// Scene1 effect shader - ShaderToy conversion (raymarching cube & sphere)
// Source: Saturday cubism experiment by skal

#include "common_uniforms"

@group(0) @binding(0) var<uniform> uniforms: CommonUniforms;

const PI: f32 = 3.141592654;
const TAU: f32 = 6.283185307;
const TOLERANCE: f32 = 0.0005;
const MAX_RAY_LENGTH: f32 = 20.0;
const MAX_RAY_MARCHES: i32 = 80;
const MAX_SHD_MARCHES: i32 = 20;
const NORM_OFF: f32 = 0.005;

fn rot(a: f32) -> mat2x2<f32> {
  let c = cos(a);
  let s = sin(a);
  return mat2x2<f32>(c, s, -s, c);
}

// HSV to RGB conversion
const hsv2rgb_K = vec4<f32>(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
fn hsv2rgb(c: vec3<f32>) -> vec3<f32> {
  let p = abs(fract(c.xxx + hsv2rgb_K.xyz) * 6.0 - hsv2rgb_K.www);
  return c.z * mix(hsv2rgb_K.xxx, clamp(p - hsv2rgb_K.xxx, vec3<f32>(0.0), vec3<f32>(1.0)), c.y);
}

// Colors (precomputed HSV conversions)
const skyCol = vec3<f32>(0.176, 0.235, 0.25); // HSV(0.57, 0.90, 0.25)
const skylineCol = vec3<f32>(0.5, 0.125, 0.025); // HSV(0.02, 0.95, 0.5)
const sunCol = vec3<f32>(0.5, 0.163, 0.025); // HSV(0.07, 0.95, 0.5)
const diffCol1 = vec3<f32>(0.4, 1.0, 1.0); // HSV(0.60, 0.90, 1.0)
const diffCol2 = vec3<f32>(0.325, 1.0, 0.975); // HSV(0.55, 0.90, 1.0)

// Lighting (normalized manually)
const sunDir1 = vec3<f32>(0.0, 0.04997, -0.99875); // normalize(0, 0.05, -1)
const lightPos1 = vec3<f32>(10.0, 10.0, 10.0);
const lightPos2 = vec3<f32>(-10.0, 10.0, -10.0);

fn sRGB(t: vec3<f32>) -> vec3<f32> {
  return mix(1.055 * pow(t, vec3<f32>(1.0/2.4)) - 0.055, 12.92 * t, step(t, vec3<f32>(0.0031308)));
}

fn aces_approx(v_in: vec3<f32>) -> vec3<f32> {
  var v = max(v_in, vec3<f32>(0.0));
  v *= 0.6;
  let a = 2.51;
  let b = 0.03;
  let c = 2.43;
  let d = 0.59;
  let e = 0.14;
  return clamp((v * (a * v + b)) / (v * (c * v + d) + e), vec3<f32>(0.0), vec3<f32>(1.0));
}

fn tanh_approx(x: f32) -> f32 {
  let x2 = x * x;
  return clamp(x * (27.0 + x2) / (27.0 + 9.0 * x2), -1.0, 1.0);
}

fn rayPlane(ro: vec3<f32>, rd: vec3<f32>, plane: vec4<f32>) -> f32 {
  return -(dot(ro, plane.xyz) + plane.w) / dot(rd, plane.xyz);
}

fn box2d(p: vec2<f32>, b: vec2<f32>) -> f32 {
  let d = abs(p) - b;
  return length(max(d, vec2<f32>(0.0))) + min(max(d.x, d.y), 0.0);
}

fn box3d(p: vec3<f32>, b: vec3<f32>) -> f32 {
  let q = abs(p) - b;
  return length(max(q, vec3<f32>(0.0))) + min(max(q.x, max(q.y, q.z)), 0.0);
}

fn sphere(p: vec3<f32>, r: f32) -> f32 {
  return length(p) - r;
}

var<private> g_rot0: mat2x2<f32>;

fn render0(ro: vec3<f32>, rd: vec3<f32>) -> vec3<f32> {
  var col = vec3<f32>(0.0);
  var sf = 1.0001 - max(dot(sunDir1, rd), 0.0);
  col += skyCol * pow((1.0 - abs(rd.y)), 8.0);
  col += clamp(vec3<f32>(mix(0.0025, 0.125, tanh_approx(0.005 / sf)) / abs(rd.y)) * skylineCol, vec3<f32>(0.0), vec3<f32>(10.0));
  sf *= sf;
  col += sunCol * 0.00005 / sf;

  let tp1 = rayPlane(ro, rd, vec4<f32>(0.0, -1.0, 0.0, 6.0));
  if (tp1 > 0.0) {
    let pos = ro + tp1 * rd;
    let pp = pos.xz;
    let db = box2d(pp, vec2<f32>(5.0, 9.0)) - 3.0;
    col += vec3<f32>(4.0) * skyCol * rd.y * rd.y * smoothstep(0.25, 0.0, db);
    col += vec3<f32>(0.8) * skyCol * exp(-0.5 * max(db, 0.0));
  }

  return clamp(col, vec3<f32>(0.0), vec3<f32>(10.0));
}

fn df(p_in: vec3<f32>) -> f32 {
  var p = p_in;
  p.x = p_in.x * g_rot0[0][0] + p_in.z * g_rot0[0][1];
  p.z = p_in.x * g_rot0[1][0] + p_in.z * g_rot0[1][1];

  // Cube
  var pc = p;
  pc -= vec3<f32>(-1.9, 0.0, 0.0);
  let dCube = box3d(pc, vec3<f32>(1.6));

  // Sphere
  var ps = p;
  ps -= vec3<f32>(1.3, 0.0, 0.0);
  let dSphere = sphere(ps, 1.2);

  // Ground plane
  let dPlane = p.y + 1.0;

  // Union
  var d = min(dCube, dSphere);
  d = min(d, dPlane);

  return d;
}

fn normal(pos: vec3<f32>) -> vec3<f32> {
  let eps = vec2<f32>(NORM_OFF, 0.0);
  var nor: vec3<f32>;
  nor.x = df(pos + eps.xyy) - df(pos - eps.xyy);
  nor.y = df(pos + eps.yxy) - df(pos - eps.yxy);
  nor.z = df(pos + eps.yyx) - df(pos - eps.yyx);
  return normalize(nor);
}

fn rayMarch(ro: vec3<f32>, rd: vec3<f32>, initt: f32) -> f32 {
  var t = initt;
  for (var i = 0; i < MAX_RAY_MARCHES; i++) {
    if (t > MAX_RAY_LENGTH) {
      t = MAX_RAY_LENGTH;
      break;
    }
    let d = df(ro + rd * t);
    if (d < TOLERANCE) {
      break;
    }
    t += d;
  }
  return t;
}

fn shadow(lp: vec3<f32>, ld: vec3<f32>, mint: f32, maxt: f32) -> f32 {
  let ds = 1.0 - 0.4;
  var t = mint;
  var nd = 1e6;
  let soff = 0.05;
  let smul = 1.5;
  for (var i = 0; i < MAX_SHD_MARCHES; i++) {
    let p = lp + ld * t;
    let d = df(p);
    if (d < TOLERANCE || t >= maxt) {
      let sd = 1.0 - exp(-smul * max(t / maxt - soff, 0.0));
      return select(mix(sd, 1.0, smoothstep(0.0, 0.025, nd)), sd, t >= maxt);
    }
    nd = min(nd, d);
    t += ds * d;
  }
  let sd = 1.0 - exp(-smul * max(t / maxt - soff, 0.0));
  return sd;
}

fn boxCol(col: vec3<f32>, nsp: vec3<f32>, rd: vec3<f32>, nnor: vec3<f32>, nrcol: vec3<f32>, nshd1: f32, nshd2: f32) -> vec3<f32> {
  var nfre = 1.0 + dot(rd, nnor);
  nfre *= nfre;

  let nld1 = normalize(lightPos1 - nsp);
  let nld2 = normalize(lightPos2 - nsp);

  var ndif1 = max(dot(nld1, nnor), 0.0);
  ndif1 *= ndif1;

  var ndif2 = max(dot(nld2, nnor), 0.0);
  ndif2 *= ndif2;

  var scol = vec3<f32>(0.0);
  let rf = smoothstep(1.0, 0.9, nfre);
  scol += diffCol1 * ndif1 * nshd1;
  scol += diffCol2 * ndif2 * nshd2;
  scol += 0.1 * (skyCol + skylineCol);
  scol += nrcol * 0.75 * mix(vec3<f32>(0.25), vec3<f32>(0.5, 0.5, 1.0), nfre);

  return mix(col, scol, rf * smoothstep(90.0, 20.0, dot(nsp, nsp)));
}

fn render1(ro: vec3<f32>, rd: vec3<f32>) -> vec3<f32> {
  let skyCol_local = render0(ro, rd);
  var col = skyCol_local;

  let nt = rayMarch(ro, rd, 0.0);
  if (nt < MAX_RAY_LENGTH) {
    let nsp = ro + rd * nt;
    let nnor = normal(nsp);

    let nref = reflect(rd, nnor);
    let nrt = rayMarch(nsp, nref, 0.2);
    var nrcol = render0(nsp, nref);

    if (nrt < MAX_RAY_LENGTH) {
      let nrsp = nsp + nref * nrt;
      let nrnor = normal(nrsp);
      let nrref = reflect(nref, nrnor);
      nrcol = boxCol(nrcol, nrsp, nref, nrnor, render0(nrsp, nrref), 1.0, 1.0);
    }

    let nshd1 = mix(0.0, 1.0, shadow(nsp, normalize(lightPos1 - nsp), 0.1, distance(lightPos1, nsp)));
    let nshd2 = mix(0.0, 1.0, shadow(nsp, normalize(lightPos2 - nsp), 0.1, distance(lightPos2, nsp)));

    col = boxCol(col, nsp, rd, nnor, nrcol, nshd1, nshd2);
  }

  return col;
}

fn effect(p: vec2<f32>) -> vec3<f32> {
  g_rot0 = rot(-0.2 * uniforms.time);

  let fov = tan(TAU / 6.0);
  let ro = vec3<f32>(0.0, 2.5, 5.0);
  let la = vec3<f32>(0.0, 0.0, 0.0);
  let up = vec3<f32>(0.1, 1.0, 0.0);

  let ww = normalize(la - ro);
  let uu = normalize(cross(up, ww));
  let vv = cross(ww, uu);
  let rd = normalize(-p.x * uu + p.y * vv + fov * ww);

  return render1(ro, rd);
}

@vertex fn vs_main(@builtin(vertex_index) i: u32) -> @builtin(position) vec4<f32> {
  var pos = array<vec2<f32>, 3>(
    vec2<f32>(-1.0, -1.0),
    vec2<f32>(3.0, -1.0),
    vec2<f32>(-1.0, 3.0)
  );
  return vec4<f32>(pos[i], 0.0, 1.0);
}

@fragment fn fs_main(@builtin(position) p: vec4<f32>) -> @location(0) vec4<f32> {
  let q = p.xy / uniforms.resolution;
  var coord = -1.0 + 2.0 * q;
  coord.x *= uniforms.resolution.x / uniforms.resolution.y;
  var col = effect(coord);
  col = aces_approx(col);
  col = sRGB(col);
  return vec4<f32>(col, 1.0);
}