"use client";

import { useCallback, useEffect, useMemo, useRef, useState } from "react";
import { Typography } from "poyraz-ui/atoms";

type TocHeading = {
  id: string;
  text: string;
  level: 2 | 3;
};

function parseHeadings(markdown: string): TocHeading[] {
  const headings: TocHeading[] = [];
  const lines = markdown.split("\n");

  for (const line of lines) {
    const match = /^(#{2,3})\s+(.+)$/.exec(line.trim());
    if (!match) continue;

    const level = match[1].length as 2 | 3;
    const raw = match[2].replace(/\*\*/g, "").replace(/\*/g, "").trim();
    const id = raw
      .toLowerCase()
      .replace(/[^a-zçğıöşü0-9\s-]/g, "")
      .replace(/\s+/g, "-")
      .replace(/-+/g, "-")
      .replace(/^-|-$/g, "");

    if (id && raw) {
      headings.push({ id, text: raw, level });
    }
  }

  return headings;
}

type BlogTocProps = {
  markdown: string;
  onNavigate?: () => void;
};

export function BlogToc({ markdown, onNavigate }: BlogTocProps) {
  const headings = useMemo(() => parseHeadings(markdown), [markdown]);
  const [activeId, setActiveId] = useState("");
  const rafRef = useRef(0);

  const handleClick = useCallback(
    (id: string) => {
      const target = document.getElementById(id);
      if (!target) return;

      target.scrollIntoView({ behavior: "smooth", block: "start" });
      setActiveId(id);
      onNavigate?.();
    },
    [onNavigate],
  );

  useEffect(() => {
    if (headings.length === 0) return;

    const headingElements = headings
      .map((heading) => ({
        id: heading.id,
        element: document.getElementById(heading.id),
      }))
      .filter((item): item is { id: string; element: HTMLElement } =>
        Boolean(item.element),
      );

    if (headingElements.length === 0) return;

    const updateActive = () => {
      let current = headingElements[0].id;

      for (const item of headingElements) {
        if (item.element.getBoundingClientRect().top <= 120) {
          current = item.id;
          continue;
        }
        break;
      }

      setActiveId(current);
    };

    const observer = new IntersectionObserver(
      () => {
        cancelAnimationFrame(rafRef.current);
        rafRef.current = requestAnimationFrame(updateActive);
      },
      {
        root: null,
        rootMargin: "-120px 0px -65% 0px",
        threshold: [0, 1],
      },
    );

    for (const item of headingElements) {
      observer.observe(item.element);
    }

    const timer = setTimeout(updateActive, 200);

    return () => {
      observer.disconnect();
      cancelAnimationFrame(rafRef.current);
      clearTimeout(timer);
    };
  }, [headings]);

  if (headings.length < 2) return null;

  return (
    <nav aria-label="İçindekiler" className="space-y-1">
      <Typography
        variant="small"
        className="mb-2 font-semibold text-foreground"
      >
        İçindekiler
      </Typography>
      {headings.map((heading, index) => (
        <button
          key={`${heading.id}-${index}`}
          type="button"
          onClick={() => handleClick(heading.id)}
          className={[
            "block w-full cursor-pointer truncate border-l-2 text-left text-xs leading-relaxed transition-colors",
            heading.level === 3 ? "pl-5" : "pl-3",
            activeId === heading.id
              ? "border-red-600 text-red-600"
              : "border-transparent text-muted-foreground hover:text-foreground",
          ].join(" ")}
        >
          {heading.text}
        </button>
      ))}
    </nav>
  );
}
