from datetime import datetime
from io import BytesIO
from pathlib import Path
from typing import Dict, Any, List

from markdown import markdown
from starlette.responses import Response
from xhtml2pdf import pisa

from open_webui.apps.webui.models.chats import ChatTitleMessagesForm


class PDFGenerator:
    """
    Description:
    The `PDFGenerator` class is designed to create PDF documents from chat messages.
    The process involves transforming markdown content into HTML and then into a PDF format,
    which can be easily returned as a response to the routes.

    It depends on xhtml2pdf for converting HTML to PDF (more details at https://github.com/xhtml2pdf/xhtml2pdf).
    I found xhtml2pdf issues when rendering list html tag, see https://github.com/xhtml2pdf/xhtml2pdf/issues/550
    and https://github.com/xhtml2pdf/xhtml2pdf/issues/756.

    Attributes:
    - `form_data`: An instance of `ChatTitleMessagesForm` containing title and messages.

    """

    def __init__(self, form_data: ChatTitleMessagesForm):
        self.html_body = None
        self.messages_html = None
        self.form_data = form_data
        self.css_style_file = Path("./backend/open_webui/static/assets/pdf-style.css")

    def build_html_message(self, message: Dict[str, Any]) -> str:
        """Build HTML for a single message."""
        role = message.get("role", "user")
        content = message.get("content", "")
        timestamp = message.get('timestamp')

        model = message.get('model') if role == 'assistant' else ''

        date_str = self.format_timestamp(timestamp) if timestamp else ''

        # extends pymdownx extension to convert markdown to html.
        # - https://facelessuser.github.io/pymdown-extensions/usage_notes/
        html_content = markdown(content, extensions=['pymdownx.extra'])

        html_message = f"""
              <div class="message">
                  <small> {date_str} </small>
                  <div>
                      <h2>
                          <strong>{role.title()}</strong>
                          <small class="text-muted">{model}</small>
                      </h2>
                  </div>
                  <div class="markdown-section">
                      {html_content}
                  </div>
              </div>
          """
        return html_message

    def create_pdf_from_html(self) -> bytes:
        """Convert HTML content to PDF and return the bytes."""
        pdf_buffer = BytesIO()
        pisa_status = pisa.CreatePDF(src=self.html_body, dest=pdf_buffer)
        if pisa_status.err:
            raise RuntimeError("Error generating PDF")

        return pdf_buffer.getvalue()

    def format_timestamp(self, timestamp: float) -> str:
        """Convert a UNIX timestamp to a formatted date string."""
        try:
            date_time = datetime.fromtimestamp(timestamp)
            return date_time.strftime("%Y-%m-%d, %H:%M:%S")
        except (ValueError, TypeError) as e:
            # Log the error if necessary
            return ''

    def generate_chat_pdf(self) -> Response:
        """
        Generate a PDF from chat messages.

        Returns:
            A FastAPI Response with the generated PDF or an error message.
        """
        try:
            # Build HTML messages
            messages_html_list: List[str] = [self.build_html_message(msg) for msg in self.form_data.messages]
            self.messages_html = '<div>' + ''.join(messages_html_list) + '</div>'

            # Generate full HTML body
            self.html_body = self.generate_html_body()

            # Create PDF
            pdf_bytes = self.create_pdf_from_html()

            # Return PDF as response
            return Response(
                content=pdf_bytes,
                media_type="application/pdf",
                headers={"Content-Disposition": "attachment;filename=chat.pdf"},
            )
        except RuntimeError as pdf_error:
            # Handle PDF generation errors
            return Response(content=str(pdf_error), status_code=500)
        except Exception as e:
            # Handle other unexpected errors
            return Response(content="An unexpected error occurred.", status_code=500)

    def generate_html_body(self) -> str:
        """Generate the full HTML body for the PDF."""
        return f"""
        <html>
            <head>
                <meta charset="UTF-8">
                <meta name="viewport" content="width=device-width, initial-scale=1.0">
                <link rel="stylesheet" href="{self.css_style_file.as_posix()}">
            </head>
            <body>
                <div class="container"> 
                    <div class="text-center">
                        <h1>{self.form_data.title}</h1>
                    </div>
                    <div>
                        {self.messages_html}
                    </div>
                </div>
            </body>
        </html>
        """