import logging
from typing import NoReturn, TypeVar

from fastapi import HTTPException, status
from sqlalchemy.orm import Session


ModelT = TypeVar("ModelT")

logger = logging.getLogger(__name__)

# ── Student-safe canonical messages ─────────────────────────────────────────
# Keep these terse and actionable. Never reference provider names, file paths,
# internal services, or exception class names.

MSG_DOCUMENT_NOT_PROCESSABLE = (
    "This document could not be processed. Please try uploading it again."
)
MSG_AUDIO_GENERATION_FAILED = "Audio generation failed. Please try again."
MSG_VIDEO_RENDER_FAILED = "Video generation failed. Please try again."
MSG_VIDEO_VALIDATION_FAILED = (
    "Video settings are invalid. Check your scene plan and try again."
)
MSG_EXTRACTION_FAILED = (
    "Questions could not be extracted from this file. Please try again."
)


def student_safe_error(
    *,
    http_status: int,
    student_message: str,
    error_code: str,
    debug_exc: BaseException | None = None,
) -> NoReturn:
    """Log *debug_exc* server-side (WARNING level) and raise an HTTPException
    whose ``detail`` only contains the student-safe *student_message*.

    Usage::

        except SomeInternalError as exc:
            student_safe_error(
                http_status=status.HTTP_422_UNPROCESSABLE_ENTITY,
                student_message=MSG_AUDIO_GENERATION_FAILED,
                error_code="AUDIO_GENERATION_FAILED",
                debug_exc=exc,
            )
    """
    if debug_exc is not None:
        logger.warning(
            "[%s] %s: %s",
            error_code,
            type(debug_exc).__name__,
            debug_exc,
        )
    raise HTTPException(
        status_code=http_status,
        detail={"code": error_code, "message": student_message},
    )


def rate_limited_error(
    message: str = "You have reached your plan limit for this month. Upgrade to continue.",
) -> NoReturn:
    """Raise HTTP 429 RATE_LIMITED with the standard student-safe error shape.

    Use this after ``check_usage_limit`` returns ``(False, reason)`` to block
    the request with a consistent, student-friendly message that never leaks
    internal details.
    """
    raise HTTPException(
        status_code=status.HTTP_429_TOO_MANY_REQUESTS,
        detail={"code": "RATE_LIMITED", "message": message},
    )


def get_or_404(db: Session, model: type[ModelT], object_id: str, label: str) -> ModelT:
    instance = db.get(model, object_id)
    if instance is None:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail=f"{label} not found",
        )
    return instance


def ensure_user_exists(db: Session, user_id: str) -> None:
    from app.models.user import User

    if db.get(User, user_id) is not None:
        return

    if user_id != "usr_demo_student":
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="User not found",
        )

    db.add(
        User(
            id="usr_demo_student",
            name="Demo Student",
            email="student@example.com",
            role="student",
            class_level="Plus Two",
            syllabus="Kerala HSE",
            preferred_language="English",
        )
    )
    db.commit()