'use client';

import React, { useEffect, useState } from 'react';

interface TocItem {
    label: string;
    href: string;
    subItems?: TocItem[];
}

interface TableOfContentsProps {
    items?: TocItem[];
    className?: string;
}

export const TableOfContents: React.FC<TableOfContentsProps> = ({ items, className = '' }) => {
    // Falls props rein kommen, diese nutzen, ansonsten leeres Array
    const initialItems = items || [];
    const [dynamicItems, setDynamicItems] = useState<TocItem[]>(initialItems);

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

        // Auto-discover headings if no items were passed
        const headings = document.querySelectorAll('h2, h3');
        const newItems: TocItem[] = [];
        let currentH2: TocItem | null = null;

        headings.forEach((heading) => {
            // Ensure the heading has an ID
            if (!heading.id) {
                heading.id = heading.textContent?.toLowerCase().replace(/[^a-z0-9]+/g, '-') || `heading-${Math.random().toString(36).substring(2, 9)}`;
            }

            const item: TocItem = {
                label: heading.textContent || '',
                href: `#${heading.id}`,
            };

            if (heading.tagName === 'H2') {
                currentH2 = { ...item, subItems: [] };
                newItems.push(currentH2);
            } else if (heading.tagName === 'H3' && currentH2) {
                currentH2.subItems?.push(item);
            } else if (heading.tagName === 'H3' && !currentH2) {
                // If an H3 appears before any H2, just add it to root
                newItems.push(item);
            }
        });

        // Verhindern vom loop via prev state check
        setDynamicItems(prev => {
            if (JSON.stringify(prev) === JSON.stringify(newItems)) return prev;
            return newItems;
        });

        // Wir brauchen hier keine deps, da wir nur einmal beim Mount des Beitrags scannen wollen.
        // Sollte items sich ändern, ist das ein Bug der AI, aber als Fallback ok.
    }, []);

    const displayItems = dynamicItems;

    if (displayItems.length === 0) return null;

    // JSON-LD for SiteNavigationElement
    const jsonLd = {
        "@context": "https://schema.org",
        "@type": "ItemList",
        "itemListElement": displayItems.map((item, index) => ({
            "@type": "SiteNavigationElement",
            "position": index + 1,
            "name": item.label,
            "url": `https://mintel.me${item.href}`
        }))
    };

    return (
        <div className={`not-prose my-12 border-l-2 border-slate-200 pl-6 ${className}`}>
            <script
                type="application/ld+json"
                dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd) }}
            />
            <p className="text-xs font-bold text-slate-400 uppercase tracking-widest mb-6">
                Inhaltsverzeichnis
            </p>
            <nav>
                <ul className="space-y-3 m-0 list-none p-0">
                    {displayItems.map((item, index) => (
                        <li key={index} className="m-0 p-0">
                            <a
                                href={item.href}
                                onClick={(e) => {
                                    e.preventDefault();
                                    const targetId = item.href.substring(1);
                                    const elem = document.getElementById(targetId);
                                    if (elem) {
                                        const y = elem.getBoundingClientRect().top + window.scrollY - 144;
                                        window.scrollTo({ top: y, behavior: 'smooth' });
                                        window.history.pushState(null, '', item.href);
                                    }
                                }}
                                className="text-slate-700 hover:text-blue-600 font-medium transition-colors no-underline block"
                            >
                                {item.label}
                            </a>
                            {item.subItems && item.subItems.length > 0 && (
                                <ul className="mt-2 ml-4 space-y-2 border-l-2 border-slate-200 pl-4 m-0 list-none">
                                    {item.subItems.map((subItem, subIndex) => (
                                        <li key={subIndex} className="m-0 p-0">
                                            <a
                                                href={subItem.href}
                                                onClick={(e) => {
                                                    e.preventDefault();
                                                    const targetId = subItem.href.substring(1);
                                                    const elem = document.getElementById(targetId);
                                                    if (elem) {
                                                        const y = elem.getBoundingClientRect().top + window.scrollY - 144;
                                                        window.scrollTo({ top: y, behavior: 'smooth' });
                                                        window.history.pushState(null, '', subItem.href);
                                                    }
                                                }}
                                                className="text-slate-500 hover:text-blue-500 text-sm transition-colors no-underline block"
                                            >
                                                {subItem.label}
                                            </a>
                                        </li>
                                    ))}
                                </ul>
                            )}
                        </li>
                    ))}
                </ul>
            </nav>
        </div>
    );
};