"""Document and binary storage helpers."""

import uuid
from pathlib import Path

import pymupdf
from fastapi import HTTPException, UploadFile

from app.config import settings

_COPY_CHUNK_SIZE = 1024 * 1024


def validate_pdf(filepath: Path) -> int:
    """Validate a PDF's magic bytes and return its page count."""
    with filepath.open("rb") as file:
        if file.read(5) != b"%PDF-":
            raise ValueError("Not a valid PDF file (missing magic bytes)")

    try:
        with pymupdf.open(filepath) as document:
            page_count = len(document)
    except Exception as err:
        raise ValueError(f"Failed to open PDF with PyMuPDF: {err}") from err

    if page_count == 0:
        raise ValueError("PDF does not contain any pages")
    return page_count


def safe_filename(filename: str | None) -> str:
    """Return a display-safe basename without allowing path components."""
    name = Path(filename or "Untitled.pdf").name.strip()
    return name or "Untitled.pdf"


async def save_upload_file(upload_file: UploadFile) -> tuple[str, int, int]:
    """Stream an uploaded PDF to storage, enforcing the configured size limit."""
    file_id = str(uuid.uuid4())
    settings.PDF_STORAGE_PATH.mkdir(parents=True, exist_ok=True)
    filepath = settings.PDF_STORAGE_PATH / f"{file_id}.pdf"
    max_bytes = settings.MAX_UPLOAD_MB * 1024 * 1024
    total_bytes = 0

    try:
        with filepath.open("wb") as destination:
            while chunk := upload_file.file.read(_COPY_CHUNK_SIZE):
                total_bytes += len(chunk)
                if total_bytes > max_bytes:
                    raise HTTPException(status_code=413, detail="File too large")
                destination.write(chunk)
    except HTTPException:
        filepath.unlink(missing_ok=True)
        raise
    except Exception as err:
        filepath.unlink(missing_ok=True)
        raise HTTPException(status_code=500, detail="Failed to save file") from err

    try:
        page_count = validate_pdf(filepath)
    except ValueError as err:
        filepath.unlink(missing_ok=True)
        raise HTTPException(status_code=400, detail=str(err)) from err

    return file_id, total_bytes, page_count


def delete_pdf_file(file_id: str) -> None:
    """Delete a PDF file from storage."""
    filepath = settings.PDF_STORAGE_PATH / f"{file_id}.pdf"
    filepath.unlink(missing_ok=True)