noz-cli/NozCli/Repl/ReplInput.cs

using Spectre.Console;

namespace NozCli.Repl;

/// Minimal readline with history + Tab-completion.
public class ReplInput
{
    private readonly List<string>       _history  = [];
    private          int                _histIdx  = -1;
    private readonly CommandRegistry    _registry;
    private          ReplContext?       _ctx;

    public ReplInput(CommandRegistry registry) => _registry = registry;

    public void SetContext(ReplContext ctx) => _ctx = ctx;

    public string? Read(string prompt)
    {
        AnsiConsole.Markup(prompt);

        var buffer  = new List<char>();
        int cursor  = 0;
        string? tab = null;   // last Tab suggestion
        int tabIdx  = 0;

        while (true)
        {
            var key = Console.ReadKey(intercept: true);

            // ── Enter ─────────────────────────────────────────────────
            if (key.Key == ConsoleKey.Enter)
            {
                Console.WriteLine();
                var result = new string(buffer.ToArray());
                if (!string.IsNullOrWhiteSpace(result))
                {
                    _history.Add(result);
                    _histIdx = -1;
                }
                return result;
            }

            // ── Ctrl-C / Ctrl-D ───────────────────────────────────────
            if (key.Key == ConsoleKey.C && key.Modifiers.HasFlag(ConsoleModifiers.Control))
            {
                Console.WriteLine();
                return null;
            }

            // ── Backspace ─────────────────────────────────────────────
            if (key.Key == ConsoleKey.Backspace)
            {
                if (cursor > 0)
                {
                    buffer.RemoveAt(cursor - 1);
                    cursor--;
                    RedrawLine(prompt, buffer, cursor);
                }
                tab = null;
                continue;
            }

            // ── Arrow up/down — history ───────────────────────────────
            if (key.Key == ConsoleKey.UpArrow && _history.Count > 0)
            {
                _histIdx = Math.Clamp(_histIdx < 0 ? _history.Count - 1 : _histIdx - 1, 0, _history.Count - 1);
                buffer   = [.. _history[_histIdx]];
                cursor   = buffer.Count;
                RedrawLine(prompt, buffer, cursor);
                continue;
            }
            if (key.Key == ConsoleKey.DownArrow)
            {
                if (_histIdx >= 0 && _histIdx < _history.Count - 1)
                {
                    _histIdx++;
                    buffer = [.. _history[_histIdx]];
                }
                else { _histIdx = -1; buffer.Clear(); }
                cursor = buffer.Count;
                RedrawLine(prompt, buffer, cursor);
                continue;
            }

            // ── Arrow left/right — cursor move ────────────────────────
            if (key.Key == ConsoleKey.LeftArrow  && cursor > 0)            { cursor--; MoveCursorTo(prompt, cursor); continue; }
            if (key.Key == ConsoleKey.RightArrow && cursor < buffer.Count) { cursor++; MoveCursorTo(prompt, cursor); continue; }

            // ── Tab — autocomplete ────────────────────────────────────
            if (key.Key == ConsoleKey.Tab)
            {
                var suggestions = GetSuggestions(new string(buffer.ToArray()));
                if (suggestions.Length == 0) continue;

                if (tab is null) tabIdx = 0;
                else             tabIdx = (tabIdx + 1) % suggestions.Length;

                tab = suggestions[tabIdx];

                // Replace word after last space with suggestion
                var parts      = new string(buffer.ToArray()).Split(' ');
                parts[^1]      = tab;
                var completed  = string.Join(' ', parts);
                buffer         = [.. completed];
                cursor         = buffer.Count;
                RedrawLine(prompt, buffer, cursor);
                continue;
            }

            tab = null;

            // ── Regular character ─────────────────────────────────────
            if (!char.IsControl(key.KeyChar))
            {
                buffer.Insert(cursor, key.KeyChar);
                cursor++;
                RedrawLine(prompt, buffer, cursor);
            }
        }
    }

    private static void RedrawLine(string prompt, List<char> buffer, int cursor)
    {
        var col = Markup.Remove(prompt).Length;
        Console.CursorLeft = 0;
        Console.Write(new string(' ', Console.WindowWidth - 1));
        Console.CursorLeft = 0;
        AnsiConsole.Markup(prompt);
        Console.Write(new string(buffer.ToArray()));
        Console.CursorLeft = col + cursor;
    }

    private static void MoveCursorTo(string prompt, int cursor) =>
        Console.CursorLeft = Markup.Remove(prompt).Length + cursor;

    private string[] GetSuggestions(string input)
    {
        if (_ctx is null) return [];

        var parts   = input.TrimStart().Split(' ', StringSplitOptions.RemoveEmptyEntries);
        var partial = parts.Length == 0 ? "" : parts[^1];

        if (parts.Length <= 1)
            return _registry.Names
                .Where(n => n.StartsWith(partial, StringComparison.OrdinalIgnoreCase))
                .Order().ToArray();

        var slugs   = _ctx.NotesInView().Select(n => n.Slug.Split('/').Last());
        var folders = _ctx.FoldersInView().Select(f => f + "/");

        return slugs.Concat(folders)
            .Where(s => s.StartsWith(partial, StringComparison.OrdinalIgnoreCase))
            .Distinct().Order().ToArray();
    }
}