using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.SignalR;
using ZB.MOM.WW.MxGateway.Server.Configuration;

namespace ZB.MOM.WW.MxGateway.Server.Dashboard.Hubs;

/// <summary>
/// SignalR hub that pushes a fresh <see cref="DashboardSnapshot"/> on every
/// snapshot refresh. New connections receive the effective configuration and the
/// current snapshot immediately via <see cref="OnConnectedAsync"/>; subsequent
/// refreshes are broadcast by <see cref="DashboardSnapshotPublisher"/> without the
/// configuration, which is startup-static and serialized only once per connection.
/// </summary>
/// <remarks>
/// Connections are counted into <see cref="DashboardSnapshotHubConnectionCounter"/>
/// so <see cref="DashboardSnapshotPublisher"/> can stop building and broadcasting
/// snapshots while nobody is watching.
/// </remarks>
[Authorize(Policy = DashboardAuthenticationDefaults.HubClientsPolicy)]
public sealed class DashboardSnapshotHub(
    IDashboardSnapshotService snapshotService,
    DashboardSnapshotHubConnectionCounter connectionCounter) : Hub
{
    /// <summary>Method name used to push snapshot updates to clients.</summary>
    public const string SnapshotMessage = "SnapshotUpdated";

    /// <summary>
    /// Method name of the one-per-connection effective-configuration push. Snapshot
    /// ticks omit the configuration, so a client keeps the copy it got here.
    /// </summary>
    public const string ConfigurationMessage = "ConfigurationUpdated";

    /// <summary>
    /// Returns the effective gateway configuration — the same object
    /// <see cref="ConfigurationMessage"/> carries — for a client that needs it again.
    /// </summary>
    /// <returns>The effective configuration.</returns>
    public EffectiveGatewayConfiguration GetConfiguration() => snapshotService.GetSnapshot().Configuration;

    /// <inheritdoc />
    public override async Task OnConnectedAsync()
    {
        // Count the viewer before seeding it, so the publisher resumes its tick
        // no later than the first snapshot this connection renders.
        connectionCounter.Increment();
        DashboardSnapshot snapshot = snapshotService.GetSnapshot();
        await Clients.Caller.SendAsync(ConfigurationMessage, snapshot.Configuration).ConfigureAwait(false);
        await Clients.Caller.SendAsync(SnapshotMessage, snapshot).ConfigureAwait(false);
        await base.OnConnectedAsync().ConfigureAwait(false);
    }

    /// <inheritdoc />
    public override async Task OnDisconnectedAsync(Exception? exception)
    {
        connectionCounter.Decrement();
        await base.OnDisconnectedAsync(exception).ConfigureAwait(false);
    }
}