#if !defined INCLUDe_SKY_CLOUDS_CUMULUS_CONGESTUS
#define INCLUDE_SKY_CLOUDS_CUMULUS_CONGESTUS

// Alternative 1st layer: distant cumulus congestus clouds

#include "common.glsl"

const float clouds_cumulus_congestus_radius =
    planet_radius + CLOUDS_CUMULUS_CONGESTUS_ALTITUDE;
const float clouds_cumulus_congestus_thickness =
    CLOUDS_CUMULUS_CONGESTUS_ALTITUDE * CLOUDS_CUMULUS_CONGESTUS_THICKNESS;
const float clouds_cumulus_congestus_top_radius =
    clouds_cumulus_congestus_radius + clouds_cumulus_congestus_thickness;
const float clouds_cumulus_congestus_distance = 30000.0;
const float clouds_cumulus_congestus_end_distance = 50000.0;
float clouds_cumulus_congestus_extinction_coeff = 0.08;
float clouds_cumulus_congestus_scattering_coeff =
    clouds_cumulus_congestus_extinction_coeff * (1.0 - 0.2 * rainStrength);

// altitude_fraction := 0 at the bottom of the cloud layer and 1 at the top
float clouds_cumulus_congestus_altitude_shaping(
    float density,
    float altitude_fraction
) {
    // Carve egg shape
    density -= sqr(linear_step(0.3, 1.0, altitude_fraction)) *
        clamp01(1.0 - 0.2 * clouds_params.cumulus_congestus_blend);

    // Reduce density at the top and bottom of the cloud
    density *= smoothstep(0.0, 0.1, altitude_fraction);
    density *= smoothstep(0.0, 0.1, 1.0 - altitude_fraction);

    return density;
}

float clouds_cumulus_congestus_density(vec3 pos) {
    const float wind_angle = CLOUDS_CUMULUS_WIND_ANGLE * degree;
    const vec2 wind_velocity =
        CLOUDS_CUMULUS_WIND_SPEED * vec2(cos(wind_angle), sin(wind_angle));

    float r = length(pos);
    if (r < clouds_cumulus_congestus_radius ||
        r > clouds_cumulus_congestus_top_radius) {
        return 0.0;
    }

    float altitude_fraction = (r - clouds_cumulus_congestus_radius) *
        rcp(clouds_cumulus_congestus_thickness);
    float distance_fraction = linear_step(
        clouds_cumulus_congestus_distance,
        clouds_cumulus_congestus_end_distance,
        length(pos.xz)
    );

    pos.xz += cameraPosition.xz * CLOUDS_SCALE;

    // 2D noise for base shape and coverage
    float noise =
        texture(
            noisetex,
            (0.000003 / CLOUDS_CUMULUS_CONGESTUS_SIZE) *
                (pos.xz +
                 wind_velocity * (world_age + 50.0 * sqr(altitude_fraction)))
        )
            .w;

    float density = 1.5 *
        sqr(linear_step(
            0.75 -
                0.15 *
                    clamp01(
                        clouds_params.cumulus_congestus_blend *
                        CLOUDS_CUMULUS_CONGESTUS_COVERAGE
                    ),
            1.0,
            sqrt(noise)
        ));
    density =
        clouds_cumulus_congestus_altitude_shaping(density, altitude_fraction);
    density *= 4.0 * distance_fraction * (1.0 - distance_fraction);
    density *= linear_step(0.0, 0.3, clouds_params.cumulus_congestus_blend);

    if (density < eps) {
        return 0.0;
    }

#ifndef PROGRAM_PREPARE
    // Curl noise used to warp the 3D noise into swirling shapes
    vec3 wind = vec3(wind_velocity * world_age, 0.0).xzy;

    // 3D worley noise for detail
    float worley_0 =
        texture(SAMPLER_WORLEY_SWIRLEY, (pos + 0.2 * wind) * 0.00005).x;
    float worley_1 =
        texture(SAMPLER_WORLEY_SWIRLEY, (pos + 0.4 * wind) * 0.00023).x;
#else
    const float worley_0 = 0.5;

    const float worley_1 = 0.5;
#endif

    float detail_fade = 0.20 * smoothstep(0.85, 1.0, 1.0 - altitude_fraction) -
        0.35 * smoothstep(0.05, 0.5, altitude_fraction) + 0.8;

    density -= (7.0 * CLOUDS_CUMULUS_CONGESTUS_DETAIL_STRENGTH) *
        sqr(clamp01(1.0 - density)) * cube(worley_0) * sqr(altitude_fraction);
    density -= (0.2 * CLOUDS_CUMULUS_CONGESTUS_DETAIL_STRENGTH) *
        sqr(worley_1) * dampen(clamp01(1.0 - density)) *
        dampen(dampen(clamp01(detail_fade + 0.5 * sqr(altitude_fraction))));

    // Adjust density so that the clouds are wispy at the bottom and hard at the
    // top
    density = max0(density);
    density = lift(clamp01(density), mix(2.0, 10.0, altitude_fraction));
    density *= sqr(linear_step(0.0, 0.5, altitude_fraction));

    return density;
}

float clouds_cumulus_congestus_optical_depth(
    vec3 ray_origin,
    vec3 ray_dir,
    float dither,
    const uint step_count
) {
    const float step_growth = 2.0;

    float step_length =
        0.1 * clouds_cumulus_congestus_thickness / float(step_count); // m

    vec3 ray_pos = ray_origin;
    vec4 ray_step = vec4(ray_dir, 1.0) * step_length;

    float optical_depth = 0.0;

    for (uint i = 0u; i < step_count; ++i, ray_pos += ray_step.xyz) {
        ray_step *= step_growth;
        optical_depth +=
            clouds_cumulus_congestus_density(ray_pos + ray_step.xyz * dither) *
            ray_step.w;
    }

    return optical_depth;
}

vec2 clouds_cumulus_congestus_scattering(
    float density,
    float light_optical_depth,
    float sky_optical_depth,
    float ground_optical_depth,
    float step_transmittance,
    float cos_theta,
    float bounced_light
) {
    vec2 scattering = vec2(0.0);

    float scatter_amount = clouds_cumulus_congestus_scattering_coeff;
    float extinct_amount = clouds_cumulus_congestus_extinction_coeff;

    float scattering_integral_times_density =
        (1.0 - step_transmittance) / clouds_cumulus_congestus_extinction_coeff;

    float powder_effect = clouds_powder_effect(2.0 * density, cos_theta);

    float phase = clouds_phase_single(cos_theta);
    vec3 phase_g = pow(vec3(0.6, 0.9, 0.3), vec3(1.0 + light_optical_depth));

    for (uint i = 0u; i < 8u; ++i) {
        scattering.x += scatter_amount *
            exp(-extinct_amount * light_optical_depth * 0.33) * phase;
        scattering.x += scatter_amount *
            exp(-extinct_amount * ground_optical_depth * 0.33) *
            isotropic_phase * bounced_light;
        scattering.y += scatter_amount *
            exp(-extinct_amount * sky_optical_depth * 0.33) * isotropic_phase;

        scatter_amount *= 0.55 *
            mix(lift(
                    clamp01(clouds_cumulus_congestus_scattering_coeff / 0.1),
                    0.33
                ),
                1.0,
                cos_theta * 0.5 + 0.5) *
            powder_effect;
        extinct_amount *= 0.4;
        phase_g *= 0.5;

        powder_effect = mix(powder_effect, sqrt(powder_effect), 0.5);

        phase = clouds_phase_multi(cos_theta, phase_g);
    }

    return scattering * scattering_integral_times_density;
}

CloudsResult draw_cumulus_congestus_clouds(
    vec3 air_viewer_pos,
    vec3 ray_dir,
    vec3 clear_sky,
    float distance_to_terrain,
    float dither
) {
    // ---------------------
    //   Raymarching Setup
    // ---------------------

    const uint primary_steps = CLOUDS_CUMULUS_CONGESTUS_PRIMARY_STEPS;
    const uint lighting_steps = CLOUDS_CUMULUS_CONGESTUS_LIGHTING_STEPS;
    const uint ambient_steps = CLOUDS_CUMULUS_CONGESTUS_AMBIENT_STEPS;

    const float min_transmittance = 0.075;

    const float planet_albedo = 0.4;
    const vec3 sky_dir = vec3(0.0, 1.0, 0.0);

    vec2 sphere_dists = intersect_spherical_shell(
        air_viewer_pos,
        ray_dir,
        clouds_cumulus_congestus_radius,
        clouds_cumulus_congestus_top_radius
    );
    vec2 cylinder_dists = intersect_cylindrical_shell(
        air_viewer_pos,
        ray_dir,
        clouds_cumulus_congestus_distance,
        clouds_cumulus_congestus_end_distance
    );
    vec2 dists = vec2(
        max(sphere_dists.x, cylinder_dists.x),
        min(sphere_dists.y, cylinder_dists.y)
    );

    bool planet_intersected =
        intersect_sphere(
            air_viewer_pos,
            ray_dir,
            min(length(air_viewer_pos) - 10.0, planet_radius)
        )
            .y >= 0.0;

    if (dists.y < 0.0 ||
        planet_intersected &&
            length(air_viewer_pos) < clouds_cumulus_congestus_radius ||
        distance_to_terrain > 0.0) {
        return clouds_not_hit;
    }

    float ray_length = dists.y - dists.x;
    float step_length = ray_length * rcp(float(primary_steps));

    vec3 ray_step = ray_dir * step_length;

    vec3 ray_origin =
        air_viewer_pos + ray_dir * (dists.x + step_length * dither);

    vec2 scattering = vec2(0.0); // x: direct light, y: skylight
    float transmittance = 1.0;

    float distance_sum = 0.0;
    float distance_weight_sum = 0.0;

    // ------------------
    //   Lighting Setup
    // ------------------

    bool moonlit = sun_dir.y < -0.04;
    vec3 light_dir = moonlit ? moon_dir : sun_dir;
    float cos_theta = dot(ray_dir, light_dir);
    float bounced_light = planet_albedo * light_dir.y * rcp_pi;

    // --------------------
    //   Raymarching Loop
    // --------------------

    for (uint i = 0u; i < primary_steps; ++i) {
        if (transmittance < min_transmittance) {
            break;
        }

        vec3 ray_pos = ray_origin + ray_step * i;

        float altitude_fraction =
            (length(ray_pos) - clouds_cumulus_congestus_radius) *
            rcp(clouds_cumulus_congestus_thickness);

        float density = clouds_cumulus_congestus_density(ray_pos);

        if (density < eps) {
            continue;
        }

        float distance_to_sample = distance(ray_origin, ray_pos);

        float step_optical_depth =
            density * clouds_cumulus_congestus_extinction_coeff * step_length;
        float step_transmittance = exp(-step_optical_depth);

#if defined PROGRAM_DEFERRED0
        vec2 hash = vec2(0.0);
#else
        vec2 hash = hash2(fract(ray_pos)); // used to dither the light rays
#endif

        float light_optical_depth = clouds_cumulus_congestus_optical_depth(
            ray_pos,
            light_dir,
            hash.x,
            lighting_steps
        );
        float sky_optical_depth = clouds_cumulus_congestus_optical_depth(
            ray_pos,
            sky_dir,
            hash.y,
            ambient_steps
        );
        float ground_optical_depth =
            mix(density, 1.0, clamp01(altitude_fraction * 2.0 - 1.0)) *
            altitude_fraction *
            clouds_cumulus_congestus_thickness; // guess optical depth to the
                                                // ground using altitude
                                                // fraction and density from
                                                // this sample

        scattering +=
            clouds_cumulus_congestus_scattering(
                density,
                light_optical_depth,
                sky_optical_depth,
                ground_optical_depth,
                step_transmittance,
                cos_theta,
                bounced_light
            ) *
            transmittance;

        transmittance *= step_transmittance;

        // Update distance to cloud
        distance_sum += distance_to_sample * density;
        distance_weight_sum += density;
    }

    // Get main light color for this layer
    vec3 light_color =
        sunlight_color * atmosphere_transmittance(ray_origin, light_dir);
    light_color = atmosphere_post_processing(light_color);
    light_color *= moonlit ? moon_color : sun_color;

    // Remap the transmittance so that min_transmittance is 0
    float clouds_transmittance =
        linear_step(min_transmittance, 1.0, transmittance);

    // Aerial perspective
    vec3 clouds_scattering =
        scattering.x * light_color + scattering.y * sky_color;
    clouds_scattering = clouds_aerial_perspective(
        clouds_scattering,
        clouds_transmittance,
        air_viewer_pos,
        ray_origin,
        ray_dir,
        clear_sky
    );

    // Fade away at the horizon
    float horizon_fade =
        mix(dampen(linear_step(0.0, 0.08, ray_dir.y)),
            1.0,
            smoothstep(
                sqr(clouds_cumulus_congestus_radius),
                sqr(clouds_cumulus_congestus_radius +
                    0.1 * clouds_cumulus_congestus_thickness),
                length_squared(air_viewer_pos)
            ));
    clouds_scattering =
        mix(clear_sky * (1.0 - clouds_transmittance),
            clouds_scattering,
            horizon_fade);

    float apparent_distance = (distance_weight_sum == 0.0)
        ? 1e6
        : (distance_sum / distance_weight_sum) +
            distance(air_viewer_pos, ray_origin);

    return CloudsResult(
        vec4(clouds_scattering, scattering.y),
        clouds_transmittance,
        apparent_distance
    );
}

#endif
