#define samples 8

#define pi 3.141592564

// Scene definition is kinda inspired by .obj file formatting but idk if I'll keep it

vec3 materials[] = vec3[](
vec3(1.000,1.000,1.000),    // white
vec3(1.000,0.067,0.157),    // red
vec3(0.027,0.945,0.259),    // green
vec3(0.318,0.553,0.992));   // blue

vec2 points[] = vec2[](
vec2(.1,-.25), 
vec2(.3,-.25), 
vec2(.1,-.05), 
vec2(.3,-.05), 
vec2(-.9,-.4), 
vec2(.8,-.4),  
vec2(-.9,-1.), 
vec2(.8,1.),   
vec2(-.4,-.3), 
vec2(-.2,-.3), 
vec2(-.4,-.1), 
vec2(-.2,-.1),
vec2(-.05,-.05),
vec2(-.05,-.15),
vec2(0,-.1),
vec2(-.1,-.1));

int segmentCount = 15;
ivec3 segments[] = ivec3[](
ivec3(0,1,1),   // ivec3(a,b,c)
ivec3(0,2,1),   // a = endpoint a index
ivec3(1,3,1),   // b = endpoint b index
ivec3(2,3,1),   // c = material index
ivec3(4,5,0),
ivec3(4,6,0),
ivec3(5,7,0),
ivec3(8,9,3),
ivec3(8,10,3),
ivec3(9,11,3),
ivec3(10,11,3),
ivec3(12,14,2),
ivec3(14,13,2),
ivec3(13,15,2),
ivec3(15,12,2));

// https://www.shadertoy.com/view/4djSRW
vec2 hash21(float p) {
	vec3 p3 = fract(vec3(p) * vec3(.1031, .1030, .0973));
	p3 += dot(p3, p3.yzx + 33.33);
    return fract((p3.xx+p3.yz)*p3.zy);

}

// Interleaved gradient noise
// https://blog.demofox.org/2022/01/01/interleaved-gradient-noise-a-different-kind-of-low-discrepancy-sequence/
float IGN(ivec2 p) {
    return mod(52.9829189f * mod(.06711056f*float(p.x) + .00583715f*float(p.y), 1.), 1.);
}

// Ray intersection with line segment
float segmentIntersect(vec2 ro, vec2 rd, vec2 a, vec2 b) {
        vec2 v1 = ro - a;
        vec2 v2 = b - a;
        vec2 v3 = vec2(-rd.y, rd.x);

        float d = dot(v2, v3);
        float t1 = cross(vec3(v2,0), vec3(v1,0)).z / d;
        float t2 = dot(v1, v3) / d;

        if (t1 >= 0.0 && (t2 >= 0.0 && t2 <= 1.0)) {
            return t1;
        }
        return 1000.;
}

//ray intersection with scene
//sceneIntersect.w is the distance, sceneIntersect.xyz is the color
vec4 sceneIntersect(vec2 ro, vec2 rd) {
    float v0 = 1000.;
    vec3 col;

    for(int i=0; i<segmentCount; i++) {

        vec2 a = points[segments[i].x];
        vec2 b = points[segments[i].y];
        
        float v1 = segmentIntersect(ro, rd, a, b);
        if(v1<v0) {
            col = materials[segments[i].z];
            v0 = v1;
        }
    }
    return vec4(col,v0);
}

//line segment SDF
float line(vec2 p, vec2 a,vec2 b) { 
    p -= a, b -= a;
    float h = clamp(dot(p, b) / dot(b, b), 0., 1.);
    return length(p - b * h);
}

//scene SDF
//sceneDist.w is the distance, sceneDist.xyz is the color
vec4 sceneDist(vec2 p) {
    float v0 = 1000.;
    vec3 col;

    for(int i=0; i<segmentCount; i++) {

        vec2 a = points[segments[i].x];
        vec2 b = points[segments[i].y];
        
        float v1 = line(p, a, b);
        if(v1<v0) {       
            col = materials[segments[i].z];
            v0 = v1;
        }
    }
    return vec4(col,v0);
}

vec2 sceneNormal(vec2 p) {
    vec2 epsilon = vec2(.001, -.001);
    return normalize(vec2(sceneDist(p+epsilon.xx).w) - vec2(sceneDist(p-epsilon.xy).w,sceneDist(p-epsilon.yx).w));
}

// ACES Tonemapping
vec3 ACESFilm(vec3 x) {

    float a = 2.51f;
    float b = 0.03f;
    float c = 2.43f;
    float d = 0.59f;
    float e = 0.14f;
    return clamp((x*(a*x + b)) / (x*(c*x + d) + e), 0.0f, 1.0f);
}

#define lightFalloff 2.
void mainImage( out vec4 fragColor, in vec2 fragCoord ) {

    vec3 col;
    vec2 p = (2.*fragCoord-iResolution.xy-.5)/iResolution.x;
    float rand = IGN(ivec2(fragCoord.xy));
    
    vec3 spot;
    vec3 gi;
    
    vec2 lightPos = vec2(sin(iTime*.5)*.75,cos(iTime*.25)*.25+.25);

    vec2 lightDir = normalize(vec2(sin(iTime*1.5),-1));
    if (iMouse.z > 0.){
        lightPos = vec2(2,-2)*iMouse.zw/iResolution.x-vec2(1.,.56);
        lightDir = normalize(2.*iMouse.xy/iResolution.x-vec2(1.,.561)-lightPos);
    }
    float lightRad = .005;
    
    if (sceneIntersect(p, normalize(lightPos-p)).w > distance(p,lightPos)) {
        spot = vec3(max((.5*float(dot(normalize(p-lightPos),lightDir))-.5)/lightRad+1.,0. ));
    }
    
    vec2 hit;
    for (int i=0; i<samples; i++) {
        vec2 ro = lightPos;
        float rot = .08*pi*((float(i)+rand)/float(samples)-.5) + atan(lightDir.y,lightDir.x);
        vec2 rd = vec2(cos(rot),sin(rot));
        vec2 lightDirSampled = rd;
        
        float d = sceneIntersect(ro, rd).w;
        hit = ro + rd*d;
        vec2 nor = sceneNormal(hit - rd*.01);
        
        ro = p;
        rd = normalize(hit-p);
        
        // Circle arc for bounce light falloff just beause I thought it looked better than inverse square law :p
        float hitDist = min(distance(p,hit)/lightFalloff,1.);
        
        vec4 lightRay = sceneIntersect(ro, rd);
        d = lightRay.w;
        
        if (d + .01 > distance(p,hit)) {
            gi += 1./float(samples) * lightRay.rgb * clamp(dot(-rd,nor),0.,1.) * ( 1.-sqrt(2.*hitDist-hitDist*hitDist) )
            * (sceneDist(p).w > .005 ? 1. : dot(sceneNormal(p),lightDirSampled)*.5+.5 );
        }
    }
    
    vec4 scene = sceneDist(p);
    col = spot*.5 + gi*1.;
    col *= scene.w > .005 ? vec3(.25) : 3.*scene.rgb;
    
    // Tonemapping
    
    col = ACESFilm(col);
    col = pow(col,vec3(1./2.2));
    
    fragColor = vec4(col,1);
}