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

namespace ZB.MOM.WW.OtOpcUa.Cluster;

/// <summary>
///     Fails the host at startup on a <see cref="MeshTransportOptions"/> shape that would leave
///     commands silently undelivered.
/// </summary>
/// <remarks>
///     Every fault caught here otherwise surfaces as an <i>absence</i> — a deployment that never
///     arrives, an alarm acknowledgement that does nothing, a node whose ack is dropped without a
///     trace. An absence has no stack trace and no failing node to point at, which makes it the
///     most expensive class of misconfiguration to diagnose in the field. Refusing to start is
///     cheaper for everyone.
/// </remarks>
public sealed class MeshTransportOptionsValidator : IValidateOptions<MeshTransportOptions>
{
    private readonly IConfiguration _configuration;
    private readonly EffectiveRoles _effectiveRoles;

    /// <summary>
    ///     DI-constructed by <c>AddValidatedOptions</c> (a plain <c>AddSingleton</c>), so constructor
    ///     dependencies are safe here. <see cref="IConfiguration"/> is still needed for the
    ///     <c>ConfigServe:GrpcListenPort</c> cross-read (the admin-side obligation below) —
    ///     <see cref="EffectiveRoles"/> is the single role authority this rule reads
    ///     roles through instead of re-deriving them.
    /// </summary>
    /// <param name="configuration">The application configuration, read for <c>ConfigServe:GrpcListenPort</c>.</param>
    /// <param name="effectiveRoles">This node's resolved effective roles.</param>
    public MeshTransportOptionsValidator(IConfiguration configuration, EffectiveRoles effectiveRoles)
    {
        _configuration = configuration;
        _effectiveRoles = effectiveRoles;
    }

    /// <summary>Validates the <see cref="MeshTransportOptions"/> for this node's roles.</summary>
    /// <param name="name">The options instance name (unused).</param>
    /// <param name="options">The options to validate.</param>
    /// <returns>A success result, or a failure listing every violated rule.</returns>
    public ValidateOptionsResult Validate(string? name, MeshTransportOptions options)
    {
        ArgumentNullException.ThrowIfNull(options);

        var errors = new List<string>();

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

        // An unrecognised mode is refused, never defaulted. The retired 'ClusterClient' value lands
        // here: a node left carrying it fails to start with the two remaining values named, rather
        // than silently falling back to Dps — which on a split-topology node cannot cross the mesh
        // boundary and would deliver nothing at all.
        if (!isDps && !isGrpc)
        {
            errors.Add(
                $"{MeshTransportOptions.SectionName}:{nameof(MeshTransportOptions.Mode)} is "
                + $"'{options.Mode}'. Expected '{MeshTransportOptions.ModeDps}' or "
                + $"'{MeshTransportOptions.ModeGrpc}'.");
        }

        if (options.ContactRefreshSeconds <= 0)
        {
            errors.Add(
                $"{MeshTransportOptions.SectionName}:{nameof(MeshTransportOptions.ContactRefreshSeconds)} "
                + $"must be greater than 0 (was {options.ContactRefreshSeconds}). Central rebuilds its "
                + "node dispatch set on this interval; a non-positive value would leave that set "
                + "frozen at whatever it held when the node booted.");
        }

        // The first Grpc block below is node-side: the PSK a driver presents (and requires), the
        // central endpoints it posts its ack to, and the two call deadlines (the admin-side rule that
        // follows it is a separate scope). Scoped to the driver role because an admin-only central node
        // dials nodes rather than being dialled, and resolves per-cluster keys at runtime through
        // MeshTransportOptions.ClusterPsks / the Secrets store, so requiring a single GrpcPsk and an
        // endpoint list of it would demand configuration it never reads. 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', is still the driver that has to dial central.
        var isDriver = _effectiveRoles.HasDriver;
        var isAdmin = _effectiveRoles.HasAdmin;

        if (isGrpc && isDriver)
        {
            if (string.IsNullOrWhiteSpace(options.GrpcPsk))
            {
                errors.Add(
                    $"{MeshTransportOptions.SectionName}:{nameof(MeshTransportOptions.GrpcPsk)} is "
                    + $"empty. Under {MeshTransportOptions.ModeGrpc} this per-cluster pre-shared key is "
                    + "the whole authentication boundary of the command plane in both directions — "
                    + "without it this node's inbound command service fails closed and every ack it "
                    + "posts to central is rejected. Supply it via the environment "
                    + $"({MeshTransportOptions.SectionName}__{nameof(MeshTransportOptions.GrpcPsk)}), in "
                    + "production as ${secret:OT-MESH-PSK-<clusterId>}.");
            }

            if (options.CentralGrpcEndpoints.Length == 0)
            {
                errors.Add(
                    $"{MeshTransportOptions.SectionName}:"
                    + $"{nameof(MeshTransportOptions.CentralGrpcEndpoints)} is empty. Under "
                    + $"{MeshTransportOptions.ModeGrpc} a driver node has nowhere to post its "
                    + "deployment ack, and every deployment would time out naming a node that is "
                    + "running perfectly. Supply them via the environment "
                    + $"({MeshTransportOptions.SectionName}__"
                    + $"{nameof(MeshTransportOptions.CentralGrpcEndpoints)}__0).");
            }

            foreach (var endpoint in options.CentralGrpcEndpoints)
            {
                if (!endpoint.StartsWith("http://", StringComparison.OrdinalIgnoreCase)
                    && !endpoint.StartsWith("https://", StringComparison.OrdinalIgnoreCase))
                {
                    errors.Add(
                        $"Central gRPC endpoint '{endpoint}' must start with 'http://' (h2c) or "
                        + "'https://' — it is a gRPC base address (scheme://host:port), not a bare "
                        + "host:port and not an Akka remoting address.");
                }
            }

            // Both deadlines are per-call and there is no retry behind them, so a non-positive value
            // is not "wait forever" — it is a call that expires before it is made, i.e. a command
            // plane that silently delivers nothing.
            if (options.DispatchTimeoutSeconds <= 0)
            {
                errors.Add(
                    $"{MeshTransportOptions.SectionName}:"
                    + $"{nameof(MeshTransportOptions.DispatchTimeoutSeconds)} must be greater than 0 "
                    + $"(was {options.DispatchTimeoutSeconds}).");
            }

            if (options.AckTimeoutSeconds <= 0)
            {
                errors.Add(
                    $"{MeshTransportOptions.SectionName}:"
                    + $"{nameof(MeshTransportOptions.AckTimeoutSeconds)} must be greater than 0 "
                    + $"(was {options.AckTimeoutSeconds}).");
            }
        }

        // The one admin-side obligation, and it is cross-read rather than a member of this options
        // class: central hosts CentralCommandService on the SAME dedicated h2c listener as the
        // config-serve endpoint (ConfigServe:GrpcListenPort) — a second cleartext HTTP/2 port would
        // buy nothing but another firewall rule. With that port unset the service is never mapped, so
        // every node's deployment ack has nowhere to land, and nothing errors: the deployment simply
        // times out naming nodes that applied perfectly. Owned here rather than by ConfigServe's own
        // validation because the requirement comes from MeshTransport:Mode, not from config-serve — a
        // Dps central node is legitimately portless.
        if (isGrpc && isAdmin)
        {
            // Read as a string, the way SplitTopologyTransportValidator reads the modes:
            // GetValue<int> THROWS on an unparseable value, and a validator whose whole job is to
            // produce a readable failure must not be the thing that crashes on a typo. Missing,
            // unparseable and non-positive all mean the same thing — nothing is bound — so they share
            // one message.
            var configServePort = _configuration[
                $"{ConfigServeOptions.SectionName}:{nameof(ConfigServeOptions.GrpcListenPort)}"];
            if (!int.TryParse(configServePort, out var port) || port <= 0)
            {
                errors.Add(
                    $"{ConfigServeOptions.SectionName}:"
                    + $"{nameof(ConfigServeOptions.GrpcListenPort)} is not set to a positive port. "
                    + $"Under {MeshTransportOptions.ModeGrpc} an admin node serves the central "
                    + "command endpoint on that listener, and without it every node's deployment ack "
                    + "has nowhere to land — the deploy would time out naming nodes that applied "
                    + "perfectly. Supply it via the environment "
                    + $"({ConfigServeOptions.SectionName}__"
                    + $"{nameof(ConfigServeOptions.GrpcListenPort)}).");
            }
        }

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