using Microsoft.Extensions.Configuration;

namespace ZB.MOM.WW.OtOpcUa.Runtime;

/// <summary>
///     The ONE definition of "this node's LocalDb is replicated to a peer" (#603). Two consumers must agree
///     on it, and used to carry separate predicates that diverged: the Host's table-registration step
///     (<c>LocalDbSetup.ReplicationIsConfigured</c> - which nodes capture changes) and the alarm-historian
///     drain gate (<c>AddAlarmHistorian</c> - which nodes stand down in favour of a peer). Lives in Runtime
///     because Host references Runtime and not the reverse.
/// </summary>
/// <remarks>
///     <para>
///         <b>Predicate: <c>LocalDb:Replication:PeerAddress</c> OR <c>LocalDb:Replication:ApiKey</c> is
///         non-blank.</b> The OR is required: only the dialling half of a pair sets <c>PeerAddress</c>, while
///         the passive half carries the shared <c>ApiKey</c> (plus a listen port) and nothing else.
///     </para>
///     <para>
///         <b>Why the drain gate takes the same predicate (it previously used PeerAddress OR
///         <c>SyncListenPort</c>).</b> The gate's question is "does a peer hold the same rows?". The passive
///         sync endpoint is fail-closed on the key, so a node with a listen port but no <c>ApiKey</c> rejects
///         every inbound stream and shares its queue with nobody - gating it would park its alarm events
///         behind a Primary that cannot deliver them. Conversely an <c>ApiKey</c>-only passive node IS
///         registered and does receive its peer's rows, so it must be gated or both halves drain. The port
///         is not evidence of a peer; the key is.
///     </para>
/// </remarks>
public static class LocalDbReplicationPolicy
{
    /// <summary>Configuration section holding the LocalDb replication options.</summary>
    public const string ReplicationSectionPath = "LocalDb:Replication";

    /// <summary>Whether this node's LocalDb replicates to a pair peer.</summary>
    /// <param name="configuration">The application configuration.</param>
    /// <returns><c>true</c> when <c>PeerAddress</c> or <c>ApiKey</c> is set under the replication section.</returns>
    public static bool IsConfigured(IConfiguration configuration)
    {
        ArgumentNullException.ThrowIfNull(configuration);
        var section = configuration.GetSection(ReplicationSectionPath);
        return !string.IsNullOrWhiteSpace(section["PeerAddress"])
            || !string.IsNullOrWhiteSpace(section["ApiKey"]);
    }
}