/**
 * Peptide News Feed — React Frontend
 *
 * A clean, accessible news feed component that displays peptide research
 * articles with title, summary, source, date, and keyword tags.
 *
 * @since 2.0.0
 */
const { useState, useEffect, useCallback, useRef, memo } = React;

/* ── Constants ──────────────────────────────────────────────────────── */

const ARTICLES_PER_PAGE = 10;
const CACHE_TTL_MS = 5 * 60 * 1000; // 5 minutes

/* ── Utilities ──────────────────────────────────────────────────────── */

/**
 * Format an ISO date string to a human-readable form.
 *
 * @param {string} dateStr ISO date string.
 * @returns {string} Formatted date (e.g., "Apr 5, 2026").
 */
function formatDate(dateStr) {
  if (!dateStr) return '';
  const d = new Date(dateStr);
  if (isNaN(d.getTime())) return dateStr;
  return d.toLocaleDateString('en-US', {
    month: 'short',
    day: 'numeric',
    year: 'numeric',
  });
}

/**
 * Calculate a human-readable relative time string.
 *
 * @param {string} dateStr ISO date string.
 * @returns {string} Relative time (e.g., "2 hours ago").
 */
function timeAgo(dateStr) {
  if (!dateStr) return '';
  const now = Date.now();
  const then = new Date(dateStr).getTime();
  if (isNaN(then)) return '';
  const diffMs = now - then;
  const diffMin = Math.floor(diffMs / 60000);
  if (diffMin < 1) return 'Just now';
  if (diffMin < 60) return `${diffMin}m ago`;
  const diffHr = Math.floor(diffMin / 60);
  if (diffHr < 24) return `${diffHr}h ago`;
  const diffDay = Math.floor(diffHr / 24);
  if (diffDay < 7) return `${diffDay}d ago`;
  return formatDate(dateStr);
}

/* ── Simple in-memory cache ─────────────────────────────────────────── */

const apiCache = new Map();

function getCached(key) {
  const entry = apiCache.get(key);
  if (!entry) return null;
  if (Date.now() - entry.ts > CACHE_TTL_MS) {
    apiCache.delete(key);
    return null;
  }
  return entry.data;
}

function setCache(key, data) {
  apiCache.set(key, { data, ts: Date.now() });
}

/* ── API Layer ──────────────────────────────────────────────────────── */

/**
 * Fetch articles from the WP REST API with caching.
 *
 * @param {string} restUrl  Base REST URL.
 * @param {number} page     Page number.
 * @param {number} count    Articles per page.
 * @param {AbortSignal} signal  Abort signal for cleanup.
 * @returns {Promise<Object>} Response data.
 */
async function fetchArticles(restUrl, page, count, signal) {
  const cacheKey = `${restUrl}:${page}:${count}`;
  const cached = getCached(cacheKey);
  if (cached) return cached;

  const url = `${restUrl}articles?count=${count}&page=${page}`;
  const resp = await fetch(url, { signal });

  if (!resp.ok) {
    throw new Error(`HTTP ${resp.status}: ${resp.statusText}`);
  }

  const data = await resp.json();
  setCache(cacheKey, data);
  return data;
}

/* ── Click Tracking ─────────────────────────────────────────────────── */

/**
 * Track an outbound click via sendBeacon or fallback XHR.
 *
 * @param {number} articleId
 */
function trackClick(articleId) {
  const config = window.peptideNewsFeed || {};
  if (!config.ajaxUrl || !config.nonce) return;

  const formData = new FormData();
  formData.append('action', 'peptide_news_track_click');
  formData.append('nonce', config.nonce);
  formData.append('article_id', articleId);
  formData.append('referrer', document.referrer || '');
  formData.append('page_url', window.location.href);
  formData.append('session_id', config.sessionId || '');

  if (navigator.sendBeacon) {
    navigator.sendBeacon(config.ajaxUrl, formData);
  } else {
    fetch(config.ajaxUrl, { method: 'POST', body: formData }).catch(() => {});
  }
}

/* ── Components ─────────────────────────────────────────────────────── */

/**
 * Single keyword tag pill.
 */
const Tag = memo(function Tag({ label }) {
  return <span className="pn-tag">{label}</span>;
});

/**
 * Single article card.
 */
const ArticleCard = memo(function ArticleCard({ article }) {
  const summary = article.ai_summary || article.excerpt || '';
  const tagSource = article.tags || article.categories || '';
  const tags = tagSource
    ? tagSource.split(',').map((t) => t.trim()).filter(Boolean).slice(0, 5)
    : [];

  const handleClick = useCallback(() => {
    trackClick(article.id);
  }, [article.id]);

  return (
    <article className="pn-article" role="article">
      <div className="pn-article-meta">
        <span className="pn-source">{article.source}</span>
        <span className="pn-separator" aria-hidden="true">&middot;</span>
        <time
          className="pn-date"
          dateTime={article.published_at}
          title={formatDate(article.published_at)}
        >
          {timeAgo(article.published_at)}
        </time>
      </div>

      <h3 className="pn-article-title">
        <a
          href={article.source_url}
          onClick={handleClick}
          target="_blank"
          rel="noopener noreferrer"
        >
          {article.title}
        </a>
      </h3>

      {summary && (
        <p className="pn-article-excerpt">{summary}</p>
      )}

      {article.author && (
        <span className="pn-author">{article.author}</span>
      )}

      {tags.length > 0 && (
        <div className="pn-tags" role="list" aria-label="Keywords">
          {tags.map((tag) => (
            <Tag key={tag} label={tag} />
          ))}
        </div>
      )}
    </article>
  );
});

/**
 * Loading skeleton placeholder.
 */
function LoadingSkeleton({ count = 3 }) {
  return (
    <div className="pn-loading" aria-busy="true" aria-label="Loading articles">
      {Array.from({ length: count }, (_, i) => (
        <div key={i} className="pn-skeleton-card">
          <div className="pn-skeleton-line pn-skeleton-meta" />
          <div className="pn-skeleton-line pn-skeleton-title" />
          <div className="pn-skeleton-line pn-skeleton-excerpt" />
          <div className="pn-skeleton-line pn-skeleton-excerpt-short" />
          <div className="pn-skeleton-tags">
            <div className="pn-skeleton-tag" />
            <div className="pn-skeleton-tag" />
            <div className="pn-skeleton-tag" />
          </div>
        </div>
      ))}
    </div>
  );
}

/**
 * Error state with retry.
 */
function ErrorMessage({ message, onRetry }) {
  return (
    <div className="pn-error" role="alert">
      <p>Unable to load articles. {message}</p>
      <button className="pn-retry-btn" onClick={onRetry} type="button">
        Try Again
      </button>
    </div>
  );
}

/**
 * Empty state.
 */
function EmptyState() {
  return (
    <div className="pn-empty">
      <p>No peptide news articles available yet. Check back soon!</p>
    </div>
  );
}

/**
 * Pagination controls.
 */
const Pagination = memo(function Pagination({ page, totalPages, onPageChange }) {
  if (totalPages <= 1) return null;

  return (
    <nav className="pn-pagination" aria-label="Article pages">
      <button
        className="pn-page-btn"
        onClick={() => onPageChange(page - 1)}
        disabled={page <= 1}
        aria-label="Previous page"
        type="button"
      >
        &larr; Newer
      </button>

      <span className="pn-page-info" aria-current="page">
        Page {page} of {totalPages}
      </span>

      <button
        className="pn-page-btn"
        onClick={() => onPageChange(page + 1)}
        disabled={page >= totalPages}
        aria-label="Next page"
        type="button"
      >
        Older &rarr;
      </button>
    </nav>
  );
});

/* ── Main Feed Component ────────────────────────────────────────────── */

/**
 * PeptideNewsFeed — root component.
 *
 * Reads configuration from window.peptideNewsFeed which is
 * localized by the PHP shortcode renderer.
 */
function PeptideNewsFeed() {
  const config = window.peptideNewsFeed || {};
  const restUrl = config.restUrl || '/wp-json/peptide-news/v1/';
  const perPage = config.count || ARTICLES_PER_PAGE;

  const [articles, setArticles] = useState([]);
  const [page, setPage] = useState(1);
  const [totalPages, setTotalPages] = useState(1);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);

  const feedRef = useRef(null);

  const loadArticles = useCallback(
    async (pageNum, signal) => {
      setLoading(true);
      setError(null);
      try {
        const data = await fetchArticles(restUrl, pageNum, perPage, signal);
        setArticles(data.articles || []);
        setTotalPages(data.total_pages || 1);
      } catch (err) {
        if (err.name !== 'AbortError') {
          setError(err.message || 'Something went wrong.');
        }
      } finally {
        setLoading(false);
      }
    },
    [restUrl, perPage]
  );

  useEffect(() => {
    const controller = new AbortController();
    loadArticles(page, controller.signal);
    return () => controller.abort();
  }, [page, loadArticles]);

  const handlePageChange = useCallback((newPage) => {
    setPage(newPage);
    // Scroll feed container into view on pagination.
    if (feedRef.current) {
      feedRef.current.scrollIntoView({ behavior: 'smooth', block: 'start' });
    }
  }, []);

  const handleRetry = useCallback(() => {
    loadArticles(page);
  }, [page, loadArticles]);

  return (
    <div className="pn-news-feed" ref={feedRef}>
      {loading && <LoadingSkeleton count={Math.min(perPage, 5)} />}

      {!loading && error && (
        <ErrorMessage message={error} onRetry={handleRetry} />
      )}

      {!loading && !error && articles.length === 0 && <EmptyState />}

      {!loading && !error && articles.length > 0 && (
        <>
          <div className="pn-articles-list" role="feed" aria-label="Peptide news articles">
            {articles.map((article) => (
              <ArticleCard key={article.id} article={article} />
            ))}
          </div>

          <Pagination
            page={page}
            totalPages={totalPages}
            onPageChange={handlePageChange}
          />
        </>
      )}
    </div>
  );
}

/* ── Mount ──────────────────────────────────────────────────────────── */

document.addEventListener('DOMContentLoaded', function () {
  const containers = document.querySelectorAll('[data-peptide-news-feed]');
  containers.forEach(function (el) {
    const root = ReactDOM.createRoot(el);
    root.render(React.createElement(PeptideNewsFeed));
  });
});