using System.Globalization;
using System.Net;
using System.Net.Sockets;
using System.Runtime.InteropServices;
using System.Security.Authentication;
using System.Security.Cryptography;
using System.Text.Json;
using VoiceCat.Crypto;
using VoiceCat.Server.Data;
using VoiceCat.Transport;

namespace VoiceCat.Server;

internal sealed record ServerConfiguration(string Directory, string BindAddress, int Port, VoiceServerOptions Options);

internal static class ServerCommand
{
    internal static ServerConfiguration Parse(string[] args, Func<string, string?> environment)
    {
        var values = new Dictionary<string, string>(StringComparer.Ordinal);
        string[] names = ["data-dir", "bind", "port", "name", "allow-guests", "max-connections", "handshake-seconds", "idle-seconds", "reaper-seconds", "auth-burst", "auth-refill-seconds"];
        string[] variables = ["DATA_DIR", "BIND_ADDRESS", "BIND_PORT", "SERVER_NAME", "ALLOW_GUESTS", "MAX_CONNECTIONS", "HANDSHAKE_TIMEOUT_SECONDS", "IDLE_TIMEOUT_SECONDS", "REAPER_INTERVAL_SECONDS", "AUTH_BURST", "AUTH_REFILL_SECONDS"];
        for (int i = 0; i < names.Length; i++) if (environment("VOICECAT_" + variables[i]) is string value) values[names[i]] = value;
        int positional = 0;
        for (int i = 0; i < args.Length; i++)
        {
            string argument = args[i];
            if (argument is "--print-config" or "--print-fingerprint" or "--admin") continue;
            if (argument == "account") { i += i + 1 < args.Length && args[i + 1] == "list" ? 1 : 2; continue; }
            if (!argument.StartsWith("--", StringComparison.Ordinal))
            {
                if (args.Contains("account")) throw new ArgumentException("Unexpected account argument; passwords are not command arguments.");
                if (positional >= 2) throw new ArgumentException("Unexpected argument.");
                values[positional++ == 0 ? "data-dir" : "port"] = argument;
                continue;
            }
            string key = argument[2..];
            if (!names.Contains(key) || ++i >= args.Length) throw new ArgumentException("Unknown option or missing value: " + argument);
            values[key] = args[i];
        }
        string Get(string key, string fallback) => values.GetValueOrDefault(key, fallback);
        int Number(string key, int fallback) => int.Parse(Get(key, fallback.ToString(CultureInfo.InvariantCulture)), CultureInfo.InvariantCulture);
        var options = new VoiceServerOptions
        {
            Name = Get("name", "VoiceCat Server"), AllowGuests = bool.Parse(Get("allow-guests", "true")), MaximumConnections = Number("max-connections", 64),
            HandshakeTimeout = TimeSpan.FromSeconds(Number("handshake-seconds", 15)), IdleTimeout = TimeSpan.FromSeconds(Number("idle-seconds", 45)),
            ReaperInterval = TimeSpan.FromSeconds(Number("reaper-seconds", 15)), AuthenticationBurst = Number("auth-burst", 5),
            AuthenticationRefillInterval = TimeSpan.FromSeconds(Number("auth-refill-seconds", 10))
        };
        options.Validate();
        int port = Number("port", 8384);
        if (port is < 0 or > 65535) throw new ArgumentException("Port must be between 0 and 65535.");
        string bind = Get("bind", "0.0.0.0");
        if (!IPAddress.TryParse(bind, out _)) throw new ArgumentException("Bind address must be an IPv4 or IPv6 literal.");
        return new(Path.GetFullPath(Get("data-dir", "voicecat-data")), bind, port, options);
    }

    internal static async Task<int> RunAsync(string[] args, TextWriter output, TextWriter error, CancellationToken cancellationToken = default)
    {
        if (args.Contains("--help"))
        {
            await output.WriteLineAsync("VoiceCat TLS/UDP server\n--data-dir PATH --bind IP --port PORT --name NAME --allow-guests true|false\n--max-connections N --handshake-seconds N --idle-seconds N --reaper-seconds N\n--auth-burst N --auth-refill-seconds N --print-config --print-fingerprint\n--health-check HOST:PORT [--expect-fingerprint SHA256]\naccount add|reset|delete|list [USERNAME] [--admin]\nAccount passwords: hidden prompt, or VOICECAT_ADMIN_PASSWORD (never command arguments).\nDefaults: 0.0.0.0:8384 TCP+UDP, ./voicecat-data; VOICECAT_* environment overrides supported.");
            return 0;
        }
        try
        {
            int healthIndex = Array.IndexOf(args, "--health-check");
            if (healthIndex >= 0)
            {
                if (healthIndex + 1 >= args.Length) throw new ArgumentException("Health endpoint required.");
                string? expected = null;
                int fingerprintIndex = Array.IndexOf(args, "--expect-fingerprint");
                if (fingerprintIndex >= 0) expected = fingerprintIndex + 1 < args.Length ? args[fingerprintIndex + 1] : throw new ArgumentException("Expected fingerprint required.");
                return await HealthCheckAsync(args[healthIndex + 1], expected, output, cancellationToken).ConfigureAwait(false);
            }
            ServerConfiguration config = Parse(args, Environment.GetEnvironmentVariable);
            if (args.Contains("--print-config")) { await output.WriteLineAsync(JsonSerializer.Serialize(config)); return 0; }
            CreateDataDirectory(config.Directory);
            int accountIndex = Array.IndexOf(args, "account");
            if (accountIndex >= 0) return await AccountAsync(args, accountIndex, config, output, cancellationToken).ConfigureAwait(false);
            if (args.Contains("--print-fingerprint"))
            {
                using var credentials = ServerCredentials.LoadOrCreate(config.Directory, config.Options.Name);
                await output.WriteLineAsync(credentials.CertificateFingerprint);
                return 0;
            }
            using var instanceLock = new FileStream(Path.Combine(config.Directory, ".server.lock"), FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None);
            using var stop = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
            ConsoleCancelEventHandler cancel = (_, e) => { e.Cancel = true; stop.Cancel(); };
            Console.CancelKeyPress += cancel;
            using var terminate = OperatingSystem.IsWindows() ? null : PosixSignalRegistration.Create(PosixSignal.SIGTERM, context => { context.Cancel = true; stop.Cancel(); });
            using var interrupt = OperatingSystem.IsWindows() ? null : PosixSignalRegistration.Create(PosixSignal.SIGINT, context => { context.Cancel = true; stop.Cancel(); });
            VoiceServer? server = null;
            try
            {
                server = new(config.Directory, new(IPAddress.Parse(config.BindAddress), config.Port), config.Options);
                server.ConnectionFailed += exception => error.WriteLine(JsonSerializer.Serialize(new { @event = "connection_closed", type = exception.GetType().Name }));
                using var credentials = ServerCredentials.LoadOrCreate(config.Directory, config.Options.Name);
                await output.WriteLineAsync(JsonSerializer.Serialize(new { @event = "ready", address = server.EndPoint.Address.ToString(), port = server.EndPoint.Port, udp_port = server.MediaEndPoint.Port,
                    certificate_fingerprint = credentials.CertificateFingerprint, identity_fingerprint = Convert.ToHexString(System.Security.Cryptography.SHA256.HashData(credentials.Identity.PublicKey)) }));
                Task stopped = Task.Delay(Timeout.Infinite, stop.Token);
                if (await Task.WhenAny(stopped, server.Completion).ConfigureAwait(false) == server.Completion) await server.Completion.ConfigureAwait(false);
                return 0;
            }
            finally
            {
                Console.CancelKeyPress -= cancel;
                stop.Cancel();
                if (server is not null) await server.DisposeAsync().AsTask().WaitAsync(TimeSpan.FromSeconds(10)).ConfigureAwait(false);
            }
        }
        catch (Exception exception) when (exception is ArgumentException or FormatException or OverflowException or IOException or InvalidOperationException or SocketException or AuthenticationException or CryptographicException or Microsoft.Data.Sqlite.SqliteException or TimeoutException || exception is OperationCanceledException && !cancellationToken.IsCancellationRequested)
        {
            await error.WriteLineAsync("VoiceCat command failed: " + exception.GetType().Name + ". Check configuration, data files and port availability.");
            return 1;
        }
    }

    private static async Task<int> HealthCheckAsync(string endpoint, string? expectedFingerprint, TextWriter output, CancellationToken cancellationToken)
    {
        int separator = endpoint.LastIndexOf(':');
        if (separator < 1 || !ushort.TryParse(endpoint[(separator + 1)..], out ushort port)) throw new ArgumentException("Health endpoint must be HOST:PORT.");
        string host = endpoint[..separator].Trim('[', ']');
        byte[]? expected = null;
        if (expectedFingerprint is not null)
        {
            try { expected = Convert.FromHexString(expectedFingerprint); } catch (FormatException) { throw new ArgumentException("Expected fingerprint must be hexadecimal."); }
            if (expected.Length != 32) throw new ArgumentException("Expected fingerprint must be SHA-256.");
        }
        string? actual = null;
        using var deadline = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken); deadline.CancelAfter(TimeSpan.FromSeconds(5));
        using var socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
        await socket.ConnectAsync(host, port, deadline.Token).ConfigureAwait(false);
        using var tls = TlsSession.CreateClient(fingerprint => { actual = fingerprint; return true; });
        await using var connection = new TlsControlConnection(socket, tls, deadline.Token, TimeSpan.FromSeconds(5));
        using MediaSessionCrypto crypto = await connection.TakeMediaCryptoAsync(deadline.Token).ConfigureAwait(false);
        if (actual is null || expected is not null && !CryptographicOperations.FixedTimeEquals(Convert.FromHexString(actual), expected)) return 1;
        await output.WriteLineAsync(JsonSerializer.Serialize(new { status = "healthy", certificate_fingerprint = actual }));
        return 0;
    }

    private static void CreateDataDirectory(string directory)
    {
        if (OperatingSystem.IsWindows()) System.IO.Directory.CreateDirectory(directory);
        else System.IO.Directory.CreateDirectory(directory, UnixFileMode.UserRead | UnixFileMode.UserWrite | UnixFileMode.UserExecute);
    }

    private static async Task<int> AccountAsync(string[] args, int index, ServerConfiguration config, TextWriter output, CancellationToken cancellationToken)
    {
        if (index + 1 >= args.Length) throw new ArgumentException("Account operation required.");
        string operation = args[index + 1];
        using var store = new AccountStore(Path.Combine(config.Directory, "voicecat.db"));
        if (operation == "list")
        {
            foreach (Account account in store.ListAccounts()) await output.WriteLineAsync(JsonSerializer.Serialize(new { account.Username, account.IsAdmin, account.CreatedAt, account.LastLogin }));
            return 0;
        }
        if (index + 2 >= args.Length || args[index + 2].StartsWith("--", StringComparison.Ordinal)) throw new ArgumentException("Username required.");
        string username = args[index + 2];
        if (operation == "delete") return store.DeleteAccount(username) ? 0 : 1;
        if (operation is not ("add" or "reset")) throw new ArgumentException("Unknown account operation.");
        string password = Environment.GetEnvironmentVariable("VOICECAT_ADMIN_PASSWORD") ?? ReadPassword();
        if (operation == "add") await store.CreateAccountAsync(username, password, args.Contains("--admin"), cancellationToken).ConfigureAwait(false);
        else if (!await store.ResetPasswordAsync(username, password, cancellationToken).ConfigureAwait(false)) return 1;
        await output.WriteLineAsync("Account updated.");
        return 0;
    }

    private static string ReadPassword()
    {
        if (Console.IsInputRedirected) return Console.ReadLine() ?? throw new ArgumentException("Password input required.");
        Console.Error.Write("Password: ");
        var characters = new List<char>();
        while (true)
        {
            ConsoleKeyInfo key = Console.ReadKey(true);
            if (key.Key == ConsoleKey.Enter) break;
            if (key.Key == ConsoleKey.Backspace) { if (characters.Count != 0) characters.RemoveAt(characters.Count - 1); }
            else if (!char.IsControl(key.KeyChar) && characters.Count < 1024) characters.Add(key.KeyChar);
        }
        Console.Error.WriteLine();
        return new string(characters.ToArray());
    }
}