"""B03 파일 입력 저장 엔진."""

import os
import tempfile
from pathlib import Path

from fastapi import UploadFile

from B03_FileInput.B03_FileInput_Schema import FileUploadDescriptor
from common_util.common_util_storage import get_project_stage_path
from config.config_system import UPLOAD_CHUNK_SIZE_BYTES, UPLOAD_MAX_MB


def resolve_upload_destination(
    project_root: str | Path,
    descriptor: FileUploadDescriptor,
) -> Path:
    """검증된 파일의 B03 입력 저장 경로를 생성해 반환한다."""
    stage_root = Path(get_project_stage_path(str(project_root), "B03_FileInput")).resolve()
    file_type = Path(descriptor.original_filename).suffix.lower().lstrip(".")
    destination = (stage_root / "input" / file_type / descriptor.original_filename).resolve()

    if os.path.commonpath((stage_root, destination)) != str(stage_root):
        raise ValueError("업로드 저장 경로가 B03 단계 폴더를 벗어났습니다.")

    destination.parent.mkdir(parents=True, exist_ok=True)
    return destination


async def save_upload_stream(upload: UploadFile, destination: Path) -> int:
    """업로드 스트림을 크기 제한 내에서 임시 파일에 기록한 뒤 교체한다."""
    maximum_bytes = UPLOAD_MAX_MB * 1024 * 1024
    written_bytes = 0
    temporary_path: Path | None = None

    try:
        with tempfile.NamedTemporaryFile(
            mode="wb",
            dir=destination.parent,
            prefix=f".{destination.name}.",
            suffix=".upload",
            delete=False,
        ) as temporary:
            temporary_path = Path(temporary.name)
            while chunk := await upload.read(UPLOAD_CHUNK_SIZE_BYTES):
                written_bytes += len(chunk)
                if written_bytes > maximum_bytes:
                    raise ValueError(f"파일 크기는 {UPLOAD_MAX_MB}MB를 초과할 수 없습니다.")
                temporary.write(chunk)
            temporary.flush()
            os.fsync(temporary.fileno())

        if written_bytes == 0:
            raise ValueError("빈 파일은 업로드할 수 없습니다.")
        os.replace(temporary_path, destination)
        temporary_path = None
        return written_bytes
    finally:
        if temporary_path is not None:
            temporary_path.unlink(missing_ok=True)