"use client";

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

export type TestimonialFlowItem = {
  quote: string;
  name: string;
  role?: string;
  /** Face picture. Without it the first letter of the name shows. */
  avatar?: string;
};

type TestimonialFlowProps = {
  items: TestimonialFlowItem[];
  title?: string;
  /** Small line above the title. */
  eyebrow?: string;
  subtitle?: string;
  /** Most columns on a wide screen. */
  columns?: number;
  /** Smallest column width in pixels. Fewer columns fit when narrow. */
  minWidth?: number;
  /** Pixels per second. */
  speed?: number;
  /** Card colour. */
  tile?: string;
  /** Sets the height of the moving part. */
  boxClassName?: string;
  /** h2 by default. */
  headingAs?: ElementType;
  /** Set padding and colours here. */
  className?: string;
};

const GAP = 16;
const MASK = "linear-gradient(180deg, transparent, #000 9%, #000 91%, transparent)";

function Card({ item, tile }: { item: TestimonialFlowItem; tile: string }) {
  return (
    <figure className="rounded-2xl border border-current/10 p-5" style={{ backgroundColor: tile }}>
      <blockquote className="text-sm leading-relaxed text-pretty opacity-90">{item.quote}</blockquote>
      <figcaption className="mt-4 flex items-center gap-3">
        {item.avatar ? (
          <img src={item.avatar} alt="" className="size-9 rounded-full object-cover" />
        ) : (
          <span aria-hidden className="grid size-9 place-items-center rounded-full bg-current/10 text-sm font-semibold">
            {item.name.charAt(0)}
          </span>
        )}
        <span className="min-w-0 text-sm">
          <span className="block font-semibold">{item.name}</span>
          {item.role && <span className="block truncate opacity-60">{item.role}</span>}
        </span>
      </figcaption>
    </figure>
  );
}

function Column({ items, reverse, speed, tile }: { items: TestimonialFlowItem[]; reverse: boolean; speed: number; tile: string }) {
  const reduce = useReducedMotion();
  const box = useRef<HTMLDivElement>(null);
  const belt = useRef<HTMLDivElement>(null);
  const run = useRef<HTMLDivElement>(null);
  const anim = useRef<Animation | null>(null);
  const frame = useRef(0);
  const [copies, setCopies] = useState(2);

  useEffect(() => {
    if (!box.current || !run.current) return;
    const watcher = new ResizeObserver(() => {
      const height = run.current?.offsetHeight ?? 0;
      if (!height) return;
      setCopies(reduce ? 1 : Math.ceil((box.current?.offsetHeight ?? 0) / height) + 1);
      anim.current?.effect?.updateTiming({ duration: (height / speed) * 1000 });
    });
    watcher.observe(box.current);
    watcher.observe(run.current);
    return () => watcher.disconnect();
  }, [reduce, speed]);

  useEffect(() => {
    if (reduce || !box.current || !belt.current || !run.current) return;
    const moving = belt.current.animate(
      { transform: ["translateY(0)", `translateY(${-100 / copies}%)`] },
      { duration: Math.max(1, (run.current.offsetHeight / speed) * 1000), iterations: Infinity, direction: reverse ? "reverse" : "normal" },
    );
    anim.current = moving;
    const onScreen = new IntersectionObserver(([entry]) => {
      if (entry.isIntersecting) moving.play();
      else moving.pause();
    });
    onScreen.observe(box.current);
    return () => {
      cancelAnimationFrame(frame.current);
      onScreen.disconnect();
      moving.cancel();
      anim.current = null;
    };
  }, [copies, reduce, reverse, speed]);

  const glide = (to: number) => {
    cancelAnimationFrame(frame.current);
    const step = () => {
      const moving = anim.current;
      if (!moving) return;
      const next = moving.playbackRate + (to - moving.playbackRate) * 0.14;
      moving.playbackRate = Math.abs(to - next) < 0.01 ? to : next;
      if (moving.playbackRate !== to) frame.current = requestAnimationFrame(step);
    };
    step();
  };

  return (
    <div
      ref={box}
      tabIndex={copies === 1 ? 0 : undefined}
      onPointerEnter={() => glide(0)}
      onPointerLeave={() => glide(1)}
      className="h-full min-w-0 flex-1 overflow-hidden motion-reduce:overflow-y-auto"
    >
      <div ref={belt}>
        {Array.from({ length: copies }, (_, copy) => (
          <div key={copy} ref={copy === 0 ? run : undefined} aria-hidden={copy > 0 || undefined} className="grid" style={{ gap: GAP, paddingBottom: GAP }}>
            {items.map((item) => (
              <Card key={item.name + item.quote} item={item} tile={tile} />
            ))}
          </div>
        ))}
      </div>
    </div>
  );
}

/* TestimonialFlow: columns of quotes drifting up and down at an even pace, with no seam. A column eases to a stop under the pointer. Under reduced motion they stand still and scroll by hand. */
export function TestimonialFlow({
  items,
  title,
  eyebrow,
  subtitle,
  columns = 3,
  minWidth = 260,
  speed = 24,
  tile = "#15122a",
  boxClassName = "h-[34rem]",
  headingAs: Heading = "h2",
  className = "bg-[#0b0a14] px-5 py-16 text-white",
}: TestimonialFlowProps) {
  const id = useId();
  const wrap = useRef<HTMLDivElement>(null);
  const [fit, setFit] = useState(columns);
  const count = Math.max(1, Math.min(fit, columns, items.length));

  useEffect(() => {
    if (!wrap.current) return;
    const watcher = new ResizeObserver(([entry]) => {
      setFit(Math.floor((entry.contentRect.width + GAP) / (minWidth + GAP)));
    });
    watcher.observe(wrap.current);
    return () => watcher.disconnect();
  }, [minWidth]);

  return (
    <section aria-labelledby={title ? id : undefined} className={`@container ${className}`}>
      {title && (
        <header className="mx-auto mb-8 max-w-2xl text-center">
          {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 ref={wrap} className={`mx-auto flex max-w-6xl ${boxClassName}`} style={{ gap: GAP, maskImage: MASK, WebkitMaskImage: MASK }}>
        {Array.from({ length: count }, (_, c) => (
          <Column key={c} items={items.filter((_, i) => i % count === c)} reverse={c % 2 === 1} speed={speed} tile={tile} />
        ))}
      </div>
    </section>
  );
}