"""
Extracts a text snippet from a file so an LLM suggestion can be based on
what's actually in the file, not just its name — helps most for the
genuinely opaque cases (scans, "Download (3).jpg"-style names) that a
filename-only guess can't do anything with.

.md/.txt need nothing extra. .pdf/.docx/.xlsx each need one small
pip-installed library:

    pip install pypdf python-docx openpyxl --break-system-packages

If a library isn't installed, that format quietly returns None (treated
as "no content available", falls back to filename-only) rather than
crashing anything — one missing library never blocks the others.
"""

from pathlib import Path
from typing import Optional

_MAX_CHARS = 2000  # a snippet is enough for a topic guess; keeps the LLM prompt small and fast


def extract_text(path: Path) -> Optional[str]:
    ext = path.suffix.lower()
    try:
        if ext in (".md", ".txt", ".csv"):
            return _read_plain(path)
        if ext == ".pdf":
            return _read_pdf(path)
        if ext == ".docx":
            return _read_docx(path)
        if ext == ".xlsx":
            return _read_xlsx(path)
    except Exception:
        return None  # a corrupt/unreadable file falls back to filename-only, not a crash
    return None  # unsupported format


def _read_plain(path: Path) -> str:
    return path.read_text(encoding="utf-8", errors="ignore")[:_MAX_CHARS]


def _read_pdf(path: Path) -> Optional[str]:
    try:
        from pypdf import PdfReader
    except ImportError:
        return None
    reader = PdfReader(str(path))
    chunks = []
    total = 0
    for page in reader.pages[:3]:  # first few pages is plenty for a topic guess
        text = page.extract_text() or ""
        chunks.append(text)
        total += len(text)
        if total > _MAX_CHARS:
            break
    return "".join(chunks)[:_MAX_CHARS]


def _read_docx(path: Path) -> Optional[str]:
    try:
        import docx
    except ImportError:
        return None
    document = docx.Document(str(path))
    text = "\n".join(p.text for p in document.paragraphs)
    return text[:_MAX_CHARS]


def _read_xlsx(path: Path) -> Optional[str]:
    try:
        import openpyxl
    except ImportError:
        return None
    wb = openpyxl.load_workbook(str(path), read_only=True, data_only=True)
    parts = []
    total = 0
    for ws in wb.worksheets[:2]:
        for row in ws.iter_rows(max_row=20, values_only=True):
            line = " ".join(str(c) for c in row if c is not None)
            parts.append(line)
            total += len(line)
            if total > _MAX_CHARS:
                break
        if total > _MAX_CHARS:
            break
    return "\n".join(parts)[:_MAX_CHARS]