"use client";

import { useEffect, useRef } from "react";
import { useReducedMotion } from "motion/react";

type FloatingPlanetProps = {
  /** Three six-digit hex colours for the cloud bands. */
  colors?: [string, string, string];
  /** Show the rings. */
  rings?: boolean;
  /** Show twinkling stars behind it. */
  stars?: boolean;
  /** 1 is the default pace; 2 is twice as fast. */
  speed?: number;
  /** Name read out by screen readers. */
  label?: string;
  /** Set the size here. */
  className?: string;
};

const MAX_PIXELS = 1400000;
const VERTEX = `attribute vec2 p;void main(){gl_Position=vec4(p,0.,1.);}`;

const FRAGMENT = `precision highp float;
uniform vec2 res,drift;
uniform vec3 up,c1,c2,c3;
uniform float time,bob,rings,stars;
const vec3 sun=vec3(-.62,.42,.66);
float hash(vec3 p){return fract(sin(dot(p,vec3(12.9898,78.233,37.719)))*43758.5453);}
float noise(vec3 p){
  vec3 i=floor(p),f=fract(p);
  f=f*f*(3.-2.*f);
  return mix(mix(mix(hash(i),hash(i+vec3(1.,0.,0.)),f.x),mix(hash(i+vec3(0.,1.,0.)),hash(i+vec3(1.,1.,0.)),f.x),f.y),
             mix(mix(hash(i+vec3(0.,0.,1.)),hash(i+vec3(1.,0.,1.)),f.x),mix(hash(i+vec3(0.,1.,1.)),hash(i+vec3(1.,1.,1.)),f.x),f.y),f.z);
}
float fbm(vec3 p){
  float v=0.,a=.5;
  for(int i=0;i<4;i++){v+=a*noise(p);p=p*2.03+7.1;a*=.5;}
  return v;
}
float band(float r){
  float s=(r-1.38)/.82;
  if(s<0.||s>1.)return 0.;
  float a=.55+.28*sin(s*38.)+.17*sin(s*91.+1.);
  a*=smoothstep(0.,.06,s)*(1.-smoothstep(.9,1.,s));
  a*=smoothstep(.02,.05,abs(s-.62));
  return clamp(a,0.,1.)*rings;
}
vec4 over(vec4 a,vec4 b){return a+b*(1.-a.a);}
void main(){
  float side=min(res.x,res.y);
  vec2 uv=(gl_FragCoord.xy-.5*res)/(.5*side);
  vec3 o=vec3(0.,0.,6.),d=normalize(vec3(uv,-2.6));
  vec3 C=vec3(drift.x,bob+drift.y,0.);
  vec3 e1=normalize(cross(up,vec3(0.,0.,1.))),e3=cross(e1,up);
  vec4 col=vec4(0.);
  if(stars>0.){
    vec2 g=(uv-drift*.05)*22.,cell=floor(g);
    float k=hash(vec3(cell,1.));
    if(k>.86){
      vec2 spot=fract(g)-.5-(vec2(hash(vec3(cell,2.)),hash(vec3(cell,3.)))-.5)*.6;
      float s=(1.-smoothstep(0.,.07+k*.04,length(spot)))*(.55+.45*sin(time*(1.+k*3.)+k*40.));
      col=vec4(vec3(s),s*.9);
    }
  }
  vec3 q=o-C;
  float b=dot(q,d),miss=sqrt(max(dot(q,q)-b*b,0.)),h=1.-miss*miss;
  float tBall=h>0.?-b-sqrt(h):1e5;
  float tRing=dot(C-o,up)/dot(d,up);
  vec3 onRing=o+d*tRing-C;
  float ring=tRing>0.?band(length(onRing)):0.;
  float aura=exp(-max(miss-1.,0.)*9.)*.5;
  col=over(vec4(c1*aura,aura*.9),col);
  vec4 hoop=vec4(0.);
  if(ring>0.){
    float toSun=dot(onRing,sun);
    float seen=toSun<0.?smoothstep(.96,1.06,sqrt(max(dot(onRing,onRing)-toSun*toSun,0.))):1.;
    vec3 tone=mix(c2,c3,.5+.5*sin(length(onRing)*24.))*(.12+.95*seen);
    hoop=vec4(tone*ring,ring);
  }
  if(tRing>tBall)col=over(hoop,col);
  if(h>0.){
    vec3 n=q+d*tBall;
    float spin=time*.12;
    vec3 l=vec3(dot(n,e1),dot(n,up),dot(n,e3));
    vec3 s=vec3(l.x*cos(spin)-l.z*sin(spin),l.y,l.x*sin(spin)+l.z*cos(spin));
    float w=fbm(s*vec3(3.,9.,3.));
    vec3 body=mix(c1,c2,sin(l.y*11.+w*5.)*.5+.5);
    body=mix(body,c3,smoothstep(.5,.72,fbm(s*vec3(2.,14.,2.)+3.)));
    float cross_=-dot(n,up)/dot(sun,up);
    float shade=cross_>0.?1.-.75*band(length(n+sun*cross_)):1.;
    float lit=smoothstep(-.12,.95,dot(n,sun))*shade;
    vec3 surface=body*(.05+1.15*lit)+c1*pow(1.+dot(d,n),3.)*.75*lit;
    float cover=1.-smoothstep(1.-3.2/side,1.,miss);
    col=over(vec4(surface*cover,cover),col);
  }
  if(tRing<=tBall)col=over(hoop,col);
  gl_FragColor=col;
}`;

const rgb = (hex: string) => [1, 3, 5].map((i) => parseInt(hex.slice(i, i + 2), 16) / 255);

function program(gl: WebGLRenderingContext) {
  const made = gl.createProgram();
  for (const [type, text] of [[gl.VERTEX_SHADER, VERTEX], [gl.FRAGMENT_SHADER, FRAGMENT]] as const) {
    const shader = gl.createShader(type);
    if (!made || !shader) return null;
    gl.shaderSource(shader, text);
    gl.compileShader(shader);
    gl.attachShader(made, shader);
  }
  if (!made) return null;
  gl.linkProgram(made);
  return gl.getProgramParameter(made, gl.LINK_STATUS) ? made : null;
}

/* FloatingPlanet: a ringed planet with drifting cloud bands bobs in space and leans gently toward the mouse. Runs only while on screen. */
export function FloatingPlanet({
  colors = ["#a78bfa", "#f472b6", "#fde68a"],
  rings = true,
  stars = true,
  speed = 1,
  label = "A ringed planet floating in space",
  className = "aspect-square w-80",
}: FloatingPlanetProps) {
  const reduce = useReducedMotion();
  const boxRef = useRef<HTMLDivElement>(null);
  const plainRef = useRef<HTMLDivElement>(null);
  const hues = colors.join();

  useEffect(() => {
    const box = boxRef.current;
    const plain = plainRef.current;
    if (!box || !plain) return;
    const canvas = document.createElement("canvas");
    canvas.setAttribute("aria-hidden", "true");
    canvas.style.cssText = "position:absolute;inset:0;width:100%;height:100%";
    const gl = canvas.getContext("webgl", { alpha: true, antialias: false });
    const made = gl && program(gl);
    if (!gl || !made) return;
    gl.useProgram(made);
    gl.bindBuffer(gl.ARRAY_BUFFER, gl.createBuffer());
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([-1, -1, 3, -1, -1, 3]), gl.STATIC_DRAW);
    const corner = gl.getAttribLocation(made, "p");
    gl.enableVertexAttribArray(corner);
    gl.vertexAttribPointer(corner, 2, gl.FLOAT, false, 0, 0);
    const at = (name: string) => gl.getUniformLocation(made, name);

    const [one, two, three] = hues.split(",").map(rgb);
    gl.uniform3fv(at("c1"), one);
    gl.uniform3fv(at("c2"), two);
    gl.uniform3fv(at("c3"), three);
    gl.uniform1f(at("rings"), rings ? 1 : 0);
    gl.uniform1f(at("stars"), stars ? 1 : 0);

    let raf = 0;
    let last = 0;
    let inView = false;
    let time = reduce ? 5 : 0;
    let lookX = 0;
    let lookY = 0;
    let goalX = 0;
    let goalY = 0;

    const draw = () => {
      const lean = -0.42 + lookX * 0.1;
      const front = 0.34 + lookY * 0.12;
      const size = Math.hypot(Math.sin(lean), Math.cos(lean), front);
      gl.uniform3f(at("up"), Math.sin(lean) / size, Math.cos(lean) / size, front / size);
      gl.uniform2f(at("drift"), lookX * 0.09, lookY * 0.09);
      gl.uniform1f(at("bob"), reduce ? 0 : Math.sin(time * 0.8) * 0.07);
      gl.uniform1f(at("time"), time % 1000);
      gl.drawArrays(gl.TRIANGLES, 0, 3);
    };

    const frame = (now: number) => {
      const dt = Math.min(0.05, (now - last) / 1000 || 0);
      last = now;
      time += dt * speed;
      lookX += (goalX - lookX) * 0.06;
      lookY += (goalY - lookY) * 0.06;
      draw();
      raf = inView ? requestAnimationFrame(frame) : 0;
    };

    const start = () => {
      if (inView && !raf && !reduce) raf = requestAnimationFrame(frame);
    };

    const fit = () => {
      const { width, height } = box.getBoundingClientRect();
      if (!width || !height) return;
      const scale = Math.min(Math.max(window.devicePixelRatio, 1.5), 2, Math.sqrt(MAX_PIXELS / (width * height)));
      canvas.width = Math.round(width * scale);
      canvas.height = Math.round(height * scale);
      gl.viewport(0, 0, canvas.width, canvas.height);
      gl.uniform2f(at("res"), canvas.width, canvas.height);
      draw();
    };

    const point = (e: PointerEvent) => {
      if (e.pointerType !== "mouse") return;
      const r = box.getBoundingClientRect();
      goalX = ((e.clientX - r.left) / r.width - 0.5) * 2;
      goalY = (0.5 - (e.clientY - r.top) / r.height) * 2;
    };
    const leave = () => {
      goalX = 0;
      goalY = 0;
    };

    fit();
    box.append(canvas);
    plain.hidden = true;
    const sized = new ResizeObserver(fit);
    sized.observe(box);
    const watch = new IntersectionObserver(([entry]) => {
      inView = entry.isIntersecting;
      start();
    });
    watch.observe(box);
    const lost = () => {
      canvas.remove();
      plain.hidden = false;
    };
    canvas.addEventListener("webglcontextlost", lost);
    box.addEventListener("pointermove", point);
    box.addEventListener("pointerleave", leave);

    return () => {
      cancelAnimationFrame(raf);
      sized.disconnect();
      watch.disconnect();
      canvas.removeEventListener("webglcontextlost", lost);
      box.removeEventListener("pointermove", point);
      box.removeEventListener("pointerleave", leave);
      gl.getExtension("WEBGL_lose_context")?.loseContext();
      canvas.remove();
      plain.hidden = false;
    };
  }, [hues, rings, stars, speed, reduce]);

  return (
    <div ref={boxRef} role="img" aria-label={label} className={`relative overflow-hidden ${className}`}>
      <div
        ref={plainRef}
        className="absolute left-1/2 top-1/2 aspect-square h-[38%] -translate-x-1/2 -translate-y-1/2 rounded-full"
        style={{ background: `radial-gradient(circle at 30% 30%, ${colors[2]}, ${colors[1]} 45%, ${colors[0]} 100%)` }}
      />
    </div>
  );
}