const express = require('express');
const axios = require('axios');
const xml2js = require('xml2js');
const NodeCache = require('node-cache');
const router = express.Router();

const cache = new NodeCache({ stdTTL: 3600 });

const PUBMED_BASE_URL = 'https://eutils.ncbi.nlm.nih.gov/entrez/eutils';

async function searchPubMed(query, maxResults = 100) {
  try {
    const cacheKey = `search_${query}_${maxResults}`;
    const cached = cache.get(cacheKey);
    if (cached) return cached;

    // Add filters to exclude review papers, meta-analyses, and systematic reviews
    const filteredQuery = `(${query}) NOT Review[Publication Type] NOT Meta-Analysis[Publication Type] NOT Systematic Review[Publication Type]`;

    const searchUrl = `${PUBMED_BASE_URL}/esearch.fcgi?db=pubmed&term=${encodeURIComponent(filteredQuery)}&retmax=${maxResults}&retmode=json`;
    const response = await axios.get(searchUrl);
    
    const result = {
      count: parseInt(response.data.esearchresult.count),
      ids: response.data.esearchresult.idlist || []
    };
    
    cache.set(cacheKey, result);
    return result;
  } catch (error) {
    throw new Error(`PubMed search failed: ${error.message}`);
  }
}

async function fetchPaperDetails(ids) {
  try {
    if (!ids.length) return [];
    
    const cacheKey = `details_${ids.join(',')}`;
    const cached = cache.get(cacheKey);
    if (cached) return cached;

    const fetchUrl = `${PUBMED_BASE_URL}/efetch.fcgi?db=pubmed&id=${ids.join(',')}&retmode=xml`;
    
    // Add timeout and retry logic for PubMed API
    const response = await axios.get(fetchUrl, {
      timeout: 10000,
      headers: {
        'User-Agent': 'PubMedAIExplorer/1.0'
      }
    });
    
    const parser = new xml2js.Parser();
    const result = await parser.parseStringPromise(response.data);
    
    const papers = [];
    const articles = result.PubmedArticleSet?.PubmedArticle || [];
    
    articles.forEach(article => {
      const medlineCitation = article.MedlineCitation?.[0];
      if (medlineCitation) {
        const articleData = medlineCitation.Article?.[0];
        if (articleData) {
          papers.push({
            pmid: medlineCitation.PMID?.[0]?._,
            title: articleData.ArticleTitle?.[0] || 'No title',
            abstract: articleData.Abstract?.AbstractText?.[0]?._ || articleData.Abstract?.AbstractText?.[0] || '',
            authors: articleData.AuthorList?.Author?.map(author => {
              const lastName = author.LastName?.[0] || '';
              const foreName = author.ForeName?.[0] || '';
              return `${foreName} ${lastName}`.trim();
            }) || [],
            journal: articleData.Journal?.Title?.[0] || '',
            pubDate: medlineCitation.DateCompleted?.[0]?.Year?.[0] || 
                     medlineCitation.DateRevised?.[0]?.Year?.[0] || ''
          });
        }
      }
    });
    
    cache.set(cacheKey, papers);
    return papers;
  } catch (error) {
    throw new Error(`Failed to fetch paper details: ${error.message}`);
  }
}

router.get('/search', async (req, res) => {
  try {
    const { query, maxResults = 20 } = req.query;
    if (!query) {
      return res.status(400).json({ error: 'Query parameter is required' });
    }

    const searchResult = await searchPubMed(query, maxResults);
    const papers = await fetchPaperDetails(searchResult.ids.slice(0, 10));
    
    res.json({
      totalCount: searchResult.count,
      papers: papers
    });
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

router.get('/paper/:pmid', async (req, res) => {
  try {
    const { pmid } = req.params;
    console.log(`Fetching paper details for PMID: ${pmid}`);
    
    const papers = await fetchPaperDetails([pmid]);
    console.log(`Found ${papers.length} papers for PMID: ${pmid}`);
    
    if (papers.length === 0) {
      console.log(`No paper found for PMID: ${pmid}`);
      return res.status(404).json({ error: 'Paper not found' });
    }
    
    console.log(`Returning paper:`, papers[0].title);
    res.json(papers[0]);
  } catch (error) {
    const { pmid } = req.params;
    console.error(`Error fetching paper ${pmid}:`, error.message);
    res.status(500).json({ error: error.message });
  }
});

module.exports = router;