using System.Net;
using System.Net.Sockets;
using FinalFactory.Rendezvous.Contracts;

namespace FinalFactory.Rendezvous.TestClient;

internal enum TestClientMode
{
    Host,
    Browse,
    Watch,
    Join,
}

internal sealed class TestClientOptions
{
    internal TestClientMode Mode { get; init; }
    internal Uri ServiceUri { get; init; } = new("http://127.0.0.1:5000/");
    internal IPEndPoint Mediator { get; init; } = new(IPAddress.Loopback, 9050);
    internal GameId GameId { get; init; } = new("space-game");
    internal EnvironmentId EnvironmentId { get; init; } = new("development");
    internal RegionId RegionId { get; init; } = new("local");
    internal uint ProtocolVersion { get; init; } = 1;
    internal string BuildVersion { get; init; } = "test-client";
    internal string DisplayName { get; init; } = "Rendezvous diagnostic host";
    internal string PublisherCredentialEnvironmentVariable { get; init; } =
        "RENDEZVOUS_PUBLISHER_CREDENTIAL";
    internal Dictionary<string, string> Metadata { get; init; } = new(StringComparer.Ordinal);
    internal NetworkEndpoint? DedicatedFallback { get; init; }
    internal SessionListingId? ListingId { get; init; }
    internal int LocalPort { get; init; }
    internal int PageSize { get; init; } = 20;
    internal TimeSpan OperationTimeout { get; init; } = TimeSpan.FromSeconds(20);
    internal TimeSpan? RunDuration { get; init; }
    internal bool Script { get; init; }
    internal bool Json { get; init; }
    internal bool ExitAfterEcho { get; init; }
    internal bool ExerciseReconnect { get; init; }
    internal bool ExerciseReset { get; init; }
}

internal sealed class TestClientParseResult
{
    private TestClientParseResult(TestClientOptions? options, string? error, bool showHelp)
    {
        Options = options;
        Error = error;
        ShowHelp = showHelp;
    }

    internal TestClientOptions? Options { get; }
    internal string? Error { get; }
    internal bool ShowHelp { get; }
    internal bool Succeeded => Options is not null;

    internal static TestClientParseResult Success(TestClientOptions options) => new(options, null, false);
    internal static TestClientParseResult Failure(string error) => new(null, error, false);
    internal static TestClientParseResult Help() => new(null, null, true);
}

internal static class TestClientOptionParser
{
    internal const string Usage = """
        Rendezvous diagnostic client

        Usage:
          rendezvous-test-client host [options]
          rendezvous-test-client browse [options]
          rendezvous-test-client watch [options]
          rendezvous-test-client join [options]

        Common options:
          --service URL                 HTTP(S) Rendezvous base URL
          --mediator IP:PORT            UDP mediator endpoint
          --game ID                     Game scope (default: space-game)
          --environment ID              Environment scope (default: development)
          --protocol NUMBER             Exact gameplay protocol (default: 1)
          --region ID                   Region filter/publication (default: local)
          --timeout-seconds NUMBER      Bounded startup/traversal stage, 1-300 (default: 20)
          --port NUMBER                 Caller-owned gameplay UDP port; 0 chooses one
          --page-size NUMBER            Bounded browser page size, 1-100 (default: 20)
          --script                      Never prompt; select the first compatible listing
          --json                        Emit one versioned JSON event per line
          --help                        Show this help

        Host options:
          --publisher-credential-env NAME  Environment variable containing the credential
          --display-name TEXT           Public listing name
          --build-version TEXT          Public build version
          --metadata KEY=VALUE          Bounded public metadata; may be repeated
          --fallback IP:PORT            Optional policy-authorized dedicated fallback
          --run-seconds NUMBER          Stop after 1-86400 seconds
          --exit-after-echo             Stop after an authenticated ping/echo/ack exchange

        Watch options:
          --run-seconds NUMBER          Stop after 1-86400 seconds
          --exercise-reconnect          Disconnect after an update and verify ordered replay
          --exercise-reset              Corrupt the snapshot cursor and verify reset/refresh

        Join options:
          --listing UUID                Join an exact listing; otherwise browse/select

        Credentials are accepted only through the named environment variable. They are never
        accepted on the command line and are never written to human or JSON output.
        """;

    internal static TestClientParseResult Parse(string[] args)
    {
        if (args.Length == 0 || args.Length == 1 && IsHelp(args[0]))
        {
            return TestClientParseResult.Help();
        }
        if (args.Length > 64)
        {
            return TestClientParseResult.Failure("Too many command-line arguments.");
        }
        if (!TryMode(args[0], out TestClientMode mode))
        {
            return TestClientParseResult.Failure("The first argument must be host, browse, or join.");
        }

        Uri serviceUri = new("http://127.0.0.1:5000/");
        IPEndPoint mediator = new(IPAddress.Loopback, 9050);
        string game = "space-game";
        string environment = "development";
        string region = "local";
        uint protocol = 1;
        string buildVersion = "test-client";
        string displayName = "Rendezvous diagnostic host";
        string credentialEnvironmentVariable = "RENDEZVOUS_PUBLISHER_CREDENTIAL";
        Dictionary<string, string> metadata = new(StringComparer.Ordinal);
        NetworkEndpoint? dedicatedFallback = null;
        SessionListingId? listingId = null;
        int localPort = 0;
        int pageSize = 20;
        int timeoutSeconds = 20;
        int? runSeconds = null;
        bool script = false;
        bool json = false;
        bool exitAfterEcho = false;
        bool exerciseReconnect = false;
        bool exerciseReset = false;
        HashSet<string> seen = new(StringComparer.Ordinal);

        for (int index = 1; index < args.Length; index++)
        {
            string option = args[index];
            if (IsHelp(option))
            {
                return TestClientParseResult.Help();
            }
            if (option is "--script" or "--json" or "--exit-after-echo"
                or "--exercise-reconnect" or "--exercise-reset")
            {
                if (!seen.Add(option))
                {
                    return TestClientParseResult.Failure($"Option {option} was specified more than once.");
                }
                script |= option == "--script";
                json |= option == "--json";
                exitAfterEcho |= option == "--exit-after-echo";
                exerciseReconnect |= option == "--exercise-reconnect";
                exerciseReset |= option == "--exercise-reset";
                continue;
            }
            if (!option.StartsWith("--", StringComparison.Ordinal)
                || index + 1 >= args.Length)
            {
                return TestClientParseResult.Failure("Every option must use the form --name value.");
            }

            string value = args[++index];
            if (value.Length is 0 or > 512)
            {
                return TestClientParseResult.Failure($"Option {option} has an invalid value length.");
            }
            if (option != "--metadata" && !seen.Add(option))
            {
                return TestClientParseResult.Failure($"Option {option} was specified more than once.");
            }

            switch (option)
            {
                case "--service":
                    if (!TryServiceUri(value, out serviceUri))
                    {
                        return TestClientParseResult.Failure("The service URL must be absolute HTTP(S), credential-free, and query-free.");
                    }
                    break;
                case "--mediator":
                    if (!IPEndPoint.TryParse(value, out IPEndPoint? parsedMediator)
                        || parsedMediator.Port == 0)
                    {
                        return TestClientParseResult.Failure("The mediator must be an IP endpoint with a non-zero port.");
                    }
                    mediator = parsedMediator;
                    break;
                case "--game":
                    game = value;
                    break;
                case "--environment":
                    environment = value;
                    break;
                case "--region":
                    region = value;
                    break;
                case "--protocol":
                    if (!uint.TryParse(value, out protocol) || protocol == 0)
                    {
                        return TestClientParseResult.Failure("The protocol must be a positive integer.");
                    }
                    break;
                case "--build-version":
                    buildVersion = value;
                    break;
                case "--display-name":
                    displayName = value;
                    break;
                case "--publisher-credential-env":
                    if (!IsEnvironmentVariableName(value))
                    {
                        return TestClientParseResult.Failure("The credential environment-variable name is invalid.");
                    }
                    credentialEnvironmentVariable = value;
                    break;
                case "--metadata":
                    if (!TryMetadata(value, metadata))
                    {
                        return TestClientParseResult.Failure("Metadata must be a unique KEY=VALUE pair with a non-empty key.");
                    }
                    break;
                case "--fallback":
                    if (!IPEndPoint.TryParse(value, out IPEndPoint? fallbackEndpoint)
                        || fallbackEndpoint.Port == 0)
                    {
                        return TestClientParseResult.Failure("The fallback must be an IP endpoint with a non-zero port.");
                    }
                    dedicatedFallback = new NetworkEndpoint
                    {
                        AddressFamily = fallbackEndpoint.AddressFamily == AddressFamily.InterNetwork
                            ? AddressFamilyKind.Ipv4
                            : AddressFamilyKind.Ipv6,
                        Address = fallbackEndpoint.Address.ToString(),
                        Port = fallbackEndpoint.Port,
                    };
                    break;
                case "--listing":
                    if (!Guid.TryParse(value, out Guid parsedListing) || parsedListing == Guid.Empty)
                    {
                        return TestClientParseResult.Failure("The listing must be a non-empty UUID.");
                    }
                    listingId = new SessionListingId(parsedListing);
                    break;
                case "--port":
                    if (!int.TryParse(value, out localPort) || localPort is < 0 or > 65_535)
                    {
                        return TestClientParseResult.Failure("The local UDP port must be between 0 and 65535.");
                    }
                    break;
                case "--page-size":
                    if (!int.TryParse(value, out pageSize)
                        || pageSize is < 1 or > ContractLimits.BrowserPageMaxItems)
                    {
                        return TestClientParseResult.Failure("The page size is outside the contract limit.");
                    }
                    break;
                case "--timeout-seconds":
                    if (!int.TryParse(value, out timeoutSeconds) || timeoutSeconds is < 1 or > 300)
                    {
                        return TestClientParseResult.Failure("The timeout must be between 1 and 300 seconds.");
                    }
                    break;
                case "--run-seconds":
                    if (!int.TryParse(value, out int parsedRunSeconds)
                        || parsedRunSeconds is < 1 or > 86_400)
                    {
                        return TestClientParseResult.Failure("The host run duration must be between 1 and 86400 seconds.");
                    }
                    runSeconds = parsedRunSeconds;
                    break;
                default:
                    return TestClientParseResult.Failure($"Unknown option {option}.");
            }
        }

        if (!IsSlug(game, ContractLimits.GameIdMaxCharacters)
            || !IsSlug(environment, ContractLimits.EnvironmentIdMaxCharacters)
            || !IsSlug(region, ContractLimits.RegionIdMaxCharacters)
            || !ContractValidation.IsBuildVersionValid(buildVersion)
            || !ContractValidation.IsDisplayNameValid(displayName)
            || !ContractValidation.IsMetadataValid(metadata))
        {
            return TestClientParseResult.Failure("One or more game, environment, region, build, or display values violate v1 limits.");
        }
        if (listingId.HasValue && mode != TestClientMode.Join
            || runSeconds.HasValue && mode is not (TestClientMode.Host or TestClientMode.Watch)
            || exitAfterEcho && mode != TestClientMode.Host
            || exerciseReconnect && mode != TestClientMode.Watch
            || exerciseReset && mode != TestClientMode.Watch
            || exerciseReconnect && exerciseReset
            || metadata.Count > 0 && mode != TestClientMode.Host
            || dedicatedFallback is not null && mode != TestClientMode.Host
            || seen.Contains("--publisher-credential-env") && mode != TestClientMode.Host
            || seen.Contains("--display-name") && mode != TestClientMode.Host
            || seen.Contains("--build-version") && mode != TestClientMode.Host)
        {
            return TestClientParseResult.Failure("One or more options do not apply to the selected mode.");
        }

        return TestClientParseResult.Success(new TestClientOptions
        {
            Mode = mode,
            ServiceUri = serviceUri,
            Mediator = mediator,
            GameId = new(game),
            EnvironmentId = new(environment),
            RegionId = new(region),
            ProtocolVersion = protocol,
            BuildVersion = buildVersion,
            DisplayName = displayName,
            PublisherCredentialEnvironmentVariable = credentialEnvironmentVariable,
            Metadata = metadata,
            DedicatedFallback = dedicatedFallback,
            ListingId = listingId,
            LocalPort = localPort,
            PageSize = pageSize,
            OperationTimeout = TimeSpan.FromSeconds(timeoutSeconds),
            RunDuration = runSeconds.HasValue
                ? TimeSpan.FromSeconds(runSeconds.Value)
                : mode == TestClientMode.Host && script
                    ? TimeSpan.FromSeconds(timeoutSeconds)
                    : null,
            Script = script,
            Json = json,
            ExitAfterEcho = exitAfterEcho,
            ExerciseReconnect = exerciseReconnect,
            ExerciseReset = exerciseReset,
        });
    }

    private static bool TryMode(string value, out TestClientMode mode) =>
        Enum.TryParse(value, true, out mode) && Enum.IsDefined(mode);

    private static bool IsHelp(string value) => value is "--help" or "-h" or "help";

    private static bool TryServiceUri(string value, out Uri uri)
    {
        uri = null!;
        if (!Uri.TryCreate(value, UriKind.Absolute, out Uri? parsed)
            || parsed.Scheme is not ("http" or "https")
            || !string.IsNullOrEmpty(parsed.UserInfo)
            || !string.IsNullOrEmpty(parsed.Query)
            || !string.IsNullOrEmpty(parsed.Fragment))
        {
            return false;
        }

        UriBuilder builder = new(parsed) { Path = parsed.AbsolutePath.TrimEnd('/') + "/" };
        uri = builder.Uri;
        return true;
    }

    private static bool IsEnvironmentVariableName(string value)
    {
        if (value.Length is 0 or > 64 || !(char.IsLetter(value[0]) || value[0] == '_'))
        {
            return false;
        }
        return value.All(static character =>
            char.IsAsciiLetterOrDigit(character) || character == '_');
    }

    private static bool TryMetadata(string value, Dictionary<string, string> metadata)
    {
        int separator = value.IndexOf('=');
        if (separator is < 1 or > ContractLimits.MetadataKeyMaxBytes
            || metadata.Count >= ContractLimits.MetadataMaxKeys)
        {
            return false;
        }
        string key = value[..separator];
        string metadataValue = value[(separator + 1)..];
        return !string.IsNullOrWhiteSpace(key)
            && ContractValidation.IsUtf8LengthWithin(key, ContractLimits.MetadataKeyMaxBytes)
            && ContractValidation.IsUtf8LengthWithin(metadataValue, ContractLimits.MetadataValueMaxBytes)
            && metadata.TryAdd(key, metadataValue);
    }

    private static bool IsSlug(string value, int maximumCharacters) =>
        value.Length is > 0
        && value.Length <= maximumCharacters
        && value[0] is >= 'a' and <= 'z'
        && value.All(static character => character is >= 'a' and <= 'z'
            or >= '0' and <= '9'
            or '-');
}