#ifndef VEC3_H
#define VEC3_H

#include "rayTracer.h"

class vec3 {
    public:
        double e[3];

        vec3() : e{0, 0, 0} {}
        vec3(double e0, double e1, double e2) : e{e0, e1, e2} {}

        double x() const {
            return e[0];
        }

        double y() const {
            return e[1];
        }

        double z() const {
            return e[2];
        }

        vec3 operator-()const {
            return vec3(-e[0], -e[1], -e[2]);
        }

        double operator[](int i) const {
            return e[i];
        }

        double& operator[](int i) {
            return e[i];
        }

        vec3& operator+=(const vec3& v) {
            e[0] += v.e[0];
            e[1] += v.e[1];
            e[2] += v.e[2];

            return *this;
        }

        vec3& operator*=(double t) {
            e[0] *= t;
            e[1] *= t;
            e[2] *= t;

            return *this;
        }

        vec3& operator/=(double t) {
            return *this *= 1/t;
        }

        double length() const {
            return sqrt(lengthSquared());
        }

        double lengthSquared() const {
            return e[0]*e[0] + e[1]*e[1] + e[2]*e[2];
        }

        bool nearZero() const {
            // Return true if the vector is close to zero in all dimensions. 
            auto s = 1e-8;
            return (fabs(e[0]) < s) && (fabs(e[1]) < s) && (fabs(e[2]) < s);
        }

        static vec3 random() {
            return vec3(randomDouble(), randomDouble(), randomDouble());
        }

        static vec3 random(double min, double max) {
            return vec3(randomDouble(min,max), randomDouble(min,max), randomDouble(min,max));
        }

};

// point3 is just an alias for vec3, but useful for geometric clarity in the code.
using point3 = vec3;

// Vector Utility Functions. 
inline std::ostream& operator<<(std::ostream& out, const vec3& v) {
    return out << v.e[0] << ' ' << v.e[1] << ' ' << v.e[2];
}

inline vec3 operator+(const vec3& u, const vec3& v) {
    return vec3(u.e[0] + v.e[0], u.e[1] + v.e[1], u.e[2] + v.e[2]);
}

inline vec3 operator-(const vec3& u, const vec3& v) {
    return vec3(u.e[0] - v.e[0], u.e[1] - v.e[1], u.e[2] - v.e[2]);
}

inline vec3 operator*(const vec3& u, const vec3& v) {
    return vec3(u.e[0] * v.e[0], u.e[1] * v.e[1], u.e[2] * v.e[2]);
}

inline vec3 operator*(double t, const vec3& v) {
    return vec3(t * v.e[0], t * v.e[1], t * v.e[2]);
}

inline vec3 operator*(const vec3& v, double t) {
    return t * v;
}

inline vec3 operator/(const vec3& v, double t) {
    return (1/t) * v;
}

inline double dot(const vec3& u, const vec3& v) {
    return u.e[0] * v.e[0]
         + u.e[1] * v.e[1]
         + u.e[2] * v.e[2];
}

inline vec3 cross(const vec3& u, const vec3& v) {
    return vec3(u.e[1] * v.e[2] - u.e[2] * v.e[1],
                u.e[2] * v.e[0] - u.e[0] * v.e[2],
                u.e[0] * v.e[1] - u.e[1] * v.e[0]);
}

inline vec3 unitVector(const vec3& v) {
    return v / v.length();
}

inline vec3 randomInUnitDisk(void) {
    while (true) {
        auto p = vec3(randomDouble(-1, 1), randomDouble(-1, 1), 0);
        if (p.lengthSquared() < 1) return p;
    }
}

inline vec3 randomInUnitSphere() {
    while (true) {
        auto p = vec3::random(-1,1);
        if (p.lengthSquared() < 1)
            return p;
    }
}

inline vec3 randomUnitVector() {
    return unitVector(randomInUnitSphere());
}

inline vec3 randomOnHemisphere(const vec3& normal) {
    vec3 onUnitSphere = randomUnitVector();
    if (dot(onUnitSphere, normal) > 0.0) // In the same hemisphere as the normal
        return onUnitSphere;
    else
        return -onUnitSphere;
}

inline vec3 reflect(const vec3& v, const vec3& n) {
    return v - 2 * dot(v, n) * n;
}

inline vec3 refract(const vec3& uv, const vec3& n, double etaiOverEtat) {
    auto cosTheta = fmin(dot(-uv, n), 1.0);
    vec3 rOutPerp =  etaiOverEtat * (uv + cosTheta * n);
    vec3 rOutParallel = -sqrt(fabs(1.0 - rOutPerp.lengthSquared())) * n;
    return rOutPerp + rOutParallel;
}

#endif