namespace ZB.MOM.WW.OtOpcUa.Runtime.Drivers;

/// <summary>
///     Pure diff between the currently-running driver children (keyed by
///     <c>DriverInstance.DriverInstanceId</c>) and the target spec list from a freshly-applied
///     deployment artifact. The DriverHostActor consumes the three lists and calls
///     spawn / ApplyDelta / stop on its child actors accordingly.
/// </summary>
/// <param name="ToSpawn">Specs with no current child — create a new actor.</param>
/// <param name="ToApplyDelta">Specs whose child exists but config JSON or type differs.</param>
/// <param name="ToStop">DriverInstanceIds currently running but missing from the new artifact, or now disabled.</param>
public sealed record DriverSpawnPlan(
    IReadOnlyList<DriverInstanceSpec> ToSpawn,
    IReadOnlyList<DriverInstanceSpec> ToApplyDelta,
    IReadOnlyList<string> ToStop);

public static class DriverSpawnPlanner
{
    /// <summary>
    ///     Compute the spawn/delta/stop sets. Disabled entries in <paramref name="target"/> are
    ///     treated as "not desired here": if a child exists for the id it goes into ToStop,
    ///     otherwise the row is dropped entirely (no spawn for a disabled driver).
    /// </summary>
    /// <param name="current">The currently running driver children keyed by ID.</param>
    /// <param name="target">The target driver instances from the deployment artifact.</param>
    /// <returns>The computed <see cref="DriverSpawnPlan"/> with spawn, apply-delta, and stop sets.</returns>
    public static DriverSpawnPlan Compute(
        IReadOnlyDictionary<string, DriverChildSnapshot> current,
        IReadOnlyList<DriverInstanceSpec> target)
    {
        var toSpawn = new List<DriverInstanceSpec>();
        var toDelta = new List<DriverInstanceSpec>();
        var toStop = new List<string>();

        var targetById = new Dictionary<string, DriverInstanceSpec>(StringComparer.Ordinal);
        foreach (var spec in target) targetById[spec.DriverInstanceId] = spec;

        foreach (var (id, snap) in current)
        {
            if (!targetById.TryGetValue(id, out var spec) || !spec.Enabled)
            {
                toStop.Add(id);
                continue;
            }
            // A driver TYPE change can't be reinitialized in-place (factory-bound) — stop + respawn.
            // A RESILIENCE-CONFIG change likewise forces a respawn: the CapabilityInvoker (and its
            // resolved options) is bound to the child actor at spawn time, so the only way a changed
            // ResilienceConfig takes effect is to rebuild the child. The factory invalidates the stale
            // cached pipelines on the respawn's Create call. (A pure DriverConfig change stays an
            // in-place delta — no reconnect — because it doesn't touch the resilience pipeline.)
            if (!string.Equals(snap.DriverType, spec.DriverType, StringComparison.Ordinal)
                || !string.Equals(snap.ResilienceConfig, spec.ResilienceConfig, StringComparison.Ordinal))
            {
                toStop.Add(id);
                toSpawn.Add(spec);
                continue;
            }
            if (!string.Equals(snap.LastConfigJson, spec.DriverConfig, StringComparison.Ordinal))
            {
                toDelta.Add(spec);
            }
        }

        foreach (var (id, spec) in targetById)
        {
            if (!spec.Enabled) continue;
            if (current.ContainsKey(id)) continue;
            toSpawn.Add(spec);
        }

        return new DriverSpawnPlan(toSpawn, toDelta, toStop);
    }
}

/// <summary>Snapshot of one running driver child as the host sees it. Used as the diff input.</summary>
/// <param name="DriverType">The driver type name the child was spawned for.</param>
/// <param name="LastConfigJson">The <c>DriverConfig</c> JSON the child currently serves.</param>
/// <param name="ResilienceConfig">The per-instance <c>ResilienceConfig</c> JSON the child's invoker was built with (null = tier defaults).</param>
public sealed record DriverChildSnapshot(string DriverType, string LastConfigJson, string? ResilienceConfig = null);
