"""Attachment storage on the local filesystem (a named Docker volume in
production). Files live at ATTACHMENTS_DIR/<ncr_id>/<uuid><ext>; metadata is
kept in the attachments table."""
import re
import uuid
from pathlib import Path

from fastapi import UploadFile

from app.config import get_settings

ALLOWED_EXTENSIONS = {
    # images (camera capture on tablets produces jpg/png/heic)
    ".jpg", ".jpeg", ".png", ".gif", ".webp", ".heic", ".heif", ".bmp", ".tiff", ".tif",
    # documents
    ".pdf", ".doc", ".docx", ".xls", ".xlsx", ".csv", ".txt", ".msg", ".eml",
}

IMAGE_EXTENSIONS = {
    ".jpg", ".jpeg", ".png", ".gif", ".webp", ".heic", ".heif", ".bmp", ".tiff", ".tif",
}

CHUNK_SIZE = 1024 * 1024


class UploadValidationError(Exception):
    pass


def _safe_filename(name: str) -> str:
    name = Path(name or "upload").name
    return re.sub(r"[^\w.\- ()]", "_", name)[:255] or "upload"


async def save_attachment(upload: UploadFile, ncr_id: int) -> dict:
    """Validate and persist an uploaded file. Returns metadata for the
    Attachment row. Raises UploadValidationError on type/size violations."""
    settings = get_settings()
    original = _safe_filename(upload.filename or "upload")
    ext = Path(original).suffix.lower()
    if ext not in ALLOWED_EXTENSIONS:
        raise UploadValidationError(
            f"File type '{ext or 'unknown'}' is not allowed. "
            f"Allowed: {', '.join(sorted(ALLOWED_EXTENSIONS))}"
        )

    stored_rel = f"{ncr_id}/{uuid.uuid4().hex}{ext}"
    dest = Path(settings.attachments_dir) / stored_rel
    dest.parent.mkdir(parents=True, exist_ok=True)

    size = 0
    max_bytes = settings.max_upload_bytes
    try:
        with dest.open("wb") as out:
            while chunk := await upload.read(CHUNK_SIZE):
                size += len(chunk)
                if size > max_bytes:
                    raise UploadValidationError(
                        f"File exceeds the {settings.max_upload_mb} MB limit."
                    )
                out.write(chunk)
    except UploadValidationError:
        dest.unlink(missing_ok=True)
        raise
    except Exception:
        dest.unlink(missing_ok=True)
        raise
    if size == 0:
        dest.unlink(missing_ok=True)
        raise UploadValidationError("Uploaded file is empty.")

    return {
        "original_filename": original,
        "stored_path": stored_rel,
        "content_type": upload.content_type or "application/octet-stream",
        "size_bytes": size,
        "is_image": ext in IMAGE_EXTENSIONS,
    }


def attachment_abs_path(stored_path: str) -> Path:
    settings = get_settings()
    base = Path(settings.attachments_dir).resolve()
    p = (base / stored_path).resolve()
    if not str(p).startswith(str(base)):
        raise UploadValidationError("Invalid attachment path.")
    return p