in vec4 vpeye;
in vec4 vneye;
uniform bool u_shadow_receiver;
uniform samplerCube shadowMap[MAX_LIGHTS];

//// From http://fabiensanglard.net/shadowmappingVSM/index.php
float chebyshevUpperBound(float distance, vec3 dir, int light_index) {
    distance = distance/20;
    vec2 moments = texture(shadowMap[light_index], dir).rg;
    
    // Surface is fully lit. as the current fragment is before the light occluder
    if (distance <= moments.x) {
        return 1.0;
    }
    
    // The fragment is either in shadow or penumbra. We now use chebyshev's upperBound to check
    // How likely this pixel is to be lit (p_max)
    float variance = moments.y - (moments.x*moments.x);
    //variance = max(variance, 0.000002);
    variance = max(variance, 0.00002);
    
    float d = distance - moments.x;
    float p_max = variance / (variance + d*d);
    
    return p_max;
}

vec4 shadowmap(in vec4 peye, in vec4 neye) {
    float shadowFactor = 0.0;
    vec3 fragment = vec3(peye);

    int total_casters = 0;
    for (int i = 0; i < u_num_lights; i++) {
        light_t light = u_lights[i];
        float factor = 0.0;

        if (light.type == LIGHT_DIRECTIONAL) {
            // shadowFactor = chebyshevUpperBound(distance, light.dir);
        } else if (light.type == LIGHT_POINT) {
            total_casters++;
            vec3 light_pos = (view * vec4(light.pos, 1.0)).xyz;
            vec3 dir = light_pos - fragment;
            vec4 sc = inv_view * vec4(dir, 0.0);
            factor += chebyshevUpperBound(length(dir), -sc.xyz, i);
        } else if (light.type == LIGHT_SPOT) {
            // shadowFactor = chebyshevUpperBound(distance, light.pos);
        }

        shadowFactor += factor;
    }

    if (u_num_lights == 0) { 
        shadowFactor = 1.0;
    } else {
        shadowFactor /= total_casters;
    }

    return vec4(vec3(shadowFactor), 1.0);
}

vec4 shadowing() {
    if (u_shadow_receiver) {
        return shadowmap(vpeye, vneye);
    } else {
        return vec4(1.0);
    }
}