// modules/terrain/clouds.js — Procedural cloud layer
import * as THREE from 'three';

const CLOUD_LAYER_Y = -6.0;
const CLOUD_DIMENSIONS = 120;
const CLOUD_THICKNESS = 15;
const CLOUD_OPACITY = 0.6;

const cloudGeometry = new THREE.BoxGeometry(CLOUD_DIMENSIONS, CLOUD_THICKNESS, CLOUD_DIMENSIONS, 8, 4, 8);

const CloudShader = {
  uniforms: {
    'uTime': { value: 0.0 },
    'uCloudColor': { value: new THREE.Color(0x88bbff) },
    'uNoiseScale': { value: new THREE.Vector3(0.015, 0.015, 0.015) },
    'uDensity': { value: 0.8 },
  },
  vertexShader: `
    varying vec3 vWorldPosition;
    void main() {
      vWorldPosition = (modelMatrix * vec4(position, 1.0)).xyz;
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
    }
  `,
  fragmentShader: `
    uniform float uTime;
    uniform vec3 uCloudColor;
    uniform vec3 uNoiseScale;
    uniform float uDensity;
    varying vec3 vWorldPosition;

    vec3 mod289(vec3 x) { return x - floor(x * (1.0 / 289.0)) * 289.0; }
    vec4 mod289(vec4 x) { return x - floor(x * (1.0 / 289.0)) * 289.0; }
    vec4 permute(vec4 x) { return mod289(((x * 34.0) + 1.0) * x); }
    vec4 taylorInvSqrt(vec4 r) { return 1.79284291400159 - 0.85373472095314 * r; }
    float snoise(vec3 v) {
      const vec2 C = vec2(1.0/6.0, 1.0/3.0);
      const vec4 D = vec4(0.0, 0.5, 1.0, 2.0);
      vec3 i  = floor(v + dot(v, C.yyy));
      vec3 x0 = v - i + dot(i, C.xxx);
      vec3 g  = step(x0.yzx, x0.xyz);
      vec3 l  = 1.0 - g;
      vec3 i1 = min(g.xyz, l.zxy);
      vec3 i2 = max(g.xyz, l.zxy);
      vec3 x1 = x0 - i1 + C.xxx;
      vec3 x2 = x0 - i2 + C.yyy;
      vec3 x3 = x0 - D.yyy;
      i = mod289(i);
      vec4 p = permute(permute(permute(
              i.z + vec4(0.0, i1.z, i2.z, 1.0))
            + i.y + vec4(0.0, i1.y, i2.y, 1.0))
            + i.x + vec4(0.0, i1.x, i2.x, 1.0));
      float n_ = 0.142857142857;
      vec3 ns = n_ * D.wyz - D.xzx;
      vec4 j  = p - 49.0 * floor(p * ns.z * ns.z);
      vec4 x_ = floor(j * ns.z);
      vec4 y_ = floor(j - 7.0 * x_);
      vec4 x  = x_ * ns.x + ns.yyyy;
      vec4 y  = y_ * ns.x + ns.yyyy;
      vec4 h  = 1.0 - abs(x) - abs(y);
      vec4 b0 = vec4(x.xy, y.xy);
      vec4 b1 = vec4(x.zw, y.zw);
      vec4 s0 = floor(b0) * 2.0 + 1.0;
      vec4 s1 = floor(b1) * 2.0 + 1.0;
      vec4 sh = -step(h, vec4(0.0));
      vec4 a0 = b0.xzyw + s0.xzyw * sh.xxyy;
      vec4 a1 = b1.xzyw + s1.xzyw * sh.zzww;
      vec3 p0 = vec3(a0.xy, h.x);
      vec3 p1 = vec3(a0.zw, h.y);
      vec3 p2 = vec3(a1.xy, h.z);
      vec3 p3 = vec3(a1.zw, h.w);
      vec4 norm = taylorInvSqrt(vec4(dot(p0,p0), dot(p1,p1), dot(p2,p2), dot(p3,p3)));
      p0 *= norm.x; p1 *= norm.y; p2 *= norm.z; p3 *= norm.w;
      vec4 m = max(0.6 - vec4(dot(x0,x0), dot(x1,x1), dot(x2,x2), dot(x3,x3)), 0.0);
      m = m * m;
      return 42.0 * dot(m*m, vec4(dot(p0,x0), dot(p1,x1), dot(p2,x2), dot(p3,x3)));
    }

    void main() {
      vec3 noiseCoord = vWorldPosition * uNoiseScale + vec3(uTime * 0.003, 0.0, uTime * 0.002);
      float noiseVal  = snoise(noiseCoord)       * 0.500;
      noiseVal       += snoise(noiseCoord * 2.0) * 0.250;
      noiseVal       += snoise(noiseCoord * 4.0) * 0.125;
      noiseVal /= 0.875;
      float density = smoothstep(0.25, 0.85, noiseVal * 0.5 + 0.5);
      density *= uDensity;
      float layerBottom = ${(CLOUD_LAYER_Y - CLOUD_THICKNESS * 0.5).toFixed(1)};
      float yNorm = (vWorldPosition.y - layerBottom) / ${CLOUD_THICKNESS.toFixed(1)};
      float fadeFactor = smoothstep(0.0, 0.15, yNorm) * smoothstep(1.0, 0.85, yNorm);
      gl_FragColor = vec4(uCloudColor, density * fadeFactor * ${CLOUD_OPACITY.toFixed(1)});
      if (gl_FragColor.a < 0.04) discard;
    }
  `,
};

export const cloudMaterial = new THREE.ShaderMaterial({
  uniforms: CloudShader.uniforms,
  vertexShader: CloudShader.vertexShader,
  fragmentShader: CloudShader.fragmentShader,
  transparent: true,
  depthWrite: false,
  blending: THREE.AdditiveBlending,
  side: THREE.DoubleSide,
});

const clouds = new THREE.Mesh(cloudGeometry, cloudMaterial);
clouds.position.y = CLOUD_LAYER_Y;

export function init(scene) {
  scene.add(clouds);
}

export function update(elapsed) {
  cloudMaterial.uniforms.uTime.value = elapsed;
}