"""
Upload validation helpers.

Validates file extension and size against settings before persisting to storage.
"""
from __future__ import annotations

import os

from django.conf import settings


class UploadValidationError(Exception):
    pass


def validate_upload(file) -> None:
    """
    Validate an uploaded file against configured size and extension limits.
    Raises UploadValidationError on violation.
    """
    ext = os.path.splitext(file.name)[1].lower()
    allowed = [e.lower() for e in getattr(settings, "ALLOWED_UPLOAD_EXTENSIONS", [])]
    max_size = getattr(settings, "MAX_UPLOAD_SIZE_BYTES", 100 * 1024 * 1024)

    if allowed and ext not in allowed:
        raise UploadValidationError(
            f"File extension '{ext}' is not allowed. Permitted: {', '.join(allowed)}"
        )

    if file.size > max_size:
        max_mb = max_size // (1024 * 1024)
        raise UploadValidationError(
            f"File size {file.size} bytes exceeds limit of {max_mb} MB."
        )


def save_upload(file, org_id: str, uploader) -> object:
    """Persist an uploaded file and create a MediaAsset record."""
    import uuid
    import mimetypes
    from django.conf import settings as s
    from .models import MediaAsset, ScanStatus

    ext = os.path.splitext(file.name)[1].lower()
    storage_root = getattr(s, "MEDIA_ROOT", "/tmp/media")
    relative_path = os.path.join("uploads", str(org_id), f"{uuid.uuid4().hex}{ext}")
    full_path = os.path.join(storage_root, relative_path)
    os.makedirs(os.path.dirname(full_path), exist_ok=True)

    with open(full_path, "wb") as dest:
        for chunk in file.chunks():
            dest.write(chunk)

    mime_type, _ = mimetypes.guess_type(file.name)

    asset = MediaAsset.objects.create(
        uploaded_by=uploader,
        org_id=org_id,
        file_name=file.name,
        file_path=relative_path,
        file_size=file.size,
        mime_type=mime_type or "",
        extension=ext,
        scan_status=ScanStatus.PENDING,
    )

    # Enqueue async scan
    from .tasks import scan_media_asset_task
    scan_media_asset_task.delay(str(asset.id))

    return asset