"use client";

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

type LiquidImageProps = {
  src: string;
  alt: string;
  /** Size of the waves. 1 is a soft swell. */
  waves?: number;
  /** Set the size here. */
  className?: string;
};

const DROPS = 3;
const REST = 0.4;
const VERTEX = `attribute vec2 p;varying vec2 v;void main(){v=p*.5+.5;gl_Position=vec4(p,0.,1.);}`;

const FRAGMENT = `precision highp float;
varying vec2 v;
uniform sampler2D t;
uniform vec2 fit;
uniform float u,amp,box;
uniform vec3 drops[${DROPS}];
void main(){
  vec2 o=vec2(sin(v.y*9.+u*1.1)+sin(v.y*17.-u*.7)*.5,cos(v.x*8.-u*.9)+sin((v.x+v.y)*13.+u*.6)*.5)*.0075*amp;
  for(int i=0;i<${DROPS};i++){
    vec2 q=(v-drops[i].xy)*vec2(box,1.);
    float r=max(length(q),.0001);
    float gap=r-drops[i].z*.7;
    o+=q/r*sin(gap*55.)*exp(-gap*gap*90.)*exp(-drops[i].z*2.4)*.035;
  }
  gl_FragColor=texture2D(t,((v+o)-.5)*fit*.965+.5);
}`;

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;
}

/* LiquidImage: the picture sits under water. It swells gently, swells more on hover, and a click or tap drops a ring into it. Runs only while on screen. */
export function LiquidImage({ src, alt, waves = 1, className = "aspect-video" }: LiquidImageProps) {
  const reduce = useReducedMotion();
  const boxRef = useRef<HTMLDivElement>(null);

  useEffect(() => {
    const box = boxRef.current;
    if (!box || reduce) 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);
    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 drops = Array.from({ length: DROPS }, () => ({ x: 0, y: 0, born: -100 }));
    let nextDrop = 0;
    let raf = 0;
    let ready = false;
    let inView = false;
    let amp = REST;
    let goal = REST;
    const image = new Image();
    image.crossOrigin = "anonymous";

    const draw = (now: number) => {
      const seconds = now / 1000;
      amp += (goal - amp) * 0.06;
      gl.uniform1f(at("u"), seconds % 1000);
      gl.uniform1f(at("amp"), amp * waves);
      gl.uniform3fv(at("drops"), drops.flatMap((d) => [d.x, d.y, seconds - d.born]));
      gl.drawArrays(gl.TRIANGLES, 0, 3);
    };

    const frame = (now: number) => {
      draw(now);
      raf = inView ? requestAnimationFrame(frame) : 0;
    };

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

    const fit = () => {
      const { width, height } = box.getBoundingClientRect();
      if (!width || !height) return;
      const dpr = Math.min(window.devicePixelRatio, 2);
      canvas.width = Math.round(width * dpr);
      canvas.height = Math.round(height * dpr);
      gl.viewport(0, 0, canvas.width, canvas.height);
      if (!ready) return;
      const shape = width / height / (image.naturalWidth / image.naturalHeight);
      gl.uniform2f(at("fit"), Math.min(1 / shape, 1), Math.min(shape, 1));
      gl.uniform1f(at("box"), width / height);
      draw(performance.now());
    };

    const drop = (e: PointerEvent) => {
      const r = box.getBoundingClientRect();
      drops[nextDrop] = { x: (e.clientX - r.left) / r.width, y: 1 - (e.clientY - r.top) / r.height, born: performance.now() / 1000 };
      nextDrop = (nextDrop + 1) % DROPS;
    };
    const enter = (e: PointerEvent) => {
      if (e.pointerType === "mouse") goal = 1;
    };
    const leave = () => {
      goal = REST;
    };

    image.onload = () => {
      gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, true);
      gl.bindTexture(gl.TEXTURE_2D, gl.createTexture());
      for (const wrap of [gl.TEXTURE_WRAP_S, gl.TEXTURE_WRAP_T]) gl.texParameteri(gl.TEXTURE_2D, wrap, gl.CLAMP_TO_EDGE);
      gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
      gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGB, gl.RGB, gl.UNSIGNED_BYTE, image);
      ready = true;
      fit();
      box.append(canvas);
      start();
    };
    image.src = src;

    const sized = new ResizeObserver(fit);
    sized.observe(box);
    const watch = new IntersectionObserver(([entry]) => {
      inView = entry.isIntersecting;
      start();
    });
    watch.observe(box);
    const lost = () => canvas.remove();
    canvas.addEventListener("webglcontextlost", lost);
    box.addEventListener("pointerdown", drop);
    box.addEventListener("pointerenter", enter);
    box.addEventListener("pointerleave", leave);

    return () => {
      cancelAnimationFrame(raf);
      sized.disconnect();
      watch.disconnect();
      image.onload = null;
      canvas.removeEventListener("webglcontextlost", lost);
      box.removeEventListener("pointerdown", drop);
      box.removeEventListener("pointerenter", enter);
      box.removeEventListener("pointerleave", leave);
      gl.getExtension("WEBGL_lose_context")?.loseContext();
      canvas.remove();
    };
  }, [src, waves, reduce]);

  return (
    <div ref={boxRef} className={`relative overflow-hidden ${className}`}>
      {/* eslint-disable-next-line @next/next/no-img-element */}
      <img src={src} alt={alt} className="absolute inset-0 size-full object-cover" />
    </div>
  );
}