using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Options;

namespace ZB.MOM.WW.OtOpcUa.Cluster;

/// <summary>
///     Node-side selection of the transport a node's live-telemetry stream is carried over
///     (per-cluster mesh Phase 5). The dark switch that lets a node stop publishing telemetry over
///     the mesh-wide DistributedPubSub topic and instead serve it over a dedicated gRPC stream that
///     does not require sharing a gossip ring with whoever is watching.
/// </summary>
public sealed class TelemetryOptions
{
    /// <summary>Configuration section name.</summary>
    public const string SectionName = "Telemetry";

    /// <summary>Publish telemetry over the mesh-wide DistributedPubSub topic — the default.</summary>
    public const string ModeDps = "Dps";

    /// <summary>Serve telemetry over a dedicated gRPC stream.</summary>
    public const string ModeGrpc = "Grpc";

    /// <summary>
    ///     <see cref="ModeDps"/> (default) or <see cref="ModeGrpc"/>. Any other value fails host
    ///     start.
    /// </summary>
    public string Mode { get; set; } = ModeDps;

    /// <summary>
    ///     Dedicated gRPC listen port for the telemetry stream. <c>0</c> (the default) disables it —
    ///     nothing is bound. Required on a driver-role node under <see cref="ModeGrpc"/>.
    /// </summary>
    public int GrpcListenPort { get; set; }

    /// <summary>
    ///     Shared bearer key the serve-side interceptor checks. Supply via the environment
    ///     (<c>Telemetry__ApiKey</c>) — never commit it. Required under <see cref="ModeGrpc"/> on any
    ///     roled node — fail-closed against hosting an un-keyed telemetry surface.
    /// </summary>
    public string ApiKey { get; set; } = string.Empty;
}

/// <summary>
///     Central-side selection of how central dials a node for live telemetry (per-cluster mesh
///     Phase 5). Mirrors <see cref="TelemetryOptions"/>'s mode but carries the dial-side knobs
///     (contact refresh cadence, per-call timeout) instead of a listen port.
/// </summary>
public sealed class TelemetryDialOptions
{
    /// <summary>Configuration section name.</summary>
    public const string SectionName = "TelemetryDial";

    /// <summary>Read telemetry from the mesh-wide DistributedPubSub topic — the default.</summary>
    public const string ModeDps = "Dps";

    /// <summary>Dial nodes' dedicated gRPC telemetry streams.</summary>
    public const string ModeGrpc = "Grpc";

    /// <summary>
    ///     <see cref="ModeDps"/> (default) or <see cref="ModeGrpc"/>. Any other value fails host
    ///     start.
    /// </summary>
    public string Mode { get; set; } = ModeDps;

    /// <summary>
    ///     Shared bearer key; must equal a dialled node's <see cref="TelemetryOptions.ApiKey"/>.
    ///     Supply via the environment (<c>TelemetryDial__ApiKey</c>) — never commit it. Required
    ///     under <see cref="ModeGrpc"/>.
    /// </summary>
    public string ApiKey { get; set; } = string.Empty;

    /// <summary>How often central refreshes its set of dialable node contacts, in seconds.</summary>
    public int ContactRefreshSeconds { get; set; } = 60;

    /// <summary>
    ///     Deadline, in seconds, for a gRPC telemetry dial to deliver its first event. A live node answers a
    ///     fresh subscribe at once (it replays its health/resilience snapshots), so a dial still silent at the
    ///     deadline is one that never connected — it is cancelled and re-dialled. Bounds establishment only;
    ///     an established stream is kept alive by HTTP/2 keepalive pings, not by this value. Values below 1
    ///     are treated as 1.
    /// </summary>
    public int CallTimeoutSeconds { get; set; } = 30;
}

/// <summary>
///     Fails the host at startup on a <see cref="TelemetryOptions"/> shape that would leave a node
///     unable to serve its live-telemetry stream.
/// </summary>
/// <remarks>
///     Like <see cref="ConfigSourceOptionsValidator"/>, every fault caught here otherwise surfaces as
///     an <i>absence</i> — a telemetry consumer that simply never sees data from this node, with no
///     stack trace and no failing node to point at; refusing to start is cheaper to diagnose.
/// </remarks>
public sealed class TelemetryOptionsValidator : IValidateOptions<TelemetryOptions>
{
    private readonly EffectiveRoles _effectiveRoles;

    /// <summary>
    ///     DI-constructed by <c>AddValidatedOptions</c> (a plain <c>AddSingleton</c>), so a
    ///     constructor dependency is safe here. This validator's only use of configuration is this
    ///     node's roles, so it takes <see cref="EffectiveRoles"/> — the single role authority
    ///     — directly rather than <see cref="IConfiguration"/>.
    /// </summary>
    /// <param name="effectiveRoles">The node's resolved roles, the single role authority.</param>
    public TelemetryOptionsValidator(EffectiveRoles effectiveRoles)
    {
        _effectiveRoles = effectiveRoles;
    }

    /// <summary>Validates the telemetry options against this node's roles.</summary>
    /// <param name="name">The named options instance, or <see langword="null"/> for the default.</param>
    /// <param name="options">The options to validate.</param>
    /// <returns>Success, or a failure listing every invalid setting.</returns>
    public ValidateOptionsResult Validate(string? name, TelemetryOptions options)
    {
        ArgumentNullException.ThrowIfNull(options);

        var errors = new List<string>();

        var isDps = string.Equals(options.Mode, TelemetryOptions.ModeDps, StringComparison.OrdinalIgnoreCase);
        var isGrpc = string.Equals(options.Mode, TelemetryOptions.ModeGrpc, StringComparison.OrdinalIgnoreCase);

        if (!isDps && !isGrpc)
        {
            errors.Add(
                $"{TelemetryOptions.SectionName}:{nameof(TelemetryOptions.Mode)} is '{options.Mode}'. "
                + $"Expected '{TelemetryOptions.ModeDps}' or '{TelemetryOptions.ModeGrpc}'.");
        }

        // EffectiveRoles is the single role authority — its precedence already
        // applies the OTOPCUA_ROLES fallback and its normalization already folds case, so
        // a node configured only through the env var, or spelled 'Driver', still satisfies the
        // Grpc-mode requirements below.
        var isDriver = _effectiveRoles.HasDriver;

        if (isGrpc)
        {
            if (isDriver && options.GrpcListenPort <= 0)
            {
                errors.Add(
                    $"Cluster:Roles has 'driver' and {TelemetryOptions.SectionName}:"
                    + $"{nameof(TelemetryOptions.Mode)} is '{TelemetryOptions.ModeGrpc}', but "
                    + $"{TelemetryOptions.SectionName}:{nameof(TelemetryOptions.GrpcListenPort)} is "
                    + $"{options.GrpcListenPort}. A driver node in Grpc telemetry mode must set "
                    + $"{TelemetryOptions.SectionName}:{nameof(TelemetryOptions.GrpcListenPort)}.");
            }

            if (_effectiveRoles.Gossiped.Count > 0 && string.IsNullOrEmpty(options.ApiKey))
            {
                errors.Add(
                    $"{TelemetryOptions.SectionName}:{nameof(TelemetryOptions.ApiKey)} is empty. Under "
                    + $"{TelemetryOptions.ModeGrpc} the shared bearer key is the whole authentication "
                    + "boundary to this node's telemetry surface; without it every dial is rejected. "
                    + $"Supply it via the environment ({TelemetryOptions.SectionName}__ApiKey).");
            }
        }

        return errors.Count == 0
            ? ValidateOptionsResult.Success
            : ValidateOptionsResult.Fail(string.Join(" ", errors));
    }
}

/// <summary>
///     Fails the host at startup on a <see cref="TelemetryDialOptions"/> shape that would leave
///     central unable to dial a node's live-telemetry stream.
/// </summary>
public sealed class TelemetryDialOptionsValidator : IValidateOptions<TelemetryDialOptions>
{
    /// <summary>Validates the telemetry dial options.</summary>
    /// <param name="name">The named options instance, or <see langword="null"/> for the default.</param>
    /// <param name="options">The options to validate.</param>
    /// <returns>Success, or a failure listing every invalid setting.</returns>
    public ValidateOptionsResult Validate(string? name, TelemetryDialOptions options)
    {
        ArgumentNullException.ThrowIfNull(options);

        var errors = new List<string>();

        var isDps = string.Equals(
            options.Mode, TelemetryDialOptions.ModeDps, StringComparison.OrdinalIgnoreCase);
        var isGrpc = string.Equals(
            options.Mode, TelemetryDialOptions.ModeGrpc, StringComparison.OrdinalIgnoreCase);

        if (!isDps && !isGrpc)
        {
            errors.Add(
                $"{TelemetryDialOptions.SectionName}:{nameof(TelemetryDialOptions.Mode)} is "
                + $"'{options.Mode}'. Expected '{TelemetryDialOptions.ModeDps}' or "
                + $"'{TelemetryDialOptions.ModeGrpc}'.");
        }

        if (isGrpc && string.IsNullOrEmpty(options.ApiKey))
        {
            errors.Add(
                $"{TelemetryDialOptions.SectionName}:{nameof(TelemetryDialOptions.ApiKey)} is empty. "
                + $"Under {TelemetryDialOptions.ModeGrpc} the shared bearer key is the whole "
                + "authentication boundary to a node's telemetry surface; without it every dial is "
                + $"rejected. Supply it via the environment ({TelemetryDialOptions.SectionName}__ApiKey).");
        }

        return errors.Count == 0
            ? ValidateOptionsResult.Success
            : ValidateOptionsResult.Fail(string.Join(" ", errors));
    }
}