"use client";

import { useId, useRef, type ElementType, type PointerEvent, type ReactNode } from "react";
import { motion, useReducedMotion } from "motion/react";

export type FeatureGridItem = {
  title: string;
  text: string;
  icon?: ReactNode;
  /** Makes the whole cell a link. */
  href?: string;
};

type FeatureGridProps = {
  items: FeatureGridItem[];
  title?: string;
  /** Small line above the title. */
  eyebrow?: string;
  subtitle?: string;
  /** Smallest cell width in pixels. Sets how many columns fit. */
  minWidth?: number;
  /** Colour of the light and the icons. */
  color?: string;
  /** Cell colour. Match it to the page behind. */
  cell?: string;
  /** h2 by default. */
  headingAs?: ElementType;
  /** Set padding and colours here. */
  className?: string;
};

/* FeatureGrid: a grid of features divided by hairlines. A single light follows the pointer and picks out the lines and cells near it. */
export function FeatureGrid({
  items,
  title,
  eyebrow,
  subtitle,
  minWidth = 240,
  color = "#a78bfa",
  cell = "#0b0a14",
  headingAs: Heading = "h2",
  className = "bg-[#0b0a14] px-5 py-16 text-white",
}: FeatureGridProps) {
  const reduce = useReducedMotion();
  const id = useId();
  const grid = useRef<HTMLDivElement>(null);

  const move = (e: PointerEvent) => {
    const box = grid.current;
    if (!box || e.pointerType !== "mouse") return;
    const rect = box.getBoundingClientRect();
    box.style.setProperty("--fg-x", `${e.clientX - rect.left}px`);
    box.style.setProperty("--fg-y", `${e.clientY - rect.top}px`);
    box.style.setProperty("--fg-on", "1");
  };
  const leave = () => grid.current?.style.setProperty("--fg-on", "0");

  // The cells are opaque, so the layer under them shows only in the 1px gaps. The layer over them tints the cells.
  const light = (radius: number, tint: string) => ({
    opacity: "var(--fg-on, 0)",
    background: `radial-gradient(${radius}px circle at var(--fg-x, 50%) var(--fg-y, 50%), ${tint}, transparent 70%)`,
  });

  return (
    <section aria-labelledby={title ? id : undefined} className={`@container ${className}`}>
      {title && (
        <header className="mx-auto mb-8 max-w-2xl text-center">
          {eyebrow && <p className="mb-2 text-xs font-medium tracking-[0.2em] uppercase opacity-70">{eyebrow}</p>}
          <Heading id={id} className="text-[clamp(1.5rem,6cqw,2.5rem)] leading-tight font-semibold tracking-tight text-balance">
            {title}
          </Heading>
          {subtitle && <p className="mt-3 text-pretty opacity-70">{subtitle}</p>}
        </header>
      )}
      <div
        ref={grid}
        onPointerMove={move}
        onPointerLeave={leave}
        className="relative mx-auto max-w-6xl overflow-hidden rounded-2xl border border-current/15 bg-current/15"
      >
        <div aria-hidden className="pointer-events-none absolute inset-0 transition-opacity duration-300" style={light(260, color)} />
        <ul className="relative grid gap-px" style={{ gridTemplateColumns: `repeat(auto-fit, minmax(min(${minWidth}px, 100%), 1fr))` }}>
          {items.map((item, i) => {
            const body = (
              <>
                {item.icon && (
                  <span className="mb-3 block w-fit" style={{ color }}>
                    {item.icon}
                  </span>
                )}
                <span className="block font-semibold">{item.title}</span>
                <span className="mt-1 block text-sm text-pretty opacity-70">{item.text}</span>
              </>
            );
            return (
              <li key={item.title} style={{ backgroundColor: cell }}>
                <motion.div
                  className="h-full"
                  initial={reduce ? { opacity: 0 } : { opacity: 0, y: 14 }}
                  whileInView={reduce ? { opacity: 1 } : { opacity: 1, y: 0 }}
                  viewport={{ once: true, amount: 0.2 }}
                  transition={{ duration: 0.5, delay: Math.min(i, 8) * 0.05, ease: [0.16, 1, 0.3, 1] }}
                >
                  {item.href ? (
                    <a href={item.href} className="block h-full p-5">
                      {body}
                    </a>
                  ) : (
                    <div className="h-full p-5">{body}</div>
                  )}
                </motion.div>
              </li>
            );
          })}
        </ul>
        <div aria-hidden className="pointer-events-none absolute inset-0 transition-opacity duration-300" style={light(240, `${color}1f`)} />
      </div>
    </section>
  );
}