"use client";

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

type SphereWorldProps = {
  /** Three six-digit hex colours. The spheres take turns. */
  colors?: [string, string, string];
  /** How many spheres, the big one included. 2 to 24. */
  count?: number;
  /** 1 is the default pace; 2 is twice as fast. */
  speed?: number;
  /** Six-digit hex colour behind the spheres. */
  background?: string;
  /** 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 = (count: number) => `precision highp float;
uniform vec2 res;
uniform mat3 cam;
uniform vec3 back,glow;
uniform vec4 balls[${count}];
uniform vec3 hues[${count}];
const vec3 sun=vec3(.5,.7,.51);
bool first(vec3 o,vec3 d,out float t,out vec3 c,out vec3 h,out float r){
  t=1e5;
  for(int i=0;i<${count};i++){
    vec3 q=o-balls[i].xyz;
    float b=dot(q,d),e=b*b-dot(q,q)+balls[i].w*balls[i].w;
    if(e<0.)continue;
    float x=-b-sqrt(e);
    if(x>.002&&x<t){t=x;c=balls[i].xyz;h=hues[i];r=balls[i].w;}
  }
  return t<1e4;
}
float lit(vec3 p){
  float l=1.;
  for(int i=0;i<${count};i++){
    vec3 q=p-balls[i].xyz;
    float b=dot(q,sun);
    if(b<0.)l=min(l,smoothstep(balls[i].w*.86,balls[i].w*1.16,sqrt(max(dot(q,q)-b*b,0.))));
  }
  return l;
}
vec3 shade(vec3 p,vec3 n,vec3 h){
  return h*(.1+.25*(n.y*.5+.5)+.95*max(dot(n,sun),0.)*lit(p));
}
vec3 room(vec3 d){
  return mix(back,glow,pow(max(d.y*.5+.5,0.),3.)*.8)+smoothstep(.93,.97,dot(d,sun))*.7;
}
void main(){
  vec2 uv=(gl_FragCoord.xy-.5*res)/(.5*min(res.x,res.y));
  vec3 o=cam*vec3(0.,0.,7.),d=cam*normalize(vec3(uv,-2.7));
  vec3 col=back+glow*.2*exp(-dot(uv,uv)*1.3);
  float t,r;vec3 c,h;
  if(first(o,d,t,c,h,r)){
    vec3 p=o+d*t,n=(p-c)/r,s=reflect(d,n);
    col=shade(p,n,h);
    float f=pow(1.+dot(d,n),4.);
    float t2,r2;vec3 c2,h2;
    vec3 far=room(s);
    if(first(p+n*.004,s,t2,c2,h2,r2)){vec3 q=p+n*.004+s*t2;far=shade(q,(q-c2)/r2,h2);}
    col=mix(col,far,.1+.7*f);
    col+=pow(max(dot(s,sun),0.),60.)*.8;
  }
  gl_FragColor=vec4(col,1.);
}`;

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

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

/* SphereWorld: lit spheres circle one big sphere and show in each other's surface. Drag or use the arrow keys to walk around them. Runs only while on screen. */
export function SphereWorld({
  colors = ["#a78bfa", "#22d3ee", "#f472b6"],
  count = 14,
  speed = 1,
  background = "#0b0a14",
  label = "Spheres circling a large sphere",
  className = "aspect-square w-80",
}: SphereWorldProps) {
  const reduce = useReducedMotion();
  const boxRef = useRef<HTMLDivElement>(null);
  const plainRef = useRef<HTMLDivElement>(null);
  const hues = colors.join();
  const total = Math.max(2, Math.min(24, Math.round(count)));

  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: false, antialias: false });
    const made = gl && program(gl, fragment(total));
    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 tints = hues.split(",").map(rgb);
    gl.uniform3fv(at("back"), rgb(background));
    gl.uniform3fv(at("glow"), tints[0]);
    gl.uniform3fv(at("hues"), Array.from({ length: total }, (_, i) => tints[i % 3]).flat());

    const moons = Array.from({ length: total - 1 }, (_, i) => {
      const ring = 1.55 + ((i * 0.37) % 1) * 1.1;
      const seed = (i + 1) * 2.399;
      return { ring, size: 0.13 + ((i * 0.61) % 1) * 0.24, lean: Math.sin(seed) * 0.42, phase: seed * 1.7, pace: (0.5 + ((i * 0.83) % 1) * 0.6) / Math.sqrt(ring) };
    });

    let raf = 0;
    let last = 0;
    let inView = false;
    let time = reduce ? 3 : 0;
    let yaw = 0.3;
    let pitch = 0.32;
    let drift = 0;
    let dragging = false;
    let lastX = 0;
    let lastY = 0;

    const draw = () => {
      const c = Math.cos(yaw), s = Math.sin(yaw), ct = Math.cos(pitch), st = Math.sin(pitch);
      gl.uniformMatrix3fv(at("cam"), false, [c, 0, s, st * s, ct, -st * c, -ct * s, st, ct * c]);
      const balls = [0, 0, 0, 1];
      for (const m of moons) {
        const a = m.phase + time * m.pace * speed;
        balls.push(Math.cos(a) * m.ring, Math.sin(a) * m.lean * m.ring, Math.sin(a) * m.ring, m.size);
      }
      gl.uniform4fv(at("balls"), balls);
      gl.drawArrays(gl.TRIANGLES, 0, 3);
    };

    const frame = (now: number) => {
      const dt = Math.min(0.05, (now - last) / 1000 || 0);
      last = now;
      if (!reduce) time += dt;
      if (!dragging) {
        yaw += drift;
        drift *= 0.94;
      }
      draw();
      raf = inView && !reduce ? requestAnimationFrame(frame) : 0;
    };

    const wake = () => {
      if (inView && !raf) 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 down = (e: PointerEvent) => {
      dragging = true;
      drift = 0;
      lastX = e.clientX;
      lastY = e.clientY;
      box.setPointerCapture(e.pointerId);
    };
    const move = (e: PointerEvent) => {
      if (!dragging) return;
      const step = (e.clientX - lastX) * 0.008;
      yaw += step;
      pitch = Math.max(-1.1, Math.min(1.1, pitch + (e.clientY - lastY) * 0.006));
      drift = reduce ? 0 : step;
      lastX = e.clientX;
      lastY = e.clientY;
      wake();
    };
    const up = () => {
      dragging = false;
      wake();
    };
    const key = (e: KeyboardEvent) => {
      const turn = { ArrowLeft: [-0.2, 0], ArrowRight: [0.2, 0], ArrowUp: [0, -0.15], ArrowDown: [0, 0.15] }[e.key];
      if (!turn) return;
      e.preventDefault();
      yaw += turn[0];
      pitch = Math.max(-1.1, Math.min(1.1, pitch + turn[1]));
      wake();
    };

    fit();
    box.append(canvas);
    plain.hidden = true;
    const sized = new ResizeObserver(fit);
    sized.observe(box);
    const watch = new IntersectionObserver(([entry]) => {
      inView = entry.isIntersecting;
      wake();
    });
    watch.observe(box);
    const lost = () => {
      canvas.remove();
      plain.hidden = false;
    };
    canvas.addEventListener("webglcontextlost", lost);
    box.addEventListener("pointerdown", down);
    box.addEventListener("pointermove", move);
    box.addEventListener("pointerup", up);
    box.addEventListener("pointercancel", up);
    box.addEventListener("keydown", key);

    return () => {
      cancelAnimationFrame(raf);
      sized.disconnect();
      watch.disconnect();
      canvas.removeEventListener("webglcontextlost", lost);
      box.removeEventListener("pointerdown", down);
      box.removeEventListener("pointermove", move);
      box.removeEventListener("pointerup", up);
      box.removeEventListener("pointercancel", up);
      box.removeEventListener("keydown", key);
      gl.getExtension("WEBGL_lose_context")?.loseContext();
      canvas.remove();
      plain.hidden = false;
    };
  }, [hues, total, speed, background, reduce]);

  return (
    <div
      ref={boxRef}
      role="img"
      aria-label={label}
      tabIndex={0}
      className={`relative cursor-grab touch-pan-y overflow-hidden active:cursor-grabbing ${className}`}
      style={{ background }}
    >
      <div
        ref={plainRef}
        className="absolute left-1/2 top-1/2 aspect-square h-1/2 -translate-x-1/2 -translate-y-1/2 rounded-full"
        style={{ background: `radial-gradient(circle at 35% 30%, #fff8, ${colors[0]} 40%, ${background} 100%)` }}
      />
    </div>
  );
}