'use client';

import { useState, useEffect, useMemo, useRef, useCallback } from 'react';
import ReactMarkdown from 'react-markdown';
import remarkGfm from 'remark-gfm';
import { TableOfContents } from './table-of-contents';
import { ArticleEditor } from './article-editor';
import { RelatedArticles } from './related-articles';

interface ArticleStreamProps {
  title: string;
  slug: string;
  decodedTitle: string;
  isEditMode: boolean;
  onEditModeChange: (editing: boolean) => void;
}

export interface TocItem {
  id: string;
  text: string;
  level: number;
}

function generateSlug(text: string): string {
  return text
    .toLowerCase()
    .replace(/[^a-z0-9\s-]/g, '')
    .replace(/\s+/g, '-')
    .replace(/-+/g, '-')
    .trim();
}

function extractHeadings(markdown: string): TocItem[] {
  const headingRegex = /^(#{2,3})\s+(.+)$/gm;
  const headings: TocItem[] = [];
  let match;

  while ((match = headingRegex.exec(markdown)) !== null) {
    const level = match[1].length;
    const text = match[2].replace(/\*\*/g, '').replace(/\*/g, '').trim();
    const id = generateSlug(text);
    headings.push({ id, text, level });
  }

  return headings;
}

const remarkPlugins = [remarkGfm];

export function ArticleStream({ title, slug, decodedTitle, isEditMode, onEditModeChange }: ArticleStreamProps) {
  const [content, setContent] = useState('');
  const [isLoading, setIsLoading] = useState(true);
  const [error, setError] = useState<string | null>(null);
  const pendingContentRef = useRef<string | null>(null);
  const rafIdRef = useRef<number | null>(null);

  const headings = useMemo(() => extractHeadings(content), [content]);

  const scheduleContentUpdate = useCallback((newContent: string) => {
    pendingContentRef.current = newContent;
    if (rafIdRef.current === null) {
      rafIdRef.current = requestAnimationFrame(() => {
        rafIdRef.current = null;
        if (pendingContentRef.current !== null) {
          setContent(pendingContentRef.current);
        }
      });
    }
  }, []);

  useEffect(() => {
    let isCancelled = false;

    async function fetchStream() {
      try {
        const response = await fetch(`/api/ai-article?title=${encodeURIComponent(title)}`);

        if (!response.ok) {
          throw new Error('Failed to fetch article');
        }

        const reader = response.body?.getReader();
        if (!reader) {
          throw new Error('No response body');
        }

        const decoder = new TextDecoder();
        let buffer = '';
        let insideArticle = false;
        let displayContent = '';

        while (true) {
          const { done, value } = await reader.read();

          if (done || isCancelled) break;

          const chunk = decoder.decode(value, { stream: true });
          buffer += chunk;

          if (!insideArticle && buffer.includes('<article>')) {
            insideArticle = true;
            setIsLoading(false);
            buffer = buffer.split('<article>')[1] || '';
          }

          if (insideArticle) {
            if (buffer.includes('</article>')) {
              displayContent += buffer.split('</article>')[0];
              setContent(displayContent);
              break;
            }

            displayContent += buffer;
            buffer = '';

            if (!isCancelled) {
              scheduleContentUpdate(displayContent);
            }
          }
        }

        reader.releaseLock();
      } catch (err) {
        if (!isCancelled) {
          setError(err instanceof Error ? err.message : 'An error occurred');
          setIsLoading(false);
        }
      }
    }

    fetchStream();

    return () => {
      isCancelled = true;
      if (rafIdRef.current !== null) {
        cancelAnimationFrame(rafIdRef.current);
        rafIdRef.current = null;
      }
    };
  }, [title, scheduleContentUpdate]);

  const handleSaved = (newContent: string) => {
    setContent(newContent);
    onEditModeChange(false);
  };

  if (error) {
    return (
      <div className="text-center py-12">
        <p className="text-destructive mb-4">{error}</p>
        <p className="text-muted-foreground">
          Unable to generate article. Please try again later.
        </p>
      </div>
    );
  }

  if (isLoading) {
    return (
      <div className="flex gap-8">
        <aside className="hidden lg:block w-64 flex-shrink-0">
          <div className="sticky top-24 space-y-8">
            <div className="animate-pulse space-y-3">
              <div className="h-4 bg-muted rounded w-24 mb-4" />
              <div className="h-3 bg-muted rounded w-full" />
              <div className="h-3 bg-muted rounded w-5/6" />
              <div className="h-3 bg-muted rounded w-4/5" />
              <div className="h-3 bg-muted rounded w-full" />
              <div className="h-3 bg-muted rounded w-3/4" />
            </div>
            <div className="animate-pulse space-y-3">
              <div className="h-4 bg-muted rounded w-24 mb-4" />
              <div className="h-3 bg-muted rounded w-full" />
              <div className="h-3 bg-muted rounded w-5/6" />
              <div className="h-3 bg-muted rounded w-4/5" />
            </div>
          </div>
        </aside>
        <div className="flex-1 min-w-0 animate-pulse space-y-4">
          <div className="h-8 bg-muted rounded w-3/4" />
          <div className="h-4 bg-muted rounded w-full" />
          <div className="h-4 bg-muted rounded w-full" />
          <div className="h-4 bg-muted rounded w-5/6" />
          <div className="h-64 bg-muted rounded w-full mt-6" />
          <div className="h-4 bg-muted rounded w-full" />
          <div className="h-4 bg-muted rounded w-full" />
          <div className="h-4 bg-muted rounded w-4/5" />
          <div className="h-6 bg-muted rounded w-1/2 mt-6" />
          <div className="h-4 bg-muted rounded w-full" />
          <div className="h-4 bg-muted rounded w-full" />
          <div className="h-4 bg-muted rounded w-3/4" />
        </div>
      </div>
    );
  }

  if (isEditMode) {
    return (
      <div className="flex gap-8">
        <aside className="hidden lg:block w-64 flex-shrink-0">
          <div className="sticky top-24">
            <RelatedArticles title={decodedTitle} currentSlug={slug} />
          </div>
        </aside>
        <div className="flex-1 min-w-0">
          <ArticleEditor
            slug={slug}
            initialContent={content}
            onCancel={() => onEditModeChange(false)}
            onSaved={handleSaved}
          />
        </div>
      </div>
    );
  }

  return (
    <div className="flex gap-8">
      <aside className="hidden lg:block w-64 flex-shrink-0">
        <div className="sticky top-24 space-y-8">
          <TableOfContents headings={headings} />
          <div className="border-t border-border pt-8">
            <RelatedArticles title={decodedTitle} currentSlug={slug} />
          </div>
        </div>
      </aside>
      <div className="flex-1 min-w-0 article-content">
        <ReactMarkdown
          remarkPlugins={remarkPlugins}
          components={{
            h2: ({ children }) => {
              const text = String(children).replace(/\*\*/g, '').replace(/\*/g, '');
              const id = generateSlug(text);
              return <h2 id={id}>{children}</h2>;
            },
            h3: ({ children }) => {
              const text = String(children).replace(/\*\*/g, '').replace(/\*/g, '');
              const id = generateSlug(text);
              return <h3 id={id}>{children}</h3>;
            },
            img: ({ src, alt }) => (
              // eslint-disable-next-line @next/next/no-img-element
              <img
                src={src}
                alt={alt || ''}
                className="w-full max-w-md mx-auto rounded-lg my-6"
                loading="lazy"
              />
            ),
            a: ({ href, children }) => (
              <a
                href={href}
                target={href?.startsWith('http') ? '_blank' : undefined}
                rel={href?.startsWith('http') ? 'noopener noreferrer' : undefined}
              >
                {children}
              </a>
            ),
          }}
        >
          {content}
        </ReactMarkdown>
      </div>
    </div>
  );
}