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/** @jsxImportSource ../jsx */
import { effect } from "../ef.js";
import { type JSXChildren } from "../jsx/jsx";

import { cx } from "./nav.module.css";

const EL_KIND = "nav_link";

const idToOffsetTopMap = new Map<string, number>();

function onScrollEnd() {
  const { scrollTop } = document.body;

  // This margin works like scroll-padding-top
  const topmostY = Math.min(...idToOffsetTopMap.values());

  let closest: readonly [number, string] | null = null;
  for (const [id, top] of idToOffsetTopMap) {
    const dy = top - scrollTop - topmostY;
    if (
      !closest ||
      (closest[0] > 0 && dy < closest[0]) ||
      (dy < 0 && dy > closest[0])
    ) {
      closest = [dy, id];
      continue;
    }
  }

  const currents = document.querySelectorAll(
    `[data-kind="${EL_KIND}"][data-current]`,
  );
  currents.forEach((el) => {
    el.removeAttribute("data-current");
  });

  if (!closest) {
    return;
  }

  const [, id] = closest;
  const target = document.querySelector(
    `[data-kind="${EL_KIND}"][href="#${id}"]`,
  );
  if (!target) {
    return;
  }

  target.setAttribute("data-current", "");
}

interface NavProps {
  class?: string;

  ulClass?: string;

  children: JSXChildren;

  onESC?(): void;
}

export function Nav({
  children,
  class: className,
  ulClass,
  onESC,
  ...rest
}: NavProps) {
  effect(() => {
    requestAnimationFrame(() => {
      onScrollEnd();
    });

    document.body.addEventListener("scrollend", onScrollEnd, { passive: true });

    return () => {
      document.body.removeEventListener("scrollend", onScrollEnd);
    };
  });

  return (
    <nav
      {...rest}
      class={className ?? false}
      onKeyDown={(ev: Event) => {
        if (!(ev instanceof KeyboardEvent) || ev.key !== "Escape") {
          return;
        }

        onESC?.();
      }}
    >
      <ul class={[cx.list, ulClass].filter(Boolean).join(" ")}>{children}</ul>
    </nav>
  );
}

interface NavItemProps {
  href: string;

  children: JSXChildren;
}

const HASH_PATTERN = /^#(\S+)$/;

function register(href: string) {
  effect(() => {
    if (HASH_PATTERN.test(href)) {
      const [, id] = href.match(HASH_PATTERN)!;

      requestAnimationFrame(() => {
        const target = document.getElementById(id);
        if (!target) {
          return;
        }

        idToOffsetTopMap.set(id, target.offsetTop);
      });

      return () => {
        idToOffsetTopMap.delete(id);
      };
    }
  });
}

export function NavItem({ href, children }: NavItemProps) {
  register(href);

  return (
    <li class={cx.item}>
      <a class={cx.link} href={href} data-kind={EL_KIND}>
        {children}
      </a>
    </li>
  );
}

interface NavGroupProps {
  label: JSXChildren;

  href?: string;

  children: JSXChildren;
}

export function NavGroup({ label, children, href }: NavGroupProps) {
  if (href) {
    register(href);
  }

  return (
    <li class={cx.item}>
      {href ? (
        <a href={href} class={cx.link} data-kind={EL_KIND}>
          {label}
        </a>
      ) : (
        <span class={cx.groupLabel}>{label}</span>
      )}
      <ul class={cx.list}>{children}</ul>
    </li>
  );
}