#pragma once

#include "CoreMinimal.h"

/**
 * Luminance statistics of a screenshot, the numbers of the shot sidecar JSON (DESIGN_UE.md section 9.2).
 * All values are of the sRGB-ENCODED pixels (what a person sees in the PNG), scaled to 0..1, with Rec.709
 * weights: luma = 0.2126 R + 0.7152 G + 0.0722 B. Pure functions, no engine state, so tests can feed synthetic images.
 */
struct FDescentLumaStats
{
	int32 Width = 0;
	int32 Height = 0;
	/** Mean luma of the whole frame. */
	double MeanLuma = 0.0;
	/** Mean luma of the central 40 percent x 40 percent of the frame (x and y from 30 to 70 percent). */
	double CentreLuma = 0.0;
	/** Fraction of pixels with any channel above 8/255. Near 0 means a black or unrendered frame. */
	double NonBlack = 0.0;
	/** 99th percentile of the per-pixel luma (resolution 1/1020). */
	double P99Luma = 0.0;
	/** Mean of each channel, 0..1. */
	double MeanR = 0.0;
	double MeanG = 0.0;
	double MeanB = 0.0;
	/**
	 * How much there is to see in the central 40 x 40 percent (fix list after M3, requirement V1: rock in the lamp must read as rock).
	 * The rectangle is cut into blocks of Width / 160 pixels (8 at 1280), which averages film grain away.
	 * CentreDetail: the mean Michelson contrast |a - b| / (a + b + 0.02) of neighbouring blocks: edges, facets, veins. A smooth gradient
	 * (the lamp's own falloff) gives almost 0, a flat grey disc 0. CentreRms: standard deviation / mean of the block lumas (includes the falloff).
	 */
	double CentreDetail = 0.0;
	double CentreRms = 0.0;
};

namespace Descent::Image
{
	/** Luma of one pixel, 0..1. */
	THEDESCENT_API double Luma01(const FColor& C);

	/** Whole-frame statistics. Pixels is row-major, top row first, Width * Height long; an empty or mismatched image gives zeros. */
	THEDESCENT_API FDescentLumaStats ComputeStats(TConstArrayView64<FColor> Pixels, int32 Width, int32 Height);

	/** Mean luma of the rectangle X0..X1 x Y0..Y1 given as fractions of the frame (0..1, origin top left). */
	THEDESCENT_API double MeanLumaRect(TConstArrayView64<FColor> Pixels, int32 Width, int32 Height, double X0, double Y0, double X1, double Y1);

	/** Block contrast of a rectangle given as fractions of the frame: see FDescentLumaStats::CentreDetail / CentreRms. */
	THEDESCENT_API void BlockContrastRect(TConstArrayView64<FColor> Pixels, int32 Width, int32 Height, double X0, double Y0, double X1, double Y1, double& OutDetail, double& OutRms);

	/** Mean luma of the pixels whose centre is between R0 and R1 pixels from (Cx, Cy) (pixels, origin top left). */
	THEDESCENT_API double MeanLumaRing(TConstArrayView64<FColor> Pixels, int32 Width, int32 Height, double Cx, double Cy, double R0, double R1);
}