using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
using ZB.MOM.WW.OtOpcUa.Runtime.Drivers;

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

/// <summary>
///     A singleton snapshot of the alarm-history drain decision, so code that lives outside an actor
///     can ask "should this node be draining the alarm queue right now?".
/// </summary>
/// <remarks>
///     <para>
///         Exists for the alarm store-and-forward drain. That drain runs on a timer owned by the
///         sink, not on an actor mailbox, so it cannot receive <c>RedundancyStateChanged</c>
///         directly — but it must be role-scoped, because the queue it drains replicates to the
///         pair peer and two draining nodes would deliver every event twice.
///     </para>
///     <para>
///         Deliberately publishes the <i>decision</i> rather than the role that produced it, so
///         <see cref="PrimaryGatePolicy"/> stays the single place that decides.
///     </para>
///     <para>
///         <b>This is not the device-write gate.</b> It is fed by
///         <see cref="PrimaryGatePolicy.ShouldDrainAlarmHistory"/>, which opens on an unknown role
///         where <see cref="PrimaryGatePolicy.ShouldServiceAsPrimary"/> closes. The naming is
///         explicit about the consumer for that reason: an earlier revision published the
///         write-gate verdict here, and on a cluster with several driver nodes but no configured
///         redundancy it suspended the drain everywhere, so alarm history accumulated on every node
///         and left none.
///     </para>
/// </remarks>
public interface IRedundancyRoleView
{
    /// <summary>Whether this node should be draining the alarm store-and-forward queue right now.</summary>
    bool ShouldDrainAlarmHistory { get; }

    /// <summary>Records a fresh decision. Called by <c>DriverHostActor</c> on every redundancy snapshot.</summary>
    /// <param name="shouldDrainAlarmHistory">
    ///     The decision <see cref="PrimaryGatePolicy.ShouldDrainAlarmHistory"/> produced.
    /// </param>
    void Publish(bool shouldDrainAlarmHistory);
}

/// <summary>
///     A singleton snapshot of the continuous-historization <b>capture</b> decision (Gitea #537), so
///     the recorder can ask "should this node be recording historized values right now?".
/// </summary>
/// <remarks>
///     <para>
///         A separate interface from <see cref="IRedundancyRoleView"/> even though one object
///         implements both, because the two are registered on different terms:
///         <c>IRedundancyRoleView</c> is registered by <c>AddAlarmHistorian</c> and so exists only
///         where the alarm section is enabled, while this one is registered unconditionally on every
///         driver-role node. Piggybacking on the alarm registration would silently drop the
///         historization gate on any pair that runs historization without alarm history — the same
///         registration accident Gitea #511 documents on the neighbouring verdict.
///     </para>
///     <para>
///         Publishes the <i>decision</i> rather than the role, so
///         <see cref="PrimaryGatePolicy.ShouldRecordHistorizedValues"/> stays the single place that
///         decides. Note it is <b>not</b> the alarm drain verdict: the two policies agree on the role
///         rule but disagree on what makes a peer relevant (a queue-sharing replication partner vs. a
///         node serving the same address space), and the wrong peer notion in either direction is a
///         silent gap.
///     </para>
/// </remarks>
public interface IHistorizationRoleView
{
    /// <summary>Whether this node should be capturing continuous-historization values right now.</summary>
    bool ShouldRecordHistorizedValues { get; }

    /// <summary>Records a fresh decision. Called by <c>DriverHostActor</c> on every redundancy snapshot.</summary>
    /// <param name="shouldRecordHistorizedValues">
    ///     The decision <see cref="PrimaryGatePolicy.ShouldRecordHistorizedValues"/> produced.
    /// </param>
    void PublishHistorizationRole(bool shouldRecordHistorizedValues);
}

/// <summary>
///     Thread-safe <see cref="IRedundancyRoleView"/> + <see cref="IDriverPrimaryRoleSource"/> +
///     <see cref="IHistorizationRoleView"/>, each backed by its own volatile field.
/// </summary>
/// <remarks>
///     <para>
///         <b>Two verdicts, one object, on purpose.</b> Both are published from the same
///         <c>DriverHostActor</c> snapshot handler and both are read off-actor, so a second class
///         would duplicate the publish plumbing to hold a second bool. They are kept as distinct
///         <i>properties</i> rather than collapsed into one because they are genuinely different
///         decisions from different policies — see <see cref="IRedundancyRoleView"/>'s remarks on why
///         the drain gate must open on an unknown role where the data-plane gate closes. Collapsing
///         them is the bug that live gate already found once.
///     </para>
/// </remarks>
public sealed class RedundancyRoleView : IRedundancyRoleView, IDriverPrimaryRoleSource, IHistorizationRoleView
{
    // Seeded with the decision for "role unknown" rather than a bare false. An unpublished view and a
    // node whose role nothing ever reports are genuinely the same situation, and they must behave the
    // same: a deployment that runs no redundancy at all never publishes here, and defaulting closed
    // would silently stop its alarm history forever.
    private volatile bool _shouldDrainAlarmHistory =
        PrimaryGatePolicy.ShouldDrainAlarmHistory(localRole: null, queueSharingPeerIsPrimary: false);

    // Seeded from the same policy that will later publish here, for the unknown-role/no-peer case:
    // a node nothing has reported a role for, on a cluster with no driver peer, is a single-node
    // deployment and may claim. The moment a snapshot arrives this is replaced by the real verdict,
    // and a multi-driver cluster's unknown role denies.
    private volatile bool _shouldActAsPrimary =
        PrimaryGatePolicy.ShouldServiceAsPrimary(localRole: null, driverMemberCount: 1);

    // Seeded for the unknown-role case from the same policy that will later publish here: a node
    // nothing has reported a role for captures, exactly as an unpaired or single-node deployment must.
    // Defaulting closed would leave a deployment that never publishes a role with no trend data at all.
    private volatile bool _shouldRecordHistorizedValues =
        PrimaryGatePolicy.ShouldRecordHistorizedValues(localRole: null, addressSpaceSharingPeerIsPrimary: false);

    /// <inheritdoc/>
    public bool ShouldDrainAlarmHistory => _shouldDrainAlarmHistory;

    /// <inheritdoc/>
    public bool ShouldRecordHistorizedValues => _shouldRecordHistorizedValues;

    /// <inheritdoc/>
    public bool ShouldActAsPrimary => _shouldActAsPrimary;

    /// <inheritdoc/>
    public void Publish(bool shouldDrainAlarmHistory) => _shouldDrainAlarmHistory = shouldDrainAlarmHistory;

    /// <inheritdoc/>
    public void PublishPrimaryRole(bool shouldActAsPrimary) => _shouldActAsPrimary = shouldActAsPrimary;

    /// <inheritdoc/>
    public void PublishHistorizationRole(bool shouldRecordHistorizedValues)
        => _shouldRecordHistorizedValues = shouldRecordHistorizedValues;
}