using Microsoft.Extensions.Options;
using MxGateway.Contracts;

namespace MxGateway.Server.Configuration;

public sealed class GatewayOptionsValidator : IValidateOptions<GatewayOptions>
{
    private const int MinimumMaxMessageBytes = 1024;
    private const int MaximumMaxMessageBytes = 256 * 1024 * 1024;

    public ValidateOptionsResult Validate(string? name, GatewayOptions options)
    {
        List<string> failures = [];

        ValidateAuthentication(options.Authentication, failures);
        ValidateWorker(options.Worker, failures);
        ValidateSessions(options.Sessions, failures);
        ValidateEvents(options.Events, failures);
        ValidateDashboard(options.Dashboard, failures);
        ValidateProtocol(options.Protocol, failures);

        return failures.Count == 0
            ? ValidateOptionsResult.Success
            : ValidateOptionsResult.Fail(failures);
    }

    private static void ValidateAuthentication(AuthenticationOptions options, List<string> failures)
    {
        if (!Enum.IsDefined(options.Mode))
        {
            failures.Add("MxGateway:Authentication:Mode must be a supported authentication mode.");
            return;
        }

        if (options.Mode == AuthenticationMode.ApiKey)
        {
            AddIfBlank(
                options.SqlitePath,
                "MxGateway:Authentication:SqlitePath is required when API-key authentication is enabled.",
                failures);
            AddIfInvalidPath(
                options.SqlitePath,
                "MxGateway:Authentication:SqlitePath must be a valid filesystem path.",
                failures);
            AddIfBlank(
                options.PepperSecretName,
                "MxGateway:Authentication:PepperSecretName is required when API-key authentication is enabled.",
                failures);
        }
    }

    private static void ValidateWorker(WorkerOptions options, List<string> failures)
    {
        AddIfBlank(options.ExecutablePath, "MxGateway:Worker:ExecutablePath is required.", failures);
        AddIfInvalidPath(
            options.ExecutablePath,
            "MxGateway:Worker:ExecutablePath must be a valid filesystem path.",
            failures);

        if (!string.IsNullOrWhiteSpace(options.ExecutablePath)
            && !string.Equals(Path.GetExtension(options.ExecutablePath), ".exe", StringComparison.OrdinalIgnoreCase))
        {
            failures.Add("MxGateway:Worker:ExecutablePath must point to a .exe file.");
        }

        if (!string.IsNullOrWhiteSpace(options.WorkingDirectory))
        {
            AddIfInvalidPath(
                options.WorkingDirectory,
                "MxGateway:Worker:WorkingDirectory must be a valid filesystem path.",
                failures);
        }

        if (!Enum.IsDefined(options.RequiredArchitecture))
        {
            failures.Add("MxGateway:Worker:RequiredArchitecture must be a supported worker architecture.");
        }

        AddIfNotPositive(
            options.StartupTimeoutSeconds,
            "MxGateway:Worker:StartupTimeoutSeconds must be greater than zero.",
            failures);
        AddIfNotPositive(
            options.ShutdownTimeoutSeconds,
            "MxGateway:Worker:ShutdownTimeoutSeconds must be greater than zero.",
            failures);
        AddIfNotPositive(
            options.HeartbeatIntervalSeconds,
            "MxGateway:Worker:HeartbeatIntervalSeconds must be greater than zero.",
            failures);
        AddIfNotPositive(
            options.HeartbeatGraceSeconds,
            "MxGateway:Worker:HeartbeatGraceSeconds must be greater than zero.",
            failures);

        if (options.HeartbeatGraceSeconds < options.HeartbeatIntervalSeconds)
        {
            failures.Add(
                "MxGateway:Worker:HeartbeatGraceSeconds must be greater than or equal to HeartbeatIntervalSeconds.");
        }

        if (options.MaxMessageBytes is < MinimumMaxMessageBytes or > MaximumMaxMessageBytes)
        {
            failures.Add(
                $"MxGateway:Worker:MaxMessageBytes must be between {MinimumMaxMessageBytes} and {MaximumMaxMessageBytes}.");
        }
    }

    private static void ValidateSessions(SessionOptions options, List<string> failures)
    {
        AddIfNotPositive(
            options.DefaultCommandTimeoutSeconds,
            "MxGateway:Sessions:DefaultCommandTimeoutSeconds must be greater than zero.",
            failures);
        AddIfNotPositive(options.MaxSessions, "MxGateway:Sessions:MaxSessions must be greater than zero.", failures);
    }

    private static void ValidateEvents(EventOptions options, List<string> failures)
    {
        AddIfNotPositive(options.QueueCapacity, "MxGateway:Events:QueueCapacity must be greater than zero.", failures);

        if (!Enum.IsDefined(options.BackpressurePolicy))
        {
            failures.Add("MxGateway:Events:BackpressurePolicy must be a supported backpressure policy.");
        }
    }

    private static void ValidateDashboard(DashboardOptions options, List<string> failures)
    {
        if (options.Enabled)
        {
            AddIfBlank(options.PathBase, "MxGateway:Dashboard:PathBase is required when the dashboard is enabled.", failures);
            if (!string.IsNullOrWhiteSpace(options.PathBase) && !options.PathBase.StartsWith('/'))
            {
                failures.Add("MxGateway:Dashboard:PathBase must start with '/'.");
            }
        }

        AddIfNotPositive(
            options.SnapshotIntervalMilliseconds,
            "MxGateway:Dashboard:SnapshotIntervalMilliseconds must be greater than zero.",
            failures);
        AddIfNegative(
            options.RecentFaultLimit,
            "MxGateway:Dashboard:RecentFaultLimit must be greater than or equal to zero.",
            failures);
        AddIfNegative(
            options.RecentSessionLimit,
            "MxGateway:Dashboard:RecentSessionLimit must be greater than or equal to zero.",
            failures);
    }

    private static void ValidateProtocol(ProtocolOptions options, List<string> failures)
    {
        if (options.WorkerProtocolVersion != GatewayContractInfo.WorkerProtocolVersion)
        {
            failures.Add(
                $"MxGateway:Protocol:WorkerProtocolVersion must be {GatewayContractInfo.WorkerProtocolVersion}.");
        }
    }

    private static void AddIfBlank(string? value, string message, List<string> failures)
    {
        if (string.IsNullOrWhiteSpace(value))
        {
            failures.Add(message);
        }
    }

    private static void AddIfNotPositive(int value, string message, List<string> failures)
    {
        if (value <= 0)
        {
            failures.Add(message);
        }
    }

    private static void AddIfNegative(int value, string message, List<string> failures)
    {
        if (value < 0)
        {
            failures.Add(message);
        }
    }

    private static void AddIfInvalidPath(string? value, string message, List<string> failures)
    {
        if (string.IsNullOrWhiteSpace(value))
        {
            return;
        }

        try
        {
            _ = Path.GetFullPath(value);
        }
        catch (ArgumentException)
        {
            failures.Add(message);
        }
        catch (NotSupportedException)
        {
            failures.Add(message);
        }
        catch (PathTooLongException)
        {
            failures.Add(message);
        }
    }
}