using System;
using System.Globalization;
using System.Windows;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Threading;

namespace ytLive.Services.Compositor;

/// <summary>
/// The free-tier branding flash: a "made with LlamaCasty!" credit that is COMPOSITED
/// INTO THE OUTPUT (recording or stream), not merely shown in the preview.
/// <para>2026-09-26. This used to exist only as a WPF <c>BrandFlashLayer</c> in
/// <c>PreviewPane.xaml</c> — a 0.25-opacity centred TextBlock the creator could see and
/// no viewer ever could. The compositor has carried an unused <c>flashFrame</c> slot
/// since then; this type is the producer that finally feeds it. It is wired on the
/// PER-FRAME path only: <c>SceneGraph.GetBakedBase</c> also accepts a <c>flashFrame</c>,
/// and that one is a trap — <c>SceneRegion.Matches</c> compares element ids only, so a
/// flash folded into the baked static base would freeze there and never expire.</para>
/// <para>The credit is deliberately obnoxious (creator directive 2026-09-26): full-opacity
/// neon, a different random position every presentation, and a hard sell every 30–60s.
/// It is gated on LICENCE state, never on a UI toggle — see <see cref="Enabled"/>.</para>
/// </summary>
public sealed class BrandFlashPresenter : IDisposable
{
    /// <summary>The credit line, kept identical to the old preview TextBlock so the
    /// wording can never drift between the preview and the broadcast.</summary>
    public const string Text = "made with LlamaCasty!";

    // Presentation envelope (creator-specified 2026-09-26): 500ms fade in, the credit
    // held at full opacity for 1000ms, then a 500ms fade out — 2000ms end to end.
    public const double FadeInSeconds = 0.5;
    public const double HoldSeconds = 1.0;
    public const double FadeOutSeconds = 0.5;
    public const double PresentationSeconds = FadeInSeconds + HoldSeconds + FadeOutSeconds;

    /// <summary>Cadence: <c>rand(0, 30s) + 30s</c> ⇒ a flash every 30–60s, so it never
    /// lands on a beat a viewer could tune out.</summary>
    public const int IntervalFloorMs = 30_000;
    public const int IntervalJitterMs = 30_000;

    /// <summary>The first flash lands shortly after go-live (the stream-start
    /// impression); the random cadence takes over from there.</summary>
    public const double FirstFlashDelaySeconds = 5.0;

    /// <summary>Master-space canvas. Global overlays in this codebase are authored at
    /// master size and scaled by the compositor.</summary>
    public const int MasterWidth = 1920;
    public const int MasterHeight = 1080;

    /// <summary>Neon recipe taken from the established overlay look (see commit
    /// message): a bright near-white CORE plus a feathered multi-radius HALO, with the
    /// red and blue channels pushed in OPPOSITE directions — Maxon's "Chromatic Glow"
    /// notes the green channel is all but invisible behind white text once R and B are
    /// split, which is exactly the look.</summary>
    private static readonly Color NeonRed = Color.FromRgb(0xe9, 0x45, 0x60);  // brand red, exact
    private static readonly Color NeonBlue = Color.FromRgb(0x4d, 0x8b, 0xff); // brand blue #0f3460 lifted for luminance
    private static readonly Color CoreColor = Colors.White;

    /// <summary>Font size chosen so the credit spans roughly half the master width:
    /// big enough to read as advertising, small enough that the random placement has
    /// real travel room (a full-width line could only ever sit at x≈0).</summary>
    private const double FontSize = 120;
    private const double GlowPadding = 34;
    private const double TickSeconds = 0.033;

    private readonly Random _random;
    private readonly DispatcherTimer? _timer;
    private readonly object _gate = new();

    private bool _enabled = true;
    private bool _running;
    private double _sinceStart;
    private double _nextFlashAt;      // absolute time of the next flash, _sinceStart's reference
    private double _elapsed;            // seconds into the presentation; >= PresentationSeconds means idle
    private VideoFrame? _raster;        // tight, full-opacity glowing credit (straight alpha)
    private byte[]? _buffer;            // reused master-space BGRA — hence the Epoch bump below
    private int _atX, _atY;
    private long _epoch;

    public BrandFlashPresenter(Random? random = null)
    {
        _random = random ?? new Random();
        if (Application.Current is { } app)
        {
            _timer = new DispatcherTimer { Interval = TimeSpan.FromSeconds(TickSeconds) };
            _timer.Tick += (_, _) => Advance(TickSeconds);
        }
    }

    /// <summary>The licence gate, driven by <c>MainViewModel.IsPremium</c> (Polar
    /// validation) and NOT by a user-facing toggle: once this credit is composited into
    /// the broadcast it is the thing standing between a paying customer's stream and an
    /// advertisement, so it is re-checked on every read. A premium user mid-presentation
    /// loses the flash on the very next tick rather than at the end of the credit.</summary>
    public bool Enabled
    {
        get { lock (_gate) return _enabled; }
        set
        {
            lock (_gate)
            {
                if (_enabled == value) return;
                _enabled = value;
                if (!value)
                {
                    // Licence state only ever goes premium → no flash. Cut the current
                    // presentation short instead of running it out ungated.
                    _elapsed = PresentationSeconds;
                    _timer?.Stop();
                }
            }
        }
    }

    /// <summary>True while a credit is on screen (drives the preview's visibility).</summary>
    public bool IsPresenting
    {
        get { lock (_gate) return _enabled && _elapsed < PresentationSeconds; }
    }

    /// <summary>Begin the cadence: first flash <see cref="FirstFlashDelaySeconds"/>
    /// after the call, then every <c>rand(30s) + 30s</c>.</summary>
    public void Start()
    {
        EnsureRaster();
        lock (_gate)
        {
            _running = true;
            _sinceStart = 0;
            _nextFlashAt = FirstFlashDelaySeconds;
        }
        if (_enabled) _timer?.Start();
    }

    public void Stop()
    {
        lock (_gate)
        {
            _running = false;
            _elapsed = PresentationSeconds;
        }
        _timer?.Stop();
    }

    /// <summary>Advance the presentation clock. Also the deterministic test seam: tests
    /// drive this directly and never call <see cref="Start"/>, so no timer is running
    /// and the clock only moves when the test moves it (mirrors <c>AlertOverlayLayer.Advance</c>).</summary>
    public void Advance(double deltaSeconds)
    {
        // Rasterise BEFORE taking the lock. WPF text formatting is UI-thread affine, so
        // this can hop to the dispatcher — and a blocking hop while holding _gate would
        // deadlock against a timer tick that wants the same lock.
        EnsureRaster();

        lock (_gate)
        {
            if (!_enabled) return;

            if (_running)
            {
                _sinceStart += deltaSeconds;
                if (_sinceStart >= _nextFlashAt)
                {
                    // The interval runs FROM THIS FLASH, not from Start(). An absolute
                    // deadline here made the gaps shrink every cycle (5s, then whatever
                    // was left of the previous interval) and collapse toward zero.
                    _nextFlashAt = _sinceStart + NextIntervalSeconds();
                    BeginPresentation();
                }
            }

            if (_elapsed < PresentationSeconds)
            {
                _elapsed += deltaSeconds;
                if (_elapsed >= PresentationSeconds) _elapsed = PresentationSeconds;
            }
        }

        Notify();
    }

    /// <summary>Invoked on the UI thread at the end of every tick with the frame that
    /// tick produced (null when nothing is due) — the preview's repaint hook, so the
    /// preview and the broadcast are driven by ONE clock.</summary>
    public Action<VideoFrame?>? OnFrame { get; set; }

    private void Notify()
    {
        var cb = OnFrame;
        if (cb == null) return;
        // Read OUTSIDE the state lock: the callback is arbitrary code and must never
        // run while _gate is held.
        var frame = Frame;
        if (frame == null) { cb(null); return; }

        if (Application.Current is { } app && !app.Dispatcher.CheckAccess())
        {
            // Off the UI thread (a test driving the clock). The frame's buffer is
            // recycled, so hand the deferred copy its own pixels.
            var copy = new byte[frame.BgraPixels.Length];
            Buffer.BlockCopy(frame.BgraPixels, 0, copy, 0, copy.Length);
            app.Dispatcher.BeginInvoke(() => cb(new VideoFrame(frame.Width, frame.Height, copy)));
        }
        else
        {
            cb(frame);
        }
    }

    /// <summary>Force a presentation now — the "show me the flash" path and the test seam.</summary>
    public void Show()
    {
        EnsureRaster();
        lock (_gate)
        {
            if (!_enabled) return;
            BeginPresentation();
        }
    }

    private double NextIntervalSeconds()
        => (IntervalFloorMs + _random.Next(IntervalJitterMs)) / 1000.0;

    private void BeginPresentation()
    {
        if (_raster == null) return;
        _buffer ??= new byte[MasterWidth * MasterHeight * 4];
        // A new presentation can land anywhere, so the previous credit's pixels must go
        // before this one is written or the old spot ghosts through the fade. One 8MB
        // clear per presentation (not per tick) keeps that cheap.
        Array.Clear(_buffer);
        var spot = ComputePlacement(_raster.Width, _raster.Height, MasterWidth, MasterHeight, _random);
        _atX = (int)spot.X;
        _atY = (int)spot.Y;
        _elapsed = 0;
    }

    /// <summary>
    /// The credit for the output compositor and the preview: a master-space frame holding
    /// the glowing text at this presentation's random spot, alpha-scaled to the current
    /// point on the fade envelope. Null when idle, or unlicensed.
    /// <para><b>The frame's pixel buffer is recycled across ticks</b> (only the text rect
    /// is rewritten) and its <see cref="VideoFrame.Epoch"/> is bumped every read, so the
    /// compositor's buffer-identity paste cache can never false-hit a stale credit.
    /// Consumers blit synchronously — copy the pixels if you need to keep them.</para></summary>
    public VideoFrame? Frame
    {
        get
        {
            lock (_gate)
            {
                if (!_enabled || _elapsed >= PresentationSeconds || _raster == null || _buffer == null)
                    return null;
                var opacity = OpacityAt(_elapsed);
                if (opacity <= 0) return null;
                Paint(_buffer, _raster, _atX, _atY, opacity);
                return new VideoFrame(MasterWidth, MasterHeight, _buffer) { Epoch = ++_epoch };
            }
        }
    }

    /// <summary>Full → hold → empty. Public and static so the preview and the tests
    /// agree with the renderer instead of re-deriving the curve.</summary>
    public static double OpacityAt(double elapsedSeconds)
    {
        if (elapsedSeconds < 0 || elapsedSeconds >= PresentationSeconds) return 0;
        if (elapsedSeconds < FadeInSeconds) return elapsedSeconds / FadeInSeconds;
        if (elapsedSeconds < FadeInSeconds + HoldSeconds) return 1.0;
        return 1.0 - ((elapsedSeconds - (FadeInSeconds + HoldSeconds)) / FadeOutSeconds);
    }

    /// <summary>
    /// A random top-left offset that keeps the whole credit ON the canvas. The text is a
    /// single pre-measured line, so it can never wrap — this is the "how far can the
    /// left margin travel" limit the creator described: <c>0 … (canvas - creditWidth)</c>
    /// horizontally, likewise vertically. Pure + static, so the rule is directly testable.
    /// </summary>
    public static Point ComputePlacement(int creditWidth, int creditHeight,
        int canvasWidth, int canvasHeight, Random random)
    {
        var maxX = Math.Max(0, canvasWidth - creditWidth);
        var maxY = Math.Max(0, canvasHeight - creditHeight);
        return new Point(random.Next(0, maxX + 1), random.Next(0, maxY + 1));
    }

    /// <summary>Rewrite the credit rect into the master buffer with alpha scaled to
    /// <paramref name="opacity"/>. The rect is fully overwritten each tick and the spot
    /// is fixed for the whole presentation, so nothing stale accumulates and no clear
    /// pass is needed here.</summary>
    private static void Paint(byte[] buffer, VideoFrame raster, int atX, int atY, double opacity)
    {
        for (var y = 0; y < raster.Height; y++)
        {
            var dst = ((atY + y) * MasterWidth + atX) * 4;
            var src = y * raster.Stride;
            for (var x = 0; x < raster.Width; x++)
            {
                var a = raster.BgraPixels[src + x * 4 + 3];
                if (a == 0) continue;
                buffer[dst + x * 4] = raster.BgraPixels[src + x * 4];
                buffer[dst + x * 4 + 1] = raster.BgraPixels[src + x * 4 + 1];
                buffer[dst + x * 4 + 2] = raster.BgraPixels[src + x * 4 + 2];
                buffer[dst + x * 4 + 3] = (byte)Math.Round(a * opacity);
            }
        }
    }

    /// <summary>Build the credit raster once, on the UI thread, and publish it under
    /// the lock. Called from every clock entry point, so it is a no-op after the first.</summary>
    private void EnsureRaster()
    {
        lock (_gate) { if (_raster != null) return; }
        var raster = RenderNeonText(Text);
        lock (_gate) { if (raster != null) { _raster = raster; } }
    }

    // ── rasterisation ──────────────────────────────────────────────────────────

    /// <summary>
    /// Rasterize the credit once, tight to the glyphs plus glow, on the UI thread (WPF
    /// <c>RenderTargetBitmap</c>, Pbgra32→straight alpha exactly like
    /// <see cref="AlertTickerRenderer"/>) and cached — this is per-text work, not
    /// per-frame, so the pump can afford to run every tick at 30fps.
    /// <para>The neon is a bright core plus a feathered halo: the glyphs redrawn at
    /// shrinking radii with rising alpha, the two colours offset in opposite directions,
    /// which is what makes it read as a lit tube rather than a drop shadow.</para></summary>
    private static VideoFrame? RenderNeonText(string text)
    {
        if (Application.Current is { } app && !app.Dispatcher.CheckAccess())
        {
            VideoFrame? result = null;
            app.Dispatcher.Invoke(() => result = RenderNeonText(text));
            return result;
        }

        var font = new Typeface(new FontFamily("Segoe UI"), FontStyles.Normal,
            FontWeights.Bold, FontStretches.Normal);
        var probe = new FormattedText(text, CultureInfo.InvariantCulture,
            FlowDirection.LeftToRight, font, FontSize, Brushes.White, 1.0);

        var w = (int)Math.Ceiling(probe.Width) + (int)(GlowPadding * 2);
        var h = (int)Math.Ceiling(probe.Height) + (int)(GlowPadding * 2);
        if (w <= 0 || h <= 0) return null;

        var visual = new DrawingVisual();
        using (var dc = visual.RenderOpen())
        {
            // Three halo rings per colour. Wide+dim first, then progressively tighter and
            // brighter, so the falloff is feathered instead of a hard-edged blob.
            foreach (var (radius, alpha) in new[] { (30.0, 0.16), (20.0, 0.26), (11.0, 0.40) })
            {
                DrawHalo(dc, text, font, radius, alpha, NeonRed, +1);
                DrawHalo(dc, text, font, radius, alpha, NeonBlue, -1);
            }
            // A tight white bloom hugging the glyphs sells the brightness of the tube.
            DrawHalo(dc, text, font, 4.0, 0.55, CoreColor, +1);
            // The core itself, sharp and opaque, drawn last.
            dc.DrawText(new FormattedText(text, CultureInfo.InvariantCulture,
                FlowDirection.LeftToRight, font, FontSize, new SolidColorBrush(CoreColor), 1.0),
                new Point(GlowPadding, GlowPadding));
        }

        var bitmap = new RenderTargetBitmap(w, h, 96, 96, PixelFormats.Pbgra32);
        bitmap.Render(visual);

        var pixels = new byte[w * h * 4];
        bitmap.CopyPixels(pixels, w * 4, 0);

        // Pbgra32 is premultiplied — unpremultiply, or straight-alpha source-over in the
        // compositor haloes the glyph edges.
        for (var i = 0; i < pixels.Length; i += 4)
        {
            var a = pixels[i + 3];
            if (a == 0 || a == 255) continue;
            pixels[i] = (byte)(pixels[i] * 255 / a);
            pixels[i + 1] = (byte)(pixels[i + 1] * 255 / a);
            pixels[i + 2] = (byte)(pixels[i + 2] * 255 / a);
        }
        return new VideoFrame(w, h, pixels);
    }

    private static void DrawHalo(DrawingContext dc, string text, Typeface font,
        double radius, double alpha, Color color, int direction)
    {
        var brush = new SolidColorBrush(color);
        const int spokes = 12;
        for (var i = 0; i < spokes; i++)
        {
            var angle = 2 * Math.PI * i / spokes;
            brush.Opacity = alpha;
            var ft = new FormattedText(text, CultureInfo.InvariantCulture,
                FlowDirection.LeftToRight, font, FontSize, brush, 1.0);
            dc.DrawText(ft, new Point(
                GlowPadding + Math.Cos(angle) * radius * direction,
                GlowPadding + Math.Sin(angle) * radius * direction));
        }
    }

    public void Dispose() => _timer?.Stop();
}