"use client";

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

type CubeMorphShape = "cube" | "sphere" | "diamond" | "ring";

type CubeMorphProps = {
  /** Shapes in order. It loops back to the first. */
  shapes?: CubeMorphShape[];
  /** Seconds it rests on each shape. */
  hold?: number;
  /** Two six-digit hex colours. */
  colors?: [string, string];
  /** 1 is the default turning pace; 2 is twice as fast. */
  speed?: number;
  /** What the button says to screen readers. */
  label?: string;
  /** Set the size here. */
  className?: string;
};

const ALL_SHAPES: CubeMorphShape[] = ["cube", "sphere", "diamond", "ring"];
const MAX_PIXELS = 900000;
const MORPH = 1.3;
const VERTEX = `attribute vec2 p;void main(){gl_Position=vec4(p,0.,1.);}`;

const FRAGMENT = `precision highp float;
uniform vec2 res;
uniform vec4 mixer;
uniform mat3 turn;
uniform vec3 c1,c2;
const vec3 sun=vec3(.45,.68,.58);
float cube(vec3 p){vec3 q=abs(p)-.72;return length(max(q,0.))+min(max(q.x,max(q.y,q.z)),0.)-.11;}
float diamond(vec3 p){p=abs(p);return (p.x+p.y+p.z-1.42)*.577;}
float ring(vec3 p){return length(vec2(length(p.xz)-.74,p.y))-.3;}
float map(vec3 p){
  p=turn*p;
  return mixer.x*cube(p)+mixer.y*(length(p)-1.05)+mixer.z*diamond(p)+mixer.w*ring(p);
}
vec3 normal(vec3 p){
  vec2 e=vec2(.004,-.004);
  return normalize(e.xyy*map(p+e.xyy)+e.yyx*map(p+e.yyx)+e.yxy*map(p+e.yxy)+e.xxx*map(p+e.xxx));
}
void main(){
  float side=min(res.x,res.y);
  vec2 uv=(gl_FragCoord.xy-.5*res)/(.5*side);
  vec3 o=vec3(0.,0.,4.),d=normalize(vec3(uv,-2.45));
  float t=2.1,best=1.,bestT=t;
  for(int i=0;i<64;i++){
    float m=map(o+d*t);
    if(m<best){best=m;bestT=t;}
    if(m<.0002||t>6.)break;
    t+=m*.9;
  }
  if(best<.0002)bestT=t;
  float a=1.-smoothstep(0.,3.5/side,best);
  if(a<=0.){gl_FragColor=vec4(0.);return;}
  vec3 p=o+d*bestT,n=normal(p),r=reflect(d,n);
  float f=pow(1.+dot(d,n),3.);
  vec3 col=mix(c1,c2,clamp(.34+.55*n.y+.25*n.x,0.,1.))*(.2+.9*max(dot(n,sun),0.));
  col+=mix(c2,c1,.5+.5*n.x)*f*1.1;
  col+=pow(max(dot(r,sun),0.),42.)*.9;
  gl_FragColor=vec4(col*a,a);
}`;

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;
}

/* CubeMorph: one solid melts from shape to shape as it turns. A click, Enter or Space moves on to the next shape at once. Runs only while on screen. */
export function CubeMorph({
  shapes = ALL_SHAPES,
  hold = 2,
  colors = ["#7c3aed", "#22d3ee"],
  speed = 1,
  label = "Change the shape",
  className = "aspect-square w-72",
}: CubeMorphProps) {
  const reduce = useReducedMotion();
  const boxRef = useRef<HTMLButtonElement>(null);
  const plainRef = useRef<HTMLSpanElement>(null);
  const order = shapes.join();
  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 [first, second] = hues.split(",").map(rgb);
    gl.uniform3fv(at("c1"), first);
    gl.uniform3fv(at("c2"), second);

    const list = order.split(",").map((name) => ALL_SHAPES.indexOf(name as CubeMorphShape));
    let raf = 0;
    let last = 0;
    let inView = false;
    let from = 0;
    let to = 0;
    let blend = 1;
    let waited = 0;
    let kick = 0;
    let angleX = 0.62;
    let angleY = 0.72;

    const draw = () => {
      const e = blend * blend * (3 - 2 * blend);
      gl.uniform4fv(at("mixer"), [0, 1, 2, 3].map((i) => (list[from] === i ? 1 - e : 0) + (list[to] === i ? e : 0)));
      const c = Math.cos(angleY), s = Math.sin(angleY), ct = Math.cos(angleX), st = Math.sin(angleX);
      gl.uniformMatrix3fv(at("turn"), false, [c, 0, s, st * s, ct, -st * c, -ct * s, st, ct * c]);
      gl.drawArrays(gl.TRIANGLES, 0, 3);
    };

    const next = () => {
      if (blend < 1 || list.length < 2) return;
      to = (from + 1) % list.length;
      blend = 0;
    };

    const frame = (now: number) => {
      const dt = Math.min(0.05, (now - last) / 1000 || 0);
      last = now;
      if (blend < 1) {
        blend = Math.min(1, blend + dt / MORPH);
        if (blend === 1) {
          from = to;
          waited = 0;
        }
      } else if ((waited += dt) >= hold) {
        next();
      }
      kick *= 0.95;
      angleY += dt * (0.5 + kick) * speed;
      angleX += dt * (0.22 + kick * 0.4) * speed;
      draw();
      raf = inView ? requestAnimationFrame(frame) : 0;
    };

    const wake = () => {
      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 click = () => {
      if (reduce) {
        if (list.length > 1) from = to = (from + 1) % list.length;
        draw();
        return;
      }
      kick = 3;
      next();
    };

    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("click", click);

    return () => {
      cancelAnimationFrame(raf);
      sized.disconnect();
      watch.disconnect();
      canvas.removeEventListener("webglcontextlost", lost);
      box.removeEventListener("click", click);
      gl.getExtension("WEBGL_lose_context")?.loseContext();
      canvas.remove();
      plain.hidden = false;
    };
  }, [order, hues, hold, speed, reduce]);

  return (
    <button ref={boxRef} type="button" aria-label={label} className={`relative block cursor-pointer rounded-2xl ${className}`}>
      <span
        ref={plainRef}
        className="absolute left-1/4 top-1/4 size-1/2 rounded-2xl"
        style={{ background: `linear-gradient(135deg, ${colors[0]}, ${colors[1]})` }}
      />
    </button>
  );
}