using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Threading;
using ytLive.Helpers;
using ytLive.Models;
using ytLive.Services.BackgroundEffects;

namespace ytLive.Services;

/// <summary>
/// Owns webcam capture sessions app-wide, refcounted by DeviceId. One device =
/// at most one capture, one shared WriteableBitmap; the last release stops and
/// disposes the source. Frames arrive on a worker thread and are coalesced onto
/// the UI dispatcher (at most one pending copy per session, using the latest
/// frame) so a 60fps device doesn't drown the render thread.
///
/// Allocation is proven, never assumed: <see cref="AcquireAsync"/> treats a
/// started reader as success only once the first frame actually arrives (within
/// <paramref name="firstFrameTimeout"/>), and an async <see cref="SourceFailed"/>
/// tears the session down and surfaces <see cref="CameraFailed"/> — no silent
/// empty box.
///
/// Background effects (TASK 51) are the ONE processing point on the camera path: per device,
/// the set of requested <see cref="WebcamEffectKey"/>s (<see cref="SetRequestedEffects"/>) is
/// rendered from each raw frame on a background worker — one segmentation per frame, smoothed
/// per camera across frames (see <see cref="MaskSmoother"/>) and shared by every variant,
/// latest-frame-drop when the worker is busy — and each variant keeps its own
/// latest frame (the compositor) and shared WriteableBitmap (the preview). The raw path is
/// untouched, so a slow or failing model never stalls the plain webcam.
/// </summary>
public sealed class CameraManager : IDisposable
{
    private sealed class EffectVariant
    {
        public WriteableBitmap? PreviewBitmap;
        public VideoFrame? LatestFrame;
        public bool FramePending;
    }

    private sealed class CameraSession
    {
        public string DeviceId { get; }
        public ICameraFrameSource Source { get; }
        public Action<VideoFrame>? FrameHandler;
        public Action<string>? FailureHandler;
        public int RefCount;
        public bool Started;
        public WriteableBitmap? PreviewBitmap;
        public VideoFrame? LatestFrame;
        public bool FramePending;
        public TaskCompletionSource<bool>? FirstFrame;
        public readonly Dictionary<WebcamEffectKey, EffectVariant> Effects = new();
        public bool EffectWorkerRunning;
        public VideoFrame? LastEffectSource;
        public readonly MaskSmoother Smoother = new();

        public CameraSession(string deviceId, ICameraFrameSource source)
        {
            DeviceId = deviceId;
            Source = source;
            RefCount = 1;
        }
    }

    private readonly ICameraEnumerator _enumerator;
    private readonly Func<string, ICameraFrameSource> _frameSourceFactory;
    private readonly Dispatcher? _uiDispatcher;
    private readonly TimeSpan _firstFrameTimeout;
    private readonly Dictionary<string, CameraSession> _sessions = new();
    private readonly Dictionary<string, HashSet<WebcamEffectKey>> _requestedEffects = new();
    private readonly object _gate = new();
    private readonly BackgroundEffectProcessor? _effects;
    private readonly EffectTimer _effectTimer = new();

    /// <summary>Raised on the UI thread when a camera's shared preview bitmap is first created.</summary>
    public event Action<string, WriteableBitmap>? PreviewBitmapChanged;

    /// <summary>Raised on the UI thread when an effect variant's preview bitmap is first created
    /// (device id, effect key, bitmap) — the effect counterpart of <see cref="PreviewBitmapChanged"/>.</summary>
    public event Action<string, WebcamEffectKey, WriteableBitmap>? EffectPreviewBitmapChanged;

    /// <summary>
    /// Raised when a capture fails: device in use, access denied, no preview source,
    /// or a started reader that never delivers a first frame within the timeout.
    /// </summary>
    public event Action<string, string>? CameraFailed;

    public CameraManager(ICameraEnumerator enumerator, Func<string, ICameraFrameSource> frameSourceFactory,
        Dispatcher? uiDispatcher = null, TimeSpan? firstFrameTimeout = null,
        BackgroundEffectProcessor? effects = null)
    {
        _enumerator = enumerator;
        _frameSourceFactory = frameSourceFactory;
        _uiDispatcher = uiDispatcher;
        _firstFrameTimeout = firstFrameTimeout ?? TimeSpan.FromSeconds(4);
        _effects = effects;
    }

    /// <summary>
    /// Declares which background-effect variants a device must render (the union over every
    /// scene's webcam config). <see cref="BackgroundEffect.None"/> keys are ignored — that's the
    /// raw path. Variants no longer requested are dropped (their worker cost stops); new ones
    /// start rendering from the next camera frame. Survives the session starting later.
    /// </summary>
    public void SetRequestedEffects(string deviceId, IEnumerable<WebcamEffectKey> keys)
    {
        if (string.IsNullOrWhiteSpace(deviceId)) return;
        lock (_gate)
        {
            var set = new HashSet<WebcamEffectKey>();
            foreach (var key in keys)
                if (key.Effect != BackgroundEffect.None) set.Add(key);
            _requestedEffects[deviceId] = set;
            if (_sessions.TryGetValue(deviceId, out var session))
                SyncVariants(session, set);
        }
    }

    /// <summary>The latest frame for a variant: the raw frame for <see cref="BackgroundEffect.None"/>,
    /// otherwise the processed frame — null until the first one is rendered (an un-processed
    /// frame is never shown in its place, so Remove never flashes the real room).</summary>
    public VideoFrame? GetLatestFrame(string deviceId, WebcamEffectKey key)
    {
        if (key.Effect == BackgroundEffect.None) return GetLatestFrame(deviceId);
        lock (_gate)
            return _sessions.TryGetValue(deviceId, out var session)
                && session.Effects.TryGetValue(key, out var variant) ? variant.LatestFrame : null;
    }

    /// <summary>The shared preview bitmap for a variant (raw bitmap for None), or null until
    /// its first frame — then <see cref="EffectPreviewBitmapChanged"/> fires.</summary>
    public WriteableBitmap? GetPreviewBitmap(string deviceId, WebcamEffectKey key)
    {
        if (key.Effect == BackgroundEffect.None) return GetPreviewBitmap(deviceId);
        lock (_gate)
            return _sessions.TryGetValue(deviceId, out var session)
                && session.Effects.TryGetValue(key, out var variant) ? variant.PreviewBitmap : null;
    }

    public ICameraEnumerator Enumerator => _enumerator;

    /// <summary>Increments the refcount for a device, starting capture the first time.</summary>
    public async Task<bool> AcquireAsync(string deviceId)
    {
        if (string.IsNullOrWhiteSpace(deviceId)) return false;

        CameraSession session;
        bool shouldStart;
        lock (_gate)
        {
            if (_sessions.TryGetValue(deviceId, out var existing))
            {
                existing.RefCount++;
                shouldStart = false;
                session = existing;
            }
            else
            {
                session = new CameraSession(deviceId, _frameSourceFactory(deviceId));
                session.FrameHandler = frame => OnFrameAvailable(session, frame);
                session.Source.FrameAvailable += session.FrameHandler;
                session.FailureHandler = message => OnSourceFailed(session, message);
                session.Source.SourceFailed += session.FailureHandler;
                if (_requestedEffects.TryGetValue(deviceId, out var requested))
                    SyncVariants(session, requested);
                _sessions[deviceId] = session;
                shouldStart = true;
            }
        }

        if (!shouldStart) return session.Started;

        session.FirstFrame = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
        try
        {
            await session.Source.StartAsync();

            // First-frame proof: "the reader started" is not "the stream is live".
            // Success requires an actual frame within the timeout, else the session
            // is rolled back and reported — never left as a silent empty preview.
            var proven = _firstFrameTimeout <= TimeSpan.Zero
                || await WaitForFirstFrameAsync(session, _firstFrameTimeout);
            if (!proven)
            {
                var reason = $"Camera '{deviceId}' started but produced no frames within {_firstFrameTimeout.TotalSeconds:0.#}s.";
                RollbackSession(session, reason);
                return false;
            }

            // Keep the SourceFailed handler subscribed: an async failure after a
            // successful start (device lost, stream state Failed) must still surface.
            session.FirstFrame = null;
            session.Started = true;
            return true;
        }
        catch (Exception ex)
        {
            RollbackSession(session, ex.Message);
            return false;
        }
    }

    /// <summary>Decrements the refcount; stops and disposes the source at zero.</summary>
    public async Task ReleaseAsync(string deviceId)
    {
        CameraSession? toStop = null;
        lock (_gate)
        {
            if (!_sessions.TryGetValue(deviceId, out var session)) return;
            if (--session.RefCount > 0) return;
            _sessions.Remove(deviceId);
            toStop = session;
        }

        if (toStop == null) return;
        toStop.Source.FrameAvailable -= toStop.FrameHandler;
        await SafeStopAsync(toStop.Source);
        toStop.PreviewBitmap = null;
    }

    /// <summary>
    /// Releases a device unconditionally (every ref), regardless of how many scenes
    /// hold it. Used on identity changes (webcam swap, layout reload) where the old
    /// device's refcount isn't known after the scenes are replaced.
    /// </summary>
    public async Task ReleaseAllAsync(string deviceId)
    {
        CameraSession? toStop = null;
        lock (_gate)
        {
            if (!_sessions.TryGetValue(deviceId, out var session)) return;
            session.RefCount = 0;
            _sessions.Remove(deviceId);
            toStop = session;
        }

        if (toStop == null) return;
        toStop.Source.FrameAvailable -= toStop.FrameHandler;
        await SafeStopAsync(toStop.Source);
        toStop.PreviewBitmap = null;
    }

    /// <summary>
    /// True while a session exists for the device — started, or still starting.
    /// Used by the app's startup resource check to avoid double-acquiring a lock
    /// that the saved identity's scene configs already hold. A rolled-back (failed)
    /// session is removed, so this goes false and the startup pass can retry.
    /// </summary>
    public bool IsRunning(string deviceId)
    {
        lock (_gate)
            return _sessions.ContainsKey(deviceId);
    }

    public VideoFrame? GetLatestFrame(string deviceId)
    {
        lock (_gate)
            return _sessions.TryGetValue(deviceId, out var session) ? session.LatestFrame : null;
    }

    /// <summary>
    /// The shared WriteableBitmap for a running session, or null when the camera
    /// hasn't produced its first frame yet. <see cref="PreviewBitmapChanged"/> only
    /// fires once (first frame), so configs created after the session started must
    /// pick the bitmap up from here.
    /// </summary>
    public WriteableBitmap? GetPreviewBitmap(string deviceId)
    {
        lock (_gate)
            return _sessions.TryGetValue(deviceId, out var session) ? session.PreviewBitmap : null;
    }

    public void Dispose()
    {
        List<CameraSession> sessions;
        lock (_gate)
        {
            sessions = new List<CameraSession>(_sessions.Values);
            _sessions.Clear();
        }

        foreach (var session in sessions)
        {
            session.Source.FrameAvailable -= session.FrameHandler;
            if (session.FailureHandler != null)
                session.Source.SourceFailed -= session.FailureHandler;
            _ = SafeStopAsync(session.Source);
        }
    }

    private static async Task<bool> WaitForFirstFrameAsync(CameraSession session, TimeSpan timeout)
    {
        var first = session.FirstFrame;
        if (first == null) return true;
        var completed = await Task.WhenAny(first.Task, Task.Delay(timeout));
        return ReferenceEquals(completed, first.Task) && first.Task.Result;
    }

    private void RollbackSession(CameraSession session, string message)
    {
        lock (_gate)
        {
            if (TryGetActiveSession(session))
                _sessions.Remove(session.DeviceId);
        }
        session.Source.FrameAvailable -= session.FrameHandler;
        if (session.FailureHandler != null)
            session.Source.SourceFailed -= session.FailureHandler;
        session.FirstFrame?.TrySetResult(false);

        var enriched = message;
        var suspects = CameraConflictProbe.GetRunningCameraApps();
        if (suspects.Count > 0)
            enriched += $" Other camera apps running: {string.Join(", ", suspects)}.";

        AppLog.Write($"CameraManager: camera '{session.DeviceId}' failed: {enriched}",
            AppLogMessageType.Error, AppLogErrorClass.Class2);
        CameraFailed?.Invoke(session.DeviceId, enriched);
        _ = SafeStopAsync(session.Source);
    }

    private void OnSourceFailed(CameraSession session, string message)
    {
        RollbackSession(session, message);
    }

    private static async Task SafeStopAsync(ICameraFrameSource source)
    {
        try
        {
            await source.StopAsync();
        }
        catch (Exception ex)
        {
            AppLog.Write($"CameraManager: stopping camera failed: {ex.Message}",
                AppLogMessageType.Error, AppLogErrorClass.Class2);
        }
    }

    private bool TryGetActiveSession(CameraSession session)
    {
        lock (_gate)
            return _sessions.TryGetValue(session.DeviceId, out var current) && ReferenceEquals(current, session);
    }

    private void OnFrameAvailable(CameraSession session, VideoFrame frame)
    {
        if (!TryGetActiveSession(session)) return;
        session.LatestFrame = frame;
        session.FirstFrame?.TrySetResult(true);
        ScheduleEffects(session);

        if (session.PreviewBitmap == null)
        {
            if (_uiDispatcher == null) return;
            if (_uiDispatcher.CheckAccess())
                EnsurePreviewBitmap(session);
            else
                _uiDispatcher.BeginInvoke(() =>
                {
                    if (TryGetActiveSession(session))
                        EnsurePreviewBitmap(session);
                }, DispatcherPriority.Render);
            return;
        }

        if (_uiDispatcher == null || _uiDispatcher.CheckAccess())
        {
            CopyFrame(session);
            return;
        }

        if (session.FramePending) return;
        session.FramePending = true;
        _uiDispatcher.BeginInvoke(() =>
        {
            session.FramePending = false;
            if (TryGetActiveSession(session) && session.PreviewBitmap != null)
                CopyFrame(session);
        }, DispatcherPriority.Render);
    }

    // Caller holds _gate. A new key inherits the last frame + bitmap of a dropped variant with
    // the SAME effect (a strength change), so neither the stream nor the preview blanks for a
    // frame while the creator drags the strength slider.
    private static void SyncVariants(CameraSession session, HashSet<WebcamEffectKey> keys)
    {
        var dropped = session.Effects.Where(kv => !keys.Contains(kv.Key)).ToList();
        foreach (var (stale, _) in dropped)
            session.Effects.Remove(stale);
        foreach (var key in keys)
        {
            if (session.Effects.ContainsKey(key)) continue;
            var heir = dropped.FirstOrDefault(kv => kv.Key.Effect == key.Effect).Value;
            session.Effects[key] = new EffectVariant
            {
                LatestFrame = heir?.LatestFrame,
                PreviewBitmap = heir?.PreviewBitmap,
            };
        }
    }

    private void ScheduleEffects(CameraSession session)
    {
        if (_effects == null) return;
        lock (_gate)
        {
            if (session.Effects.Count == 0 || session.EffectWorkerRunning) return;
            session.EffectWorkerRunning = true;
        }
        _ = Task.Run(() => RunEffectWorker(session));
    }

    /// <summary>Renders every requested variant from the newest raw frame, then loops while a
    /// newer frame has arrived; exits (and re-arms on the next frame) when caught up. One
    /// segmentation per processed frame, whatever the number of variants.</summary>
    private void RunEffectWorker(CameraSession session)
    {
        try
        {
            while (true)
            {
                VideoFrame? source;
                List<WebcamEffectKey> keys;
                lock (_gate)
                {
                    source = session.LatestFrame;
                    if (!TryGetActiveSessionLocked(session) || session.Effects.Count == 0
                        || source == null || ReferenceEquals(source, session.LastEffectSource))
                    {
                        session.EffectWorkerRunning = false;
                        return;
                    }
                    session.LastEffectSource = source;
                    keys = session.Effects.Keys.ToList();
                }

                var started = System.Diagnostics.Stopwatch.GetTimestamp();
                var mask = session.Smoother.Smooth(_effects!.TrySegment(source));
                var rendered = new List<(WebcamEffectKey Key, VideoFrame Frame)>(keys.Count);
                if (mask != null)
                    foreach (var key in keys)
                        rendered.Add((key, BackgroundEffectProcessor.Render(source, mask, key.Effect, key.Strength)));
                _effectTimer.Record(System.Diagnostics.Stopwatch.GetElapsedTime(started), source, keys.Count);

                foreach (var (key, frame) in rendered)
                {
                    EffectVariant? variant;
                    lock (_gate)
                    {
                        if (session.Effects.TryGetValue(key, out variant))
                            variant.LatestFrame = frame;
                    }
                    if (variant != null) PublishVariantPreview(session, key, variant);
                }
            }
        }
        catch (Exception ex)
        {
            lock (_gate) session.EffectWorkerRunning = false;
            AppLog.Write($"CameraManager: background effects worker failed: {ex.GetType().Name}: {ex.Message}",
                AppLogMessageType.Error, AppLogErrorClass.Class2);
        }
    }

    private void PublishVariantPreview(CameraSession session, WebcamEffectKey key, EffectVariant variant)
    {
        if (_uiDispatcher == null) return;
        lock (_gate)
        {
            if (variant.FramePending) return;
            variant.FramePending = true;
        }
        _uiDispatcher.BeginInvoke(() =>
        {
            VideoFrame? frame;
            lock (_gate)
            {
                variant.FramePending = false;
                if (!TryGetActiveSessionLocked(session) || !session.Effects.TryGetValue(key, out var current)
                    || !ReferenceEquals(current, variant)) return;
                frame = variant.LatestFrame;
            }
            if (frame == null) return;
            var bitmap = variant.PreviewBitmap;
            if (bitmap == null || bitmap.PixelWidth != frame.Width || bitmap.PixelHeight != frame.Height)
            {
                bitmap = new WriteableBitmap(frame.Width, frame.Height, 96, 96, PixelFormats.Bgra32, null);
                bitmap.WritePixels(new Int32Rect(0, 0, frame.Width, frame.Height), frame.BgraPixels, frame.Stride, 0);
                variant.PreviewBitmap = bitmap;
                EffectPreviewBitmapChanged?.Invoke(session.DeviceId, key, bitmap);
                return;
            }
            bitmap.WritePixels(new Int32Rect(0, 0, frame.Width, frame.Height), frame.BgraPixels, frame.Stride, 0);
        }, DispatcherPriority.Render);
    }

    private bool TryGetActiveSessionLocked(CameraSession session)
        => _sessions.TryGetValue(session.DeviceId, out var current) && ReferenceEquals(current, session);

    /// <summary>Perf record for the creator's-box check (TASK 51): logs the average
    /// segment + render cost once per session after 120 processed frames.</summary>
    private sealed class EffectTimer
    {
        private int _count;
        private double _totalMs;
        private bool _logged;

        public void Record(TimeSpan elapsed, VideoFrame frame, int variants)
        {
            if (_logged) return;
            _totalMs += elapsed.TotalMilliseconds;
            if (++_count < 120) return;
            _logged = true;
            AppLog.Write($"CameraManager: background effects avg {_totalMs / _count:0.0} ms/frame " +
                         $"({frame.Width}x{frame.Height}, {variants} variant(s), {_count} frames)");
        }
    }

    private void EnsurePreviewBitmap(CameraSession session)
    {
        if (session.PreviewBitmap != null || session.LatestFrame == null) return;
        var frame = session.LatestFrame;
        var bitmap = new WriteableBitmap(frame.Width, frame.Height, 96, 96, PixelFormats.Bgra32, null);
        bitmap.WritePixels(new Int32Rect(0, 0, frame.Width, frame.Height), frame.BgraPixels, frame.Stride, 0);
        session.PreviewBitmap = bitmap;
        PreviewBitmapChanged?.Invoke(session.DeviceId, bitmap);
    }

    private void CopyFrame(CameraSession session)
    {
        var bitmap = session.PreviewBitmap;
        var frame = session.LatestFrame;
        if (bitmap == null || frame == null) return;
        if (frame.Width != bitmap.PixelWidth || frame.Height != bitmap.PixelHeight) return;
        bitmap.WritePixels(new Int32Rect(0, 0, frame.Width, frame.Height), frame.BgraPixels, frame.Stride, 0);
    }
}