using Avalonia;
using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Platform.Storage;

namespace AvParser.UI.Services;

/// <summary>Asks the user for a directory.</summary>
/// <remarks>
/// An interface because the picker lives on the window, not on the view model: reaching for a
/// <c>TopLevel</c> from a view model would make it untestable and would tie it to there being a
/// window at all. Tests substitute a canned answer.
/// </remarks>
public interface IFolderPicker
{
    /// <summary>Returns the chosen directory, or null when the user cancelled.</summary>
    Task<string?> PickAsync(string title, string? startAt = null);
}

/// <inheritdoc />
public sealed class FolderPicker : IFolderPicker
{
    /// <inheritdoc />
    public async Task<string?> PickAsync(string title, string? startAt = null)
    {
        if (Application.Current?.ApplicationLifetime is not IClassicDesktopStyleApplicationLifetime desktop)
        {
            return null;
        }

        var window = desktop.MainWindow;

        if (window?.StorageProvider is not { CanPickFolder: true } storage)
        {
            return null;
        }

        var options = new FolderPickerOpenOptions { Title = title, AllowMultiple = false };

        if (!string.IsNullOrWhiteSpace(startAt) && Directory.Exists(startAt))
        {
            options.SuggestedStartLocation = await storage.TryGetFolderFromPathAsync(startAt).ConfigureAwait(true);
        }

        var chosen = await storage.OpenFolderPickerAsync(options).ConfigureAwait(true);

        return chosen.Count == 0 ? null : chosen[0].TryGetLocalPath();
    }
}