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

namespace StudentsClass
{
    class Program
    {
        static List<Student> students = new List<Student>();
        static bool running = true;
        static bool goingBack = false;
        static string userInput;

        /// <summary>
        /// The student Class.
        /// Contains the first and last name (strings), GPA (float),
        /// and major (string) of a student.
        ///
        /// All values can be empty.
        ///
        /// If first or last names are empty, they return N/A.
        ///
        /// If the major is empty, it returns N/A.
        ///
        /// If the GPA is empty it returns 0 as a float.
        /// If the GPA is less than zero it is set to 0.
        /// </summary>
        class Student
        {
            //Variables and properties
            private string firstName;
            public string FirstName
            {
                get
                {
                    return firstName != null ? firstName : "N/A";
                }
                set
                {
                    firstName = value;
                }
            }

            private string lastName;
            public string LastName
            {
                get
                {
                    return lastName != null ? lastName : "N/A";
                }
                set
                {
                    lastName = value;
                }
            }

            private float gpa;
            public float GPA
            {
                get
                {
                    return gpa != null ? gpa : 0;
                }
                set
                {
                    if(value < 0)
                    {
                        gpa = 0;
                    }
                    else
                    {
                        gpa = value;
                    }
                }
            }

            private string major;
            public string Major
            {
                get
                {
                    return major != null ? major : "N/A";
                }
                set
                {
                    major = value;
                }
            }

            public Student()
            {
                //Create an empty student
            }

            //Constructors
            public Student(string studentFirstName)
            {
                //Set the student's first name only.
                FirstName = studentFirstName;
            }

            public Student(string studentFirstName, string studentLastName)
            {
                //Set the student's first name.
                FirstName = studentFirstName;

                //Set the student's last name too.
                LastName = studentLastName;
            }

            public Student(string studentFirstName, string studentLastName, float studentGpa)
            {
                //Set the student's first name.
                FirstName = studentFirstName;

                //Set the student's last name.
                LastName = studentLastName;

                //Set the student's GPA.
                //Note, GPAs can only be positive.
                //Negative values result in 0.
                GPA = studentGpa;
            }

            public Student(string studentFirstName, string studentLastName, float studentGpa, string studentMajor)
            {
                //Set the student's first name.
                FirstName = studentFirstName;

                //Set the student's last name.
                LastName = studentLastName;

                //Set the student's GPA.
                GPA = studentGpa;

                //Set the student's major.
                Major = studentMajor;
            }
        }

        static void Main(string[] args)
        {
            //Prompt the user for data for the student.
            //Make a new student with the given information.
            //Give them the option to end their entry and check where they left off to create a proper construction.
            //Give them toe option to end the program as a whole.
            //Display student data.
            //Make it like a database console where you press 0 to exit, 1 to make new student, - to back, 2 to delete a student
            while (running)
            {
                BeginProgram(); //Start the magic
            }
        }

        public static void BeginProgram()
        {
            //User-friendly dialog instructions
            Console.WriteLine(@"
*** *** *** *** *** *** *** ***
Main Menu
    -Controls-
        1: Add a new student
        2: Delete a student
        3: Display student data
        -: Exit the program
*** *** *** *** *** *** *** ***
                ");
            Console.Write("Enter a valid value: ");

            //Main menu switch
            switch (Console.ReadLine())
            {
                //Add new student
                case "1":
                    AddNewStudent();
                    break;

                case "2":
                    DeleteAStudent();
                    break;

                case "3":
                    DisplayStudentData();
                    break;

                case "-":
                    ExitProgram();
                    break;

                default:
                    Console.WriteLine("\n\n\tMESSAGE: *Invalid value. Try again.\n");
                    break;
            }
        }

        public static void AddNewStudent()
        {
            //User-friendly dialog instructions
            Console.WriteLine(@"
*** *** *** *** *** *** *** ***
Add Students
    Enter the requested values.
    To exit, enter \
*** *** *** *** *** *** *** ***
                        ");

            string userInputFirstName = null, userInputLastName = null, userInputMajor = null;
            float userInputGPA = -1; //Instead of making it null, set it to -1 since we'll be comparing it that way.

            while (running)
            {
                if (goingBack)
                {
                    goingBack = false;

                    //Before actually going back... Since the user entered Y to starting a new student entry,
                    //start the creation update of the new student.
                    if(userInputFirstName != null && userInputLastName != null && userInputGPA >= 0 && userInputMajor != null)
                    {
                        students.Add(new Student(userInputFirstName, userInputLastName, userInputGPA, userInputMajor));
                    }
                    else
                    {
                        if (userInputFirstName != null && userInputLastName != null && userInputGPA >= 0)
                        {
                            students.Add(new Student(userInputFirstName, userInputLastName, userInputGPA));
                        }
                        else
                        {
                            if (userInputFirstName != null && userInputLastName != null)
                            {
                                students.Add(new Student(userInputFirstName, userInputLastName));
                            }
                            else
                            {
                                if (userInputFirstName != null && userInputLastName != null)
                                {
                                    students.Add(new Student(userInputFirstName, userInputLastName));
                                }
                                else
                                {
                                    if (userInputFirstName != null)
                                    {
                                        students.Add(new Student(userInputFirstName));
                                    }
                                    else
                                    {
                                        students.Add(new Student());
                                    }
                                }
                            }
                        }
                    }
                    break;
                }
                Console.Write("Would you like to create a new user? (Y for yes, N for No): ");
                userInput = Console.ReadLine();

                if(userInput.ToLower() == "y")
                {
                    //Reset values, even if they were never set.
                    userInputFirstName = null;
                    userInputLastName = null;
                    userInputMajor = null;
                    userInputGPA = -1;

                    while(true)
                    {
                        Console.Write("What is the first name of the student?: ");
                        userInput = Console.ReadLine();

                        if(userInput.Length > 0)
                        {
                            if(userInput == "\\")
                            {
                                goingBack = true;
                                break;
                            }

                            userInputFirstName = userInput;
                            break;
                        }

                        Console.WriteLine("\nInvalid entry. Please, enter a value.\n");
                    }
                    //Just a hint as to why I don't actually break down here.
                    //It'd be better to have everything happen in a central location.
                    //These if statements just send them to that central location.
                    //That way if I want to change how "goingBack" is handled,
                    //I only have to change it in one spot.

                    //It is also being checked for here because of the while loop above.
                    //The while loop has the potential of having a goingBack value come out
                    //of it. So, it's best to check right after we get out of it.
                    if (goingBack)
                    {
                        continue;
                    }


                    while(true)
                    {
                        Console.Write("What is the last name of the student?: ");
                        userInput = Console.ReadLine();

                        if (userInput.Length > 0)
                        {
                            if (userInput == "\\")
                            {
                                goingBack = true;
                                break;
                            }

                            userInputLastName = userInput;
                            break;
                        }

                        Console.WriteLine("\nInvalid entry. Please, enter a value.\n");
                    }
                    if (goingBack)
                    {
                        continue;
                    }


                    while (true)
                    {
                        Console.Write("What is the GPA of the student? (Negative numbers will result in a zeroed GPA): ");
                        userInput = Console.ReadLine();

                        if (userInput.Length > 0)
                        {
                            if (userInput == "\\")
                            {
                                goingBack = true;
                                break;
                            }

                            //If the parse was successful, break and move on to the next input.
                            //Else, retry again.
                            if (Single.TryParse(userInput, out userInputGPA))
                            {
                                break;
                            }

                            Console.WriteLine("\nInvalid entry. Please, only enter a number value.\n");
                        }
                    }
                    if (goingBack)
                    {
                        continue;
                    }

                    while(true)
                    {
                        Console.Write("What is the Major of the student?: ");
                        userInput = Console.ReadLine();

                        if (userInput.Length > 0)
                        {
                            if (userInput == "\\")
                            {
                                goingBack = true;
                                continue;
                            }

                            userInputMajor = userInput;
                            break;
                        }

                        Console.WriteLine("\nInvalid entry. Please, enter a value.\n");
                    }

                    //They have reached the end of the entry attempt. All values are entered. Create the student.
                    students.Add(new Student(userInputFirstName, userInputLastName, userInputGPA, userInputMajor));
                }

                //Don't do anything. Just go back.
                if(userInput.ToLower() == "n")
                {
                    break;
                }

            }
        }

        public static void DeleteAStudent()
        {
            //User-friendly dialog instructions
            Console.WriteLine(@"
*** *** *** *** *** *** *** ***
Delete Students
    Enter the requested values.
    To exit, enter \
*** *** *** *** *** *** *** ***
            ");
            if (students.Count > 0)
            {
                DisplayStudents();

                while (running)
                {
                    if (goingBack)
                    {
                        goingBack = false;
                        break;
                    }

                    Console.Write("Enter the number of the student you want to remove (Their numbers are to the left of their name): ");
                    userInput = Console.ReadLine();
                    int indexVal;

                    if (userInput == "\\")
                    {
                        goingBack = true;
                        continue;
                    }

                    if (Int32.TryParse(userInput, out indexVal) && indexVal >= 1 && indexVal <= students.Count())
                    {
                        Console.WriteLine(students[indexVal - 1].LastName + ", " + students[indexVal - 1].FirstName + " was deleted.");
                        students.RemoveAt(indexVal - 1);
                    }
                    else
                    {
                        Console.WriteLine("Invalid entry. Please, enter a numerical value only that is either 1 or greater and is presented on the students list.\n");
                    }
                }
            }
            else
                Console.WriteLine("No student data entered.");
        }

        public static void DisplayStudentData()
        {
            if (students.Count > 0)
                DisplayStudents(true);
            else
                Console.WriteLine("No student data entered.");
        }

        public static void DisplayStudents(bool allData = false)
        {
            int counter = 0;
            Console.WriteLine("\n\n***** STUDENTS LIST *****\n\n");
            foreach(Student stu in students)
            {
                counter++;
                Console.WriteLine(counter + ") " + stu.LastName + ", " + stu.FirstName);
                if (allData)
                    Console.WriteLine("\t GPA: " + stu.GPA + " | Major: " + stu.Major);

            }

            Console.WriteLine("\n\n*****  END OF LIST  *****\n\n");
        }

        //Stop all switch statements from looping again.
        public static void ExitProgram()
        {
            running = false;
        }
    }
}