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#include <gtest/gtest.h>
#include <random>
#include <lib/matrix/matrix/math.hpp>
#include "WelfordMean.hpp"

using namespace math;
using matrix::Vector3f;

TEST(WelfordMeanTest, NoisySignal)
{
	const float std_dev = 3.f;
	std::normal_distribution<float> standard_normal_distribution{0.f, std_dev};
	std::default_random_engine random_generator{}; // Pseudo-random generator with constant seed
	random_generator.seed(42);
	WelfordMean<float, 3> welford{};

	for (int i = 0; i < 50; i++) {
		const float noisy_value = standard_normal_distribution(random_generator);
		welford.update(Vector3f(noisy_value, noisy_value - 1.f, noisy_value + 1.f));
	}

	EXPECT_TRUE(welford.valid());
	const Vector3f mean = welford.mean();
	const Vector3f var = welford.variance();
	const float var_real = std_dev * std_dev;

	EXPECT_NEAR(mean(0), 0.f, 0.7f);
	EXPECT_NEAR(mean(1), -1.f, 0.7f);
	EXPECT_NEAR(mean(2), 1.f, 0.7f);
	EXPECT_NEAR(var(0), var_real, 0.1f);
	EXPECT_NEAR(var(1), var_real, 0.1f);
	EXPECT_NEAR(var(2), var_real, 0.1f);
}