.");
                    continue;
                }

                switch (choice) // check choice
                {
                    case 1: // case adding
                        AddApointment(); // go to add method
                        break;
                    case 2: // case view all apointments
                        ViewApointments(); // go to view all apointments
                        break;
                    case 3: // case update
                        UpdateApointment(); // go to update method
                        break;
                    case 4: // case delete
                        DeleteApointment();// go to delete method
                        break;
                    case 5: // case end execution
                        noStopping = false;// end the loop
                        break;
                    default: // default case
                        // not choice any available options
                        Console.WriteLine("Invalid choice. Please enter a number from 1-5.");
                        break;
                }
            }
        }

        static void AddApointment() // add new apointment
        {
            if (checkEntryApointment(-1)) //check if user enter valid apointment, pass -1 for adding
            {
                Console.WriteLine("Apointment added successfully.");// successfully adding
                // sort the list after adding new apointment
                apointments = apointments.OrderBy(p => p.Date).ToList(); 
            }

        }

        // check valid apointment inde=-1 for add and the index of apointment
        //    which the user wants to update it
        static bool checkEntryApointment(int index) 
        {
            try// try catch any execption
            {
                Console.Write("Enter appointment details:");
                string myString = Console.ReadLine();// read console
                int pos = myString.IndexOf(','); // to get the title
                string title = myString.Substring(0, pos);// get title
                string second = myString.Substring(pos + 1); // get the rest of line

                string[] rest = second.Split("at ");// split to get the date and location
                // parse the date which entry to be exacttly to be dddd dd/MM/yyyy',' hh:mm tt
                DateTime date = DateTime.ParseExact(rest[0], " dddd dd/MM/yyyy',' hh:mm tt ", CultureInfo.InvariantCulture);
                // rest[0]: date and rest[1] represent location
                string location = rest[1];

                if (index == -1)// to know if user want to add new apointment
                {
                    // create new object of Apointment
                    Apointment apoint = new Apointment { Title = title, Date = date, Location = location };
                    // add new apointment to list
                    apointments.Add(apoint);
                    return true; // return true to addApointment method
                }
                else // else to update details of updated Apointment
                {
                    // update date
                    apointments[index].Date = date;
                    // update title
                    apointments[index].Title = title;
                    // update location
                    apointments[index].Location = location;
                    return true; // return true to updateApointment method
                }

            }
            catch (Exception e) // catch if it occurs an execption
            {
                // to show where the error occurs
                Console.WriteLine("Entry must be as: title, dddd dd/MM/yyyy, hh:mm tt at location ");
                return false; // return false because no change
            }

        }

        static void ViewApointments() // view all apointments where existed
        {
            if (apointments.Count == 0) // check if the list empty
            {
                Console.WriteLine("No Apointments found.");// show message to user
                return; // exit from method
            }

            Console.WriteLine("Apointments:");// the list not empty show all Apointments
            // to show all, we make loop to pass every apointment
            foreach (Apointment apointment in apointments)
            {
                // show all details of apointment
                Console.WriteLine("{0}, {1} at {2}", apointment.Title,
                    apointment.Date.ToString("MM/dd/yyyy hh:mm tt"),
                    apointment.Location);
            }
        }

        static void UpdateApointment() // update Apointment
        {
            if (apointments.Count == 0) // list of Apointments is empty
            {
                Console.WriteLine("No Apointments found.");// show message
                return; // exit from method
            }
            // message to enter the index of appointment
            Console.Write("Enter the index of the appointment to update: ");
            if (!int.TryParse(Console.ReadLine(), out int index) // read index
                || index < 1 ||                                  // if index not valid
                index > apointments.Count)                      // index is larger of size
            {
                // message show if this entry index not valid
                Console.WriteLine("Invalid index. Please enter a number between 1 and {0}.",
                    apointments.Count);
                return;// exit from method
            }
            // index in list begin from 0 so we subtract 1 from it
            //    and then execute the check new Entry of updated apointment
            if (checkEntryApointment(index-1))
            {
                // sort the list after update this list
                apointments = apointments.OrderBy(p => p.Date).ToList();
                // show message successful
                Console.WriteLine("Apointment updated successfully.");
            }
        }

        static void DeleteApointment()// delete an appointment
        {
            if (apointments.Count == 0)// the list of appointments is empty
            {
                Console.WriteLine("No Apointments found."); // show message
                return;// exit from method
            }

            // enter the index of the apointment which the user wants to delete it
            Console.Write("Enter the index of the appointment to delete:");
            
            // check if index is invalid
            if (!int.TryParse(Console.ReadLine(), out int index) 
                || index < 1 || 
                index > apointments.Count)
            {
                // message to show the entry index is invalid
                Console.WriteLine("Invalid index. Please enter a number between 0 and {0}.", 
                    apointments.Count);
                return; //exit from method
            }

            // index in list begin from 0 so we subtract 1 from it
            apointments.RemoveAt(index-1);

            // message to show successful deletion
            Console.WriteLine("Apointment deleted successfully.");
        }
    }
}