"use client";

import { useEffect, useId, useRef, useState, type CSSProperties, type ElementType, type ReactNode } from "react";
import { AnimatePresence, motion, useReducedMotion } from "motion/react";

export type AboutCanvasChapter = {
  /** Short name on the button, such as a year. */
  label: string;
  title: string;
  text: string;
  /** What the dots spell. Keep it short: a year, a number, a word. */
  mark: string;
};

type AboutCanvasProps = {
  chapters: AboutCanvasChapter[];
  title?: string;
  /** Small line above the title. */
  eyebrow?: string;
  subtitle?: string;
  /** Goes under the story: a link or a button. */
  children?: ReactNode;
  /** Dot colour. */
  color?: string;
  /** Colour of the dots near the pointer. */
  accent?: string;
  /** How many dots. */
  dots?: number;
  /** h2 by default. */
  headingAs?: ElementType;
  /** Set padding and colours here. */
  className?: string;
};

const REACH = 70;
const font = (size: number) => `800 ${size}px system-ui, -apple-system, "Segoe UI", sans-serif`;

/** Where the dots go to spell a word in a w by h box: a shuffled list of spots. */
function spell(mark: string, w: number, h: number, count: number) {
  const page = document.createElement("canvas");
  page.width = w;
  page.height = h;
  const ctx = page.getContext("2d", { willReadFrequently: true });
  if (!ctx) return [];
  ctx.font = font(100);
  ctx.font = font(Math.min((100 * w * 0.9) / ctx.measureText(mark).width, h * 0.8));
  ctx.textAlign = "center";
  ctx.textBaseline = "middle";
  ctx.fillText(mark, w / 2, h / 2);
  const data = ctx.getImageData(0, 0, w, h).data;
  const lit: [number, number][] = [];
  for (let y = 0; y < h; y += 2) {
    for (let x = 0; x < w; x += 2) {
      if (data[(y * w + x) * 4 + 3] > 128) lit.push([x, y]);
    }
  }
  for (let i = lit.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [lit[i], lit[j]] = [lit[j], lit[i]];
  }
  return Array.from({ length: count }, (_, i) => lit[i % lit.length] ?? [w / 2, h / 2]);
}

/* AboutCanvas: a company story in chapters. Each chapter sends a cloud of dots flying into a new word or number, and the dots near the pointer scatter. It stops off screen. */
export function AboutCanvas({
  chapters,
  title,
  eyebrow,
  subtitle,
  children,
  color = "#a78bfa",
  accent = "#22d3ee",
  dots = 2000,
  headingAs: Heading = "h2",
  className = "bg-[#0b0a14] px-5 py-16 text-white",
}: AboutCanvasProps) {
  const reduce = useReducedMotion();
  const id = useId();
  const canvasRef = useRef<HTMLCanvasElement>(null);
  const [active, setActive] = useState(0);
  const chapter = chapters[active];
  const word = useRef(chapter.mark);
  const retarget = useRef<() => void>(undefined);

  useEffect(() => {
    const canvas = canvasRef.current;
    const ctx = canvas?.getContext("2d");
    if (!canvas || !ctx) return;
    const still = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const parts = Array.from({ length: dots }, () => ({ x: Math.random(), y: Math.random(), vx: 0, vy: 0, tx: 0, ty: 0, wait: 0, hot: 0 }));
    let w = 0;
    let h = 0;
    let frame = 0;
    let pointer: { x: number; y: number } | null = null;

    const draw = () => {
      ctx.clearRect(0, 0, w, h);
      for (const p of parts) {
        ctx.fillStyle = p.hot > 0.1 ? accent : color;
        ctx.globalAlpha = 0.75 + p.hot * 0.25;
        ctx.beginPath();
        ctx.arc(p.x, p.y, 1.3, 0, Math.PI * 2);
        ctx.fill();
      }
      ctx.globalAlpha = 1;
    };

    const aim = () => {
      if (!w || !h) return;
      spell(word.current, w, h, dots).forEach(([x, y], i) => {
        const p = parts[i];
        p.tx = x;
        p.ty = y;
        p.wait = Math.random() * 16;
        if (still) {
          p.x = x;
          p.y = y;
        }
      });
      draw();
    };

    const loop = () => {
      for (const p of parts) {
        if (p.wait > 0) p.wait -= 1;
        else {
          p.vx += (p.tx - p.x) * 0.018;
          p.vy += (p.ty - p.y) * 0.018;
        }
        p.hot *= 0.93;
        if (pointer) {
          const dx = p.x - pointer.x;
          const dy = p.y - pointer.y;
          const gap = Math.hypot(dx, dy) || 1;
          if (gap < REACH) {
            const push = (1 - gap / REACH) * 2.4;
            p.vx += (dx / gap) * push;
            p.vy += (dy / gap) * push;
            p.hot = 1;
          }
        }
        p.vx *= 0.84;
        p.vy *= 0.84;
        p.x += p.vx;
        p.y += p.vy;
      }
      draw();
      frame = requestAnimationFrame(loop);
    };

    const resize = () => {
      const scale = Math.min(window.devicePixelRatio || 1, 2);
      const first = !w;
      w = canvas.clientWidth;
      h = canvas.clientHeight;
      canvas.width = w * scale;
      canvas.height = h * scale;
      ctx.setTransform(scale, 0, 0, scale, 0, 0);
      if (first) {
        for (const p of parts) {
          p.x *= w;
          p.y *= h;
        }
      }
      aim();
    };

    const move = (e: PointerEvent) => {
      if (e.pointerType !== "mouse") return;
      const rect = canvas.getBoundingClientRect();
      pointer = { x: e.clientX - rect.left, y: e.clientY - rect.top };
    };
    const leave = () => {
      pointer = null;
    };

    const watcher = new ResizeObserver(resize);
    watcher.observe(canvas);
    const onScreen = new IntersectionObserver(([entry]) => {
      cancelAnimationFrame(frame);
      frame = entry.isIntersecting && !still ? requestAnimationFrame(loop) : 0;
    });
    onScreen.observe(canvas);
    retarget.current = aim;
    if (!still) {
      canvas.addEventListener("pointermove", move);
      canvas.addEventListener("pointerleave", leave);
    }

    return () => {
      cancelAnimationFrame(frame);
      retarget.current = undefined;
      watcher.disconnect();
      onScreen.disconnect();
      canvas.removeEventListener("pointermove", move);
      canvas.removeEventListener("pointerleave", leave);
    };
  }, [accent, color, dots]);

  const open = (i: number) => {
    setActive(i);
    word.current = chapters[i].mark;
    retarget.current?.();
  };

  return (
    <section aria-labelledby={title ? id : undefined} className={`@container ${className}`} style={{ "--ac-color": color } as CSSProperties}>
      <div className="mx-auto grid max-w-6xl items-center gap-6 @3xl:grid-cols-2 @3xl:gap-12">
        <div>
          {title && (
            <header className="mb-6">
              {eyebrow && <p className="mb-2 text-xs font-medium tracking-[0.2em] uppercase opacity-70">{eyebrow}</p>}
              <Heading id={id} className="text-[clamp(1.5rem,6cqw,2.5rem)] leading-tight font-semibold tracking-tight text-balance">
                {title}
              </Heading>
              {subtitle && <p className="mt-3 text-pretty opacity-70">{subtitle}</p>}
            </header>
          )}
          <div className="flex flex-wrap gap-2">
            {chapters.map((item, i) => {
              const on = i === active;
              return (
                <button
                  key={item.label}
                  type="button"
                  aria-pressed={on}
                  onClick={() => open(i)}
                  className={`rounded-full border px-3.5 py-1.5 text-sm tabular-nums transition-colors ${on ? "border-[var(--ac-color)] text-[var(--ac-color)]" : "border-current/15 opacity-70 hover:opacity-100"}`}
                >
                  {item.label}
                </button>
              );
            })}
          </div>
          <div aria-live="polite" className="mt-5 min-h-32">
            <AnimatePresence mode="wait" initial={false}>
              <motion.div
                key={active}
                initial={{ opacity: 0, y: reduce ? 0 : 10 }}
                animate={{ opacity: 1, y: 0 }}
                exit={{ opacity: 0, y: reduce ? 0 : -10 }}
                transition={{ duration: reduce ? 0 : 0.25 }}
              >
                <h3 className="text-lg font-semibold">{chapter.title}</h3>
                <p className="mt-1.5 text-pretty opacity-70">{chapter.text}</p>
              </motion.div>
            </AnimatePresence>
          </div>
          {children && <div className="mt-5">{children}</div>}
        </div>
        <canvas ref={canvasRef} aria-hidden className="aspect-[3/2] w-full" />
      </div>
    </section>
  );
}