// SPDX-License-Identifier: MIT

#include "gfx/rgba.hpp"

#include <algorithm>
#include <math.h>
#include <stdint.h>

#include "helpers.hpp" // assume

#include "gfx/main.hpp" // options

// Based on inverting the "Modern - Accurate" formula used by SameBoy
// since commit b5a611c5db46d6a0649d04d24d8d6339200f9ca1 (Dec 2020),
// with gaps in the scale curve filled by polynomial interpolation.
// clang-format off: vertically align columns of values
static std::array<uint8_t, 256> reverse_curve{
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  1,  1,  1,  1,  1,
    1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  2,  2,  2,  3,  3,  3,
    3,  3,  3,  3,  3,  4,  4,  4,  4,  4,  4,  4,  5,  5,  5,  5,
    5,  5,  5,  6,  6,  6,  6,  6,  6,  7,  7,  7,  7,  7,  7,  7,
    7,  8,  8,  8,  8,  8,  8,  9,  9,  9,  9,  9,  10, 10, 10, 10,
    10, 10, 11, 11, 11, 11, 11, 11, 12, 12, 12, 12, 12, 13, 13, 13,
    13, 13, 14, 14, 14, 14, 14, 14, 15, 15, 15, 15, 15, 16, 16, 16,
    16, 16, 16, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 19, 19,
    19, 19, 19, 20, 20, 20, 20, 20, 20, 21, 21, 21, 21, 21, 21, 22,
    22, 22, 22, 22, 22, 22, 23, 23, 23, 23, 23, 23, 24, 24, 24, 24,
    24, 24, 24, 25, 25, 25, 25, 25, 25, 25, 25, 26, 26, 26, 26, 26,
    26, 26, 26, 27, 27, 27, 27, 27, 27, 27, 27, 27, 28, 28, 28, 28,
    28, 28, 28, 28, 28, 28, 29, 29, 29, 29, 29, 29, 29, 29, 29, 29,
    29, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30,
    31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31,
    31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31,
};
// clang-format on

uint16_t Rgba::cgbColor() const {
	if (isTransparent()) {
		return transparent;
	}
	assume(isOpaque());

	uint8_t r = red, g = green, b = blue;
	if (options.useColorCurve) {
		double g_linear = pow(g / 255.0, 2.2), b_linear = pow(b / 255.0, 2.2);
		double g_adjusted = std::clamp((g_linear * 4 - b_linear) / 3, 0.0, 1.0);
		g = round(pow(g_adjusted, 1 / 2.2) * 255);
		r = reverse_curve[r];
		g = reverse_curve[g];
		b = reverse_curve[b];
	} else {
		r >>= 3;
		g >>= 3;
		b >>= 3;
	}
	return r | g << 5 | b << 10;
}

uint8_t Rgba::grayIndex() const {
	assume(isGray());
	// 2bpp shades are inverted from RGB PNG; %00 = white, %11 = black
	uint8_t gray = 255 - red;
	if (options.palSpecType == Options::DMG) {
		assume(!options.hasTransparentPixels);
		// Reduce gray shade from 0..<256 to 0..<4, then map to color index,
		// then reduce to 0..<nbColorsPerPal
		return options.dmgColors[gray * 4 / 256] * options.nbColorsPerPal / 4;
	}
	// Reduce gray shade from 0..<256 to hasTransparentPixels..<nbColorsPerPal
	// Note that `maxOpaqueColors()` already takes `hasTransparentPixels` into account
	return gray * options.maxOpaqueColors() / 256 + options.hasTransparentPixels;
}