using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Transport;

namespace ZB.MOM.WW.ScadaBridge.DeploymentManager;

/// <summary>
/// <see cref="IStaleInstanceProbe"/> backed by the deployment flattening pipeline.
/// Re-flattens an instance through <see cref="IFlatteningPipeline"/> and returns
/// the computed revision hash — the exact same value
/// <c>DeploymentService.GetDeploymentComparisonAsync</c> compares against the
/// deployed snapshot to decide staleness. Hosted in DeploymentManager so the
/// Transport component (which references only Commons + TemplateEngine) can probe
/// staleness without taking a DeploymentManager project reference.
/// </summary>
public sealed class StaleInstanceProbe : IStaleInstanceProbe
{
    private readonly IFlatteningPipeline _flatteningPipeline;

    /// <summary>Initializes a new <see cref="StaleInstanceProbe"/>.</summary>
    /// <param name="flatteningPipeline">The deployment flattening pipeline used to recompute the current revision hash.</param>
    public StaleInstanceProbe(IFlatteningPipeline flatteningPipeline)
    {
        _flatteningPipeline = flatteningPipeline ?? throw new ArgumentNullException(nameof(flatteningPipeline));
    }

    /// <inheritdoc />
    public async Task<string?> GetCurrentRevisionHashAsync(int instanceId, CancellationToken cancellationToken = default)
    {
        // The pipeline returns a Result; a flatten failure (e.g. unresolvable
        // template chain mid-import) yields null so the caller treats the
        // instance as "staleness indeterminate" and skips it. Flattening reuses
        // the scoped ITemplateEngineRepository, so it observes template rows the
        // in-flight import has staged on the shared change tracker.
        var result = await _flatteningPipeline
            .FlattenAndValidateAsync(instanceId, cancellationToken)
            .ConfigureAwait(false);
        return result.IsSuccess ? result.Value.RevisionHash : null;
    }
}