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 Copyright (c) 2022-2023 Xiamen Yaji Software Co., Ltd.

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#pragma once

#include <cmath>
#include <functional>
#include "base/std/container/vector.h"
#include "core/TypedArray.h"
#include "math/Math.h"
#include "math/Vec3.h"

namespace cc {
namespace gi {

#define SH_BASIS_COUNT 9

class LightProbeSampler {
public:
    /**
     *  generate one sample from sphere uniformly
     */
    static Vec3 uniformSampleSphere(float u1, float u2);

    /**
     *  generate ucount1 * ucount2 samples from sphere uniformly
     */
    static ccstd::vector<Vec3> uniformSampleSphereAll(uint32_t sampleCount);

    /**
     *  probability density function of uniform distribution on spherical surface
     */
    static inline float uniformSpherePdf() { return 1.0F / (4.0F * math::PI); }
};

/**
 * Spherical Harmonics utility class
 */
class SH {
public:
    using BasisFunction = std::function<float(const Vec3& v)>;

    /**
     * update ubo data by coefficients
     */
    static void updateUBOData(Float32Array& data, int32_t offset, ccstd::vector<Vec3>& coefficients);

    /**
     * recreate a function from sh coefficients, which is same as SHEvaluate in shader
     */
    static Vec3 shaderEvaluate(const Vec3& normal, ccstd::vector<Vec3>& coefficients);

    /**
     * recreate a function from sh coefficients
     */
    static Vec3 evaluate(const Vec3& sample, const ccstd::vector<Vec3>& coefficients);

    /**
     * project a function to sh coefficients
     */
    static ccstd::vector<Vec3> project(const ccstd::vector<Vec3>& samples, const ccstd::vector<Vec3>& values);

    /**
     * calculate irradiance's sh coefficients from radiance's sh coefficients directly
     */
    static ccstd::vector<Vec3> convolveCosine(const ccstd::vector<Vec3>& radianceCoefficients);

    /**
     * return basis function count
     */
    static inline uint32_t getBasisCount() {
        return SH_BASIS_COUNT;
    }

    /**
     * evaluate from a basis function
     */
    static inline float evaluateBasis(uint32_t index, const Vec3& sample) {
        CC_ASSERT(index < getBasisCount());
        const auto& func = basisFunctions[index];

        return func(sample);
    }

    static inline void reduceRinging(ccstd::vector<Vec3>& coefficients, float lambda) {
        if (lambda == 0.0F) {
            return;
        }

        for (int32_t l = 0; l <= LMAX; ++l) {
            auto level = static_cast<float>(l);
            float scale = 1.0F / (1.0F + lambda * level * level * (level + 1) * (level + 1));
            for (int32_t m = -l; m <= l; ++m) {
                const int32_t i = toIndex(l, m);
                coefficients[i] *= scale;
            }
        }
    }

private:
    static inline float lambda(int32_t l) {
        return std::sqrt((4.0F * math::PI) / (2.0F * static_cast<float>(l) + 1.0F));
    }

    static inline int32_t toIndex(int32_t l, int32_t m) {
        return l * l + l + m;
    }

    static constexpr int32_t LMAX = 2;
    static ccstd::vector<BasisFunction> basisFunctions;
    static ccstd::vector<float> basisOverPI;
};

} // namespace gi
} // namespace cc