"""General-purpose logging utilities with task context support."""

import logging
import os
import sys
from contextvars import ContextVar

LOGGER_LEVEL = getattr(logging, os.environ.get('LOGGER_LEVEL', 'INFO'))

# This variable is unique to each thread/task execution
task_id_var: ContextVar[str] = ContextVar('task_id', default='')


class TaskContextFilter(logging.Filter):
    """Filter that injects the current task_id into log records."""

    def filter(self, record: logging.LogRecord) -> bool:
        """Attach the current task ID to the record.

        Args:
            record: The log record.

        Returns:
            bool: Always True, indicating the record should be processed.
        """
        record.task_id = task_id_var.get()
        return True


class TaskContextFormatter(logging.Formatter):
    """Formatter that conditionally includes task_id if present."""

    def format(self, record: logging.LogRecord) -> str:
        """Format the log record, including task_id only if present.

        Args:
            record: The log record.

        Returns:
            str: Formatted log message.
        """
        # Build format string based on whether task_id is present (non-empty)
        task_id_fmt = '[%(task_id)s]' if record.task_id else ''  # type: ignore[attr-defined]
        fmt = f'[%(name)s][%(asctime)s][%(levelname)s]{task_id_fmt} %(message)s'

        # Update both _fmt and _style for compatibility
        self._style._fmt = fmt
        self._fmt = fmt

        return super().format(record)


def create_handler(level: int | None = None) -> logging.Handler:
    """Create a configured handler with task context support.

    Args:
        level: Optional logging level. If not provided, uses LOGGER_LEVEL.

    Returns:
        Configured StreamHandler that can be added to a logger.
    """
    handler = logging.StreamHandler(sys.stdout)
    handler.setLevel(level or LOGGER_LEVEL)
    handler.setFormatter(TaskContextFormatter())
    handler.addFilter(TaskContextFilter())
    return handler