varying vec2 uv;
varying vec3 vert_position;
varying vec3 normal_vector;

uniform sampler2D textureSampler;
// uniform sampler2D normalSampler;
#if (QUALITY_LEVEL > 0)
// uniform sampler2D specularSampler;
#endif
uniform samplerCube skyboxSampler;

uniform vec3 camera_position;
uniform mat4 rot_from_torque_mat;
uniform mat4 rot_to_torque_mat;
uniform mat4 model_mat;
uniform vec4 ambient_color;
uniform vec4 sun_color;
uniform vec3 sun_direction;

float tanh(float x) {
    return (exp(2.0 * x) - 1.0) / (exp(2.0 * x) + 1.0);
}

float sigmoid(float x) {
    return 0.5 + 0.5 * tanh(2.0 * x - 1.0);
}

float atanh(float x) {
    return 0.5 * log((1.0 + x) / (1.0 - x));
}

float invSigmoid(float x) {
    return 0.5 + 0.5 * atanh(2.0 * x - 1.0);
}

vec2 uvFromNormal(vec3 normal_vector) {
    normal_vector = mat3(model_mat) * normal_vector;
    vec2 ret = vec2((atan(normal_vector.y, normal_vector.x) + 3.14159265) / (2 * 3.14159265),
                    (atan(-normal_vector.z, sqrt(normal_vector.x * normal_vector.x +
                                                 normal_vector.y * normal_vector.y)) +
                     3.14159265 / 2.0) /
                        3.14159265);
    return ret;
}

void main() {
    // Correct UV based on texture scale
    vec2 scaled_uv = uv;

    // Texture values
    vec4 material_color = texture2D(textureSampler, uvFromNormal(normal_vector));

    // Normalize the light vector so we can dot it
    vec3 light_normal = normalize(-sun_direction);

    // Cosine of the angle from the light to the normal
    float cosTheta = clamp(dot(normal_vector, light_normal), 0, 1);

    // Sun color is multiplied by angle for bump mapping, then clamped to [0, 1] so we don't clip
    vec4 effectiveSun = sun_color * cosTheta;

    // Ambient color first
    effectiveSun += ambient_color;

    // Clamp sun so we don't clip
    effectiveSun = vec4(clamp(effectiveSun.r, 0, 1), clamp(effectiveSun.g, 0, 1),
                        clamp(effectiveSun.b, 0, 1), 1);

    // Worldspace normal taking normal mapping into account
    vec3 normal_model = normal_vector;  // normalize(reflect(-normal_vector, normal_color));
    // Direction from camera to vertex
    vec3 camera_direction = normalize(vert_position - camera_position);
    // Reflect the camera off the normal so we know where on the skysphere to show
    vec3 camera_reflection = reflect(camera_direction, normal_model);

    float reflectAmount = material_color.a * 0.3;
    float refractAmount = material_color.a;

    // Refraction -- warning: Whirligig-level math ahead
    float ior = 1.3;  // This is actually water, not glass, but glass doesn't look as sexy
    vec3 refraction1 = normalize(refract(camera_direction, normal_model, 1.0 / ior));
    // Now we need to compute what happens when the ray *leaves* the marble.
    // Thank goodness the marble is a sphere, because the normal and position are equal up to a
    // constant factor. Because this math is scale-invariant, we can act like the marble has radius
    // 1 and not 0.2. Then we want to figure out when a ray with start position Vn (normal_model)
    // and direction Vr (refraction1) leaves the sphere. This can be determined by solving the
    // equation ||Vn + t Vr||^2 = 1 for t > 0. Good thing I still have my Maple license! According
    // to Maple, the solution is (-Vn * Vr +/- sqrt(||Vr||^2 - ||Vr x Vn||^2))/||Vr||^2. Obviously
    // we want the higher solution.
    float t = (-dot(normal_model, refraction1) +
               sqrt(dot(refraction1, refraction1) -
                    dot(cross(normal_model, refraction1), cross(normal_model, refraction1)))) /
              dot(refraction1, refraction1);
    vec3 outNormal = normalize(normal_model + t * refraction1);
    vec3 refraction2 = refract(refraction1, -outNormal, ior);
    vec4 refractionColor = textureCube(skyboxSampler, refraction2);
    refractAmount = invSigmoid(0.01 + 0.98 * refractAmount);
    refractAmount += 0.7 * dot(normal_model, camera_direction);
    refractAmount = sigmoid(refractAmount);

    vec4 back_color = texture2D(textureSampler, uvFromNormal(outNormal));
    refractionColor =
        mix(vec4(back_color.rgb * effectiveSun.rgb, 1), refractionColor, back_color.a);

    // Reflected coordinates onto the given skybox
    vec3 skyboxR = camera_reflection;
    // Get the color from the skybox
    vec4 reflectionColor = textureCube(skyboxSampler, skyboxR);
    // Apply the reflected skybox color
    reflectAmount = invSigmoid(0.01 + 0.98 * reflectAmount);
    reflectAmount -= 0.7 * (2.0 * -dot(normal_model, camera_direction) - 1.0);
    reflectAmount = sigmoid(reflectAmount);
    reflectAmount = 0.95 * reflectAmount;

    gl_FragColor =
        vec4(mix(mix(material_color.rgb * effectiveSun.rgb, refractionColor.rgb, refractAmount),
                 reflectionColor.rgb, reflectAmount),
             1);
}