Program.cs

using AdvancedMathCalculator.Models;
using AdvancedMathCalculator.Services;
using AdvancedMathCalculator.Utilities;

namespace AdvancedMathCalculator;

internal class Program
{
    private static readonly HistoryService History = new();

    private static void Main()
    {
        bool running = true;

        while (running)
        {
            ShowMenu();
            string choice = InputHelper.ReadText("Choose an option: ");
            Console.Clear();

            try
            {
                switch (choice)
                {
                    case "1":
                        BasicOperation();
                        break;
                    case "2":
                        PowerOperation();
                        break;
                    case "3":
                        SquareRootOperation();
                        break;
                    case "4":
                        PercentageOperation();
                        break;
                    case "5":
                        FactorialOperation();
                        break;
                    case "6":
                        PermutationOperation();
                        break;
                    case "7":
                        CombinationOperation();
                        break;
                    case "8":
                        RepeatingDecimalOperation();
                        break;
                    case "9":
                        FractionToDecimalOperation();
                        break;
                    case "10":
                        DerivativeOperation();
                        break;
                    case "11":
                        LinearExpressionOperation();
                        break;
                    case "12":
                        History.Show();
                        break;
                    case "0":
                        running = false;
                        Console.WriteLine("Program closed.");
                        break;
                    default:
                        Console.WriteLine("Invalid option.");
                        break;
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error: " + ex.Message);
            }

            if (running)
            {
                InputHelper.Pause();
            }
        }
    }

    private static void ShowMenu()
    {
        Console.WriteLine("ADVANCED MATH CALCULATOR");
        Console.WriteLine("========================");
        Console.WriteLine("1  - Basic arithmetic");
        Console.WriteLine("2  - Power");
        Console.WriteLine("3  - Square root");
        Console.WriteLine("4  - Percentage");
        Console.WriteLine("5  - Factorial");
        Console.WriteLine("6  - Permutation nPr");
        Console.WriteLine("7  - Combination nCr");
        Console.WriteLine("8  - Repeating decimal to fraction");
        Console.WriteLine("9  - Fraction to repeating decimal");
        Console.WriteLine("10 - Polynomial derivative");
        Console.WriteLine("11 - Linear expression value");
        Console.WriteLine("12 - Operation history");
        Console.WriteLine("0  - Exit");
        Console.WriteLine("========================");
    }

    private static void BasicOperation()
    {
        Console.WriteLine("BASIC ARITHMETIC");
        Console.WriteLine("================");

        double a = InputHelper.ReadDouble("First number: ");
        string op = InputHelper.ReadText("Operator (+, -, *, /): ");
        double b = InputHelper.ReadDouble("Second number: ");

        double result = op switch
        {
            "+" => CalculatorEngine.Add(a, b),
            "-" => CalculatorEngine.Subtract(a, b),
            "*" => CalculatorEngine.Multiply(a, b),
            "/" => CalculatorEngine.Divide(a, b),
            _ => throw new ArgumentException("Unknown operator.")
        };

        Console.WriteLine($"Result: {result}");
        History.Add($"{a} {op} {b} = {result}");
    }

    private static void PowerOperation()
    {
        double number = InputHelper.ReadDouble("Number: ");
        double exponent = InputHelper.ReadDouble("Exponent: ");
        double result = CalculatorEngine.Power(number, exponent);

        Console.WriteLine($"Result: {result}");
        History.Add($"{number}^{exponent} = {result}");
    }

    private static void SquareRootOperation()
    {
        double number = InputHelper.ReadDouble("Number: ");
        double result = CalculatorEngine.SquareRoot(number);

        Console.WriteLine($"Result: {result}");
        History.Add($"sqrt({number}) = {result}");
    }

    private static void PercentageOperation()
    {
        double total = InputHelper.ReadDouble("Total value: ");
        double percent = InputHelper.ReadDouble("Percent: ");
        double result = CalculatorEngine.Percentage(total, percent);

        Console.WriteLine($"{percent}% of {total} = {result}");
        History.Add($"{percent}% of {total} = {result}");
    }

    private static void FactorialOperation()
    {
        int number = InputHelper.ReadInteger("Number: ", 0, 1000);
        var result = CombinatoricsService.Factorial(number);

        Console.WriteLine($"{number}! = {result}");
        History.Add($"{number}! = {result}");
    }

    private static void PermutationOperation()
    {
        int n = InputHelper.ReadInteger("n: ", 0);
        int r = InputHelper.ReadInteger("r: ", 0);
        var result = CombinatoricsService.Permutation(n, r);

        Console.WriteLine($"P({n},{r}) = {result}");
        History.Add($"P({n},{r}) = {result}");
    }

    private static void CombinationOperation()
    {
        int n = InputHelper.ReadInteger("n: ", 0);
        int r = InputHelper.ReadInteger("r: ", 0);
        var result = CombinatoricsService.Combination(n, r);

        Console.WriteLine($"C({n},{r}) = {result}");
        History.Add($"C({n},{r}) = {result}");
    }

    private static void RepeatingDecimalOperation()
    {
        Console.WriteLine("Examples: 0.(3), 0.1(6), 2.34(56)");
        string input = InputHelper.ReadText("Repeating decimal: ");
        Fraction fraction = RepeatingDecimalService.ConvertToFraction(input);

        Console.WriteLine($"{input} = {fraction}");
        History.Add($"{input} = {fraction}");
    }

    private static void FractionToDecimalOperation()
    {
        int numerator = InputHelper.ReadInteger("Numerator: ");
        int denominator = InputHelper.ReadInteger("Denominator: ");
        Fraction fraction = new(numerator, denominator);
        string result = RepeatingDecimalService.FractionToDecimal(fraction);

        Console.WriteLine($"{fraction} = {result}");
        History.Add($"{fraction} = {result}");
    }

    private static void DerivativeOperation()
    {
        Console.WriteLine("Example: 3x^2 + 2x - 5");
        string expression = InputHelper.ReadText("f(x) = ");
        string derivative = PolynomialDerivativeService.Derive(expression);

        Console.WriteLine($"f'(x) = {derivative}");
        History.Add($"d/dx ({expression}) = {derivative}");
    }

    private static void LinearExpressionOperation()
    {
        Console.WriteLine("Expression format: ax + b");
        double a = InputHelper.ReadDouble("a: ");
        double x = InputHelper.ReadDouble("x: ");
        double b = InputHelper.ReadDouble("b: ");
        double result = CalculatorEngine.EvaluateLinearExpression(a, x, b);

        Console.WriteLine($"f({x}) = {result}");
        History.Add($"{a}x + {b}, x={x} => {result}");
    }
}