# app/modules/dev_tools/services/sql_query_service.py
"""
SQL Query Service

Provides safe, read-only SQL query execution and saved query CRUD operations.
Security layers:
1. Regex-based DML/DDL rejection
2. SET TRANSACTION READ ONLY on PostgreSQL
3. Statement timeout (30s)
4. Automatic rollback after every execution
"""

import re
import time
from datetime import UTC, datetime
from decimal import Decimal
from typing import Any
from uuid import UUID

from sqlalchemy import text
from sqlalchemy.orm import Session

from app.exceptions.base import ResourceNotFoundException, ValidationException
from app.modules.dev_tools.models.saved_query import SavedQuery

# Forbidden SQL keywords — matches whole words, case-insensitive
_FORBIDDEN_PATTERN = re.compile(
    r"\b(INSERT|UPDATE|DELETE|DROP|ALTER|CREATE|TRUNCATE|GRANT|REVOKE|COPY|VACUUM|REINDEX)\b",
    re.IGNORECASE,
)


class QueryValidationError(ValidationException):
    """Raised when a query contains forbidden SQL statements."""

    def __init__(self, message: str):
        super().__init__(message=message, field="sql")


def _strip_sql_comments(sql: str) -> str:
    """Remove SQL comments (-- line comments and /* block comments */)."""
    # Remove block comments
    result = re.sub(r"/\*.*?\*/", " ", sql, flags=re.DOTALL)
    # Remove line comments
    result = re.sub(r"--[^\n]*", " ", result)
    return result


def validate_query(sql: str) -> None:
    """Validate that the SQL query is SELECT-only (no DML/DDL)."""
    stripped = sql.strip().rstrip(";")
    if not stripped:
        raise QueryValidationError("Query cannot be empty.")

    # Strip comments before checking for forbidden keywords
    code_only = _strip_sql_comments(stripped)
    match = _FORBIDDEN_PATTERN.search(code_only)
    if match:
        raise QueryValidationError(
            f"Forbidden SQL keyword: {match.group().upper()}. Only SELECT queries are allowed."
        )


def _make_json_safe(value: Any) -> Any:
    """Convert a database value to a JSON-serializable representation."""
    if value is None:
        return None
    if isinstance(value, int | float | bool):
        return value
    if isinstance(value, Decimal):
        return float(value)
    if isinstance(value, datetime):
        return value.isoformat()
    if isinstance(value, UUID):
        return str(value)
    if isinstance(value, bytes):
        return f"<bytes({len(value)})>"
    if isinstance(value, list | dict):
        return value
    return str(value)


def execute_query(db: Session, sql: str) -> dict:
    """
    Execute a read-only SQL query and return results.

    Returns:
        dict with columns, rows, row_count, truncated, execution_time_ms
    """
    validate_query(sql)

    max_rows = 1000
    connection = db.connection()

    try:
        # Set read-only transaction and statement timeout
        connection.execute(text("SET TRANSACTION READ ONLY"))
        connection.execute(text("SET statement_timeout = '30s'"))

        start = time.perf_counter()
        result = connection.execute(text(sql))
        columns = list(result.keys()) if result.returns_rows else []
        rows_raw = result.fetchmany(max_rows + 1)
        elapsed_ms = round((time.perf_counter() - start) * 1000, 2)
        truncated = len(rows_raw) > max_rows
        rows_raw = rows_raw[:max_rows]

        rows = [
            [_make_json_safe(cell) for cell in row] for row in rows_raw
        ]

        return {
            "columns": columns,
            "rows": rows,
            "row_count": len(rows),
            "truncated": truncated,
            "execution_time_ms": elapsed_ms,
        }
    except (QueryValidationError, ValidationException):
        raise
    except Exception as e:  # noqa: EXC003
        raise QueryValidationError(str(e)) from e
    finally:
        db.rollback()


# ---------------------------------------------------------------------------
# Saved Query CRUD
# ---------------------------------------------------------------------------


def list_saved_queries(db: Session) -> list[SavedQuery]:
    """List all saved queries ordered by name."""
    return db.query(SavedQuery).order_by(SavedQuery.name).all()  # noqa: SVC-005


def create_saved_query(
    db: Session,
    *,
    name: str,
    sql_text: str,
    description: str | None,
    created_by: int,
) -> SavedQuery:
    """Create a new saved query."""
    query = SavedQuery(
        name=name,
        sql_text=sql_text,
        description=description,
        created_by=created_by,
    )
    db.add(query)
    db.flush()
    db.refresh(query)
    return query


def update_saved_query(
    db: Session,
    query_id: int,
    *,
    name: str | None = None,
    sql_text: str | None = None,
    description: str | None = None,
) -> SavedQuery:
    """Update an existing saved query. Raises ResourceNotFoundException if not found."""
    query = db.query(SavedQuery).filter(SavedQuery.id == query_id).first()
    if not query:
        raise ResourceNotFoundException("SavedQuery", str(query_id))
    if name is not None:
        query.name = name
    if sql_text is not None:
        query.sql_text = sql_text
    if description is not None:
        query.description = description
    db.flush()
    db.refresh(query)
    return query


def delete_saved_query(db: Session, query_id: int) -> None:
    """Delete a saved query. Raises ResourceNotFoundException if not found."""
    query = db.query(SavedQuery).filter(SavedQuery.id == query_id).first()
    if not query:
        raise ResourceNotFoundException("SavedQuery", str(query_id))
    db.delete(query)
    db.flush()


def record_query_run(db: Session, query_id: int) -> None:
    """Increment run_count and update last_run_at for a saved query."""
    query = db.query(SavedQuery).filter(SavedQuery.id == query_id).first()
    if query:
        query.run_count = (query.run_count or 0) + 1
        query.last_run_at = datetime.now(UTC)
        db.flush()