noz-cli/NozCli/Commands/SyncCommand.cs

using NozCli.Core.Client;
using NozCli.Core.Models;
using NozCli.Repl;
using NozCli.Security;
using Spectre.Console;

namespace NozCli.Commands;

/// sync <local-path> — pulls notes from the server into a local directory.
/// Only downloads notes whose server hash differs from the local file hash.
/// Uses Parallel.ForEachAsync (8 concurrent) for fast bulk downloads.
public class SyncCommand : ICommand
{
    public string Name        => "sync";
    public string Description => "Pull notes from server to a local directory (hash-diffed)";
    public string Usage       => "sync <local-path> [--all] [--dry-run]";

    private const int Concurrency = 8;

    public async Task ExecuteAsync(string[] args, ReplContext ctx, CancellationToken ct = default)
    {
        var localPath = args.FirstOrDefault(a => !a.StartsWith("--"));
        var force     = args.Contains("--all");
        var dryRun    = args.Contains("--dry-run");

        if (localPath is null)
        {
            AnsiConsole.MarkupLine("[red]Usage: sync <local-path> [--all] [--dry-run][/]");
            return;
        }

        localPath = Path.GetFullPath(localPath);

        // Determine which notes to sync (respect current topic/subpath)
        var candidates = ctx.CurrentTopic is null
            ? ctx.NoteCache
            : ctx.NotesInView().ToList();

        if (candidates is IEnumerable<NoteInfo> enumerable)
            candidates = enumerable.ToList();

        var noteList = (List<NoteInfo>)candidates;

        if (noteList.Count == 0)
        {
            AnsiConsole.MarkupLine("[yellow]No notes in current view.[/]");
            return;
        }

        // Diff: which notes actually need downloading?
        var toDownload = new List<NoteInfo>();

        foreach (var note in noteList)
        {
            if (!SlugGuard.IsValid(note.Slug))
            {
                AnsiConsole.MarkupLine($"[yellow]⚠ Skipped unsafe slug from server:[/] {note.Slug}");
                continue;
            }

            var filePath = SlugGuard.ToSafePath(localPath, note.Slug);

            if (!force && note.Hash is not null && File.Exists(filePath))
            {
                var localContent = await File.ReadAllTextAsync(filePath, ct);
                var localHash    = HashHelper.Sha256(localContent);
                if (localHash == note.Hash) continue;
            }

            toDownload.Add(note);
        }

        var unchanged = noteList.Count - toDownload.Count;

        if (toDownload.Count == 0)
        {
            AnsiConsole.MarkupLine($"[green]✓ All {noteList.Count} notes up to date.[/]");
            return;
        }

        if (dryRun)
        {
            AnsiConsole.MarkupLine($"[dim]Dry run — would download {toDownload.Count} notes, {unchanged} unchanged.[/]");
            foreach (var n in toDownload)
                AnsiConsole.MarkupLine($"  [dim]↓[/] {n.Slug}");
            return;
        }

        AnsiConsole.MarkupLine($"[dim]Downloading {toDownload.Count} notes  ·  {unchanged} unchanged  ·  concurrency {Concurrency}[/]");
        AnsiConsole.WriteLine();

        int downloaded = 0, failed = 0;
        var failedSlugs = new System.Collections.Concurrent.ConcurrentBag<string>();
        var lockObj     = new object();

        await AnsiConsole.Progress()
            .Columns(
                new TaskDescriptionColumn(),
                new ProgressBarColumn(),
                new PercentageColumn(),
                new SpinnerColumn())
            .StartAsync(async progress =>
            {
                var task = progress.AddTask($"[cyan]↓ syncing[/]", maxValue: toDownload.Count);

                await Parallel.ForEachAsync(
                    toDownload,
                    new ParallelOptions { MaxDegreeOfParallelism = Concurrency, CancellationToken = ct },
                    async (note, innerCt) =>
                    {
                        try
                        {
                            var content  = await ctx.Api.GetNoteAsync(note.Slug, innerCt);
                            var filePath = SlugGuard.ToSafePath(localPath, note.Slug)!;

                            Directory.CreateDirectory(Path.GetDirectoryName(filePath)!);
                            await File.WriteAllTextAsync(filePath, content.Markdown, innerCt);

                            lock (lockObj) downloaded++;
                        }
                        catch (Exception ex) when (ex is not OperationCanceledException)
                        {
                            failedSlugs.Add(note.Slug);
                            lock (lockObj) failed++;
                        }
                        finally
                        {
                            task.Increment(1);
                        }
                    });
            });

        AnsiConsole.WriteLine();
        AnsiConsole.MarkupLine(
            $"[green]↓ {downloaded} downloaded[/]  " +
            $"[dim]{unchanged} unchanged[/]" +
            (failed > 0 ? $"  [red]{failed} failed[/]" : ""));

        if (failed > 0)
        {
            foreach (var slug in failedSlugs.Order())
                AnsiConsole.MarkupLine($"  [red]✗[/] {slug}");
        }
    }

}