spectre.console/src/Spectre.Console/Extensions/AnsiConsoleExtensions.Input.cs

namespace Spectre.Console;

/// <summary>
/// Contains extension methods for <see cref="IAnsiConsole"/>.
/// </summary>
public static partial class AnsiConsoleExtensions
{
    internal static async Task<string> ReadLine(this IAnsiConsole console, Style? style, bool secret, IEnumerable<string>? items = null, CancellationToken cancellationToken = default)
    {
        if (console is null)
        {
            throw new ArgumentNullException(nameof(console));
        }

        style ??= Style.Plain;
        var text = string.Empty;

        var autocomplete = new List<string>(items ?? Enumerable.Empty<string>());

        while (true)
        {
            var rawKey = await console.Input.ReadKeyAsync(true, cancellationToken).ConfigureAwait(false);
            if (rawKey == null)
            {
                continue;
            }

            var key = rawKey.Value;
            if (key.Key == ConsoleKey.Enter)
            {
                return text;
            }

            if (key.Key == ConsoleKey.Tab && autocomplete.Count > 0)
            {
                var replace = AutoComplete(autocomplete, text);
                if (!string.IsNullOrEmpty(replace))
                {
                    // Render the suggestion
                    console.Write("\b \b".Repeat(text.Length), style);
                    console.Write(replace);
                    text = replace;
                    continue;
                }
            }

            if (key.Key == ConsoleKey.Backspace)
            {
                if (text.Length > 0)
                {
                    text = text.Substring(0, text.Length - 1);
                    console.Write("\b \b");
                }

                continue;
            }

            if (!char.IsControl(key.KeyChar))
            {
                text += key.KeyChar.ToString();
                console.Write(secret ? "*" : key.KeyChar.ToString(), style);
            }
        }
    }

    private static string AutoComplete(List<string> autocomplete, string text)
    {
        var found = autocomplete.Find(i => i == text);
        var replace = string.Empty;

        if (found == null)
        {
            // Get the closest match
            var next = autocomplete.Find(i => i.StartsWith(text, true, CultureInfo.InvariantCulture));
            if (next != null)
            {
                replace = next;
            }
            else if (string.IsNullOrEmpty(text))
            {
                // Use the first item
                replace = autocomplete[0];
            }
        }
        else
        {
            // Get the next match
            var index = autocomplete.IndexOf(found) + 1;
            if (index >= autocomplete.Count)
            {
                index = 0;
            }

            replace = autocomplete[index];
        }

        return replace;
    }
}