using ytLive.Helpers;
using ytLive.Models;

namespace ytLive.Services.BackgroundEffects;

/// <summary>
/// Applies a webcam's <see cref="BackgroundEffect"/> to one captured frame (TASK 51).
/// Pure pixel work over the <see cref="VideoFrame"/> seam — WPF-free and thread-agnostic,
/// so the camera's processing worker can call it before the frame reaches the preview bitmap
/// and the compositor.
///
/// <list type="bullet">
/// <item><see cref="BackgroundEffect.None"/> returns the SAME frame instance — a true
/// passthrough, no copy.</item>
/// <item><see cref="BackgroundEffect.Remove"/> returns a copy whose alpha is the person mask,
/// RGB untouched, <c>IsOpaque = false</c> — the compositor's straight-alpha blend then shows
/// the layers below the webcam. Strength = edge softness (0 = crisp cut-out, 1 = the model's
/// raw soft mask).</item>
/// <item><see cref="BackgroundEffect.Blur"/> returns a copy where the background is replaced
/// by a blurred version of itself and the person stays sharp. Strength = blur amount.</item>
/// </list>
///
/// The mask is computed ONCE per camera frame (<see cref="TrySegment"/>) and then rendered for
/// every effect variant in use (<see cref="Render"/>). A segmenter that returns no mask (or
/// throws) never drops the layer: the frame passes through and the failure is logged once.
/// </summary>
public sealed class BackgroundEffectProcessor
{
    public const double DefaultStrength = 0.5;

    /// <summary>The background is blurred at 1/<see cref="BlurDownscale"/> resolution and
    /// upsampled while blending — a strong blur at a fraction of the cost.</summary>
    internal const int BlurDownscale = 4;

    /// <summary>Box-blur radius (in downscaled pixels) at strength 0 and 1.</summary>
    internal const int MinBlurRadius = 1;
    internal const int MaxBlurRadius = 12;

    private readonly IPersonSegmenter _segmenter;
    private bool _loggedFailure;

    public BackgroundEffectProcessor(IPersonSegmenter segmenter)
    {
        _segmenter = segmenter;
    }

    public VideoFrame Apply(VideoFrame frame, BackgroundEffect effect, double strength = DefaultStrength)
    {
        if (effect == BackgroundEffect.None) return frame;
        var mask = TrySegment(frame);
        return mask == null ? frame : Render(frame, mask, effect, strength);
    }

    /// <summary>Runs the segmenter once; null (logged once) when it can't produce a usable mask.</summary>
    public SegmentationMask? TrySegment(VideoFrame frame)
    {
        SegmentationMask? mask;
        try
        {
            mask = _segmenter.Segment(frame);
        }
        catch (Exception ex)
        {
            LogFailureOnce($"{ex.GetType().Name}: {ex.Message}");
            return null;
        }

        if (mask == null || mask.Width < 1 || mask.Height < 1 || mask.Values.Length < mask.Width * mask.Height)
        {
            LogFailureOnce("segmenter returned no usable mask");
            return null;
        }
        return mask;
    }

    public static VideoFrame Render(VideoFrame frame, SegmentationMask mask, BackgroundEffect effect, double strength)
    {
        var s = Math.Clamp(strength, 0, 1);
        return effect switch
        {
            BackgroundEffect.Remove => ApplyRemove(frame, mask, s),
            BackgroundEffect.Blur => ApplyBlur(frame, mask, s),
            _ => frame,
        };
    }

    internal static VideoFrame ApplyRemove(VideoFrame frame, SegmentationMask mask, double strength)
    {
        var src = frame.BgraPixels;
        var dst = new byte[src.Length];
        Buffer.BlockCopy(src, 0, dst, 0, src.Length);

        // Edge feather: map the mask's [0.5 - w, 0.5 + w] band to alpha 0..1.
        var w = (float)(0.05 + 0.45 * strength);
        var lo = 0.5f - w;
        var span = 2 * w;

        var width = frame.Width;
        var height = frame.Height;
        var stride = frame.Stride;
        for (var y = 0; y < height; y++)
        {
            var my = MaskCoord(y, height, mask.Height);
            var row = y * stride;
            for (var x = 0; x < width; x++)
            {
                var m = SampleBilinear(mask, MaskCoord(x, width, mask.Width), my);
                var a = Math.Clamp((m - lo) / span, 0f, 1f);
                var p = row + x * 4 + 3;
                dst[p] = (byte)(a * src[p] + 0.5f);
            }
        }

        return new VideoFrame(width, height, dst) { Epoch = frame.Epoch, IsOpaque = false };
    }

    internal static VideoFrame ApplyBlur(VideoFrame frame, SegmentationMask mask, double strength)
    {
        var width = frame.Width;
        var height = frame.Height;
        var src = frame.BgraPixels;
        var stride = frame.Stride;

        // 1. Downscale by box-averaging BlurDownscale×BlurDownscale blocks (3 float channels).
        var f = BlurDownscale;
        var sw = (width + f - 1) / f;
        var sh = (height + f - 1) / f;
        var small = new float[sw * sh * 3];
        for (var sy = 0; sy < sh; sy++)
        {
            var y0 = sy * f;
            var y1 = Math.Min(height, y0 + f);
            for (var sx = 0; sx < sw; sx++)
            {
                var x0 = sx * f;
                var x1 = Math.Min(width, x0 + f);
                float b = 0, g = 0, r = 0;
                var n = 0;
                for (var y = y0; y < y1; y++)
                {
                    var p = y * stride + x0 * 4;
                    for (var x = x0; x < x1; x++, p += 4)
                    {
                        b += src[p]; g += src[p + 1]; r += src[p + 2];
                        n++;
                    }
                }
                var o = (sy * sw + sx) * 3;
                small[o] = b / n; small[o + 1] = g / n; small[o + 2] = r / n;
            }
        }

        // 2. Three separable box-blur passes ≈ a gaussian.
        var radius = (int)Math.Round(MinBlurRadius + (MaxBlurRadius - MinBlurRadius) * strength);
        var scratch = new float[small.Length];
        for (var pass = 0; pass < 3; pass++)
        {
            BoxBlurHorizontal(small, scratch, sw, sh, radius);
            BoxBlurVertical(scratch, small, sw, sh, radius);
        }

        // 3. Blend: person (mask) keeps the source pixel, background takes the upsampled blur.
        var dst = new byte[src.Length];
        for (var y = 0; y < height; y++)
        {
            var my = MaskCoord(y, height, mask.Height);
            var by = (y + 0.5f) / f - 0.5f;
            var row = y * stride;
            for (var x = 0; x < width; x++)
            {
                var m = SampleBilinear(mask, MaskCoord(x, width, mask.Width), my);
                var p = row + x * 4;
                if (m >= 1f)
                {
                    dst[p] = src[p]; dst[p + 1] = src[p + 1]; dst[p + 2] = src[p + 2]; dst[p + 3] = src[p + 3];
                    continue;
                }
                SampleSmall(small, sw, sh, (x + 0.5f) / f - 0.5f, by, out var bb, out var bg, out var br);
                var k = 1f - m;
                dst[p] = (byte)Math.Clamp(src[p] * m + bb * k + 0.5f, 0, 255);
                dst[p + 1] = (byte)Math.Clamp(src[p + 1] * m + bg * k + 0.5f, 0, 255);
                dst[p + 2] = (byte)Math.Clamp(src[p + 2] * m + br * k + 0.5f, 0, 255);
                dst[p + 3] = src[p + 3];
            }
        }

        return new VideoFrame(width, height, dst) { Epoch = frame.Epoch, IsOpaque = frame.IsOpaque };
    }

    private static void BoxBlurHorizontal(float[] input, float[] output, int w, int h, int r)
    {
        var norm = 1f / (2 * r + 1);
        for (var y = 0; y < h; y++)
        {
            var row = y * w;
            for (var c = 0; c < 3; c++)
            {
                float sum = 0;
                for (var i = -r; i <= r; i++)
                    sum += input[(row + Math.Clamp(i, 0, w - 1)) * 3 + c];
                for (var x = 0; x < w; x++)
                {
                    output[(row + x) * 3 + c] = sum * norm;
                    var add = Math.Min(w - 1, x + r + 1);
                    var sub = Math.Max(0, x - r);
                    sum += input[(row + add) * 3 + c] - input[(row + sub) * 3 + c];
                }
            }
        }
    }

    private static void BoxBlurVertical(float[] input, float[] output, int w, int h, int r)
    {
        var norm = 1f / (2 * r + 1);
        for (var x = 0; x < w; x++)
        {
            for (var c = 0; c < 3; c++)
            {
                float sum = 0;
                for (var i = -r; i <= r; i++)
                    sum += input[(Math.Clamp(i, 0, h - 1) * w + x) * 3 + c];
                for (var y = 0; y < h; y++)
                {
                    output[(y * w + x) * 3 + c] = sum * norm;
                    var add = Math.Min(h - 1, y + r + 1);
                    var sub = Math.Max(0, y - r);
                    sum += input[(add * w + x) * 3 + c] - input[(sub * w + x) * 3 + c];
                }
            }
        }
    }

    private static void SampleSmall(float[] img, int w, int h, float x, float y, out float b, out float g, out float r)
    {
        var x0 = (int)MathF.Floor(x);
        var y0 = (int)MathF.Floor(y);
        var fx = x - x0;
        var fy = y - y0;
        var x1 = Math.Clamp(x0 + 1, 0, w - 1);
        var y1 = Math.Clamp(y0 + 1, 0, h - 1);
        x0 = Math.Clamp(x0, 0, w - 1);
        y0 = Math.Clamp(y0, 0, h - 1);
        var i00 = (y0 * w + x0) * 3;
        var i01 = (y0 * w + x1) * 3;
        var i10 = (y1 * w + x0) * 3;
        var i11 = (y1 * w + x1) * 3;
        var w00 = (1 - fx) * (1 - fy);
        var w01 = fx * (1 - fy);
        var w10 = (1 - fx) * fy;
        var w11 = fx * fy;
        b = img[i00] * w00 + img[i01] * w01 + img[i10] * w10 + img[i11] * w11;
        g = img[i00 + 1] * w00 + img[i01 + 1] * w01 + img[i10 + 1] * w10 + img[i11 + 1] * w11;
        r = img[i00 + 2] * w00 + img[i01 + 2] * w01 + img[i10 + 2] * w10 + img[i11 + 2] * w11;
    }

    private static float MaskCoord(int pixel, int frameSize, int maskSize)
        => (pixel + 0.5f) * maskSize / frameSize - 0.5f;

    private static float SampleBilinear(SegmentationMask mask, float x, float y)
    {
        var x0 = (int)MathF.Floor(x);
        var y0 = (int)MathF.Floor(y);
        var fx = x - x0;
        var fy = y - y0;
        var x1 = Math.Clamp(x0 + 1, 0, mask.Width - 1);
        var y1 = Math.Clamp(y0 + 1, 0, mask.Height - 1);
        x0 = Math.Clamp(x0, 0, mask.Width - 1);
        y0 = Math.Clamp(y0, 0, mask.Height - 1);
        var v = mask.Values;
        var top = v[y0 * mask.Width + x0] * (1 - fx) + v[y0 * mask.Width + x1] * fx;
        var bottom = v[y1 * mask.Width + x0] * (1 - fx) + v[y1 * mask.Width + x1] * fx;
        return Math.Clamp(top * (1 - fy) + bottom * fy, 0f, 1f);
    }

    private void LogFailureOnce(string reason)
    {
        if (_loggedFailure) return;
        _loggedFailure = true;
        AppLog.Write($"BackgroundEffectProcessor: passing webcam through — {reason}");
    }
}