import logging
import re
import shutil
import tempfile
from io import BytesIO
from pathlib import Path
from zipfile import ZipFile

import defusedxml.ElementTree as ET
from defusedxml.common import DefusedXmlException
from docling_core.types.doc import DoclingDocument, DocumentOrigin
from typing_extensions import override

from docling.backend.abstract_backend import DeclarativeDocumentBackend
from docling.backend.html_backend import HTMLDocumentBackend
from docling.datamodel.backend_options import EpubBackendOptions, HTMLBackendOptions
from docling.datamodel.base_models import InputFormat
from docling.datamodel.document import InputDocument
from docling.exceptions import DocumentLoadError

_log = logging.getLogger(__name__)


class EpubDocumentBackend(DeclarativeDocumentBackend):
    """Backend for converting EPUB files to DoclingDocument format.

    EPUB files are essentially ZIP archives containing XHTML content files.
    This backend extracts the content and delegates to HTMLDocumentBackend
    for processing the XHTML structure.

    Note:
        This module enforces limits when extracting EPUB archives for image processing.
            These limits prevent malicious EPUBs from exhausting disk space or memory
            through decompression bombs. Limits can be configured via
            EpubBackendOptions.

    Known Limitations:
        Internal anchor links (e.g., footnote references) are converted but
            the target anchor IDs are not preserved in the final Markdown output.
            This is a limitation of the HTML-to-DoclingDocument conversion process.
            Links like [1](#note-1) will be present, but the corresponding anchor
            targets may not be accessible in the exported Markdown.
    """

    def __init__(
        self,
        in_doc: InputDocument,
        path_or_stream: BytesIO | Path,
        options: EpubBackendOptions | None = None,
    ):
        if options is None:
            options = EpubBackendOptions()
        super().__init__(in_doc, path_or_stream, options)

        _log.debug("Starting EpubDocumentBackend...")

        self.path_or_stream = path_or_stream
        self.valid = False
        self.epub_zip: ZipFile | None = None
        self.content_files: list[str] = []
        self.metadata: dict[str, str] = {}
        self.temp_dir: Path | None = None

        try:
            # Open the EPUB file as a ZIP archive
            if isinstance(self.path_or_stream, BytesIO):
                self.epub_zip = ZipFile(self.path_or_stream, "r")
            elif isinstance(self.path_or_stream, Path):
                self.epub_zip = ZipFile(self.path_or_stream, "r")
            else:
                raise ValueError("path_or_stream must be BytesIO or Path")

            # Parse the EPUB structure
            self._parse_epub_structure()
            self.valid = True

            _log.debug(f"Found {len(self.content_files)} content files in EPUB")
        except Exception as e:
            _log.error(f"Failed to initialize EPUB backend: {e}")
            raise DocumentLoadError(
                f"Could not initialize EPUB backend for file with hash {self.document_hash}."
            ) from e

    def _parse_epub_structure(self):
        """Parse the EPUB structure to find content files and metadata."""
        if not self.epub_zip:
            return

        # Read container.xml to find the content.opf file
        try:
            container_data = self.epub_zip.read("META-INF/container.xml")
            container_root = ET.fromstring(container_data)

            # Find the content.opf path
            ns = {"container": "urn:oasis:names:tc:opendocument:xmlns:container"}
            rootfile = container_root.find(".//container:rootfile", ns)

            if rootfile is None:
                raise ValueError("Could not find rootfile in container.xml")

            opf_path = rootfile.get("full-path")
            if not opf_path:
                raise ValueError("Could not find full-path in rootfile")

            # Parse content.opf to get the reading order
            opf_data = self.epub_zip.read(opf_path)
            opf_root = ET.fromstring(opf_data)

            # Extract metadata
            self._extract_metadata(opf_root)

            # Get the base directory for content files
            opf_dir = str(Path(opf_path).parent)
            if opf_dir == ".":
                opf_dir = ""

            # Extract spine (reading order)
            ns_opf = {"opf": "http://www.idpf.org/2007/opf"}
            spine = opf_root.find(".//opf:spine", ns_opf)
            manifest = opf_root.find(".//opf:manifest", ns_opf)

            if spine is None or manifest is None:
                raise ValueError("Could not find spine or manifest in content.opf")

            # Build manifest map (id -> href)
            manifest_map = {}
            for item in manifest.findall("opf:item", ns_opf):
                item_id = item.get("id")
                href = item.get("href")
                if item_id and href:
                    manifest_map[item_id] = href

            # Get content files in reading order
            for itemref in spine.findall("opf:itemref", ns_opf):
                idref = itemref.get("idref")
                if idref and idref in manifest_map:
                    href = manifest_map[idref]
                    # Construct full path
                    if opf_dir:
                        full_path = f"{opf_dir}/{href}"
                    else:
                        full_path = href
                    self.content_files.append(full_path)

            _log.debug(f"Content files in reading order: {self.content_files}")

        except DefusedXmlException as e:
            _log.error(f"Security issue detected while parsing EPUB XML: {e}")
            raise RuntimeError(
                "EPUB file contains potentially malicious XML content"
            ) from e
        except Exception as e:
            _log.error(f"Error parsing EPUB structure: {e}")
            raise

    def _safe_extract_epub(self, target_dir: Path) -> bool:
        """Safely extract EPUB contents with zip-bomb protection.

        Args:
            target_dir: Directory to extract files to

        Returns:
            True if extraction succeeded, False if limits were exceeded

        Raises:
            RuntimeError: If extraction fails due to I/O errors
        """
        if not self.epub_zip:
            return False

        total_bytes = 0
        member_count = 0
        max_total_bytes = self.options.max_total_bytes
        max_file_bytes = self.options.max_file_bytes
        max_member_count = self.options.max_member_count

        try:
            for member in self.epub_zip.infolist():
                member_count += 1
                if member_count > max_member_count:
                    _log.warning(
                        f"EPUB archive exceeds member count limit ({max_member_count})"
                    )
                    return False

                # Check uncompressed size
                if member.file_size > max_file_bytes:
                    _log.warning(
                        f"EPUB member {member.filename} exceeds size limit "
                        f"({member.file_size} > {max_file_bytes} bytes)"
                    )
                    return False

                total_bytes += member.file_size
                if total_bytes > max_total_bytes:
                    _log.warning(
                        f"EPUB archive exceeds total size limit ({max_total_bytes} bytes)"
                    )
                    return False

                # Extract the member
                self.epub_zip.extract(member, target_dir)

            _log.debug(
                f"Successfully extracted {member_count} members ({total_bytes} bytes)"
            )
            return True

        except Exception as e:
            _log.error(f"Error during EPUB extraction: {e}")
            raise RuntimeError(f"Failed to extract EPUB archive: {e}") from e

    def _extract_metadata(self, opf_root):
        """Extract metadata from the OPF file."""
        ns_dc = {"dc": "http://purl.org/dc/elements/1.1/"}
        ns_opf = {"opf": "http://www.idpf.org/2007/opf"}

        metadata = opf_root.find(".//opf:metadata", ns_opf)
        if metadata is None:
            return

        # Extract common metadata fields
        for field in [
            "title",
            "creator",
            "publisher",
            "date",
            "language",
            "identifier",
        ]:
            element = metadata.find(f"dc:{field}", ns_dc)
            if element is not None and element.text:
                self.metadata[field] = element.text

        _log.debug(f"Extracted metadata: {self.metadata}")

    def _fix_image_paths(self, html_content: str, content_file_path: str) -> str:
        """Convert relative image paths to paths relative to temp directory root.

        Args:
            html_content: HTML content with image references
            content_file_path: Path of the current XHTML file (for resolving relative paths)

        Returns:
            HTML content with fixed image paths
        """
        if not self.temp_dir:
            return html_content

        # Get the directory of the current content file
        content_dir = Path(content_file_path).parent

        def replace_image_src(match):
            src = match.group(1)

            # Skip data URIs and absolute URLs
            if src.startswith(("data:", "http://", "https://", "/")):
                return match.group(0)

            # Resolve relative path and make it relative to temp_dir
            if content_dir:
                image_path = content_dir / src
            else:
                image_path = Path(src)

            # Normalize the path
            try:
                # Return the modified src attribute with path relative to temp_dir
                return f'src="{image_path}"'
            except Exception as e:
                _log.warning(f"Failed to resolve image path {src}: {e}")
                return match.group(0)

        # Pattern to match src attributes in img tags
        pattern = r'src="([^"]+)"'
        return re.sub(pattern, replace_image_src, html_content)

    def _fix_internal_links(self, html_content: str) -> str:
        """Fix internal links that reference other XHTML files.

        When combining multiple XHTML files into one HTML document, links like
        'endnotes.xhtml#note-1' need to be converted to '#note-1' since all
        content is now in a single file.

        Args:
            html_content: HTML content with potentially broken internal links

        Returns:
            HTML content with fixed internal links
        """
        # Pattern to match href attributes that reference .xhtml files with anchors
        # Examples: href="endnotes.xhtml#note-1" or href="chapter-1.xhtml#section-2"
        pattern = r'href="([^"]*\.xhtml)(#[^"]*)"'

        # Replace with just the anchor part
        fixed_content = re.sub(pattern, r'href="\2"', html_content)

        return fixed_content

    @override
    def is_valid(self) -> bool:
        return self.valid

    @override
    def unload(self):
        """Clean up resources."""
        if self.epub_zip:
            self.epub_zip.close()
            self.epub_zip = None
        if isinstance(self.path_or_stream, BytesIO):
            self.path_or_stream.close()
        self.path_or_stream = None

        # Clean up temporary directory
        if self.temp_dir and self.temp_dir.exists():
            try:
                shutil.rmtree(self.temp_dir)
                _log.debug(f"Cleaned up temporary directory: {self.temp_dir}")
            except Exception as e:
                _log.warning(
                    f"Failed to clean up temporary directory {self.temp_dir}: {e}"
                )
            self.temp_dir = None

    @classmethod
    @override
    def supports_pagination(cls) -> bool:
        return False

    @classmethod
    @override
    def supported_formats(cls) -> set[InputFormat]:
        return {InputFormat.EPUB}

    @override
    def convert(self) -> DoclingDocument:
        """Convert the EPUB file to a DoclingDocument.

        This method extracts all content files from the EPUB and processes
        them sequentially using the HTMLDocumentBackend.
        """
        _log.debug("Converting EPUB...")

        if not self.is_valid() or not self.epub_zip:
            raise RuntimeError(
                f"Cannot convert EPUB with hash {self.document_hash} because the backend failed to init."
            )

        # Create document origin
        origin = DocumentOrigin(
            filename=self.file.name or "file",
            mimetype="application/epub+zip",
            binary_hash=self.document_hash,
        )

        # Initialize the main document
        doc = DoclingDocument(name=self.file.stem or "file", origin=origin)

        # Extract EPUB to temporary directory if images need to be fetched
        # This allows the HTML backend to access images from the filesystem
        if self.options.fetch_images and self.options.enable_local_fetch:
            try:
                self.temp_dir = Path(tempfile.mkdtemp(prefix="docling_epub_"))
                _log.debug(f"Extracting EPUB to temporary directory: {self.temp_dir}")
                if not self._safe_extract_epub(self.temp_dir):
                    _log.warning(
                        "EPUB extraction aborted due to size/count limits. "
                        "Images will not be available."
                    )
                    # Clean up the temp directory since extraction failed
                    if self.temp_dir and self.temp_dir.exists():
                        shutil.rmtree(self.temp_dir)
                    self.temp_dir = None
            except Exception as e:
                _log.warning(f"Failed to extract EPUB to temp directory: {e}")
                if self.temp_dir and self.temp_dir.exists():
                    shutil.rmtree(self.temp_dir)
                self.temp_dir = None

        # Concatenate all XHTML content into a single HTML document
        combined_html_parts = [
            '<!DOCTYPE html><html><head><meta charset="utf-8"/></head><body>'
        ]

        # TODO: leverage `self.metadata` once DoclingDocument supports file metadata

        # Process each content file in reading order
        for content_file in self.content_files:
            try:
                _log.debug(f"Reading content file: {content_file}")

                # Read the XHTML content
                xhtml_data = self.epub_zip.read(content_file)
                xhtml_text = xhtml_data.decode("utf-8")

                # Extract the body content from the XHTML
                # Simple extraction - find content between <body> tags
                body_match = re.search(
                    r"<body[^>]*>(.*?)</body>", xhtml_text, re.DOTALL | re.IGNORECASE
                )

                if body_match:
                    body_content = body_match.group(1)
                else:
                    # If no body tags, use the whole content
                    body_content = xhtml_text

                # Fix internal links: convert file.xhtml#anchor to #anchor
                # This is necessary because we're combining all XHTML files into one HTML
                body_content = self._fix_internal_links(body_content)

                # Fix image paths if we extracted to temp directory
                if self.temp_dir:
                    body_content = self._fix_image_paths(body_content, content_file)

                combined_html_parts.append(body_content)

            except Exception as e:
                _log.warning(f"Failed to read content file {content_file}: {e}")
                continue

        combined_html_parts.append("</body></html>")
        combined_html = "\n".join(combined_html_parts)

        # Now process the combined HTML with HTMLDocumentBackend
        html_stream = BytesIO(combined_html.encode("utf-8"))

        epub_options = self.options
        html_options = HTMLBackendOptions(
            enable_local_fetch=epub_options.enable_local_fetch,
            enable_remote_fetch=epub_options.enable_remote_fetch,
            fetch_images=epub_options.fetch_images,
            infer_furniture=False,
            add_title=False,  # We already added the title
        )

        if self.temp_dir:
            dummy_file = self.temp_dir / "combined.html"
            html_options.source_uri = str(dummy_file)
            _log.debug(f"Set HTML backend source_uri to: {html_options.source_uri}")

        in_doc = InputDocument(
            path_or_stream=html_stream,
            format=InputFormat.HTML,
            backend=HTMLDocumentBackend,
            filename="combined.html",
            backend_options=html_options,
        )

        html_backend = HTMLDocumentBackend(
            in_doc=in_doc,
            path_or_stream=html_stream,
            options=html_options,
        )

        # Convert and return the combined document
        doc = html_backend.convert()

        # Update the origin to reflect it's an EPUB
        doc.origin = DocumentOrigin(
            filename=self.file.name or "file",
            mimetype="application/epub+zip",
            binary_hash=self.document_hash,
        )
        doc.name = self.file.stem or "file"

        html_stream.close()

        return doc
