using System.Runtime.InteropServices;
using System.Threading.Channels;

// The public, safe C# surface over libvoicecat. Everything below is a thin wrapper around
// NativeMethods — see docs/architecture.md §4 ("the core owns audio; C# only orchestrates").
namespace VoiceCat.Interop;

public sealed class VoiceCatClient : IDisposable
{
    private readonly VoiceCatClientHandle _handle = new();
    private readonly GCHandle _selfHandle;

    // Native string buffers backing vc_config — must outlive the WHOLE client lifetime, not
    // just vc_client_create(): client_name/client_version are read later, whenever connect()
    // actually runs on io_thread_ (vc_client just stores the raw pointers from vc_config by
    // value, it does not copy the string data). Freed in Dispose(), after vc_client_destroy
    // has returned (which synchronously joins every internal thread, so nothing can still be
    // reading these pointers by then).
    private nint _clientNamePtr;
    private nint _clientVersionPtr;
    private nint _tofuStorePathPtr;

    private readonly Channel<VoiceCatEvent> _events =
        Channel.CreateUnbounded<VoiceCatEvent>(new UnboundedChannelOptions
        {
            SingleReader = true,
            SingleWriter = true,
        });

    // on_level fires far more often than on_event and intermediate values are visually
    // irrelevant — coalesce to "latest sample per stream_id" instead of queuing every one.
    private readonly System.Collections.Concurrent.ConcurrentDictionary<uint, float> _latestLevels = new();

    /// <summary>Raised from PumpEvents() (i.e. on whatever thread calls it — see that method's
    /// doc comment) for every event, in order, never coalesced.</summary>
    public event Action<VoiceCatEvent>? EventReceived;

    /// <summary>Raised from PumpEvents() with the latest RMS level per stream_id since the
    /// last pump.</summary>
    public event Action<uint, float>? LevelChanged;

    public unsafe VoiceCatClient(string clientName, string clientVersion,
        VcLogLevel logLevel = VcLogLevel.Info, string? tofuStorePath = null)
    {
        _selfHandle = GCHandle.Alloc(this, GCHandleType.Normal);

        _clientNamePtr = Marshal.StringToCoTaskMemUTF8(clientName);
        _clientVersionPtr = Marshal.StringToCoTaskMemUTF8(clientVersion);
        _tofuStorePathPtr = tofuStorePath is null ? 0 : Marshal.StringToCoTaskMemUTF8(tofuStorePath);

        var cfg = new VcConfigNative
        {
            ClientName = _clientNamePtr,
            ClientVersion = _clientVersionPtr,
            LogLevel = logLevel,
            TofuStorePath = _tofuStorePathPtr,
        };

        var cb = new VcCallbacksNative
        {
            OnEvent = (nint)(delegate* unmanaged<nint, VcEventNative*, void>)&NativeCallbacks.OnEvent,
            OnLevel = (nint)(delegate* unmanaged<nint, uint, float, void>)&NativeCallbacks.OnLevel,
            User = GCHandle.ToIntPtr(_selfHandle),
        };

        nint native = NativeMethods.vc_client_create(in cfg, cb);
        _handle.SetHandle(native);
        if (_handle.IsInvalid)
        {
            FreeConfigStrings();
            _selfHandle.Free();
            throw new InvalidOperationException("vc_client_create failed.");
        }
    }

    /// <summary>
    /// Drains every event/level sample queued since the last call. Call this from a
    /// System.Windows.Forms.Timer.Tick on the UI thread (~30-50ms) — this is the boundary
    /// where the core's own event-delivery thread hands off to the UI thread; see
    /// docs/architecture.md §3 and this project's README for why a Timer + Channel was chosen
    /// over a message-only window + PostMessage.
    /// </summary>
    public void PumpEvents()
    {
        while (_events.Reader.TryRead(out var ev))
            EventReceived?.Invoke(ev);

        if (!_latestLevels.IsEmpty)
        {
            foreach (var (streamId, rms) in _latestLevels)
                LevelChanged?.Invoke(streamId, rms);
            _latestLevels.Clear();
        }
    }

    internal void EnqueueEvent(VoiceCatEvent ev)
    {
        // Temporary diagnostic (manual debugging session) — confirms the native callback
        // chain (UnmanagedCallersOnly -> GCHandle resolve -> here) actually fires, independent
        // of whether the UI-thread drain (PumpEvents) ever sees it.
        Console.WriteLine($"[VoiceCatClient] EnqueueEvent (native thread): {ev}");
        _events.Writer.TryWrite(ev);
    }
    internal void EnqueueLevel(uint streamId, float rms) => _latestLevels[streamId] = rms;

    // ── Connection & auth ────────────────────────────────────────────────────────────────
    public VcResult Connect(string host, ushort port) =>
        NativeMethods.vc_connect(_handle.DangerousGetHandle(), host, port);

    public VcResult Disconnect() =>
        NativeMethods.vc_disconnect(_handle.DangerousGetHandle());

    public VcResult AuthenticateGuest(string nickname) =>
        NativeMethods.vc_authenticate_guest(_handle.DangerousGetHandle(), nickname);

    public VcResult AuthenticateUser(string username, string password) =>
        NativeMethods.vc_authenticate_user(_handle.DangerousGetHandle(), username, password);

    // ── TOFU server-identity gate (M4) ──────────────────────────────────────────────────────
    public VcResult ConfirmServerIdentity(bool accept) =>
        NativeMethods.vc_confirm_server_identity(_handle.DangerousGetHandle(), accept ? 1 : 0);

    /// <summary>The Ed25519 identity fingerprint from ServerHello, hex-formatted — display
    /// only, NOT the value the TOFU gate pins on (see VcTofuStatus's doc comment). Empty
    /// string if not yet available.</summary>
    public string GetServerIdentityDisplay()
    {
        nint c = _handle.DangerousGetHandle();
        NativeMethods.vc_get_server_identity_display(c, 0, 0, out nuint len);
        if (len == 0) return string.Empty;

        nint buf = Marshal.AllocHGlobal((int)len + 1);
        try
        {
            NativeMethods.vc_get_server_identity_display(c, buf, len + (nuint)1, out _);
            return Marshal.PtrToStringUTF8(buf) ?? string.Empty;
        }
        finally
        {
            Marshal.FreeHGlobal(buf);
        }
    }

    // ── Channels ─────────────────────────────────────────────────────────────────────────
    /// <summary>Result arrives as a VcEventType.JoinResult event, not via this return value
    /// (which only reflects "request queued" — see voicecat.h's vc_join_channel doc comment).
    /// NOTE: no in-tree channel has a server-side password to check yet (M5+ feature) — this
    /// path is wired but not yet exercisable end-to-end.</summary>
    public VcResult JoinChannel(uint channelId, string? password = null) =>
        NativeMethods.vc_join_channel(_handle.DangerousGetHandle(), channelId, password);

    public VcResult LeaveChannel() =>
        NativeMethods.vc_leave_channel(_handle.DangerousGetHandle());

    public List<ChannelInfo> ListChannels()
    {
        NativeMethods.vc_list_channels(_handle.DangerousGetHandle(), out var native);
        return Marshaling.ToManaged(ref native);
    }

    public List<UserInfo> ListUsers()
    {
        NativeMethods.vc_list_users(_handle.DangerousGetHandle(), out var native);
        return Marshaling.ToManaged(ref native);
    }

    public List<StreamSummary> ListUserStreams(uint userId)
    {
        var r = NativeMethods.vc_list_user_streams(_handle.DangerousGetHandle(), userId, out var native);
        return r == VcResult.Ok ? Marshaling.ToManaged(ref native) : new List<StreamSummary>();
    }

    // ── Local media streams ─────────────────────────────────────────────────────────────────
    public (VcResult Result, uint StreamId) StartStream(VcStreamKind kind, string label)
    {
        nint labelPtr = Marshal.StringToCoTaskMemUTF8(label);
        try
        {
            var desc = new VcStreamDescNative { Kind = kind, DeviceId = 0, Label = labelPtr };
            var r = NativeMethods.vc_stream_start(_handle.DangerousGetHandle(), in desc, out uint streamId);
            return (r, streamId);
        }
        finally
        {
            Marshal.FreeCoTaskMem(labelPtr);
        }
    }

    public VcResult StopStream(uint streamId) =>
        NativeMethods.vc_stream_stop(_handle.DangerousGetHandle(), streamId);

    public VcResult SetInputDevice(uint streamId, string? deviceId) =>
        NativeMethods.vc_set_input_device(_handle.DangerousGetHandle(), streamId, deviceId);

    public VcResult SetInputMode(VcInputMode mode) =>
        NativeMethods.vc_set_input_mode(_handle.DangerousGetHandle(), mode);

    public VcResult SetVadThreshold(float threshold) =>
        NativeMethods.vc_set_vad_threshold(_handle.DangerousGetHandle(), threshold);

    public VcResult SetPushToTalk(bool active) =>
        NativeMethods.vc_set_push_to_talk(_handle.DangerousGetHandle(), active ? 1 : 0);

    public VcResult SetSelfMute(bool micMuted, bool deafened) =>
        NativeMethods.vc_set_self_mute(_handle.DangerousGetHandle(), micMuted ? 1 : 0, deafened ? 1 : 0);

    public VcResult SetRemoteStream(uint userId, uint streamId, float gain, bool muted, bool noiseReduction) =>
        NativeMethods.vc_set_remote_stream(_handle.DangerousGetHandle(), userId, streamId, gain,
            muted ? 1 : 0, noiseReduction ? 1 : 0);

    public (VcResult Result, AudioConfigInfo? Config) GetStreamAudioConfig(uint userId, uint streamId)
    {
        var r = NativeMethods.vc_get_stream_audio_config(_handle.DangerousGetHandle(), userId,
            streamId, out var native);
        return (r, r == VcResult.Ok ? Marshaling.ToManaged(in native) : null);
    }

    // ── Text ─────────────────────────────────────────────────────────────────────────────
    public VcResult SendText(VcTextScope scope, uint targetId, string utf8) =>
        NativeMethods.vc_send_text(_handle.DangerousGetHandle(), scope, targetId, utf8);

    // ── Device enumeration (works pre-connect) ──────────────────────────────────────────────
    public List<DeviceInfo> ListDevices(VcDeviceKind kind)
    {
        NativeMethods.vc_list_devices(_handle.DangerousGetHandle(), kind, out var native);
        return Marshaling.ToManaged(ref native);
    }

    // ── Lifecycle ────────────────────────────────────────────────────────────────────────
    // NativeMethods.vc_version_string/vc_result_string return raw pointers to static, never-
    // freed string literals — see NativeMethods.cs's comment for why we don't let LibraryImport
    // auto-marshal these as `string` (it would try to free a static literal and corrupt the
    // heap). Marshal.PtrToStringUTF8 just reads; it never frees.
    public static string VersionString =>
        Marshal.PtrToStringUTF8(NativeMethods.vc_version_string()) ?? string.Empty;

    public static string ResultString(VcResult code) =>
        Marshal.PtrToStringUTF8(NativeMethods.vc_result_string(code)) ?? string.Empty;

    public void Dispose()
    {
        _handle.Dispose(); // runs vc_client_destroy (joins every internal thread) synchronously
        FreeConfigStrings();
        if (_selfHandle.IsAllocated) _selfHandle.Free();
    }

    private void FreeConfigStrings()
    {
        if (_clientNamePtr != 0) { Marshal.FreeCoTaskMem(_clientNamePtr); _clientNamePtr = 0; }
        if (_clientVersionPtr != 0) { Marshal.FreeCoTaskMem(_clientVersionPtr); _clientVersionPtr = 0; }
        if (_tofuStorePathPtr != 0) { Marshal.FreeCoTaskMem(_tofuStorePathPtr); _tofuStorePathPtr = 0; }
    }
}