using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace FutureValue
{
	public partial class frmFutureValue : Form
	{
		public frmFutureValue()
		{
			InitializeComponent();
		}

		private void frmFutureValue_Load(object sender, EventArgs e)
		{
			for (int i = 1; i <= 20; ++i)
				cboYears.Items.Add(i);
			cboYears.SelectedIndex = 2;
		}

		private void btnCalculate_Click(object sender, EventArgs e)
		{
			try {
				if (IsValidData()) {
					lstValues.Items.Clear();

					decimal monthlyInvestment =
						Convert.ToDecimal(txtMonthlyInvestment.Text);
					decimal yearlyInterestRate =
						Convert.ToDecimal(txtInterestRate.Text);

					int years = (int)cboYears.SelectedItem;
					int months = years * 12;
					decimal monthlyInterestRate = yearlyInterestRate / 12 / 100;

					for (int i = 1; i <= months; ++i)
						if (i % 12 == 0) {
							decimal futureValue = CalculateFutureValue(
								monthlyInvestment, monthlyInterestRate, i);
							lstValues.Items.Add("Year " + i/12 + ": "
								+ futureValue.ToString("c"));
						}
				}
			}
			catch (Exception ex) {
				MessageBox.Show(ex.Message + "\n\n" +
					ex.GetType().ToString() + "\n" +
					ex.StackTrace, "Exception");
			}
		}

		public bool IsValidData()
		{
			bool success = true;
			string errorMessage = "";

			// Validate the Monthly Investment text box
			errorMessage += IsDecimal(txtMonthlyInvestment.Text, txtMonthlyInvestment.Tag.ToString());
			errorMessage += IsWithinRange(txtMonthlyInvestment.Text, txtMonthlyInvestment.Tag.ToString(), 1, 1000);

			// Validate the Yearly Interest Rate text box
			errorMessage += IsDecimal(txtInterestRate.Text, txtInterestRate.Tag.ToString());
			errorMessage += IsWithinRange(txtInterestRate.Text, txtInterestRate.Tag.ToString(), 1, 20);

			if (errorMessage != "") {
				success = false;
				MessageBox.Show(errorMessage, "Entry Error");
			}
			return success;
		}

		public static string IsPresent(string value, string name)
		{
			string msg = "";
			if (value == "") {
				msg += name + " is a required field.\n";
			}
			return msg;
		}

		public static string IsDecimal(string value, string name)
		{
			string msg = "";
			if (!Decimal.TryParse(value, out _)) {
				msg += name + " must be a valid decimal value.\n";
			}
			return msg;
		}

		public static string IsInt32(string value, string name)
		{
			string msg = "";
			if (!Int32.TryParse(value, out _)) {
				msg += name + " must be a valid integer value.\n";
			}
			return msg;
		}

		public static string IsWithinRange(string value, string name, decimal min, decimal max)
		{
			string msg = "";
			if (Decimal.TryParse(value, out decimal number)) {
				if (number < min || number > max) {
					msg += name + " must be between " + min + " and " + max + ".\n";
				}
			}
			return msg;
		}

		private decimal CalculateFutureValue(decimal monthlyInvestment,
			decimal interestRateMonthly, int months)
		{
			decimal futureValue = 0m;
			for (int i = 0; i < months; i++) {
				futureValue = (futureValue + monthlyInvestment)
					* (1 + interestRateMonthly);
			}
			return futureValue;
		}

		private void btnExit_Click(object sender, EventArgs e)
		{
			this.Close();
		}
	}
}