AnchorCli/InputProcessor.cs

using Spectre.Console;

namespace AnchorCli
{
    internal class InputProcessor
    {
        private static void DisplayText(int left, string buffer, int index = -1, string placeholder = "", int viewportOffset = 0)
        {
            Console.CursorLeft = left;

            if (buffer.Length == 0 && index == 0)
            {
                AnsiConsole.Markup($"[grey dim]{placeholder}{new string(' ', Console.WindowWidth - 1 - left - placeholder.Length)}[/]");
                return;
            }

            var visibleWidth = Console.WindowWidth - left - 1;
            var displayStart = Math.Min(viewportOffset, Math.Max(0, buffer.Length - 1));
            var displayEnd = Math.Min(displayStart + visibleWidth, buffer.Length);
            var displayBuffer = string.Concat(buffer.AsSpan(displayStart, displayEnd - displayStart), " ");

            for (var i = 0; i < displayBuffer.Length; i++)
            {
                var actualIndex = displayStart + i;
                if (index != -1 && actualIndex == index)
                {
                    Console.ForegroundColor = ConsoleColor.Black;
                    Console.BackgroundColor = ConsoleColor.White;
                }

                Console.Write(displayBuffer[i]);

                if (index != -1 && actualIndex == index)
                    Console.ResetColor();
            }

            // Fill remaining space with spaces
            var remainingSpaces = visibleWidth - displayBuffer.Length;
            if (remainingSpaces > 0)
                Console.Write(new string(' ', remainingSpaces));
        }

        public static string ReadLine(string placeholder = "")
        {
            Console.CursorVisible = false;
            var buffer = string.Empty;
            var index = 0;
            var viewportOffset = 0;
            var left = Console.CursorLeft;

            DisplayText(left, buffer, index, placeholder, viewportOffset);

            while (true)
            {
                var inputKey = Console.ReadKey(intercept: true);
                switch (inputKey)
                {
                    case { Key: ConsoleKey.Enter } when buffer.Length > 0:
                        DisplayText(left, buffer);
                        Console.WriteLine();
                        return buffer;

                    case { Key: ConsoleKey.Backspace } when index > 0:
                        index--;
                        buffer = buffer.Remove(index, 1);
                        break;

                    case { Key: ConsoleKey.Delete } when index < buffer.Length:
                        buffer = buffer.Remove(index, 1);
                        break;

                    case { Key: ConsoleKey.LeftArrow, Modifiers: ConsoleModifiers.Control }:
                        while (index > 0 && buffer[index - 1] == ' ')
                            index--;
                        while (index > 0 && buffer[index - 1] != ' ')
                            index--;
                        break;

                    case { Key: ConsoleKey.RightArrow, Modifiers: ConsoleModifiers.Control }:
                        while (index < buffer.Length && buffer[index] == ' ')
                            index++;
                        while (index < buffer.Length && buffer[index] != ' ')
                            index++;
                        break;

                    case { Key: ConsoleKey.LeftArrow } when index > 0:
                        index--;
                        break;

                    case { Key: ConsoleKey.RightArrow } when index < buffer.Length:
                        index++;
                        break;

                    case { Key: ConsoleKey.W, Modifiers: ConsoleModifiers.Control } when index > 0:
                        var deleteStart = index;
                        while (deleteStart > 0 && buffer[deleteStart - 1] == ' ')
                            deleteStart--;
                        while (deleteStart > 0 && buffer[deleteStart - 1] != ' ')
                            deleteStart--;
                        var charsToDelete = index - deleteStart;
                        buffer = buffer.Remove(deleteStart, charsToDelete);
                        index = deleteStart;
                        break;

                    default:
                        var keyChar = inputKey.KeyChar;
                        if (!(char.IsLetterOrDigit(keyChar) || char.IsWhiteSpace(keyChar) || char.IsPunctuation(keyChar) || char.IsSymbol(keyChar)))
                            break;

                        buffer = buffer.Insert(index, inputKey.KeyChar.ToString());
                        index++;
                        break;
                }
                // Adjust viewport for scrolling
                var visibleWidth = Console.WindowWidth - left - 1;
                if (index < viewportOffset)
                    viewportOffset = index;
                else if (index >= viewportOffset + visibleWidth)
                    viewportOffset = index - visibleWidth + 1;

                DisplayText(left, buffer, index, placeholder, viewportOffset);
            }
        }
    }
}