Easy-peasy options selector for the terminal.

selector.cs

using System;
using System.Collections.Generic;

public static class Program
{
	public static void Main()
	{
		string[] options = [
			"option 0",
			"option 1",
			"option 2",
			"option 3",
			"option 4",
			"option 5",
			"option 6",
			"option 7",
			"option 8",
			"option 10",
			"option 11",
			"option 12"
		];

		int optionIndex = Selector.Select(options);

		Console.WriteLine();
		Console.WriteLine($"Option selected: {options[optionIndex]}");
	}
}

public static class Selector
{
	public static int Select(string[] options)
	{
		int maxOptions = Math.Min(options.Length, 6);
		int startIndex = 0;
		int index = 0;

		printOptions(options, index, startIndex, maxOptions);

		while (true)
		{
			if (!Console.KeyAvailable)
				continue;

			ConsoleKeyInfo keyInfo = Console.ReadKey(true);

			// ReSharper disable once SwitchStatementHandlesSomeKnownEnumValuesWithDefault
			switch (keyInfo.Key)
			{
				case ConsoleKey.UpArrow:
					index--;

					// Ensure index doesn't go below 0
					if (index < 0)
						index = 0;

					// Move startIndex up if possible
					if (startIndex > index)
						startIndex--;

					break;

				case ConsoleKey.DownArrow:
					index++;

					// Ensure index doesn't exceed the length of options
					if (index >= options.Length)
						index = options.Length - 1;

					// Move startIndex down if necessary
					if (index >= startIndex + maxOptions)
						startIndex++;

					break;

				case ConsoleKey.Enter:
					return index;

				default:
					continue;
			}

			Console.SetCursorPosition(0, Console.CursorTop - maxOptions);
			printOptions(options, index, startIndex, maxOptions);
		}
	}

	private static void printOptions(
		IReadOnlyList<string> options,
		int index,
		int startIndex,
		int maxOptions
	)
	{
		for (int i = startIndex; i < startIndex + maxOptions; i++)
		{
			// Clear the current line
			Console.Write(new string(' ', Console.WindowWidth));

			// Set the cursor position to the beginning of the line
			Console.SetCursorPosition(0, Console.CursorTop);

			if (index == i)
			{
				Console.ForegroundColor = ConsoleColor.White;
				Console.Write(" => ");
			}
			else
			{
				Console.ForegroundColor = ConsoleColor.DarkGray;
				Console.Write(" -  ");
			}

			Console.Write(options[i]);
			Console.WriteLine();
		}

		Console.ResetColor();
	}
}