using Microsoft.EntityFrameworkCore;
using ZB.MOM.WW.OtOpcUa.Configuration;
using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
using ZB.MOM.WW.OtOpcUa.Configuration.Enums;

namespace ZB.MOM.WW.OtOpcUa.Admin.Services;

/// <summary>
///     One row per <see cref="DriverHostStatus"/> record, enriched with the owning
///     <c>ClusterNode.ClusterId</c> when available (left-join). The Admin <c>/hosts</c> page
///     groups by cluster and renders a per-node → per-driver → per-host tree.
/// </summary>
public sealed record HostStatusRow(
    string NodeId,
    string? ClusterId,
    string DriverInstanceId,
    string HostName,
    DriverHostState State,
    DateTime StateChangedUtc,
    DateTime LastSeenUtc,
    string? Detail);

/// <summary>
///     Read-side service for the Admin UI's per-host drill-down. Loads
///     <see cref="DriverHostStatus"/> rows (written by the Server process's
///     <c>HostStatusPublisher</c>) and left-joins <c>ClusterNode</c> so each row knows which
///     cluster it belongs to — the Admin UI groups by cluster for the fleet-wide view.
/// </summary>
/// <remarks>
///     The publisher heartbeat is 10s (<c>HostStatusPublisher.HeartbeatInterval</c>). The
///     Admin page also polls every ~10s and treats rows with <c>LastSeenUtc</c> older than
///     <c>StaleThreshold</c> (30s) as stale — covers a missed heartbeat tolerance plus
///     a generous buffer for clock skew and publisher GC pauses.
/// </remarks>
public sealed class HostStatusService(OtOpcUaConfigDbContext db)
{
    public static readonly TimeSpan StaleThreshold = TimeSpan.FromSeconds(30);

    public async Task<IReadOnlyList<HostStatusRow>> ListAsync(CancellationToken ct = default)
    {
        // LEFT JOIN on NodeId so a row persists even when its owning ClusterNode row hasn't
        // been created yet (first-boot bootstrap case — keeps the UI from losing sight of
        // the reporting server).
        var rows = await (from s in db.DriverHostStatuses.AsNoTracking()
                          join n in db.ClusterNodes.AsNoTracking()
                              on s.NodeId equals n.NodeId into nodeJoin
                          from n in nodeJoin.DefaultIfEmpty()
                          orderby s.NodeId, s.DriverInstanceId, s.HostName
                          select new HostStatusRow(
                              s.NodeId,
                              n != null ? n.ClusterId : null,
                              s.DriverInstanceId,
                              s.HostName,
                              s.State,
                              s.StateChangedUtc,
                              s.LastSeenUtc,
                              s.Detail)).ToListAsync(ct);
        return rows;
    }

    public static bool IsStale(HostStatusRow row) =>
        DateTime.UtcNow - row.LastSeenUtc > StaleThreshold;
}