"""PDF text extraction for ObsiGate — pypdf backend, pymupdf optional fallback."""
from __future__ import annotations

import logging
from pathlib import Path

logger = logging.getLogger(__name__)

PDF_READER: str = "pypdf"
try:
    import fitz  # pymupdf
    PDF_READER = "pymupdf"
    logger.info("PDF reader: pymupdf (high performance)")
except ImportError:
    try:
        from pypdf import PdfReader  # type: ignore
        logger.info("PDF reader: pypdf (pure Python)")
    except ImportError:
        PdfReader = None  # type: ignore
        logger.warning("No PDF reader available — install pypdf or pymupdf")


def extract_pdf_text(file_path: Path, max_chars: int = 100000) -> str:
    """Extract text from a PDF file. Returns empty string on failure."""
    if PdfReader is None and PDF_READER == "pypdf":
        return ""
    try:
        if PDF_READER == "pymupdf":
            return _extract_pymupdf(file_path, max_chars)
        else:
            return _extract_pypdf(file_path, max_chars)
    except Exception as e:
        logger.warning("Failed to extract PDF text from %s: %s", file_path, e)
        return ""


def extract_pdf_metadata(file_path: Path) -> dict:
    """Extract metadata from a PDF file."""
    info = {"pages": 0, "title": "", "author": ""}
    try:
        if PDF_READER == "pymupdf":
            doc = fitz.open(str(file_path))
            info["pages"] = doc.page_count
            meta = doc.metadata or {}
            info["title"] = meta.get("title", "")
            info["author"] = meta.get("author", "")
            doc.close()
        else:
            reader = PdfReader(str(file_path))
            info["pages"] = len(reader.pages)
            meta = reader.metadata or {}
            if meta:
                info["title"] = str(meta.get("/Title", ""))
                info["author"] = str(meta.get("/Author", ""))
    except Exception as e:
        logger.warning("Failed to extract PDF metadata from %s: %s", file_path, e)
    return info


def _extract_pymupdf(file_path: Path, max_chars: int) -> str:
    doc = fitz.open(str(file_path))
    parts = []
    total = 0
    for page in doc:
        text = page.get_text()
        if text:
            if total + len(text) > max_chars:
                remaining = max_chars - total
                if remaining > 0:
                    parts.append(text[:remaining])
                break
            parts.append(text)
            total += len(text)
    doc.close()
    return "\f".join(parts)


def _extract_pypdf(file_path: Path, max_chars: int) -> str:
    reader = PdfReader(str(file_path))
    parts = []
    total = 0
    for page in reader.pages:
        text = page.extract_text() or ""
        if text:
            if total + len(text) > max_chars:
                remaining = max_chars - total
                if remaining > 0:
                    parts.append(text[:remaining])
                break
            parts.append(text)
            total += len(text)
    return "\f".join(parts)