import os
import re
import time
import logging
import zipfile
import requests
import bibtexparser
from tqdm import tqdm
from urllib.parse import quote, urlencode
import gradio as gr
from bs4 import BeautifulSoup
import io
import asyncio
import aiohttp
from concurrent.futures import ThreadPoolExecutor, CancelledError

# Configure logging
logging.basicConfig(level=logging.INFO,
                    format='%(asctime)s - %(levelname)s: %(message)s')
logger = logging.getLogger(__name__)

class PaperDownloader:
    def __init__(self, output_dir='papers'):
        self.output_dir = output_dir
        os.makedirs(output_dir, exist_ok=True)

        # Updated download sources
        self.download_sources = [
            'https://sci-hub.ee/',
            'https://sci-hub.st/',
            'https://sci-hub.ru/',
            'https://sci-hub.ren/',
            'https://sci-hub.mksa.top/',
            'https://sci-hub.se/',
            'https://libgen.rs/scimag/'
        ]

        # Request headers
        self.headers = {
            'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36',
            'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8',
            'Accept-Language': 'en-US,en;q=0.9',
        }
        self.executor = ThreadPoolExecutor(max_workers=4)
        self.download_task = None # Added attribute

    def clean_doi(self, doi):
        """Clean and encode DOI for URL"""
        if not isinstance(doi, str):
            return None
        return quote(doi.strip()) if doi else None
    
    async def fetch_with_headers(self, session, url, timeout=10):
            """Utility method to fetch an URL with headers and timeout"""
            try:
                async with session.get(url, headers=self.headers, timeout=timeout, allow_redirects=True) as response:
                    response.raise_for_status()
                    return await response.text(), response.headers
            except Exception as e:
                logger.debug(f"Error fetching {url}: {e}")
                return None, None

    async def fetch_pdf_content(self, session, url, max_redirects=5, max_retries=2, retry_delay=1):
        """Fetch content and validate if response is PDF, following up to max_redirects redirections with retries."""
        
        current_url = url
        redirect_count = 0
        retry_count = 0

        while redirect_count <= max_redirects:
          
            try:
                while retry_count <= max_retries:
                    try:
                        logger.debug(f"Fetching PDF from {current_url} - Retry {retry_count + 1}")#ADDED
                        async with session.get(current_url, headers=self.headers, timeout=10, allow_redirects=False) as response:
                            if response.status in [301, 302, 307, 308]:
                                current_url = response.headers['Location']
                                redirect_count += 1
                                logger.debug(f"Following redirect from {url} to {current_url}")
                                break  # Break out of the retry loop for a redirect

                            response.raise_for_status()

                            if 'application/pdf' in response.headers.get('Content-Type', ''):
                                logger.debug(f"Successfully fetched PDF from {current_url}")#ADDED
                                return await response.read()
                            else:
                                logger.debug(f"Content type not PDF for {current_url}: {response.headers.get('Content-Type', '')}")
                                return None
                    except Exception as e:
                         logger.debug(f"Error getting PDF, retrying ({retry_count}/{max_retries}) from {current_url}: {e}")
                         retry_count += 1
                         await asyncio.sleep(retry_delay)
                         
                retry_count = 0  # Reset the retry count, in case there's a next redirect attempt
            except CancelledError:
                logger.info(f"Fetch PDF cancelled from: {url}")
                return None

            except Exception as e:
                logger.debug(f"Error getting PDF from {current_url}: {e}")
                return None

            
            
        logger.debug(f"Too many redirects or retries {url}, not following this link further")
        return None
        
    async def download_paper_direct_doi_async(self, session, doi):
            """Attempt to download the pdf from the landing page of the doi"""
            if not doi:
                return None
    
            try:
                doi_url = f"https://doi.org/{self.clean_doi(doi)}"
    
                # First, let's try to download the URL directly in case it is already the pdf.
                pdf_content = await self.fetch_pdf_content(session, doi_url)
                if pdf_content:
                    logger.debug(f"Direct DOI resolved to PDF from {doi_url}")
                    return pdf_content
    
                # If direct DOI link was not a pdf, fetch landing page and extract links
                text, headers = await self.fetch_with_headers(session, doi_url, timeout=15)
                if not text:
                    return None
    
                pdf_patterns = [
                    r'(https?://[^\s<>"]+?\.pdf)',
                    r'(https?://[^\s<>"]+?download/[^\s<>"]+)',
                    r'(https?://[^\s<>"]+?\/pdf\/[^\s<>"]+)',
                    ]
                 
                pdf_urls = []
                for pattern in pdf_patterns:
                    pdf_urls.extend(re.findall(pattern, text))
    
                # Attempt each pdf url and break when you find a PDF content.
                for pdf_url in pdf_urls:
                    pdf_content = await self.fetch_pdf_content(session, pdf_url)
                    if pdf_content:
                        logger.debug(f"Found PDF from: {pdf_url}")
                        return pdf_content
    
            except Exception as e:
                logger.debug(f"Error trying to get the PDF from {doi}: {e}")
                return None
            
    async def download_paper_scihub_async(self, session, doi):
        """Improved method to download paper from Sci-Hub using async requests"""
        if not doi:
            logger.warning("DOI not provided")
            return None
    
        
        for base_url in self.download_sources:
           
            try:
                scihub_url = f"{base_url}{self.clean_doi(doi)}"
                text, headers = await self.fetch_with_headers(session, scihub_url, timeout=15)
                if not text:
                    continue
                    

                # Search for multiple PDF URL patterns
                pdf_patterns = [
                    r'(https?://[^\s<>"]+?\.pdf)',
                    r'(https?://[^\s<>"]+?download/[^\s<>"]+)',
                    r'(https?://[^\s<>"]+?\/pdf\/[^\s<>"]+)',
                ]
            

                pdf_urls = []
                for pattern in pdf_patterns:
                    pdf_urls.extend(re.findall(pattern, text))
            

                # Try downloading from found URLs, but iterate over ALL
                for pdf_url in pdf_urls:
                    pdf_content = await self.fetch_pdf_content(session,pdf_url)
                    if pdf_content:
                        logger.debug(f"Found PDF from: {pdf_url}")
                        return pdf_content
                    
            except Exception as e:
                 logger.debug(f"Error trying to download {doi} from {base_url}: {e}")

        
        return None

    async def download_paper_libgen_async(self, session, doi):
        """Download from Libgen, handles the query and the redirection"""
        if not doi:
            return None

        base_url = 'https://libgen.rs/scimag/'
        try:
            search_url = f"{base_url}?q={self.clean_doi(doi)}"
            text, headers = await self.fetch_with_headers(session, search_url, timeout=10)

            if not text or "No results" in text:
                logger.debug(f"No results for DOI: {doi} on libgen")
                return None

            soup = BeautifulSoup(text, 'html.parser')

            links = soup.select('table.c > tbody > tr:nth-child(2) > td:nth-child(1) > a')

            if links:
                link = links[0]
                pdf_url = link['href']
                pdf_content = await self.fetch_pdf_content(session, pdf_url)
                if pdf_content:
                    logger.debug(f"Found PDF from: {pdf_url}")
                    return pdf_content
        except Exception as e:
            logger.debug(f"Error trying to download {doi} from libgen: {e}")
        return None

    async def download_paper_google_scholar_async(self, session, doi):
        """Search google scholar to find an article with the given doi, try to get the pdf"""
        if not doi:
            return None

        try:
            query = f'doi:"{doi}"'
            params = {'q': query}
            url = f'https://scholar.google.com/scholar?{urlencode(params)}'

            text, headers = await self.fetch_with_headers(session, url, timeout=10)
            if not text:
                return None

            soup = BeautifulSoup(text, 'html.parser')

            # Find any links with [PDF]
            links = soup.find_all('a', string=re.compile(r'\[PDF\]', re.IGNORECASE))

            if links:
                pdf_url = links[0]['href']
                pdf_content = await self.fetch_pdf_content(session,pdf_url)
                if pdf_content:
                  logger.debug(f"Found PDF from: {pdf_url}")
                  return pdf_content

        except Exception as e:
            logger.debug(f"Google Scholar error for {doi}: {e}")

        return None
    
    async def download_paper_crossref_async(self, session, doi):
            """Alternative search method using Crossref"""
            if not doi:
                return None
    
            try:
                # Search for open access link
                url = f"https://api.crossref.org/works/{doi}"
                response = await session.get(url, headers=self.headers, timeout=10)
    
                if response.status == 200:
                    data = await response.json()
                    work = data.get('message', {})
    
                    # Search for open access links
                    links = work.get('link', [])
                    for link in links:
                        if link.get('content-type') == 'application/pdf':
                            pdf_url = link.get('URL')
                            if pdf_url:
                                pdf_content = await self.fetch_pdf_content(session, pdf_url)
                                if pdf_content:
                                    logger.debug(f"Found PDF from: {pdf_url}")
                                    return pdf_content
            except Exception as e:
                logger.debug(f"Crossref error for {doi}: {e}")
            return None

    async def download_with_retry_async(self, doi, max_retries=3):
        """
        Intenta descargar un paper con múltiples estrategias y un número limitado de reintentos.
        
        Args:
            doi (str): DOI del paper a descargar
            max_retries (int): Número máximo de reintentos
        
        Returns:
            bytes or None: Contenido del PDF o None si no se puede descargar
        """
        if not doi:
            logger.warning("DOI no proporcionado")
            return None
    
        # Estrategias de descarga en orden de preferencia
        download_strategies = [
            self.download_paper_direct_doi_async,
            self.download_paper_scihub_async,
            self.download_paper_libgen_async,
            self.download_paper_google_scholar_async,
            self.download_paper_crossref_async
        ]
    
        async with aiohttp.ClientSession() as session:
            for retry in range(max_retries):
                logger.info(f"Intento de descarga {retry + 1} para DOI: {doi}")
                
                # Probar cada estrategia de descarga
                for strategy in download_strategies:
                    try:
                        logger.info(f"Trying strategy {strategy.__name__} for DOI {doi}") # ADDED
                        pdf_content = await strategy(session, doi)
                        if pdf_content:
                            logger.info(f"Descarga exitosa de {doi} usando {strategy.__name__}")
                            return pdf_content
                    except CancelledError:
                         logger.info(f"Download cancelled on strategy: {strategy.__name__} with DOI {doi}")
                         return None # return here in order to stop retry

                    except Exception as e:
                        logger.debug(f"Error en estrategia {strategy.__name__} para {doi}: {e}") #ADDED
                    
                    
                # Si ninguna estrategia funcionó, esperar un poco antes de reintentar
                await asyncio.sleep(1)  # Pequeña pausa entre reintentos
                
                if retry == max_retries -1: #log all if it does not works on max retries.
                      logger.warning(f"FALLO FINAL: No se pudo descargar DOI {doi} después de {max_retries} intentos")


            # Si se agotan todos los reintentos
            return None

    def _download_single_doi(self, doi, progress_callback, cancel_event): # removed async keyword
            """Descargar un único DOI con retroalimentación de progreso"""
            if not doi:
                progress_callback(None, "Error: DOI no proporcionado", "Error: DOI no proporcionado")
                return None
            logger.info(f"Starting download process for DOI: {doi}")
            
            try:
                
                async def call_async():# Added this in order to execute correctly on executor

                   pdf_content = await self.download_with_retry_async(doi)
                   if pdf_content:
                        logger.info(f"Downloaded PDF for DOI: {doi}")
                        filename = f"{str(doi).replace('/', '_').replace('.', '_')}.pdf"
                        filepath = os.path.join(self.output_dir, filename)

                        # Escribir contenido del PDF
                        
                        open(filepath, 'wb').write(pdf_content)
                       
                        logger.info(f"Saved PDF to file: {filepath}")

                        logger.info(f"Descarga exitosa: {filename}")
                        
                        progress_callback(filepath, f"Descargado exitosamente: <a href='https://doi.org/{doi}'>{doi}</a>", "")
                        
                        
                   else:
                        logger.warning(f"No se pudo descargar: {doi}")
                        progress_callback(None, f"No se pudo descargar {doi}", f'<a href="https://doi.org/{doi}">{doi}</a>')
            
                asyncio.run(call_async()) #added the loop event here
                
            except CancelledError:
               logger.info(f"Download Cancelled DOI: {doi}")
               progress_callback(None, f"Download cancelled {doi}","Download Cancelled" )
               
            except Exception as e:
               logger.error(f"Error processing {doi}: {e}")
               progress_callback(None, f"Error processing {doi}: {e}", f"Error processing {doi}: {e}" )
               
    
    def download_multiple_dois(self, dois_text, progress_callback, cancel_event): #removed async here
            """Download multiple DOIs"""
             # Validar entrada
            if not dois_text:
                progress_callback(None, "Error: No DOIs provided", "Error: No DOIs provided",)
                return None

            # Sanitizar y filtrar DOIs
            # Eliminar líneas vacías, espacios en blanco, y DOIs duplicados
            dois = list(set([doi.strip() for doi in dois_text.split('\n') if doi.strip()]))
            
            # Validar lista de DOIs
            if not dois:
                progress_callback(None, "Error: No valid DOIs provided", "Error: No valid DOIs provided")
                return None
    
            # Listas para rastrear resultados
            downloaded_files = []      # Rutas de archivos descargados
            failed_dois = []           # DOIs que no se pudieron descargar
            downloaded_links = []      # Links de DOIs descargados
          

            for doi in dois:
                    self._download_single_doi(doi, lambda a,b,c: progress_callback(a,b,c, doi) , cancel_event )
                    if cancel_event.is_set():
                         logger.info("Downloads cancelled on multiple dois download")
                         progress_callback(None,  "Downloads cancelled","Downloads cancelled") # early return on cancelled
                         return None #break here when is cancelled

                    result = self.results_dict.get(doi, (None,None,"")) # obtain from self.results

                    # Manejar diferentes tipos de resultados
                    if isinstance(result, Exception):
                        # Excepción inesperada
                        error_msg = f"Unexpected error: {str(result)}"
                        logger.error(f"Error downloading {doi}: {error_msg}")
                        failed_dois.append(f'<a href="https://doi.org/{doi}">{doi}</a> - {error_msg}')
                    
                    elif result[0] is None:
                        # Descarga fallida (resultado de download_single_doi_async)
                        error_msg = result[1]
                        logger.warning(f"Failed to download {doi}: {error_msg}")
                        failed_dois.append(f'<a href="https://doi.org/{doi}">{doi}</a> - {error_msg}')
                    
                    else:
                        # Descarga exitosa
                        filepath = result[0]
                        
                        # Generar nombre de archivo único
                        filename = f"{str(doi).replace('/', '_').replace('.', '_')}.pdf"
                        filepath_unique = os.path.join(self.output_dir, filename)
                        
                        try:
                            # Renombrar archivo
                            os.rename(filepath, filepath_unique)
                            
                            # Añadir a lista de archivos descargados
                            downloaded_files.append(filepath_unique)
                            downloaded_links.append(f'<a href="https://doi.org/{doi}">{doi}</a>')
                        
                        except Exception as rename_error:
                            logger.error(f"Error renaming file for {doi}: {rename_error}")
                            failed_dois.append(f'<a href="https://doi.org/{doi}">{doi}</a> - Error saving file')


                    
                    
            # Crear archivo ZIP si hay archivos descargados
            zip_filename = None
            if downloaded_files:
                zip_filename = 'papers.zip'
                loop = asyncio.get_running_loop()
            
                # Ejecutar creación de ZIP en un executor para no bloquear
                loop.run_in_executor(
                    self.executor, 
                    lambda: self.create_zip(zip_filename, downloaded_files)
                )
                logger.info(f"ZIP file created: {zip_filename}")
        

            # Devolver resultados
            progress_callback( zip_filename if downloaded_files else None, "\n".join(downloaded_links),"\n".join(failed_dois))
            return
            
    def process_bibtex(self, bib_file, progress_callback, cancel_event):# removed async here
            """Process BibTeX file and download papers with multiple strategies and reports UI updates using a callback"""
            # Read BibTeX file content from the uploaded object
            try:
                with open(bib_file.name, 'r', encoding='utf-8') as f:
                    bib_content = f.read()
            except Exception as e:
                logger.error(f"Error reading uploaded file {bib_file.name}: {e}")
                progress_callback(None, f"Error reading uploaded file {bib_file.name}: {e}", f"Error reading uploaded file {bib_file.name}: {e}" )
                return None

            # Parse BibTeX data
            try:
                bib_database = bibtexparser.loads(bib_content)
            except Exception as e:
                logger.error(f"Error parsing BibTeX data: {e}")
                progress_callback(None,f"Error parsing BibTeX data: {e}", f"Error parsing BibTeX data: {e}")
                return None

            # Extract DOIs
            dois = [entry.get('doi') for entry in bib_database.entries if entry.get('doi')]
            logger.info(f"Found {len(dois)} DOIs to download")

             # Result lists
            downloaded_files = []
            failed_dois = []
            downloaded_links = []

            for doi in dois:

                 self._download_single_doi(doi,  lambda a,b,c: progress_callback(a,b,c, doi), cancel_event )
                 if cancel_event.is_set():
                       logger.info("Download Cancelled in bibtex mode")
                       progress_callback(None, "Download Cancelled", "Download Cancelled")
                       return None #cancel if requested
                       
                 result = self.results_dict.get(doi, (None,None,"")) # obtain from self.results
            
                 if isinstance(result, Exception):
                    # Excepción inesperada
                    error_msg = f"Unexpected error: {str(result)}"
                    logger.error(f"Error downloading {doi}: {error_msg}")
                    failed_dois.append(f'<a href="https://doi.org/{doi}">{doi}</a> - {error_msg}')
                
                 elif result[0] is None:
                    # Descarga fallida (resultado de download_single_doi_async)
                    error_msg = result[1]
                    logger.warning(f"Failed to download {doi}: {error_msg}")
                    failed_dois.append(f'<a href="https://doi.org/{doi}">{doi}</a> - {error_msg}')
                
                 else:
                    # Descarga exitosa
                    filepath = result[0]
                    
                    # Unique filename for zip
                    filename = f"{str(doi).replace('/', '_').replace('.', '_')}_{i}.pdf"
                    filepath_unique = os.path.join(self.output_dir, filename)
                    os.rename(filepath, filepath_unique)
                    downloaded_files.append(filepath_unique)
                    downloaded_links.append(f'<a href="https://doi.org/{doi}">{doi}</a>')


            if downloaded_files:
                zip_filename = 'papers.zip'
                loop = asyncio.get_running_loop()
                loop.run_in_executor(self.executor, lambda:  self.create_zip(zip_filename,downloaded_files))
                logger.info(f"ZIP file created: {zip_filename}")
    
            progress_callback(zip_filename, "\n".join(downloaded_links), "\n".join(failed_dois)) #after process finishes
            return

    def create_zip(self, zip_filename, files):
        """Crea un archivo zip con los pdfs descargados"""
        with zipfile.ZipFile(zip_filename, 'w', zipfile.ZIP_DEFLATED) as zf:
            for file in files:
                zf.write(file, os.path.basename(file))
    def cancel_download(self):
           if self.download_task:
                self.cancel_event.set()
                # Cancel the download task if it exists and it is cancelable
                
                self.download_task.cancel()

def create_gradio_interface():
    """Create Gradio interface for Paper Downloader"""
    downloader = PaperDownloader()

    downloader.results_dict = {}  #shared results dict, since it runs on different threads

    def update_progress( message="", logs=""):
      return  gr.Textbox.update(value=f"{message}"),gr.Textbox.update(value=f"<pre>{logs}</pre>")
    

    def download_papers(bib_file, doi_input, dois_input):
            cancel_event = asyncio.Event() # Create cancellation event for every submission.
            downloader.cancel_event = cancel_event # store the event so that it is available to stop the process
            
            def custom_progress_callback(filepath, message, fail_message, doi=None): #new callback to send to the execution function

                    logger.info(f"Callback message: {message}") # log each callback msg
                   
                    #store data for single or multiple mode on download_papers execution.
                    if doi:
                          downloader.results_dict[doi] = (filepath, message,fail_message)

                    updates = update_progress(message)

                    return updates
                

            if bib_file:
                # Check file type
                 if not bib_file.name.lower().endswith('.bib'):
                    return None, "Error: Please upload a .bib file", "Error: Please upload a .bib file", None
                    
                downloader.download_task = downloader.executor.submit(
                        downloader.process_bibtex, 
                         bib_file,
                        lambda a,b,c:  update_progress(a,f"{b}<br>{c}"), #convert for ui output, the return data will contain the HTML
                        cancel_event # Added cancelllation event.
                )
              
                return None,"","",None
             
            elif doi_input:
                
                downloader.download_task = downloader.executor.submit( #changed async execution method
                         downloader._download_single_doi, 
                          doi_input, 
                           lambda a,b,c: update_progress(a,f"{b}<br>{c}")  , #callback function, format output and send html info, removed lambda from executor calls
                           cancel_event  # Add cancellation event.
                      )
                
                return  None, "","", None
            
            elif dois_input:
                downloader.download_task = downloader.executor.submit( #changed async execution method
                        downloader.download_multiple_dois,
                         dois_input,
                       lambda a,b,c: update_progress(a,f"{b}<br>{c}") ,#callback function
                        cancel_event #Add cancellation event.
                  )
                 
                return  None, "","", None

            else:
               return None, "Please provide a .bib file, a single DOI, or a list of DOIs", "Please provide a .bib file, a single DOI, or a list of DOIs","", None

    

    # Gradio Interface
    interface = gr.Interface(
        fn=download_papers,
        inputs=[
            gr.File(file_types=['.bib'], label="Upload BibTeX File"),
            gr.Textbox(label="Enter Single DOI", placeholder="10.xxxx/xxxx"),
            gr.Textbox(label="Enter Multiple DOIs (one per line)", placeholder="10.xxxx/xxxx\n10.yyyy/yyyy\n..."),
           
        ],
        outputs=[
            gr.File(label="Download Papers (ZIP) or Single PDF"),
            gr.Textbox(label="""
                Found DOIs
            """),
             gr.Textbox(label="""
                Missed DOIs
            """),
              gr.Textbox(label="""
            Logs
            """, lines = 10),
            gr.File(label="Downloaded Single PDF")
        ],
         
        title="🔬 Academic Paper Batch Downloader",
        description="Upload a BibTeX file or enter DOIs to download PDFs. We'll attempt to fetch PDFs from multiple sources like Sci-Hub, Libgen, Google Scholar and Crossref. You can use any of the three inputs at any moment.",
        theme="Hev832/Applio",
        examples=[
            ["example.bib", None, None],  # Bibtex File
            [None, "10.1038/nature12373", None],  # Single DOI
            [None, None, "10.1109/5.771073\n10.3390/horticulturae8080677"],  # Multiple DOIs
        ],
        css="""
        .gradio-container {
            background-color: black;
        }
        .gr-interface {
            max-width: 800px;
            margin: 0 auto;
        }
        .gr-box {
            background-color: black;
            border-radius: 10px;
            box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
        }
           .output-text a {
               color: #007bff; /* Blue color for hyperlinks */
            }
            .logs_box {
                
            }
        """,
         
        
        cache_examples=False,
    )

    interface.load= """
      () => {
        
        return []
      }
     """
    # Adding clear button
    with gr.Row():
          
           interface.stop_btn= gr.Button(value="Stop Downloads")
           
    interface.stop_btn.click(lambda: downloader.cancel_download(), outputs=None) #added function in object downloader
    
    return interface

def main():
    interface = create_gradio_interface()
    interface.launch()

if __name__ == "__main__":
    main()