from __future__ import annotations

import uuid
from datetime import datetime, timedelta

from sqlalchemy import select
from sqlalchemy.orm import Session

from app.core.errors import AppError
from app.models.data_quality import DataQualityIssue


def issue_due_at(detected_at: datetime, severity: str) -> datetime:
    """Return the local operational SLA deadline for a newly detected issue."""
    return detected_at + {
        "high": timedelta(hours=4),
        "medium": timedelta(days=1),
        "low": timedelta(days=3),
    }.get(severity, timedelta(days=1))


def has_open_issue(
    db: Session,
    rule_type: str,
    entity_type: str,
    entity_id: uuid.UUID,
) -> bool:
    return (
        db.scalar(
            select(DataQualityIssue.id).where(
                DataQualityIssue.rule_type == rule_type,
                DataQualityIssue.entity_type == entity_type,
                DataQualityIssue.entity_id == entity_id,
                DataQualityIssue.status == "open",
            )
        )
        is not None
    )


def new_scan_ref(prefix: str) -> str:
    """Generate a stable human-readable prefix with a concurrent-safe suffix."""
    return f"{prefix}-{uuid.uuid4().hex[:10].upper()}"


def load_open_issue(db: Session, public_ref: str, *, lock: bool = True) -> DataQualityIssue:
    statement = select(DataQualityIssue).where(DataQualityIssue.public_ref == public_ref)
    if lock:
        statement = statement.with_for_update().execution_options(populate_existing=True)
    issue = db.scalar(statement)
    if issue is None:
        raise AppError("ISSUE_NOT_FOUND", "Data quality issue not found.", status_code=404)
    if issue.status != "open":
        raise AppError(
            "ISSUE_NOT_OPEN",
            f"Issue is '{issue.status}', not 'open'.",
            status_code=409,
        )
    return issue