using System.Buffers.Binary;
using System.Text;

namespace AVEVA.Historian.Client.Wcf;

internal static class HistorianOpen2Protocol
{
    public static byte[] SerializeLegacyVersion1(HistorianOpen2Request request)
    {
        using MemoryStream stream = new();
        using BinaryWriter writer = new(stream, Encoding.Unicode, leaveOpen: true);

        writer.Write((ushort)1);
        WriteHistorianString(writer, request.HostName);
        WriteHistorianString(writer, request.ProcessName);
        writer.Write(request.ProcessId);
        WriteHistorianString(writer, request.UserName);
        writer.Write((uint)request.Password.Length);
        writer.Write(request.Password);
        writer.Write(request.ClientType);
        writer.Write(request.ClientVersion);
        writer.Write(request.ConnectionMode);
        WriteMetadataNamespace(writer, request.MetadataNamespace);
        return stream.ToArray();
    }

    public static byte[] SerializeNativeVersion3(HistorianOpen2Request request, HistorianClientCommonInfo commonInfo)
    {
        using MemoryStream stream = new();
        using BinaryWriter writer = new(stream, Encoding.Unicode, leaveOpen: true);

        writer.Write((byte)3);
        WriteNativeOpenConnectionContent(writer, request, commonInfo);
        return stream.ToArray();
    }

    public static byte[] SerializeNativeOpenConnection3Version6(
        HistorianOpen2Request request,
        HistorianClientCommonInfo commonInfo,
        Guid clientKey,
        byte[]? credentialBlock = null)
    {
        using MemoryStream stream = new();
        using BinaryWriter writer = new(stream, Encoding.Unicode, leaveOpen: true);

        writer.Write((byte)6);
        writer.Write(clientKey.ToByteArray());
        writer.Write((byte)0);
        WriteNativeOpenConnectionContent(writer, request, commonInfo, credentialBlock, useCompactMetadataNamespace: true);
        return stream.ToArray();
    }

    /// <summary>
    /// Builds the native 2023 R2 <b>version-8</b> OpenConnection request — the format the stock client
    /// uses, which (unlike v6) carries a <paramref name="connectionType"/> byte (Event vs Process). The
    /// tail is the same <see cref="HistorianClientCommonInfo"/> v6 emits; the head is the v8 layout
    /// decoded from a live capture (docs/reverse-engineering/grpc-event-query-capture.md): version 8,
    /// two marker bytes, the client-key GUID, a username <c>HistorianString</c>, a length-prefixed
    /// credential token, then ClientType / ConnectionType / flag / a constant word / compact metadata
    /// namespace / two empty strings. The credential token is normally an ECDH-derived blob in the
    /// native cert path; this serializer sends it as supplied (zeroed for the Negotiate-auth path,
    /// mirroring how the v6 request already sends a zeroed credential block and relies on the separate
    /// ValidateClientCredential handshake for authentication).
    /// </summary>
    public static byte[] SerializeNativeOpenConnectionVersion8(
        HistorianClientCommonInfo commonInfo,
        Guid clientKey,
        byte connectionType,
        byte connectionFlag,
        string userName,
        byte[] credentialToken)
    {
        using MemoryStream stream = new();
        using BinaryWriter writer = new(stream, Encoding.Unicode, leaveOpen: true);

        writer.Write((byte)8);                        // [0] format version 8
        writer.Write((byte)0xF0);                     // [1] constant marker
        writer.Write(new byte[19]);                   // [2..20] zero padding
        writer.Write((byte)1);                        // [21] constant marker
        writer.Write(clientKey.ToByteArray());        // [22..37] per-session client key
        WriteHistorianString(writer, userName);       // username (UTF-16 HistorianString)
        writer.Write((ushort)credentialToken.Length); // credential-token length (u16)
        writer.Write(credentialToken);                // credential token (zeroed for the Negotiate path)
        writer.Write((byte)4);                        // ClientType = 4
        writer.Write(connectionType);                 // ConnectionType (Event = 1 / Process = 2)
        writer.Write(connectionFlag);                 // type flag (Event = 1 / Process = 0)
        writer.Write((ushort)3);                      // constant word observed at [97..98]
        WriteCompactMetadataNamespace(writer, HistorianMetadataNamespace.Empty);
        WriteHistorianString(writer, string.Empty);
        WriteHistorianString(writer, string.Empty);
        WriteClientCommonInfo(writer, commonInfo);    // tail: FormatVersion 3 => no ClientDllVersion
        writer.Write(0u);                             // trailing terminator
        return stream.ToArray();
    }

    private static void WriteNativeOpenConnectionContent(
        BinaryWriter writer,
        HistorianOpen2Request request,
        HistorianClientCommonInfo commonInfo,
        byte[]? credentialBlock = null,
        bool useCompactMetadataNamespace = false)
    {
        byte[] secretBytes = credentialBlock ?? request.Password;
        WriteHistorianString(writer, request.HostName);
        checked
        {
            writer.Write((ushort)secretBytes.Length);
        }

        writer.Write(secretBytes);
        writer.Write(request.ClientType);
        writer.Write(request.ConnectionMode);
        if (useCompactMetadataNamespace)
        {
            WriteCompactMetadataNamespace(writer, request.MetadataNamespace);
        }
        else
        {
            WriteMetadataNamespace(writer, request.MetadataNamespace);
        }

        WriteHistorianString(writer, string.Empty);
        WriteHistorianString(writer, string.Empty);
        WriteClientCommonInfo(writer, commonInfo);
    }

    public static HistorianNativeError? TryReadNativeError(ReadOnlySpan<byte> buffer)
    {
        if (buffer.Length < 5)
        {
            return null;
        }

        byte type = buffer[0];
        uint code = BinaryPrimitives.ReadUInt32LittleEndian(buffer[1..5]);
        return new HistorianNativeError(type, code, GetKnownErrorName(code));
    }

    public static HistorianLegacyOpen2Output? TryReadLegacyOpen2Output(ReadOnlySpan<byte> buffer)
    {
        if (buffer.Length != 32)
        {
            return null;
        }

        uint handle = BinaryPrimitives.ReadUInt32LittleEndian(buffer[..4]);
        Guid storageSessionId = new(buffer.Slice(4, 16));
        long connectTime = BinaryPrimitives.ReadInt64LittleEndian(buffer.Slice(20, 8));
        uint serverStatus = BinaryPrimitives.ReadUInt32LittleEndian(buffer.Slice(28, 4));
        return new HistorianLegacyOpen2Output(handle, storageSessionId, connectTime, serverStatus);
    }

    public static HistorianNativeOpen3Output? TryReadNativeOpen3Output(ReadOnlySpan<byte> buffer)
    {
        if (buffer.Length < 29)
        {
            return null;
        }

        byte protocolVersion = buffer[0];
        if (protocolVersion is not (2 or 3))
        {
            return null;
        }

        int minimumLength = protocolVersion >= 3 ? 37 : 29;
        if (buffer.Length < minimumLength)
        {
            return null;
        }

        uint handle = BinaryPrimitives.ReadUInt32LittleEndian(buffer.Slice(1, 4));
        Guid storageSessionId = new(buffer.Slice(5, 16));
        long connectTime = BinaryPrimitives.ReadInt64LittleEndian(buffer.Slice(21, 8));
        long? serverTime = null;
        if (protocolVersion >= 3)
        {
            serverTime = BinaryPrimitives.ReadInt64LittleEndian(buffer.Slice(29, 8));
        }

        byte[] trailingBytes = buffer[minimumLength..].ToArray();
        return new HistorianNativeOpen3Output(
            protocolVersion,
            handle,
            storageSessionId,
            connectTime,
            serverTime,
            trailingBytes);
    }

    public static byte[] EncodeWidePassword(string password)
    {
        return string.IsNullOrEmpty(password) ? [] : Encoding.Unicode.GetBytes(password);
    }

    private static void WriteMetadataNamespace(BinaryWriter writer, HistorianMetadataNamespace metadataNamespace)
    {
        writer.Write(metadataNamespace.HasValue ? (byte)1 : (byte)0);
        WriteHistorianString(writer, metadataNamespace.Namespace);
        WriteHistorianString(writer, metadataNamespace.TagPrefix);
        WriteHistorianString(writer, metadataNamespace.PropertyPrefix);
    }

    private static void WriteCompactMetadataNamespace(BinaryWriter writer, HistorianMetadataNamespace metadataNamespace)
    {
        if (!metadataNamespace.HasValue
            || metadataNamespace.Namespace.Length != 0
            || metadataNamespace.TagPrefix.Length != 0
            || metadataNamespace.PropertyPrefix.Length != 0)
        {
            throw new ProtocolEvidenceMissingException("OpenConnection3 non-empty metadata namespace");
        }

        writer.Write((byte)1);
        WriteCompactEmptyString(writer);
        WriteCompactEmptyString(writer);
        WriteCompactEmptyString(writer);
    }

    private static void WriteCompactEmptyString(BinaryWriter writer)
    {
        writer.Write((ushort)1);
        writer.Write((byte)0);
    }

    private static void WriteHistorianString(BinaryWriter writer, string value)
    {
        writer.Write((uint)value.Length);
        if (value.Length > 0)
        {
            writer.Write(Encoding.Unicode.GetBytes(value));
        }
    }

    private static void WriteClientCommonInfo(BinaryWriter writer, HistorianClientCommonInfo commonInfo)
    {
        writer.Write(commonInfo.FormatVersion);
        WriteHistorianString(writer, commonInfo.ServerNodeName);
        WriteHistorianString(writer, commonInfo.ClientNodeName);
        writer.Write(commonInfo.ProcessId);
        writer.Write(commonInfo.HcalVersion);
        WriteHistorianString(writer, commonInfo.ProcessName);
        WriteHistorianString(writer, commonInfo.Proxy);
        WriteHistorianString(writer, commonInfo.DataSourceId);
        writer.Write(commonInfo.ShardId.ToByteArray());
        writer.Write(commonInfo.ClientVersion);
        if (commonInfo.FormatVersion >= 3)
        {
            writer.Write(commonInfo.ClientTimestamp);
        }

        if (commonInfo.FormatVersion >= 4)
        {
            WriteHistorianString(writer, commonInfo.ClientDllVersion);
        }
    }

    private static string? GetKnownErrorName(uint code)
    {
        return code switch
        {
            1 => "Failure",
            73 => "InvalidPacketVersion",
            171 => "AuthenticationFailed",
            _ => null
        };
    }
}

internal sealed record HistorianOpen2Request(
    string HostName,
    string ProcessName,
    uint ProcessId,
    string UserName,
    byte[] Password,
    byte ClientType,
    ushort ClientVersion,
    uint ConnectionMode,
    HistorianMetadataNamespace MetadataNamespace);

internal sealed record HistorianMetadataNamespace(
    bool HasValue,
    string Namespace,
    string TagPrefix,
    string PropertyPrefix)
{
    public static HistorianMetadataNamespace Empty { get; } = new(true, string.Empty, string.Empty, string.Empty);
}

internal sealed record HistorianNativeError(byte Type, uint Code, string? Name);

internal sealed record HistorianLegacyOpen2Output(
    uint Handle,
    Guid StorageSessionId,
    long ConnectTimeFileTimeUtc,
    uint ServerStatus);

internal sealed record HistorianNativeOpen3Output(
    byte ProtocolVersion,
    uint Handle,
    Guid StorageSessionId,
    long ConnectTimeFileTimeUtc,
    long? ServerTimeFileTimeUtc,
    byte[] TrailingBytes);

internal sealed record HistorianClientCommonInfo(
    byte FormatVersion,
    string ServerNodeName,
    string ClientNodeName,
    uint ProcessId,
    ushort HcalVersion,
    string ProcessName,
    string Proxy,
    string DataSourceId,
    Guid ShardId,
    uint ClientVersion,
    ulong ClientTimestamp,
    string ClientDllVersion);